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Research Article| February 01, 2011
Nonuniform Groundwater Discharge across a Streambed: Heat as a Tracer
Jannick Kolbjørn Jensen
Jannick Kolbjørn Jensen *
Dep. of Geography and Geology, Univ. of Copenhagen, Øster Voldgade 10, 1350 Copenhagen K, Denmark
Corresponding author (jkj@geo.ku.dk).
Peter Engesgaard
Vadose Zone Journal (2011) 10 (1): 98–109.
Jannick Kolbjørn Jensen, Peter Engesgaard; Nonuniform Groundwater Discharge across a Streambed: Heat as a Tracer
. Vadose Zone Journal ; 10 (1): 98–109. doi: https://doi.org/10.2136/vzj2010.0005
Time series analysis of continuous streambed temperature during a period of 47 d revealed that discharge to a stream is nonuniform, with strongly increasing vertical fluxes throughout the top 20 cm of the streambed–aquifer interface. An analytical solution to the transient heat transport equation was used to analyze several pairs of observed amplitude damping with depth. A nonuniform pattern in discharge across the stream width was also observed, which could have been caused by lateral or horizontal flow. Head measurements in a meadow area and below the stream showed strong convergence of flow near the streambed. Seepage meter measurements in the middle of the stream often resulted in highly variable flux estimates, which could have been caused by hyporheic flow due to the presence of a gravel layer. Discharge and recharge to the stream at the bank near the meadow was relatively steady throughout the period. On the other hand, discharge to the stream at the opposite bank near a steep hillslope decreased significantly toward the end of the period (early June), which was attributed to a drop in the water table on this side of the stream. The results from the time series analysis were compared with seepage meter measurements and the results from a steady-state analytical solution to the heat transport equation. The different methods agreed on the pattern of discharge across the stream width, and the mean values during the studied period generally agreed well but with different ranges.
Time series of temperature profiles from multilevel probes installed within a streambed cross-section showed nonuniform discharge with strongly increasing vertical fluxes within the top 20 cm of the streambed–aquifer interface. Differences in conditions for lateral inflow to the stream could be a possible cause for the discharge variation.
SWI, sediment–water interface
The European Union (EU) Water Framework Directive requires EU member countries to administer their water resources in an integrated fashion, where the ecological statuses of different water bodies are treated together. In this respect, groundwater–surface water interactions play a central role (Dahl et al., 2007). In the Skjern River Catchment (SRC) in Denmark, groundwater–stream and groundwater–lake interactions have been investigated at various scales. For example, Kidmose et al. (2011) modeled lake-scale seepage patterns at a flow-through lake in the upper parts of the SRC to see how seepage is affected by lake bathymetry and the depositional character of the lake bed sediments. On-land and offshore geophysical explorations have helped to improve the inclusion of the lake in the regional groundwater flow model, improving the model's ability to simulate the observed seepage patterns.
Heat has been used in many studies as a natural tracer to assess groundwater–surface water exchange at various scales. The seasonal changes in temperature contrasts between the surface water and deeper groundwater make it possible to quantify the direction and magnitude of the exchange (Constantz, 2008). At the kilometer scale, distributed temperature sensing has been used to study groundwater–lake and groundwater–stream interactions (Selker et al., 2006a,b). At the meter scale, point or profile measurements of temperature have been popular for some time (Constantz, 2008). A number of investigations have relied on synoptic measurements, where point measurements of temperature either at a given depth below the streambed (Conant, 2004; Schmidt et al., 2007) or at several depths (Schmidt et al., 2006; Anibas et al., 2009) were used to estimate streambed water exchange. The measurements were usually obtained by pushing a temperature probe into the bed sediments and recording the temperatures after sufficient equilibration time (minutes) or measuring temperature directly in wells (Duque et al., 2010). An advantage of this approach is that several hundreds of meters of a stream can be mapped in a relatively short time to reveal spatial heterogeneity in water exchange (Conant, 2004; Schmidt et al., 2007). Other investigations have relied on time series data at a single depth (Silliman and Booth, 1993; Constantz et al., 2001) or several depths below the streambed (Constantz et al., 2002; Keery et al., 2007). The advantage of this approach is that temporal changes in water exchange can be quantified along a given stream reach (e.g., Keery et al., 2007) or used to determine stream flow frequency and duration for ephemeral streams (Constantz et al., 2001; Duque et al., 2010).
Analytical one-dimensional models solving the heat transport equation have been popular to interpret temperature data at the scale of a streambed because of their simplicity and because the heat flow parameters vary much less across a range of sediment textures than, for example, hydraulic conductivity (Constantz and Stonestrom, 2003). In some cases, more sophisticated one- or two-dimensional numerical models have been used (Constantz, 2008), but the use of numerical models generally requires more information to be operational and therefore can be difficult to apply. Analytical solutions, however, are limited to strictly steady, uniform vertical flow. The analytical solutions are furthermore often based on an assumption of steady-state heat transport (Schmidt et al., 2006; Anibas et al., 2009), where fixed surface water and groundwater temperatures are specified at the two boundaries, using the solution derived by Bredehoeft and Papaopulos (1965). Schornberg et al. (2010) demonstrated that the one-dimensional analytical solutions give reasonable results for discharge (in the following, we use the term discharge to indicate a positive and upward flow of groundwater to the stream and recharge to indicate a negative and downward flow of water from the stream) rates >0.1 m d−1 but only during periods with the greatest contrast in stream water and groundwater temperatures, i.e., typically during winter and summer. Hatch et al. (2006) developed a time series analysis based on an analytical transient solution previously given by Stallman (1965) and Goto et al. (2005). They showed that it is possible to relate exchange fluxes to amplitude damping and phase changes as a function of depth below the streambed. Their analysis was still based on the assumption of one-dimensional steady uniform vertical flow but had the advantage that amplitude damping and phase changes could be computed from sensor pairs located at different depths. Therefore it was not necessary to know the stream temperature, which often is affected by frequencies different from the diurnal signal, e.g., annual frequencies, but also high-frequency noise due to shading by clouds, the effects of vegetation, etc. (Keery et al., 2007). Keery et al. (2007) extended this method and developed a dynamic harmonic regression technique, where the damping and phase change of the temperature signal is directly computed.
In many systems with significant aquifer–stream interaction, the exchange of water between the two systems cannot always be regarded as strictly vertical. A lateral or horizontal flow component will often be present, making the interpretation with the analytical solutions more difficult. Lateral or horizontal flow can occur on various scales: exchange with shallow groundwater systems at the stream banks (Modica et al., 1997, 1998), from hyporheic flow with stream water driven into the streambeds and re-entering the stream farther downstream (Hannah et al., 2009), or from geologic heterogeneities in the streambed or underlying aquifer (Schornberg et al., 2010).
The objectives of this work were (i) to evaluate if discharge to a small stream reach can be regarded as uniform across the streambed by performing a time series analysis of streambed temperature data, and (ii) to evaluate the error introduced by simulating temperature profiles assuming uniform steady-state discharge. This work builds on the time series analysis presented by Hatch et al. (2006) and Keery et al. (2007) but extends their investigations by using multiple sensor pairs below a streambed. Hatch et al. (2006) collected temperature time series at depths of 0.1 and 0.4 m and found temporal changes in recharge fluxes of −3.2 to −0.8 m d−1 based on one pair of sensors. They were not able to use temperature data from the deep sensor and, thus, only had recharge fluxes at one depth. Keery et al. (2007) installed sensors at depths of 0.1 and 0.2 m, but only the shallowest sensor at 0.1 m was used together with the stream temperature. In both of these studies it was therefore not possible to investigate changes in flux with depth. The purpose of our work has therefore been to obtain high-resolution time series data on temperature mainly in the upper 0 to 20 cm of a streambed, allowing us to quantify the change in exchange fluxes across a streambed. Three temperature stations were installed in the stream to depths of approximately 2.5 m below the sediment–water interface (SWI), with a total of 14 sensors at each station and with three to six sensor pairs in the upper 20 cm near the SWI. Two stations were located near the banks and one in the middle of the stream, which furthermore allowed us to investigate the differences in exchange fluxes across the stream width.
Field Site
The Holtum Stream field site is located in Jutland, Denmark, on a glacial floodplain valley west of the last glacial maximum of the Weichsel ice period. The western part of Jutland was the only ice-free part of Scandinavia during the last glacial period. The present landscape is therefore dominated by floodplain sediments on top of deposits from the previous Saale ice period. The contributing catchment is around 126 km2, forming the upper part of the Skjern River basin (Fig. 1 ). The mean annual precipitation is 888 mm yr−1 (1970–2007) and mean annual air temperature is around 9°C (2008).
Stream flow is approximately east to west at the field site, with an annual mean of 1.3 m3 s−1 in 2005 to 2007. Stream temperatures typically range from 16°C in the summer to 2°C in the winter. A low-lying meadow area is found to the north of the stream. A man-made hill with steep slopes and a tree plantation (cut down in the spring of 2008) borders the southern stream bank. Streambed sediments are dominated by sand, sometimes with a layer of coarse boulders in the middle of the stream. Groundwater levels in the meadow area are higher than the stream stage and groundwater flow is toward the stream. The meadow area is always wet, with free-standing water. A small pond is found in the middle and often a small canal connects the pond directly to the stream (seen as a dark shadow from the pond past Piezometer 16 and to the stream, Fig. 1).
Field Methods
Synoptic measurements of hydraulic heads and temperature profiles were conducted during a period of about 9 mo. In addition to this, continuous temperature distributions in the streambed were monitored every 20 min during a 53-d period in the spring of 2008, with a significant rate of change in temperature of the stream water (from 8 to14°C). Seepage meter measurements were conducted 26 d after this period to get an independent estimate of discharge to the stream.
Hydraulic Characterization of Discharge to Stream
Piezometer Network
Twenty-one piezometers were installed in the early spring of 2008 (Fig. 1). The piezometers are constructed of metal pipes (2-cm i.d.) equipped with a 9-cm-long metal screen. The piezometers were pushed 1 to 3.7 m into the subsurface using a pneumatic hammer. Piezometers P1, P2, P3, and P13 were installed in the streambed, the rest in the meadow area. All piezometers were leveled using a standard total station (CTS-1, Topcon Positioning Systems, Livermore, CA) relative to a fixed point above sea level (measured using a Trimble R8 global positioning system, Trimble Navigation Ltd, Sunnyvale, CA). Right after installation, each piezometer was pumped clean for finer sediments that may have been pushed through the screen. The hydraulic heads were measured during a period of about 9 mo.
Seepage Meter
Discharge to the stream was measured with seepage meters at three locations in the stream (upstream of temperature stations T1, T2 and T3; see below) on 2 July 2008 (Fig. 2 ). Each seepage meter was constructed from the bottom part of a steel drum, with a diameter of 57 cm (Lee, 1977). The seepage meters were assembled with fitting valves, 1.5-cm i.d., designed for reducing the effect of friction (Rosenberry, 2005). A 4-L plastic collection bag was attached to the valve. The collection bag was covered with a rigid plastic casing to minimize the effect of stream-flow-induced seepage from movement of the bag (Murdoch and Kelly, 2003; Rosenberry, 2008). The seepage meters were installed as near as possible to the individual temperature stations (and thus called S1, S2, and S3; see below) without influencing the temperature measurement itself. The seepage meters were left to equilibrate for 24 h before any measurements were taken. In total, 12, 22, and 34 measurements were performed at S1, S2, and S3, respectively.
Temperature Characterization of Discharge to Stream
Several synoptic temperature measurements were taken with a Model TP 62 temperature probe similar to that used by Schmidt et al. (2006). The probe has a length of 151 cm, with six temperature sensors distributed unevenly across the lower 50 cm. The sensors have an equilibration time of about 10 min. Some conduction of heat through the metal probe is to be expected and the measurements are therefore best at demonstrating qualitatively how the temperature pattern changes below a stream during a season.
Three permanent temperature stations (T1, T2, and T3) were established in April 2008, Fig. 2. Each temperature station consisted of two separate pipes: a 4.2-m-long metal pipe, which was constructed and installed in the same way as the piezometers, and a plastic pipe carefully pushed 0.65 m into the streambed. A second plastic pipe with four temperature sensors in the lower 1.6 m of the pipe was installed inside the metal pipe. The metal pipe would also lead to some conduction of heat, but the temperature data from these depths were nearly constant and therefore not used in the time series analysis (see below). The temperature data from the deepest sensor (2.95 m under the SWI), however, was used to specify the ambient groundwater temperature as a lower boundary condition in the steady-state heat transport solution (see below).
There were 10 temperature sensors in the plastic pipe positioned directly into the streambed. The first and most shallow sensor measured the stream temperature and the rest measured streambed temperatures from right under the streambed surface and down to a depth of approximately 0.65 m (depending on scouring and sedimentation, however). All 14 sensors in a station were connected to a multiplexer located at the top of the plastic pipe positioned directly into the streambed (Fig. 2). All data from the three multiplexers were sent to a datalogger located in a box in the meadow (Fig. 2).
The temperature sensors were made of thermocouples having an absolute accuracy of about ±1°C. All the sensors were made from the same coil of cable and it was assumed that the accuracy of all the sensors was the same. Thermocouples have the advantage of being easy to deploy because they can be fabricated as needed from a thermocouple cable. Each thermocouple end installed in the plastic pipes was welded to a copper ring, which was placed in a groove carved on the outside of the plastic pipe and then covered by a thin layer of plastic insulation to resist water. This approach was used in an attempt to ensure good contact between the individual temperature sensors and the streambed sediments. Thermocouples operate on the principle that dissimilar metals in a circuit develop a voltage proportional to the temperature difference between their connections (Stonestrom and Constantz, 2003).
A disadvantage of using thermocouples is that a known reference temperature inside the box with the multiplexer has to be measured. The reference temperature was measured with a thermistor with a calibrated accuracy of 0.2°C. This can lead to small errors, which will influence the temperature measurements for the entire streambed profile (J. Constantz, personal communication, 2008). To reduce this error, the multiplexer box and the reference temperature measurement point were insulated with rubber foam. The temperature records were still corrected, however, for the influence of any small fluctuations inside the multiplexer box, which could be the result of small temperature differences between the reference point and the individual attachments of the thermocouple cable ends in the multiplexer box (J. Constantz and R. Niswonger, personal communication, 2008). Temperatures were measured at each sensor every minute and the mean temperature during a 20-min period was stored in the datalogger. The period of temperature measurements was from 21 April to 6 June 2008.
Conduction and convection of heat in the upper part of the streambed is assumed to be governed by the one-dimensional conduction–convection equation (Stallman, 1965; Goto et al., 2005; Hatch et al., 2006):
\[\frac{{\partial}T}{{\partial}t}{=}\mathrm{{\alpha}}_{\mathrm{e}}\frac{{\partial}^{2}T}{{\partial}z^{2}}{-}\frac{n\mathrm{{\nu}}_{\mathrm{f}}}{\mathrm{{\gamma}}}\frac{{\partial}T}{{\partial}z}\]
where T(z,t) is temperature (°C), which varies with time t (s) and depth z (m), αe is the effective thermal diffusivity (m2 s−1), γ is the ratio of the volumetric heat capacity of the streambed to the fluid (= ρc/ρfcf, where ρc is the volumetric heat capacity of the saturated sediment–fluid system [J m−3 °C−1], ρ is the density of the sediment–fluid system [kg m−3], c is the specific heat capacity of the sediment–fluid system [J kg−1 °C−1], ρfcf is the volumetric heat capacity of the fluid [J m−3 °C−1], ρf is the density of the fluid [kg m−3], and cf is the specific heat of the fluid [J kg−1 °C−1]), n is porosity, and vf is the pore water velocity (m s−1).
The effective thermal diffusivity is defined as (Ingebritsen and Sanford, 1998)
\[{\alpha}_{\mathrm{e}}{=}\frac{\mathrm{{\kappa}}_{\mathrm{e}}}{\mathrm{{\rho}}c}\]
where κe is the effective thermal conductivity (W m−1 °C−1). Thermal dispersion is ignored because the thermal conductivity of different materials is relatively high and efficient in homogenizing any local temperature variations, making the influence of hydrodynamic dispersion less important in heat transport than in solute transport (Ingebritsen and Sanford, 1998).
Steady-State Solution
The steady-state analytical solution to Eq. [1] is (Bredehoeft and Papaopulos, 1965)
\[T(z){=}T_{s}{+}(T_{g}{-}T_{s})\frac{\mathrm{exp}\left[N_{\mathrm{pe}}(z/L){-}1\right]}{\mathrm{exp}(N_{\mathrm{pe}}{-}1)}\]
where Ts is the stream temperature (°C), Tg is the groundwater temperature (°C) at a depth L under the streambed (m), and Npe is the Peclet number expressing the ratio of convection to conduction:
\[N_{\mathrm{pe}}{=}\frac{q_{\mathrm{z}}\mathrm{{\rho}}_{\mathrm{f}}c_{\mathrm{f}}L}{{\kappa}_{\mathrm{e}}}\]
where qz is the vertical Darcy flux (m s−1). The steady-state solution is most suitable in periods where there is a marked difference in temperature between the groundwater and stream and during periods with stable temperatures as, for example, in winter and summer (e.g., Schmidt et al., 2006; Anibas et al., 2009).
Transient Solution
The solution to Eq. [1] given sinusoidal variations in stream temperature at the streambed surface is (Hatch et al., 2006)
\begin{eqnarray*}&&T(z,t){=}A\mathrm{exp}\left(\frac{\mathrm{{\upsilon}}z}{2\mathrm{{\alpha}}_{\mathrm{e}}}{-}\frac{z}{2\mathrm{{\alpha}}_{\mathrm{e}}}\sqrt{\frac{\mathrm{{\epsilon}}{+}\mathrm{{\upsilon}}^{2}}{2}}\right)\\&&{\times}\mathrm{cos}\left(\frac{2\mathrm{{\pi}}t}{P}{-}\frac{z}{2\mathrm{{\alpha}}_{\mathrm{e}}}\sqrt{\frac{\mathrm{{\epsilon}}{-}{\upsilon}^{2}}{2}}\right)\end{eqnarray*}
where A is the amplitude of temperature variations at the streambed–aquifer interface (°C), P is the period of temperature variations (s) defined by P = 1/f, where f is the frequency (cycles s−1), and ε is defined by
\[\mathrm{{\epsilon}}{=}\sqrt{\mathrm{{\upsilon}}^{4}{+}\left(\frac{8\mathrm{{\pi}}\mathrm{{\alpha}}_{\mathrm{e}}}{P}\right)^{2}}\]
The rate of penetration of the thermal front, v, is proportional to the pore water velocity and defined by v = nvf/γ (modified from Hatch et al., 2006). The exponential term on the right-hand side of Eq. [5] defines the damping of temperature amplitude variations with depth into the streambed. The cosine term defines the shift in phase with depth. As a result, the predicted temperatures at different depths are a nonlinear function of the thermal properties of the sediment and fluid, the fluid velocity, and the frequency of surface temperature variations (Hatch et al., 2006).
Hatch et al. (2006) proposed a method for quantifying exchange fluxes based on phase and amplitude variations between pairs of subsurface sensors (Fig. 3 ). Equation [5] is separated into components and solved for the ratio of amplitude variations between pairs of temperature measurement points at different depths:
\[\mathrm{{\upsilon}}_{A_{\mathrm{r}}}{=}\frac{2\mathrm{{\alpha}_{e}}}{{\Delta}z}\mathrm{ln}A_{\mathrm{r}}{+}\sqrt{\frac{\mathrm{{\epsilon}}{+}\mathrm{{\upsilon}}^{2}}{2}}\]
where Ar is the ratio of the amplitude at the deep (Ad) and shallow (As) locations, Ad/As; or it is solved for the phase shift between the two measurement points (Δϕ):
\[\mathrm{{\upsilon}}_{{\Delta}\mathrm{{\phi}}}{=}\sqrt{\mathrm{{\epsilon}}{-}2\left(\frac{{\Delta}\mathrm{{\phi}}4\mathrm{{\pi}}\mathrm{{\alpha}}_{\mathrm{e}}}{P{\Delta}z}\right)}\]
where it has been assumed that the sediment properties do not change between the two points.
The thermal front velocity, v, appears on both sides of the equations, explicitly or embedded in the ε term, requiring that Eq. [7] and [8] be solved iteratively. The Darcy flux (qz) is then found from v = nvf/γ = qz/γ. Equations [7] and [8] were used to quantify vertical temporal changes in discharge to the stream during the period with continuous thermal data. Before using Eq. [7] and [8], the temperature data were filtered using a band-pass filter to obtain a diurnal signal. Due to filtering edge effects (Hatch et al., 2006), the data record was shortened to 47 d.
Groundwater Flow and Seepage Meter
The isopotential lines in the meadow area and below the stream along the transect (Fig. 1) are shown in Fig. 4 . The data are from 12 June 2008. The stream stage was 50.6 m, giving an overall horizontal gradient of 0.018 and a vertical gradient below the stream of approximately 0.67. The interpreted flow lines converge below the streambed and indicate that a significant amount of groundwater will discharge to the stream, not just from the adjacent meadow area but also from deeper parts. At the bank near the meadow area, there could be a significant horizontal component of discharge to the stream, while in the middle of the stream, discharge will be more vertical. In the northern and most shallow part of the meadow, groundwater discharges directly to the surface; this probably explains why standing water is almost always found in these areas.
The mean discharges measured by the seepage meters were very different among the three sites: 0.07 m d−1 for S1 with a minimum and maximum of 0.06 and 0.08 m d−1, respectively; 1.34 m d−1 for S2 with a minimum and maximum of 0.56 and 2.05 m d−1, respectively; and 1.73 m d−1 for S3 with a minimum and maximum of 1.41 and 1.90 m d−1, respectively. Discharge was highest near the southern bank and lowest near the northern bank. The seepage meter data from S2 were the most unsteady. This might be a result of hyporheic flow caused by the imposed velocity field around the rigid plastic casing, which would have the greatest effect in the middle of the stream where the flow velocity is highest (Murdoch and Kelly, 2003; Rosenberry, 2008). Hyporheic flow can also be induced by a sudden shift in the streambed profile, which was also the case primarily near S2. The streambed was rather irregular upstream of S2, with big differences in water depth and with turbulent stream flow. The sediments in the middle of the stream were also more loose and coarse grained, which could promote a higher degree of hyporheic flow here than at the two banks, where more fine-grained sediment materials were found.
Seasonal Temperature Distributions
Three cross-sectional temperature distributions are shown in Fig. 5 , spanning the period from late summer to the middle of winter (the end of August 2007 to the end of January 2008), recording the change from warm to cold streambed temperatures. In August there was an indication of high discharge in a distinct narrow zone 2 m from the northern bank (left-hand side of profile), where groundwater temperatures were observed near the streambed. The contrast in temperature at other locations was around 4°C. Data from September showed a cooling of the streambed, with almost uniform temperatures around 8°C, making it difficult to trace any discharge to the stream. The results from January 2008 show a two-layered temperature distribution, with about 5°C water in the shallow part of the streambed overlying 7 to 8°C water. Thus, there was no clear evidence of zones with distinct discharge to the stream. At this time the discharge to the stream looked very uniform. These snapshots of the temperature distribution indicate that the discharge to this small segment of a stream may be highly dynamic with time.
Steady-State Heat Transport Solutions
Discharge was estimated by fitting solutions of Eq. [3] to the observed temperature profiles at Stations T1, T2, and T3; an example from 20 May 2008 is given in Fig. 6 . The values of Tg and Ts in Eq. [3] were given as 8 and 11.2°C, respectively. Data were selected at 1800 h to get the maximum temperature difference between the stream and groundwater. At this time of the day, the stream temperature on average is at its highest. The characteristic time scale for heat transport by conduction is τ = l2/αe, where l is the transport length (Turcotte and Schubert, 2002). If it is assumed that the characteristic length is 10 cm, across which the temperature changes from that of groundwater to that of stream water, then τ is on the order of a few hours given the parameters in Table 1 . We therefore decided to use the 1800 h measurement of the stream water temperature as the boundary condition Ts. This is different from Schmidt et al. (2006), who used the average stream water temperature during several days. The fitting parameter in Eq. [3] was the discharge, qz. There was high discharge at T2 (0.69 m d−1) and T3 (1.17 m d−1), as shown by the 8°C warm water near the streambed. The results for the other days are summarized in Fig. 7 . The highest discharge was always recorded at T3 during the period of 1 May to 6 June 2008, followed by discharge at T2, then T1 (Fig. 7). There was a trend of increasing discharge at T2 (0.4 to 0.65 m d−1) and T3 (0.85 to 1.2 m d−1) and slightly decreasing discharge at T1. The seepage meter measurements were conducted in early July and showed slightly higher discharge at T2 (1.34 m d−1) and T3 (1.73 m d−1) and approximately the same discharge at T1 (0.07 m d−1). In general, the pattern of discharge to the stream is correct, given the limitation of both methods. For example, the analytical solution only predicted the vertical component of discharge to the stream assuming a constant discharge rate and steady-state conditions. As discussed above, there may have been horizontal components, especially near the banks and below it is shown that the discharge rate was probably not constant below the streambed. Furthermore, the assumption of steady state can be violated, which will influence the fitted discharge (Anibas et al., 2009; Schornberg et al., 2010). The seepage meter measurements also revealed that discharge can change rapidly during a single day, especially near T2, where discharge ranged from 0.56 to 2.05 m d−1.
Transient Heat Transport Solution
Unfiltered temperature time series data from T1, T2, and T3 show clear damping and phase shift with depth (Fig. 8 ). The temperature data were from the shallowest sensors. except at T1, where Sensor 4 from the top was used (due to streambed scouring). There was a clear damping of the stream temperature signal at T2 and T3, with the largest damping at T3. There was much smaller damping at T1. Qualitatively, these observations match those based on seepage meter measurements and the steady-state heat transport solution, with the highest discharge (the greatest damping) at T3 and the lowest at T1.
Figure 9 shows an example of filtered data from T1 using Sensors 4 and 7 (Sensor Pair [SP] 4) that had a spacing of 15 cm. Sensors located deeper than 20 cm resulted in uncertain estimations because of too much damping. At T2 and T3, the maximum spacing used was 9 and 4 cm, respectively, and the maximum distance from the streambed surface was 13.5 and 9 cm, respectively. Table 2 shows the different sensors used, sensor pairs, respective spacing, and relative distance of the midpoint of a sensor pair to the streambed, as illustrated in Fig. 10 for T1. After filtering, the temperature changes showed a clear diurnal signal.
Temporal exchange rates between the stream and groundwater were estimated using Eq. [6] on a daily basis for a period of 47 d from 21 April to 6 June 2008 (Fig. 11 ). Six time series are available for T1 and T2, while it was only possible to obtain three time series for T3 due to significant groundwater discharge and, hence, great damping of the stream temperature signal. The mean discharge is also shown. Previous applications of Eq. [6] only solved for the flux at one location below the streambed. We were able to estimate the exchange flux at several locations, however, given the spatial and temporal resolution of the temperature signal in our data set.
At T1, it was not possible to use data from sensors located deeper than 20 cm under the streambed (Sensor 7; Table 2; Fig. 10). Below these depths, the sensors recorded temperatures with opposite high and low peaks and, moreover, also with higher amplitudes than at sensors located above. It is not clear why this was the case. Exchange between the stream and groundwater was mostly negative (losing stream) and increased downward. Thus, the time series data suggest recharge of the aquifer at the northern bank with a mean recharge of −0.15 m d−1 during the whole period—quite different from the results obtained by seepage meter and the steady-state heat transport solution. The three upper sensor pairs (SP1, SP2, and SP3), however, showed upward flow (discharge) at certain times, e.g., around 10 to 20 May, when discharge increased upward. Also, these sensor pairs always showed less positive or negative exchange compared with the three other (deeper) pairs of sensors (SP4, SP5, and SP6). The location of the midpoints of the two sensor pairs SP3 and SP4 were the same. It is therefore possible to evaluate the order of magnitude of the error in the estimated discharge because the two fluxes should be approximately the same assuming that the change in discharge with depth did not change too dramatically. The flux at SP3, however, was consistently 0.1 m d−1 higher than at SP4. It therefore seems that the data quality and the time series analysis make it impossible to resolve fluxes with greater precision than about 0.1 m d−1. This is similar to the error estimated in a numerical analysis using the one-dimensional analytical solution on temperature profiles extracted from the results of a two-dimensional numerical heat transport model (Schornberg et al., 2010). This may also explain why it is possible to see upward flow (<0.1 m d−1) at the three upper sensor pairs at the same time as downward flow at the three lower pairs during the period of 10 to 20 May. From the other sensor pairs, the estimated discharge clearly showed a steady pattern but with a noticeable decreasing trend from 20 May to the end of the measurement period.
At T2, the exchange rate was estimated for all sensor pairs between Sensors 2 and 5 (Table 2) (<13.5 cm below the streambed). Data from sensors located deeper than this had significant damping. The exchange rates were always positive and represent discharge to the stream. Discharge was very dynamic during the first two-thirds of the period until about 22 May, after which the fluxes stabilized. The discharge in the top 13.5 cm varied from 0 to 1.8 m d−1. Before 22 May, discharge was very irregular, with no apparent pattern; sometimes the flux was highest in SP6 and lowest in SP1, sometimes highest in SP3 and lowest in SP6. This is similar to the seepage meter measurements, where great variations (0.56–2.05 m d−1) were recorded during a single day. Again, the reason for this might be hyporheic flow or a complex flow field within the more stony sediments found at T2. During the last third of the period (from 22 May), the fluxes showed less fluctuation, as at T1. The three and two sets of sensor pairs SP1 to SP3 and SP4 to SP5 predicted almost the same discharge (within the precision of 0.1 m d−1 found from the analysis of the responses in T1). The discharge therefore increased upward in a consistent way, suggesting that flow from the banks and the deeper parts converged below the middle part of the stream. From these results, it is clear that there was not a constant discharge rate below the stream (as assumed for the steady-state solution). The mean Darcy flux for the whole period was 0.80 m d−1; thus the stream was gaining water at T2 in good agreement with the results of both seepage meter measurements and the steady-state heat transport solution results. The estimated discharge 7.5 cm below the stream bottom (SP1) was approximately 1.2 m d−1, close to the mean seepage meter flux of 1.34 m d−1 (measured ∼1 mo later, however). The discharge fluxes at T2 did not show the same decreasing trend with time as observed at T1.
Discharge at T3 was estimated for three pairs of sensors, using Sensors 2, 3, and 4 (<9 cm below the streambed; Table 2). Data from sensors located lower than this showed a very high damping and were not useful in the analysis. The mean discharge for the whole period was 0.90 m d−1, indicating that the stream gained water at T3, in good agreement with the results from the seepage meter measurements and the steady-state heat transport solutions. The discharge was, as at T1, uniform and consistent more or less throughout the entire time series (28 April−31 May), with discharge increasing upward toward the stream bottom. After 3 June, Ar for SP3 was >1 and no solution was found. At this time, discharge was close to zero at this depth, indicating a negative flow, which does not seem likely. The mean seepage meter flux of 1.73 m d−1 measured in early July was much higher than predicted at the stream bottom (∼0.5 m d−1 on 6 June, SP1). There was a significant decrease in discharge toward the end of the monitoring period, which may be explained by a falling water table on this side of the stream with a steep hillslope.
Summary of Exchange Rates
Figure 12 summarizes the exchange fluxes estimated by the different methods. The temporal mean values plus the minimum and maximum values are shown. The mean values of the different temperature spacings and the results from the sensor pairs nearest to the streambed (SP1) were used in the case of the transient heat transport results. Overall, there is good agreement between the different methods in that all methods predicted a low exchange flux (recharge and discharge) at T1 and high exchange fluxes (only discharge) at T2 and T3. The mean flux measured by the seepage meters was higher than the estimates based on temperature for T2 and T3. Recall, however, that seepage meter results were all measured on a single day about 1 mo after the temperature data, whereas the results based on temperature are mean values for a 47-d period. The results from SP1 give a better agreement with the seepage meter results than using mean values of all the sensor pairs. The different seepage meter results measured at T2 can be explained by hyporheic flow caused by the presence of a gravel layer and, potentially, an added pressure-driven flow through this layer due to the installation of the seepage meter. The two temperature-based methods are in reasonable agreement; however, at T1 the transient solution predicted a low recharge flux, while the steady-state solution predicted a low discharge flux. At the moment it is not possible to explain why the transient solution gave a negative flux except that there was probably a significant horizontal flow component that made the use of both temperature-based methods problematic. The seepage meter results were somewhere in between, estimating a near-neutral exchange at T1.
The steady-state solution generally gave very good fits to individual temperature profiles (Fig. 6). The mean discharge rates compared well with the mean values obtained from the transient solutions, despite the fact that the observations from using the transient solution (Fig. 11) suggest that it is not possible to assume strictly uniform flow. This is also reflected in the larger error bars on the estimates based on the transient solution. The results from using the transient solution also demonstrate that during long periods there was a consistent trend with increase in the discharge flux (T2 and T3) as the SWI was approached. A possible explanation is that flow was not strictly vertical but rather converged near T2 and T3. Similar observations have been found from the analysis of temperature profiles in deep bore holes (Reiter, 2003).
Time series analysis of continuous streambed temperature data from three stations—two near the banks and one in the middle of the stream—shows that discharge in the upper 20 cm of the streambed was not uniform within a station or between stations. This occurred during a 47-d period in April to June of 2008, when temperature gradients between the stream and groundwater reversed. Across the stream, the exchange fluxes varied dramatically, from very little discharge (and sometimes recharge) to 0.80 to 0.94 m d−1 (on average) at the two other stations. The accuracy of the equipment and limitation of the time series analysis (e.g., neglecting heterogeneity in heat parameters in the model development, data filtering etc.) indicate that only fluxes >0.1 m d−1 could be resolved. The station with the smallest fluxes also has the most steady fluxes with time (but close to the precision of the method), while the station in the middle had the most unsteady fluxes, which we suspect to be caused by hyporheic flow due to the presence of a gravel layer in the middle of the stream. The unstable discharges were confirmed by seepage meter measurements. The third station displayed a significant decrease in discharge toward the end of the monitoring period, which may be explained by a falling water table on this side of the stream with a steep hillslope. The same phenomenon was not seen at the other bank due to the meadow area, which has a constant water table near the surface year-round. At the two stations with high discharge, fluxes varied as much as 1.6 m d−1 across just 5.5 cm. During long periods with stable discharge, the fluxes increased upward, suggesting that there is significant lateral and horizontal flow that can account for the increase in flow upward. This was confirmed by inspecting the measured flow field below the streambed and in an adjacent meadow area. Flow along the stream and hyporheic flow are other explanations that will cause nonuniform upward flow.
The results from the time series analysis were compared with seepage meter measurements and simulation results using a steady-state heat transport solution. Generally, the pattern was the same among the different methods but with noticeable differences in mean values and ranges. The order of magnitude in exchange fluxes we believe were estimated correctly by the simple analytical methods; however, numerical methods are needed to more accurately predict the spatial and temporal discharges to the stream. Previous applications of time series analysis have been limited to only one sensor pair (one depth below the streambed); however, we used several sensor pairs (several depths below the streambed) to improve our understanding of the flow pattern below a streambed.
GEOCENTER DENMARK and the Villum Kann Rasmussen Centre of Excellence HOBE provided funding. We would like to acknowledge Peer Jørgensen for help with both development and installation of the temperature equipment as well as assistance with field equipment. Thanks to J. Constantz, R. Niswonger, and A. Fisher for their help and fast email correspondence on data filtering of the initial temperature data.
Soil Science Society of America
Freely available online through the author-supported open access option.
heat flow Denmark Jutland hydrology Europe ground water hydrogeology Scandinavia Western Europe
Holtum field site in Jutland, Denmark; P1 to P21 mark the locations of the installed piezometers. The white dashed line marks the geologic profile.
Temperature stations (T1, T2, and T3) and seepage meters (S1, S2, and S3). Locations of both are indicated in schematic. Reference temperatures are measured inside the white boxes on top of each station and sent to the logger located on the pole on the meadow.
Damping and phase attenuation of temperature with depth: (a) station with temperature sensors at selected depths; (b) temperature signals in stream and two depths (subscripts s = shallow, d = deep) showing the reduction in amplitude (ΔA = As − Ad) and phase shift (Δϕ) (modified from Hatch et al., 2006).
Isopotential and interpreted flow lines along transect (Fig. 1), 12 June 2008. Stream stage is 50.6 m. Groundwater converges from the meadow area and from deeper parts below the stream. Groundwater discharges to the surface in the northern part of the transect.
Temperature distributions on 27 Aug. and 19 Sept. 2007 and 31 Jan. 2008 measured with a T62 probe. Positions shown in upper left panel are for measurements made 27 Aug. 2007; the positions on the other days were not exactly the same. The profiles are looking upstream (as in Fig. 4), with the northern bank (meadow) to the left.
Simulated and modeled temperature distributions (20 May 2008) at Stations T1, T2, and T3. The fitted exchange fluxes (qz) are shown; they are all positive, indicating upward flow (discharge).
Darcy flux estimations based on steady-state heat transport solution and on daily temperature profiles taken at 1800 h. Positive values indicate discharge to the stream.
Continuous temperature data recorded in the stream by the most shallow sensor at Stations T2 and T3 and Sensor 4 at Station T1 (due to scouring) during the period 20 to 30 May 2008. The three sensors show very different damping, indicating the highest discharge at T3 and the lowest discharge at T1.
Filtered temperature data for two temperature sensors, 4 and 7 (Sensor Pair 4), at Station T1.
Positions of uppermost sensors at Station T1 used in the time series analysis and sensor pairs (SP) with spacings (in cm) and relative distance to the streambed for Darcy flux estimations.
Exchange rates between aquifer and stream using transient heat transport solution for sensor pairs (SP) at Stations T1, T2, and T3. Negative and positive values are recharge (losing stream) and discharge (gaining stream), respectively.
Summary of estimated exchange rates at seepage meters (S) and temperature stations (T) 1, 2, and 3. The transient solution for the first sensor pair (SP1) is also shown separately because this position was nearest to the streambed–aquifer interface, illustrating the exchange fluxes nearest to the streambed. The symbols are the means of all measurements. Error bars illustrate the range. Negative and positive values are recharge (losing stream) and discharge (gaining stream), respectively.
Physical and heat parameters used in the steady-state and transient heat transport solutions at the three temperature stations T1, T2, and T3.
T1 and T3
Density of the streambed sediment-fluid system (ρ), kg m−3† transient 2000 2300
Specific heat capacity of the streambed sediment-fluid system (c), J kg−1 °C−1† transient 1401.6 1091.5
Porosity (n)‡ transient 0.3 0.3
Thermal conductivity (ke), W m−1 °C−1† transient, steady state 1.84 2.47
Density of the fluid (ρf), kg m−3§ transient, steady state 999.7 999.7
Specific heat capacity of the fluid (cf), J kg−1 °C−1§ transient, steady state 4192 4192
Depth with steady groundwater temperature (L), m‡ steady state 5 5
Groundwater temperature at depth L (Tg), °C¶ steady state 8.07 8.07
Stream temperature (Ts), °C¶
steady state
Lapham (1989).
Assumed value.
Andersen et al. (1995).
Position of each sensor pair (SP) used, spacing, and relative distance to streambed for Darcy flux estimations. Data were collected 20 May and 1 June 2008. Distance to streambed is relative because of streambed scouring but distances between individual sensor pairs are constant.
Temperature Station 1
Sensor pair
Distance to streambed
cm cm cm
T1_1_4 vs. T1_1_5 (SP1) 5 7.5 T2_1_2 vs. T2_1_3 (SP1) 2 8.0 T3_1_2 vs. T3_1_3 (SP1) 2 7.0
T1_1_4 vs. T1_1_6 (SP2) 10 10.0 T2_1_2 vs. T2_1_4 (SP2) 4 9.0 T3_1_2 vs. T3_1_4 (SP2) 4 8.0
T1_1_5 vs. T1_1_6 (SP3) 5 12.5 T2_1_3 vs. T2_1_4 (SP3) 2 10.0 T3_1_3 vs. T3_1_4 (SP3) 2 9.0
T1_1_4 vs. T1_1_7 (SP4) 15 12.5 T2_1_2 vs. T2_1_5 (SP4) 9 11.5
T1_1_6 vs. T1_1_7 (SP6)
rivers and streams
sediment-water interface
seepage
western Denmark
hyporheic flow
HOBE Project
Skjern River basin
N55°55'00" - N56°00'00", E09°00'00" - E09°10'00"
E.S.
Jespersgaard
Østergaard
Databook for chemistry and physics
. 6th ed. (In Danish.)
F&K Publ
Anibas
Fleckenstein
Volze
Batelaanl
Transient or steady-state? Using vertical temperature profiles to quantify groundwater–surface water exchange
Hydrol. Processes
Bredehoeft
Papaopulos
Rates of vertical groundwater movement estimated from the Earth's thermal profile
Water Resour. Res
Delineating and quantifying ground water discharge zones using streambed temperatures
Constantz
Heat as a tracer to determine streambed water exchanges
W00D10
, doi:10.1029/2008WR006996.
Niswonger
Analysis of temperature profiles for investigating stream losses beneath ephemeral channels
Stonestrom
Heat as a tracer of water movement near streams
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(ed.)
Heat as a tool for studying movement of groundwater near streams. Circ. 1260
Analysis of streambed temperatures in ephemeral channels to determine streamflow frequency and duration
Langhoff
Refsgaard
Review of classification systems and new multi-scale typology of groundwater–surface water interaction
J. Hydrol
Calvache
Engesgaard
Investigating river–aquifer relations using water temperature in an anthropized environment (Motril-Salobreña aquifer)
Yamano
Thermal response of sediment with vertical fluid flow to periodic temperature variation at the surface
J. Geophys. Res
, doi:10.1029/2004JB003419.
Seasonal hyporheic temperature dynamics over riffle bedforms
Revenaugh
Ruehl
Quantifying surface water–groundwater interactions using time series analysis of streambed thermal records: Method development
Ingebritsen
Groundwater in geologic processes
Cambridge Univ. Press
Keery
J.W.N.
Temporal and spatial variability of groundwater–surface water fluxes: Development and application of an analytical method using temperature time series
Kidmose
Laier
Spatial distribution of seepage at a flow-through lake: Lake Hampen, western Denmark
Vadose Zone J
(this issue).
Lapham
W.W.
Use of temperature profiles beneath streams to determine rates of vertical ground-water flow and vertical hydraulic conductivity
Water-Supply Pap
A device for measuring seepage flux in lakes and estuaries
Limnol. Oceanogr
L.N.
Evaluating the source and residence times of groundwater seepage to streams, New Jersey Coastal Plain
T.E.
Patterns and age distribution of ground-water flow to streams
Factors affecting the performance of conventional seepage meters
Using precision temperature logs to estimate horizontal and vertical groundwater flow components
Rosenberry
Integrating seepage heterogeneity with the use of ganged seepage meters
Limnol. Oceanogr. Methods
A seepage meter designed for use in flowing water
Bayer-Raich
Characterization of spatial heterogeneity of groundwater–stream water interactions using multiple depth streambed temperature measurements at the reach scale
Hydrol. Earth Syst. Sci
Evaluation and field-scale application of an analytical method to quantify groundwater discharge using mapped streambed temperatures
Schornberg
Kalbus
Simulating the effects of geologic heterogeneity and transient boundary conditions of streambed temperatures: Implications for temperature-based water flux calculations
Adv. Water Res
Selker
Thévenaz
Huwald
van de Giesen
Stejskal
Parlange
Distributed fiber-optic temperature sensing for hydrologic systems
Fiber optics opens window on stream dynamics
Geophys. Res. Lett
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Silliman
Analysis of time-series measurements of sediment temperature for identification of gaining vs. losing portions of Juday Creek, Indiana
Stallman
Steady one-Dimensional fluid flow in a semi-infinite porous medium with sinusoidal surface temperature
(ed.).
Heat as a tool for studying the movement of ground water near streams. Circ. 1260
Turcotte
Geodynamics
. 2nd ed.
Comparison of Hydrological Simulations of Climate Change Using Perturbation of Observations and Distribution-Based Scaling
Salinity Distribution in Heterogeneous Coastal Aquifers Mapped by Airborne Electromagnetics
Evaluation of Climate Input Biases and Water Balance Issues Using a Coupled Surface–Subsurface Model
An Operational Weather Radar–Based Quantitative Precipitation Estimation and its Application in Catchment Water Resources Modeling
Impact of Precipitation Spatial Resolution on the Hydrological Response of an Integrated Distributed Water Resources Model
Chapter 3. The relation of subsurface water to downslope movement and failure
Groundwater Geomorphology; The Role of Subsurface Water in Earth-Surface Processes and Landforms
Digital modeling of karst aquifers—Successes, failures, and promises
Perspectives on Karst Geomorphology, Hydrology, and Geochemistry - A Tribute Volume to Derek C. Ford and William B. White
Groundwater flood hazards and mechanisms in lowland karst terrains
Advances in Karst Research: Theory, Fieldwork and Applications
10. On the efficacy of monitoring wells in karstic carbonate aquifers
13. Analysis of hydrologic and geochemical time-series data at James Cave, Virginia: Implications for epikarst influence on recharge in Appalachian karst aquifers


We are a small value added producer focusing on seasonal soups, sauces, broths and dips. We run our own farm as well as purchase/source many local ingredients. During the summer months we run a pop up clam shack, Cans -n- Clams.


text:
Governor, First Lady to host third Recovery Reinvented event next week, announce new initiatives
Thursday, November 7, 2019 - 04:00pm
BISMARCK, N.D. – Gov. Doug Burgum and First Lady Kathryn Burgum will host the third Recovery Reinvented event next week at the Bismarck Event Center, a day focused on advocacy, building recovery support in communities, creating recovery-friendly workplaces and eliminating the shame and stigma surrounding addiction.
"This year we are focusing on giving individuals, communities and businesses the tools to create supportive cultures for recovery," First Lady Burgum said. "The incredible speakers and resources will inspire people to take that next step to either find recovery or start grassroots efforts in their communities to end stigma and empower recovery."
The daylong event from 8 a.m. to 4:30 p.m. Tuesday will feature both national and state experts focusing on addiction and recovery. The governor and first lady will announce new initiatives to support employers and businesses to create recovery-friendly workplaces, as well as programs for family members.
Featured speakers include:
Gary Mendell, the founder and CEO of Shatterproof, a national nonprofit focused on reversing the course of the addiction crisis in America. After losing his son Brian to addiction in 2011, Mendell founded Shatterproof to spare other families the tragedy his had suffered. Since founding Shatterproof in 2012, Mendell has been a national leader in the addiction space, creating solutions that will create more access to treatment for opioid and substance use disorders, including the creation of the Shatterproof National Principles of Care to guide providers, payers and patients to quality treatment. He advocates for state and federal policy changes and soon will be launching a national strategy and call to action to address stigma related to opioid and substance use disorders.
Riley Salmon is a three-time Olympian and 2008 Olympic Gold medalist for USA Men's Volleyball team. He played professional indoor volleyball for 17 seasons as well as three professional seasons for the AVP Beach Tour. Salmon struggled with addiction for the better part of 10 years and has been in recovery for 22 months. He currently serves as the head coach for the men's volleyball team at the University of Jamestown.
Carol McDaid, co-founder of McShin Foundation, is a person in long-term recovery with over 25 years of federal legislative experience in Washington, D.C. Having established one of Virginia's leading peer-to-peer recovery community organizations with her husband, her experience will translate how to effectively engage communities to support recovery. McDaid also played a strong role in the passing of landmark legislation requiring insurers to treat addiction, mental and physical health problems equally.
Dr. Leander "Russ" McDonald is the current president of United Tribes Technical College in Bismarck. McDonald is an enrolled member of the Spirit Lake Nation and a proud descendant of the Sahnish, Hidatsa, and Hunkpapa Nations. Prior to beginning his role as president of UTTC in 2014, McDonald served as chairman for the Spirit Lake Nation and was an assistant professor at the University of North Dakota Center for Rural Health. His published research focused on Native American elders' health risks and disparities, American Indian veterans' access to health care, and American Indians' behavior risk factors. An example of the power of recovery, McDonald is a person in long-term recovery for 25 years after going through treatment 16 times.
As with the previous two events, those attending will have the opportunity to receive training in how to administer naloxone, a medication designed to rapidly reverse the symptoms associated with opioid overdose in emergency situations. Doses of the medication will be available for participants to take with them after the event.
The event also will include a Recovery Resources Expo with booths of providers, resources and programs that are transforming recovery in North Dakota communities.
Recovery Reinvented is free and open to the public and registration is required. For more information or to register, visit www.recoveryreinvented.com. The event will be livestreamed on the website and viewing parties will be held in several cities, with location details to be made available on the website. Continuing education units are available for those attending the event or one of the viewing parties.
A media availability with the governor and first lady will take place at 12:15 p.m. in the lobby registration area.

redpajama_set_name: RedPajamaCommonCrawl


Looking through the citroen accessories brochure right now-is it the one that goes in the blank space under the CD player?
(14-08-2012, 07:32 PM)evdama Wrote: Looking through the citroen accessories brochure right now-is it the one that goes in the blank space under the CD player?
Re: stresseddad Oven Removal: Just followed up your link regarding your oven.
Might spend the rest of this week sniffing Berlingo vans in the hope of something warm and tasty.
It looks like theirs 2 bolts on mine and in theory the oven should slide out, (the panels around it are all bolted to hide the gaps around oven so their quite easy to take off, will get some pice and upload later on as picking it up in a lil while, will also do a write up on how easily/hard it was to remove, doing google is hopeless but have managed to read an add where they say it can be removed to turn into normal van.


text:
Heidar Helguson
Posted by watfordlegends | 00s, Interviews, Players
Iceland international striker Heidar initially signed for Watford in a club record £1.5 million deal in early 2000. His all action style of play made him a popular player with the fans, and in his final season he won the Player, Goal and Display of the Season awards. He left to join Fulham, but returned to the club on loan in 2009. In total, he played more than 200 games for the club, scoring 66 goals.
Now retired and running a B&B back in Iceland, Heidar spoke to Watford Legends while at QPR in 2012.
Hi Heidar. Thanks for talking to Watford Legends. It was Graham Taylor that signed you for Watford initially in 1999, how did the move come about?
I was playing in Norway at the time and Watford came to watch me in a few games. It was nothing more than that really, though I'm not sure how they became aware of me in the first place. But they watched me for a few games and then offered up the money that was required to sign me. It was as simple as that really, they obviously liked what they saw when they watched me play.
Were there any other clubs in for you at the time?
There were a few clubs being mentioned in the papers but at the time the only English club to show an interest in me was Watford.
Was it an easy decision to up sticks to come and play your football in the Premier League?
Yes it was, definitely. I had always wanted to play in England and Watford seemed a good club for me. Despite being the only offer on the table it still seemed a good move for me. I had always said to myself that if I had the chance to go to England then I would and luckily I got the chance.
You made your debut at home to Liverpool and managed to get on the score sheet as well.
Yes I remember it well; it was a good way to start and a fantastic memory of mine. It was a shame we didn't manage to win as that would have topped it off completely. But nonetheless it was a good way for me to start my Watford career.
How did you find working for Graham Taylor?
Yes it was good, but I must admit I appreciated him a lot more as I got older. There was a time when he was giving me some stick which at the time I didn't think was fair but looking back I have to say I deserved it and it was my fault, but looking back he was absolutely right. The second season, 2001, didn't really go well for me and that was all my fault but when you are young and stupid you don't necessarily see it that way.
Why do you think it was your fault that you had a below par season?
I don't think my head was necessarily in the right place. After I had done quite well in the Premier League I thought I had arrived but that wasn't the case. It took a while to dawn on me that I needed to keep proving I could play and that I needed to get my head down. Things didn't go great for me that year but you live and learn and it helped me in the end as I knew I had to pull my finger out. But back to your question about Graham I liked him and I have a lot to thank him for as he showed a lot of trust in me to bring me over.
You had played in several countries before coming over but they were all in Scandinavia; how did you settle into life in England and English life?
Yes we settled in well. It took a bit of time to get to know the area and what have you. I did have a bit of an issue with the training ground as that was awful! It was the training ground at Stanmore and it was terrible.
In what way?
The pitches were awful, they were just mud. And the changing rooms were about 300 years old; I think they may have even been listed! But it was good when we moved to the new training ground which is great. But overall life in England takes some getting used to but once you do it is good.
Are there any games in particular that stand out for you from your time at Watford?
Yes a few. I remember the Southampton cup game well, and then also the cup semi-finals against Liverpool. Although we lost the occasion and everything else was great to be involved in. All the hype in the weeks before would have been something I would have hated to have missed out on. Overall there were quite a few really good games that we played in but the more memorable ones were mainly cup games.
You had a very good goal scoring record overall whilst you were at Watford and partnered a few different strikers. Who would you say was your favourite strike partner form your first spell at the Vic?
I can't remember who I played with! Ha! I didn't play much with Gifton as it tended to be me or him, not together. Tommy Mooney and me didn't play together loads either. Smarty was great to play alongside and I enjoyed playing with Webber as well. Tommy Smith would probably be my first choice though. For me it is nice to lay the ball off to someone with pace so then I don't have to run!
There was a little tale that went around that when you played five a side games in training Ray had to put you and Jay DeMerit on the same team as you were both so wholehearted he was worried you would crunch each other – is that true?
Ha! I can't remember if any special point was made of that but it could well have been true! If it was done then it was done without telling us.
The Watford fans always seem to have held you in very high regard, how did you find your relationship with the fans?
Excellent, really good. I have never had any issue with any of them and they have been absolutely fantastic to me over the years. They are absolutely brilliant and that is a big reason why things went so well for me there over the years because I knew I had their support, and I knew the support was there even when things weren't going well and trust me, that really helps.
It is well known that you enjoyed playing for Ray Lewington but you were also there for the Vialli era. How did you find that?
I found it was ok and I never had any problems with Luca. I thought he was good but it just never really worked out. He didn't really fancy me as a player so I didn't play very much but even then I never had a problem with him and like I said it just never really worked out for whatever reason. Even with all the investment that was made it just never took off but I suppose that is how things go sometimes.
And when Luca moved on and Ray took over, how did you find playing for him?
I loved it, no question. I absolutely loved it. In Ray I knew I had someone who really believed in me and at the time I think that was what I needed. He came in and told me I was his main man and that was great to hear. He was in charge of the Ressies when Luca was in so I had played a few games for him then so I knew what he was like and I know he was quite pleased with my application and everything else in those games. He really did me a lot of good after the Vialli era.
There was talk in 2005 when you left that you had turned down a new contract offer to stay, is that accurate?
I initially signed for the club in 2000, and signed a new deal in 2003 which I was happy with. I chatted to Ray about it and said I would be happy to stay and play for him if we could sort a new contract out, but there was never one put forward to talk about. When it came to 2005 I had a year left on my contract and the club decided to sell me. That was when Aidy Boothroyd had taken over as manager.
How did you find working for Aidy, albeit not for too long?
Yes it wasn't long; I only played seven games for him I think but I really liked him. He came in and said that he was aiming for promotion the season after, he was very ambitious, but I'm not too sure many people believed him including some of the lads. But yes I got on really well with him and you could see he was really enthusiastic and that he would do well as it was his first managerial job. I think against everyone's judgement he managed to get the club up and did a fantastic job.
When you came to leave the Vic you went to Fulham, how did it all happen?
After that season there were rumours from early spring if I remember right, teams were watching me and stuff. To be perfectly honest I was ready to move as I knew if an offer came in I would be allowed to move due to the money problems and my contract not being extended. Once the offer came in it really wasn't something I could reject. I wanted to play in the Premier League and test myself. I had been at Watford for five and a half years as well. I had enjoyed some wonderful times but I wasn't adverse to moving on and testing myself at a new level by then.
Were Fulham the only club in for you or did you have any other offers?
No I spoke to Wigan as well. In fact I spoke to them first and had the medical and everything when we got a call saying the Fulham offer had been accepted. So I said 'thanks but no thanks' to Wigan and then travelled down to London.
I bet Wigan were a bit upset having put you through a medical already?!
Yes they were. After I had told their Chief Executive that I wasn't going to sign I then had to sit with him for half an hour in a helicopter on the way back to London, and I have to say it wasn't the most comfortable half an hour I have ever had!
Did Aidy try to sign you permanently when Watford got back into the Premier League?
He called me and we had a brief chat but it never really went anywhere. I am not sure if an offer was made or not but as far as I am aware it was just that one phone call and nothing happened after that.
We mentioned earlier just what a brilliant relationship you have with the Watford fans but there was one night when you came back to the Vic with Fulham and bagged a couple of goals in a 3-3 draw. Your celebrations in front of the Rookery seemed to annoy a few fans that night. Do you remember the night?
Yes I do. I was desperate not to lose, as ever, and I think we were 2-0 down at one point, we then went 3-2 up and Youngy equalised late on if I remember correctly. I think I equalised and then also scored our third to give us the lead.
It was an emotional night for me. It was the first time I had come back to Watford with an opposing team, and when you equalise and then put a team in the lead with only about five minutes to go then your emotions can run away with you and that is what happened that night. By me celebrating like that it certainly doesn't mean I have any less respect for Watford fans, definitely not, but I can't see the problem with it if I am perfectly honest. If I did offend anyone then I genuinely apologise. I've always celebrated my goals whoever I score against.
You came back on loan in 2009 under Malky and had another goal scoring debut.
Yes I came on, scored two and then went off injured with an injury that kept me out for six weeks!
I wasn't having the best of times at QPR when there was a new manager every other week and other shit going on, so when the opportunity came up it seemed sensible to take it. It worked out really well for me and I think I done ok again for the club and the fans. The season after that Warnock took over at QPR and pulled me back. If the loan move to Watford hadn't happened I can't say for certain that I would have stayed at QPR so I am really pleased I done it and it worked out well for both parties. I really enjoyed it.
How are you finding things currently for QPR?
I was doing OK and scoring a few goals but then I picked up an injury which has disrupted me a bit but I am on the mend now. It has gone well for me personally but we are in a bit of a precarious situation currently which we need to try and get out of. I enjoyed working for Warnock and he is a good guy, but people move on and that is the business we are in. We now have a new manager and early impressions are that he is really good. His preparation and training methods are really impressive. If we manage to stay up this year then the future is pretty bright for QPR I think.
Finally, would you ever rule out a final move back to Watford for one last spell?
No I definitely wouldn't rule it out. I have only ever had good times there so I would never rule it out.
Well we would be happy to see you in a Watford shirt again. Thanks Heidar.
You're welcome. Cheers guys.
The Emirates
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Minneapolis man charged with raping female…
Minneapolis man charged with raping female passenger on intercity bus
By Forum News Service |
CROOKSTON, Minn. — A Minneapolis man could spend 30 years behind bars after being charged with raping a woman on Jefferson Lines bus on Friday afternoon.
Mohamed Harir Ayanle, 22, has been charged with raping a female passenger on board a Jefferson Lines bus on Friday, Dec. 9, 2016, as the bus traveled between Minneapolis and Grand Forks, N.D. (Forum News Service)
Mohamed Harir Ayanle, 22, has been charged with first-degree criminal sexual conduct by inducing fear of bodily harm, a felony punishable by up to 30 years in prison, and third-degree criminal sexual conduct, a felony punishable by up to 15 years in prison.
According to the criminal complaint, Crookston police were dispatched to the University of Minnesota-Crookston on a report of criminal sexual conduct on a Jefferson Lines bus traveling between Minneapolis and Grand Forks, N.D. The victim told dispatchers another passenger threatened her with a knife and made her have sex with him.
Police pulled the bus over and talked with Ayanle, who fit the suspect description. They did not find weapons on him. The victim said the man approached her when she was sitting with her daughter, and invited her to come watch a movie with him in the back of the bus when the daughter fell asleep, shortly after the stop in Bemidji.
She told officers she went with him because he told her "he had something," which she believed was a knife, though she never said she saw a knife. Once in the back seat, the victim said, Ayanle forcibly removed her clothing and raped her.
When questioned by investigators, Ayanle said the two had intercourse but that it was consensual, according to the complaint. He denied threatening her.
Ayanle was released from custody Monday on a $5,000 bond on the condition that he does not leave Minnesota. His next court appearance is scheduled for Jan. 3.
Judge: Twin Cities German Immersion School demolition on hold but opponents must raise $2M in a week
A Ramsey County District judge on Monday granted a temporary restraining order sought by residents opposed to the demolition of the former St. Andrew's Church. The restraining order delays the Twin Cities German Immersion School's plan to demolish the building for an expansion project, but perhaps not for long. As part of her order, Judge Jennifer Frisch required residents opposed...
It's a sculpture, it's an aardvark, it's a … storage shed? Western Sculpture Park celebrates a functional new piece.
The Aardvark in the Park Festival in St. Paul on Saturday, July 27, will celebrate a quirky new sculpture. An aardvark joined the Western Sculpture Park's 15-piece collection last month. The work will serve as both art and a storage shed for youth workshops and other park programs. It provides 128 square feet of interior space to store art materials...
Congestion growing on Twin Cities metro freeways, study shows
Freeway congestion in the metro ticked up slightly last year, according to a new report. The percent of congested freeway miles was 24.2 percent last year -- up from 23.2 percent in 2017, according to the 2018 Metropolitan Freeway System Congestion Report released Monday. That's the highest percentage of congestion in the last 10 years. The analysis by the Minnesota...
Mall of America to open walk-in health clinic this fall
A walk-in clinic will open at the Mall of America in November, offering services for both workers and customers alike. The new clinic was announced Tuesday, and will be part of M Health Fairview, a partnership between Fairview Health Services and the University of Minnesota. To be located on the third floor of the Bloomington mall's east end, the 2,300-square-foot...
Lake Elmo Airport neighbors opposed to its expansion to meet
Neighbors opposed to the $10.9 million runway relocation and expansion project at the Lake Elmo Airport will meet this week. Lake Elmo Airport opened in 1951 and is one of 83 intermediate airports located in Minnesota. It's one of the state's busiest, but its 2,850-foot runway is the fifth shortest. The Metropolitan Airports Commission says a longer runway will be...
Giving is living: Twin Cities No. 1 in volunteering
Kathleen McNamara enters the classroom, pushing though the paper vines and monkeys dangling from the ceiling. She sits down in a ring of 13 preschoolers, and picks up the book "One Red Rooster." "The chicken book!" shouts one kid. "You wrote that book?" No, she says, and starts reading aloud -- her third act of volunteerism that day. McNamara is...


Family run and customer focused, the Revere Hotel prides itself on being full of charm and character.
The Revere features two popular restaurants, the Candlelight Restaurant and Doran's Courtyard Bistro, and offers a selection of lavishly decorated standard rooms and four poster luxury rooms.
A selection of single, double, twin, triple and family rooms is available.
Four four-poster bed luxury rooms are also on offer.
All guest rooms are en-suite and equipped with flat screen television, tea and coffee tray, hairdryer, trouser press, ironing facilities, laundry service, 24 hour reception and room service.
The Candlelight is the hotel's main restaurant serving traditional and French cuisine using fresh local products daily. There is an a la Carte menu.
Doran's serves innovative cuisine with a focus on Mediterranean flavours. Open Monday to Saturday in the evening only.
The hotel's bar is a comfortable place to enjoy a drink, relax or be social.
A full English breakfast is available daily.
The outdoor swimming pool and sun terrace are welcome features for a town hotel.
There is wheelchair access to the restaurants only.
The Revere is on the edge of St. Helier's main shopping area, in a quiet street leading to the waterfront, gardens and the popular St Aubin's seafront promenade.
We have stayed there 5 times now and it is great value for money.It has a public car park very close which is a bonus,parking can be a problem at some Hotels in St Helier.
Really good staff. Good food,and a friendly atmosphere.
We thought the staff were very welcoming and friendly and the food was of an excellent standard, particularly the meals in the restaurant.
The hotel has a lot of old charm and character and we enjoyed our stay very much.
A little tired looking but nevertheless clean, excellent staff, and food.
Bedroom disappointing other than that, a good holiday.
Whilst we thought the service was excellent our room was very disappointing and shabby.
The travel was all arranged well and due to a cancellation of the ferry due to very high winds, the re-booking by Bontour was excellent and I was kept fully informed.
Lovely quirky hotel, brilliant breakfast and couldn't fault the service and politeness of the staff.
Very nice hotel for the money,we have stayed there before. Really good staff very friendly and helpful ,I hope someone employs them when the hotel is demolished for the hospital extension.


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This report for Portugal forms part of the OECD Review on Evaluation and Assessment Frameworks for Improving School Outcomes (see Annex A for further details). The purpose of the Review is to explore how systems of evaluation and assessment can be used to improve the quality, equity and efficiency of school education. The Review looks at the various components of assessment and evaluation frameworks that countries use with the objective of improving student outcomes. These include student assessment, teacher appraisal, school evaluation and system evaluation.
Student learning outcomes in Portugal are around or slightly below the OECD average, depending on the skills assessed, and have shown some encouraging improvement in the last decade. Efforts which followed the 1974 Revolution to ensure access to education for all Portuguese resulted in a rapid expansion of enrolment. However, educational attainment remains a challenge. It is the lowest in the OECD area for the working-age population, with 30% of 25- to 64-year-olds having attained at least upper secondary education in 2009 (against an OECD average of 73%). Moreover, the high share of students leaving the education system too early with low skills remains a major problem. A range of reforms have been introduced in education in recent years, including new arrangements for school leadership, student learning standards, teacher appraisal, and initiatives to reduce early dropouts.
School education in Portugal
School governance in Portugal is fairly centralised. The main lines of action about the curriculum, the educational programmes, national examinations, teacher recruitment and deployment, and the budget distribution are defined centrally by the Ministry of Education and Science. There has been some devolution of responsibilities to municipalities in areas such as curricular enrichment activities, management of the schooling infrastructure, and non-teaching staff resources; as well as some autonomy granted to individual schools in areas such as the hiring of part of the staff (on fixed-term contracts, trainers for vocational courses) and the selection of textbooks. Public schooling is dominant and public schools receive the majority of their funds directly from the State budget. A major handicap for Portugal has been the very low starting point in terms of educational attainment and literacy of its population, prior to the 1974 Revolution. Nevertheless, efforts to ensure access to education for all Portuguese resulted in a rapid expansion of enrolment even if attainment levels remain a challenge. Student learning outcomes in Portugal are around or slightly below the OECD average following some progress in the last decade, depending on the skills assessed. Recent reforms include new arrangements for school leadership, the setting of learning goals, the reorgansation and redeployment of the school network, the generalisation of full day schools and the diversification of educational offerings (in particular through the promotion of vocational/professional programmes).
The evaluation and assessment framework
Evaluation and assessment in Portugal operates at four key levels: (i) system – namely through education indicators, national tests and examinations, and international student surveys; (ii) school – external inspection by the General Inspectorate of Education and school self-evaluation; (iii) teacher – through a national system of teacher performance appraisal; and (iv) student – with instruments ranging from national standardised tests to ongoing daily formative assessment in the classroom. The approach to evaluation and assessment combines central control over policy development and standard setting with a measure of devolved responsibility for the implementation of evaluation and assessment at the school level. The Ministry of Education and Science is responsible for oversight of the entire education system and plays a role in all components of the evaluation and assessment framework. The framework exists in an environment where there is an increasing trend of accountability for all school agents, the commitment to develop an evaluation culture in the education system, and a growing focus on measuring educational performance.
Student performance in Portugal is assessed by a wide range of instruments, ranging from national standardised tests to ongoing daily formative assessment in the classroom. At the national level, full-cohort educational progress national tests are conducted in Grade 4, the results from which are used as key performance measures towards national goals. These are low stakes for schools, teachers and students. Summative assessment is based on a mix of teacher-based classroom assessments and national examinations. The latter take place at the end of both the second and third cycles of basic education (Grades 6 and 9), in Portuguese language and mathematics, and in secondary education in the last year of each subject (Grade 11 or 12). However, teachers hold most responsibility for summative assessment as the weight of national examinations is never dominant for the final mark. In the first cycle of basic education (Grades 1-4), assessment is generally informal and formative and results are reported in a descriptive and qualitative format. In the second and third cycles (Grades 5-6 and Grades 7-9), the emphasis on formative and internal assessment continues but summative results are reported on an ordinal scale from 1 to 5 and there are external examinations at the end of each of the cycles.
A new national system of teacher performance appraisal was instituted in 2007 in the broader context of the integrated system of performance evaluation for public administration which applies to civil servants. Since then, teacher appraisal has undergone a range of adjustments as a result of the resistance it has faced. By the time the review team visited, a model launched in 2010 was in the process of being implemented. The main features of the model included a two-year appraisal cycle; a national framework defining reference standards, aspects to be appraised, instruments to be used and a five-level classification scheme with a school-level quota system for the top two classifications; a process internal to the school to conduct the appraisal including school-based peer evaluators; and consequences for career progression, contract renewal, monetary rewards and plan for professional development. Subsequently to the review visit and with the change of government in June 2011, a new teacher appraisal model was approved for implementation in 2012/13.
School evaluation
There are two main forms of school evaluation in Portugal: school self-evaluation and school external inspection. The latter is the responsibility of the General Inspectorate of Education and Science. A first cycle of external school evaluations was conducted from 2006 to early 2011. It involved, for each school in the system, a sequence of activities comprising a self-reflection by the school, a visit by a team with inspectors and an external member, the publication of the team's report and, in some cases, an improvement plan for the school. A second cycle of external school evaluations was launched in the 2011/12 school year following a similar approach but with the introduction of the requirement of an improvement plan for each school inspected. A distinguishing feature of external school evaluation is that it does not involve the observation of teaching and learning in the classroom. The precise nature of school selfevaluation varies across schools as the legal requirement to undertake it does not come with a prescribed approach.
Education system evaluation
A range of tools are used to monitor performance of the education system. Information on student learning outcomes is collected from educational progress national tests in Grade 4 and from national examinations in Grades 6 and 9 and in secondary education. The monitoring system also includes a range of statistics on education based on snapshot data collected from schools on a standardised format. These are the basis for annual publications with system-level indicators on education. Also, international benchmarks of student performance provided by international student surveys such as PISA have been influential in driving policy development at the system level. In addition, there has been a growing interest in undertaking studies of the impact of policy initiatives and in preparing thematic reports which can inform policy development. Particularly positive features of system evaluation include the well-established education indicators framework; the new concern for framing system evaluation in relation to educational targets; the existence of student performance data; and the qualitative analysis undertaken in thematic reports. However, system evaluation is faced with a number of challenges. These include the little emphasis on the evaluation of the education system; the lack of measures on students' socio-economic background; the little emphasis on investigating differences of student outcomes across specific groups; the limited information on the teaching and learning environment; and the room to better exploit system-level information.
Conclusions and recommendations
A major handicap for Portugal has been the very low starting point in terms of educational attainment and literacy of its population. A fifth of all 15- to 64-year-olds were illiterate in the mid-1970s and less than 5% had completed upper secondary education. Nevertheless, efforts to ensure access to education for all Portuguese resulted in a rapid expansion of enrolment. The proportion of the population that has attained at least upper secondary education grew from 14% for the generation aged 55-64 in 2009 to 48% for the generation aged 25-34 in the same year. Despite the expansion of the education system, educational attainment remains a challenge. It is the lowest in the OECD area for the working-age population, with 30% of 25- to 64-year-olds having attained at least upper secondary education in 2009 (against an OECD average of 73%). Moreover, the high share of students leaving the education system too early with low skills remains a major problem.
The OECD Review on Evaluation and Assessment Frameworks for Improving School Outcomes
The OECD Review on Evaluation and Assessment Frameworks for Improving School Outcomes is designed to respond to the strong interest in evaluation and assessment issues evident at national and international levels. It provides a description of design, implementation and use of assessment and evaluation procedures in countries; analyses strengths and weaknesses of different approaches; and provides recommendations for improvement. The Review looks at the various components of assessment and evaluation frameworks that countries use with the objective of improving student outcomes. These include student assessment, teacher appraisal, school evaluation and system evaluation. The Review focuses on primary and secondary education.
Visit programme
Composition of the review team
Graham Donaldson published his report Teaching Scotland's Future – A Report of a Review of Teacher Education in Scotland in January 2011. This Review was undertaken on behalf of the Scottish Government. Graham was Her Majesty's Senior Chief Inspector of Education from 2002 to 2010 in Scotland. In that role, he was Chief Executive of HM Inspectorate of Education and Chief Professional Adviser to the Scottish Government on all aspects of education outside the university sector. Graham began his teaching career in 1970 and taught in schools in Glasgow and Dunbartonshire. He worked as a Curriculum Evaluator for the Consultative Committee on the Curriculum. During this period, he was seconded to BP to review links between education and industry. His report, Industry and Scottish Schools, was published in 1981. He became an HM Inspector in 1983. Graham is the current President of the Standing International Conference of Inspectorates (SICI) which has 29 member inspectorates from across Europe. Graham was awarded a CB for his services to education in the 2009 Queen's Birthday Honours List.
Comparative indicators on evaluation and assessment


It has been an eternal constant for man to strive for dominance over his own. From our earliest days, many of us discover ways to best our competitors and establish ourselves to a position of power. Whether it's on the playground, in the business world, or on the field of battle, being on top is hard-wired into most of us. However, others might not be so motivated or capable. Thus, the division between master and slave comes into play, whether through natural or contrived means. And we'll be discussing this dynamic as we unapologetically dive into the nature of human slavery, its widespread history and its continued practice.
Didn't Know Blacks Owned Slaves in America?


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Dans le monde automobile une transmission de type traction désigne une transmission secondaire de véhicule par laquelle la puissance moteur est transmise uniquement aux roues avant, qui tirent le véhicule, contrairement à ceux à propulsion tels les autobus, camions, motos et quads dont seules les roues arrière sont motrices.

En France, même si l'on pourrait considérer que le fardier de Cugnot est un « véhicule à traction » des années 1770, le plus fameux véhicule de ce type est la « Citroën Traction Avant » sortie peu de temps avant la Seconde Guerre mondiale et largement utilisée durant celle-ci aussi bien par la police que par les FFI. Avant ceux de Citroën, la traction fut utilisée sur les véhicules de Latil (entreprise).

Histoire
Même si la Tracta D-1500 semble être la première automobile à traction dans les années 1920 elle ne semble pas avoir eu le même impact que la Citroën Traction Avant à partir de 1934 et utilisée, entre autres durant la Seconde Guerre mondiale en Europe.

Cette architecture, choisie par la marque Citroën dans les années 1930 pour sa célèbre Traction Avant, est maintenant adoptée dans la majorité des automobiles de faible puissance (moins de ) du fait de la simplification de la transmission, entre autres la suppression du tunnel nécessaire à l'arbre de transmission, et de la simplification de la suspension du train arrière.

Description

Du fait des règles actuelles de sécurité, la plupart des véhicules de faible puissance (moins de  environ) sont mûs par un moteur transversal placé sur l'essieu avant.

 Avantage  Le principal avantage de la traction est de regrouper tous les éléments de la propulsion du véhicule à l'avant, avec comme principal effet la suppression du tunnel de l'arbre de transmission qui crée, généralement, une excroissance sur le plancher arrière des véhicules à propulsion. L'absence de pièces mécanique en mouvement sous la partie centrale de la caisse diminue les sources de bruits parasites dans l'habitacle, ce qui rend la conduite plus agréable et améliore le confort des passagers.

 Inconvénient  Lorsque la puissance du moteur dépasse un certain niveau, l'effort sur les cardans devient important et l'adhérence plus délicate à maîtriser. Pour maîtriser l'adhérence, la plupart des tractions à forte puissance se voient équipées de différentiels pilotés ou à glissement limité pour pouvoir maîtriser leur puissance de manière convenable.

Transmission de la puissance

La traction crée des contraintes au niveau des cardans, ce qui limite la puissance moteur :

 Pour les fortes puissances, nécessaires, entre autres pour les camions, la propulsion est préférée, du fait de l'effort moindre sur les cardans et la possibilité de disposer de pièces mécaniques plus volumineuses donc plus solides.

 Pour faciliter le contrôle de véhicules puissants, on choisit fréquemment une transmission intégrale plus facile à maîtriser, surtout lorsque l'adhérence est précaire (chaussée humide, verglas ou en tout-terrain).

Traction Avant Citroën
Le terme Traction Avant, est devenu un nom propre depuis qu'il a été utilisé par le constructeur automobile Citroën en 1934 pour sa première voiture à traction. Il n'y a que dans ce cas qu'il est judicieux de parler de  (avec des majuscules).

Notes et références

Articles connexes
 Fonctionnement de l'automobile
 Propulsion
 Transmission intégrale

Configuration automobile

redpajama_set_name: RedPajamaWikipedia


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Only Triplewide in Upscale Carolina Village! All Rooms are Large with plenty of space to spread out - 2400+ SF! Two Living Areas, HUGE Master Suite, 2 Car - Oversized Garage. Updated in 2017 - 2018 with Gorgeous Vinyl Plank Flooring throughout, New Roof, New AC Unit , Fresh Interior Paint, Some New Light Fixtures. Relax with your morning Java or favorite Happy Hour beverage on your 19' X 9.2' Screen Porch and 16' X 9.6' Open Deck. Vaulted and 9 Foot Ceilings to add to the Open Feel. Gourmet Kitchen w/Breakfast Bar, Glass Front Cabinets, Open to Dining and Family Rooms. Stainless Appliances, tons of cabinets and work space. Master Suite consists of 20.8' X 15' BR with Sitting/Workout area, Big Walk In Closet + second closet, Master Bath complete with Garden Tub, Separate Shower, Double Sinks. 2 Spacious Guest Bedrooms. Gas Log FP in Family Rm. Convenient Utility Rm is 12.8' X 9.5', Washer and Dryer Convey. 2 Car Attached Garage + room for Workshop space. 55 and over Park in the gorgeous mountains of Franklin, NC. Lot Rental is $420 per month - includes water, sewer, gated entrance, road, clubhouse and common area maintenance, mowing, management fees.


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HomePosts tagged 'Ray Mann'
Ray Mann
Unmanned cargo aircraft "on the way"
15/06/2016 15/06/2016 David Learmount BAE Systems, drones, Glyn Hughes, IATA, Lufthansa, NAC, National Aeronautical Centre, pilotless cargo aircraft, Ray Mann, Thales, Unmanned cargo aircraft
A recent statement by the National Aeronautical Centre says this: "The operation of unmanned cargo aircraft (UCA) moved closer to reality as delegates from the aerospace and logistics industry met recently to discuss the way forward."
"The unique initiative, organised by the National Aeronautical Centre, West Wales Airport, took place at the Lancaster Hotel in London, in the form of a round-table discussion. It was a world first event and an important step on a road that will lead to unmanned cargo aircraft being used throughout the global logistics chain."
It's true that, for years, the industry has been talking about the practicality of freight aircraft being operated pilotlessly, on the grounds that the technology to do it exists, and unlike pilotless passenger airliners, the public wouldn't care.
This group discussion reportedly included Thales, BAE Systems, Leonardo Finmeccanica, Avio Aero, IATA, Lufthansa, Heathrow cargo "and other airline representation", and the agenda included "a wide range of potential UCA operations from intercontinental air freighters to local deliveries by small drones."
Ray Mann, Managing Director of West Wales Airport, said, "The past 20 years has seen the evolution of unmanned aircraft and although initially developed for military operations, they have demonstrated the means of having far greater potential for all sorts of civilian use. As UCA can be constructed in any size and shape depending on the task required, this first round-table discussion has been invaluable for both industries to understand how they can best respond to this growing demand."
Global Head of Cargo at IATA Glyn Hughes commented that – while it looks like a great opportunity: "For the full economic and social benefits of commercial drone technology to be realized the groundwork needs to be done now to ensure their safe integration with existing air traffic and infrastructure."
The latter will not be a rapid process.
My personal guess is that, for large freighters, single-pilot operations will precede zero-pilot ops.
That idea could really be very close, because the aircraft can be fitted with a system that enables remote piloting of the aircraft in the event of the onboard pilot becoming incapacitated or needing help.
And as the NAC says: "The initiative is set to continue with further meetings planned in the coming months."