238.3 Route Surveying
From Engineering Policy Guide
A survey is made to physically establish a location in the field. It includes the location of all man-made features in relation to the established roadway centerline in such a manner that these features can be accurately indicated on the plans. The survey also includes elevations on National Geodetic Survey (NGS) or United States Geodetic Survey (USGS) datum necessary to locate grades, culverts, bridges, and to compute excavation quantities. To ensure proper accounting for each of the various surveying tasks involved with route surveys, the correct coding must always be used.
238.3.2 Survey Methods
Two methods are used to obtain this information. One method, referred to as “conventional surveys”, obtains all of necessary information in the field. Conventional surveys may be conducted by traditional means or electronically. Traditional means include differential leveling, taping manually scribed data, cross sections and baseline-referenced topography. Electronic surveys utilize total station, data collector and computer technologies for the gathering, transfer and manipulation of field data. The district survey party chief decides which conventional survey method to use to obtain the needed information.
MoDOT CORS Real Time Network (RTN)
MoDOT Real Time Network is made up of a series of GNSS (Global Navigation Satellite System) receivers strategically located to cover the entire state at a maximum distance of 70 km, collecting data 24 hours a day. The network uses US GPS and Russian Glonass signals and is expandable to future signals such as Galileo.
All stations have been built to NGS (National Geodetic Survey) CORS (Continuously Operating Reference System) specifications. All sites will be submitted to NGS for incorporation into the national system.
Data is sent to a central server through an Internet connection for processing. Users can obtain this data in two ways:
- 1) Real Time which allows them to get instant corrections as they work.
- 2) From our web site (gpsweb.modot.mo.gov) which allows them to download files to their computer for Post Processing.
The objective of the system is to provide real time kinematic (RTK) data via the Internet for use in improving GPS data collection accuracy.
MoDOT has made access of this system available to users in the area without cost after MoDOT ensured that its needs and the needs of its other governmental partners have been met. Users of the MoDOT system must obtain a username and password, have a bluetooth cell phone capable of tethering or a data modem in their surveying equipment and a high speed, unlimited data plan through their cellular provider which has the best coverage in their area (ATT, Verizon etc.).
Cell service coverage is the key to effective use of the network however, if cellular coverage cannot be obtained in a particular area, the network has a website available for downloading data collected at the time of the field collection. This method allows a user to post process his survey results and obtain the desired level of accuracy without being connected to the network in the field.
Uses of an RTK GPS network might include: Surveying, GIS data collection, Construction, Machine Control, Automatic Vehicle Location, Asset Management, Automated road salting, Snowplow guidance, unmanned mowers.
Some of the benefits of using a of a Reference Station Network system of this type include the elimination the need for local base stations and the personnel required to “watch” the local base station, enforcement of a consistent known datum, and use of a known coordinate system.
As with any survey GPS solution, a localization file should be created for each project to orient the project coordinates to the network coordinates (state plane). This needs to be done only once and is used throughout the life of the project.
For more information on the MoDOT GPS RTK network, access the network web site at http://gpsweb.modot.mo.gov .
238.3.3 Public Relations
Survey personnel are in an excellent position to promote good public relations for MoDOT. They are usually the first representatives of the department to contact people affected by proposed highway improvements. Therefore, it is the district survey party chief’s responsibility to insure their personnel present a good appearance at all times. Additionally, the district survey party chief acquires general information concerning the proposed improvement to inform people encountered during the survey.
238.3.4 Survey Party
Members of the survey party create impressions on people encountered during the conduct of their job activities. This impression reflects upon MoDOT as an organization. Therefore, the importance of this impression cannot be over-emphasized. The survey party must perform their work by being courteous, presenting a good physical appearance, conducting themselves properly, and by giving proper advising to the people they contact during the performance of their work.
Periodic calibration checks of all survey instruments are to be conducted to insure proper operation. These checks are to be done at least once a year and are performed at an official DNR EDM range. All total stations will be sent in to a service center for calibration at least every five years. All equipment used by the survey party is kept in good condition, clean and in good adjustment, including the vehicle. Equipment stored in the vehicle is kept in neat order. All equipment is salvaged and replaced as necessary.
238.3.6 Before a Survey
Before beginning a survey, the district survey party chief is furnished a copy of the location study. They review the report to become familiar with the type of proposed improvement, the plan for improving or relocating intersections, the location and type of interchanges, and all other information necessary to complete the survey.
238.3.7 Field Notebooks
Survey notes are kept in either bound notebooks or electronic data collectors. Electronically gathered survey data is referenced in the field book. The data files themselves are to be maintained in accordance with prescribed file management policy and are kept in a manner so they are readily retrieved and easily understood. This includes the proper archiving of files to the designated computer drives, diskettes or hard copy. Standard practices of neatness, uniformity and continuity are exercised in the field notebooks. Erasures are not made. Notes are not kept on scrap paper and later copied into notebooks. Notes are entered with bold open figures and letters without crowding. Recording of items is not scattered. Field notebooks become a permanent record and the notes are kept with this in mind. A good practice is to record alignment and man-made features in one book or a series of books, record bench levels and miscellaneous surveys in another book or series of books, and record profiles, cross sections and culvert sections in another book or series of books. A separate notebook is used to record targeted points and vertical controls for photogrammetric surveys. Two or more of these items can be recorded in a single notebook when the improvement is short, or where a single item will not fill more than a few pages of the book. Recording more than one item in a book is used with discretion because of the inconvenience in handling the notebooks in the office. Each field notebook is identified and numbered on the front cover of the book and on the inside flyleaf. The field notebook also includes a complete index of the contents on the first page. Each district will catalog their field notebooks to allow ready access to survey information.
The district survey party chief maintains a daily diary in a separate bound field notebook. The diary includes a daily record of the personnel assigned to the party, their work assignment, the names and addresses of people contacted by the party and their reaction to the contact, the work performed by the party that day, and any other information that is beneficial as a part of the permanent record of the survey (see an example diary).
238.3.9 Survey Sequence
The following sequence is used when making a survey:
- Establish horizontal and vertical controls; if necessary, the centerline is established and staked
- Obtain topographic (3D) and planimetric (2D) features
- Complete miscellaneous surveys for railroads crossings, interchanges, grade separations, bridges, etc
Some of these operations may be performed concurrently. With the use of electronic data recorders, it is advisable for the designer and the surveyor to conduct a pre-survey meeting. This meeting conveys to the surveyor the limits and scope of the project plus an understanding of the information requested by the designer. The designer and the surveyor may need to review the project in the field. In some cases a post-survey meeting may prove beneficial since some information gathered in the field may have been overlooked or considered not evident during the previous meeting. It is preferable that the surveyor provides the designer with an edited digital map model once the survey is complete.
Measurements are made to the best possible accuracy consistent with the equipment used and necessary speed of completing the work. The Missouri Standard Specifications for Highway Construction provide for the payment of plan quantities for many contract items, which are measured and computed from survey data. This dictates that all survey information be carefully and accurately measured and recorded.
Taping accuracy requires proper tension on the tape, the use of hand levels or other devices to insure level taping, and particular care in setting and measuring to and from taping points. The tape is kept in good condition, free of splices and kinks. Proper tension is used on the tape. The tape is unsupported between the ends and is kept free of weeds, underbrush, and low-hanging tree limbs.
Angular accuracy requires care in sighting and compensation for instrument error. The instrument error can be compensated by a direct reading of the angle and by reversing the instrument for a duplicate reading of the angle. Line projections on tangents are double-centered to insure against introducing slight angles on tangents caused by instrument error.
Bench leveling accuracy requires unyielding turning points, a level in proper adjustment, balancing the length of backsight and foresight, and care in maintaining a plumb level rod when taking readings.
The 10-second repeating type theodolite or electronic distance measuring device (EDM) commonly available in the district is suitable for this order of work. A 100 ft. steel tape free of kinks and splices, and checked against a calibrated tape is satisfactory. The Central Office will furnish a calibrated tape if none is available in the district. An accurate thermometer that can be read to the nearest degree and is quickly influenced by changes in temperature is necessary. An accurate barometer (read to the nearest two millibars) is also necessary. A minimum of two FM radios is needed for two -way communications between survey crewmembers. A gauge to determine the proper tension on the tape is necessary. This is purchased locally or through any supplier of surveying equipment. It is of a size easily handled in the field and must register up to 35 lbs. It is calibrated before use, and periodically thereafter. Normal survey equipment includes:
- Two range poles; three tripods
- Two plumb bobs with heavy cords
- A tape clamp; two prism poles; two single mirrors; one triple mirror; two hand levels; tribrachs; reflectors; and adaptors.
238.3.15 Higher Accuracy Surveys
Survey and recording accuracy considerably better than that previously indicated might be necessary on particular surveys such as alignment control base lines for photogrammetric surveys and resulting centerline survey. Specific instructions and equipment are available for such surveys.
238.3.16 Establishing Location
The first step in a survey is the establishment of horizontal and vertical control that is located in a manner well suited for any future survey work conducted during design or construction of the project. The district survey party chief decides if this control becomes the preliminary line. If done correctly, this layout method facilitates efficient use of the survey information by all project staff. Any adjustments to the location of the proposed improvement can be made without waste of survey work.
238.3.17 2D Control Points
The survey party may establish 2D control points, staking the alignment when needed, and completing the survey. Control point intervals are not greater than 1500 ft. Additionally, a control point is set near each end of all bridges, preferably near the top of the stream bank or the embankment. The control point is a steel rod or large nail driven approximately 6 in. below the natural ground surface. In cultivated fields it is placed 12 in. or more below the ground surface. This point is referenced to at least three identifiable features such as trees, fence posts, utility poles, etc. Preferably, these references are separated by 120 degrees. Referenced points are recorded in sequential order corresponding with the number used in electronic files as the first item in the field notebook. The stations, pluses, and offsets for the referenced points will be placed on the tie sheets in the final plans. This allows adjustments to alignments to be made without confusing actual location of points in the field. Where slope measurements are used for reference points they are indicated in the field notebook.
238.3.18 3D Control Points
The survey party may establish 3D control points in lieu of performing separate procedures for 2D control points and bench levels. Control point intervals are not greater than 1500 ft. Additionally, a control point is set near each end of all bridges, preferably near the top of the stream bank or the embankment. All 3D control points are to be visible from their 2 nearest 3D control points. These control points may be established by means of 3D traversing, 2D traversing and trig levels, or 2D traversing and differential levels. The vertical element of the 3D control point is to be referenced to NAVD 88 and the horizontal element is to be referenced to the Missouri coordinate system of 1983. The 3D control point is a steel rod at least 3/8 in. in diameter and 15 in. in length or a 100d spike set below the surface of the natural ground. In cultivated fields, the control point is set at least 12 in. below the ground surface. These control points are placed outside the limits of proposed construction. This point is referenced to at least three (3) identifiable features such as trees, fence posts, utility poles, etc. Preferably, these references are separated by 120 degrees. Referenced points are recorded in sequential order corresponding with the number used in electronic files as the first item in the field notebook. The stations, pluses, and offsets for the 3D control points will be placed on the tie sheets in the final plans. This allows adjustments to alignments to be made without confusing actual location of points in the field. Where slope measurements are used for reference points they are indicated in the field notebook.
238.3.19 Identifying Location
Sometime during the survey the final location is plainly marked by painting trees, fence posts, etc. This allows the alignment to be followed at a later date after the location has become overgrown with brush and weeds and the stakes have deteriorated. This is particularly important for bridge surveys. This procedure is not applicable in urban areas or in the vicinity of rural improvements where the painting could be viewed as unsightly and objectionable.
The alignment is staked at station intervals. Each station is marked with a nail and a stake that will not rapidly deteriorate. The nail and stake are both tied with pink plastic ribbon. Each stake is marked with a black permanent marker showing station, offset, etc.
238.3.21 English Definition of Curvature
The arc definition of degree of curve is preferred for use to determine the radius for all curves. The radius of one-degree arc curve is set at 5729.57795 feet. This radius gives an arc length of 100.00000 feet for a change in direction of one-degree.
238.3.22 Metric Definition of curvature
All metric horizontal curve data is defined by radius. New horizontal curves will be in five-meter increments. Existing alignment will be soft converted to metric units using the U.S. Survey Foot (0.304800609601219 meters per foot).
238.3.23 Staking Curves
Curves are located and staked by coordinates. These coordinates may be obtained from the designer in the form of an interface file, which can be imported into an electronic data recorder and used to stake the curve. In most cases it will only be necessary to stake main curve control points (PC, PT, midpoint, PI, etc.) to check geometrics.
When staking a curve by the deflection angle method, the following formulas are used:
|English: Deflection Angle||Metric: Deflection Angle|
- L is the length of arc in ft.
- D is the degree of curvature
- R is the radius in meters
238.3.24 Benchmarks and Bench Levels
The designer supplies the district survey party chief with NGS, USC & GS, or USGS Datum to be used for the project. Permanent benchmarks are established at approximately 1000 ft. intervals along the survey centerline. The benchmarks are numbered consecutively in the direction of the survey including the last two digits of the year they are established. Bench levels, conventional threewire, or trig, are turned through each benchmark. Bench levels are run and adjusted as necessary to establish benchmark elevations prior to attempting to secure other data such as profiles, cross sections and map models. An acceptable example for recording bench levels and their adjustment is available. Target elevations are obtained along with the bench levels on photogrammetric surveys and may be used as temporary bench marks when obtaining vertical control.
238.3.25 Profiles, Cross Sections, Culvert Sections and Digital Map ModelsAfter the bench levels have been adjusted and the elevations set, the survey party is ready to proceed with profiles, cross sections, culvert sections, and digital map models. For photogrammetric surveys, only culvert sections are necessary. For conventional surveys cross sections and culvert sections are taken along with the profile. Profile elevations are obtained at all stations, PCs, PTs, and breaks in the natural ground line. Profile elevations are obtained at hilltops at sufficient intervals to properly represent the terrain. The profile elevations at sharp hillcrests are taken with a minimum spacing of 25 ft. Spacing can be increased at flatter hillcrests.
238.3.26 Culvert Sections
Culvert sections are obtained along with the profile and cross sections. A theodolite or EDM is used to establish and measure the skew angles for the base line for the proposed culvert. The skew angle is turned to the nearest 5 degrees. Skew angles for culvert base lines on curves are turned from the perpendicular to the local tangent to the curve. The culvert base line cross section follows the line of the existing ditch as near as possible. Elevations are obtained at all natural ground break points along the base line. Transverse sections or digital map models are taken along the culvert base line, back and ahead to adequately show the flow line of the existing ditch and the terrain on either side of it. If adequate transverse sections are taken additional field information will not be necessary as the design proceeds.
238.3.27 Field Notebooks
Acceptable examples for recording profiles and cross sections are available. Cross section notes are recorded exactly as illustrated to simplify interpretation by office personnel. Examples for recording culvert base lines and transverse cross sections are available. The use of electronic notebooks can be utilized throughout this entire process making it easier for designers and surveyors.
238.3.28 Man-made Features
All man-made features are accurately located through a designated corridor using electronic data collection or conventional methods. These features include buildings, building projections, outbuildings, sidewalks, paved areas, wells, cisterns, etc. The notes include a description and the dimensions of any concrete surfaces and the description and type of any wells or cisterns. Additionally, all similar items beyond the limits in a unit of improvements are located and described. The survey includes shrubbery and trees in the vicinity of improvements if needed. If done in the conventional method, the survey party must remember that the person who plots the information from the survey notes cannot be familiar with the location of the items that are to be plotted.
All existing utilities, above and below ground, are located along with other features. At all overhead crossings at least one pole on each side of the centerline is located and the clearance of the overhead facility is obtained. If these poles are within the limits of proposed right of way, additional poles (at least one pole) beyond the limits of the proposed right of way on each side of the centerline are located. All underground utilities will be located within the limits of proposed right of way. Elevations are obtained on all drainage and manholes (along with pipe size) up to the nearest manhole outside the right-of-way, or when requested on other utilities.
238.3.30 Field Notebooks
Acceptable examples for recording notes are available. Electronic field notebooks can be utilized when available.
238.3.31 Land Survey Ties
The location survey includes ties between the highway survey alignment and corners of the U.S. Public Land Survey System. A legal land survey corner is defined as one that is witnessed or monumented by a professional land surveyor. Location survey plans, with certification and seal, of these witnessed or monumented corners and reference ties, are filed with the county recorder of deeds. All physical corners of record within the right-of-way corridor must be referenced. The appropriate state land surveyor form is also completed by the surveyor for submitting to the State Land Surveyor. The survey must be tied to all physical corners of record for each ¼ section through which the survey passes. Ties must be sufficient to ensure that at least one public corner per section, and all other pertinent public corners are referenced to the highway survey alignment. The ties between the highway survey alignment and the land survey corner monument include the station and angle at the highway survey alignment, and the distance to the monument. Bound notebooks or data collectors are used for recording the field notes and observations. The description of the land survey corner monuments must be complete and definite; e.g., 4" x4" Limestone, 1/2" Steel Pin, or 1" Axle, S 1/4 cor. of Sec. 6, T56N, R14W. The project development engineer is advised early in the survey concerning the location and number of corner monuments that need to be re-established or witnessed so this work can be completed prior to submittal of plans to the Right of Way Division.
A celestial or GPS observation is made to obtain the true azimuth for use in establishing state plane coordinates and bearings. State plane bearings are shown on the plans, obtained from the computer output. A note on the first plan sheet indicates that the bearings are state plane and the zone to which they apply. On projects where state plane information is not computed, previous project bearing datum may be used. Additional information can be found in the discussion of Polaris and Sun Observations.
238.3.33 Railroad Crossings
The extent of surveys for railroad crossings will vary considerably, depending upon the effects of the roadway improvement project on the railroad facility. At all crossings the railroad alignment is precisely located in relation to the survey centerline for a minimum distance of 500 ft. on each side of the centerline. Top of rail profiles are obtained for the same distance. A survey along the railroad is also made for this same distance. This survey includes an accurate tie to a milepost or railroad alignment and to railroad drainage structures within the survey limits. If the railroad facility is affected beyond the 500 ft. limit, the survey is extended to the point that will be affected. Surveys for grade separations are conducted in addition to these requirements when applicable and are further explained in EPG 220.127.116.11 General Bridge Survey Information and EPG 18.104.22.168 Grade Separation. Much of this information, except for top of rail profiles, drainage and milepost location or alignment ties, can be obtained on a photogrammetric survey.
238.3.34 Paralleling Railroads
Where railroads parallel the survey close enough that a common right of way line will be used, or where there is a possibility of encroaching upon the railroad right of way, a milepost or alignment tie is accurately located. In addition, a survey of cultural resources is made between the proposed alignment and the railroad. The railroad is located and accurately tied to the roadway survey centerline at all curve points. Railroad curve data is obtained, if available.
Interchanges are usually surveyed by extending the survey map model to beyond the ramps. This procedure is better than attempting to survey along ramp base lines because it is difficult and impractical to establish interchange geometrics until after the survey has been completed. If ramp base lines are surveyed, the location of the ramp base lines, ramp identification, and the stationing of the base lines are consistent with common MoDOT practice. None of this is necessary for photogrammetric surveys since the information includes contours and/or cross sections covering the interchange area.
238.3.36 Bridge Surveys
Bridge surveys are required for all bridges, retaining walls and for culverts that will be classified as bridges, see EPG 722.214.171.124 Summary of Responsibilities. Plan to obtain all required field data for the bridge survey in as few trips to the job site as possible. This will include vertical control elevations for photogrammetry, streambed profile, high water elevations, offset profiles, sections under existing structures, channel sections and any other field data that may be required.
126.96.36.199 General Bridge Survey Information
A benchmark is set on each end of the proposed structure. Preferably on opposite corners of the structure.
188.8.131.52.2 Referenced Points
Referenced points are set near each end of proposed bridge. Preferably near the top of the stream bank on stream crossings.
184.108.40.206.3 Centerline and Offset Profiles
The three lines of ground profiles provide critical information used in the layout of structures. The profiles aid in determining the length of structure, minimum footing depth, allowable substructure location, span lengths, superstructure type, superstructure depth and verification of the proposed profile grade. This information is used along with the required freeboard or minimum vertical clearance.
Existing ground profiles are to be parallel to the roadway. One profile at the centerline of the roadway and the other two offset beyond the outer extents of the shoulders on either side. Offset profiles are typically obtained at 30 ft. right and left of the centerline of the structure. If this distance does not furnish representative profiles, the distance should be increased or additional offset profiles obtained as necessary to provide a true representation of the terrain features. Profiles in ditches or on existing roadway fill are not representative without supplemental profiles. Where the centerline of the roadway does not coincide with the survey centerline (e.g. surveys along the centerline of the median for divided lane facilities), an offset profile along the centerline of the roadway is required. Where dual structures for divided lane facilities are separated by more than 64 ft., offset profiles are obtained on each side of each structure. These profiles cannot be taken from cross sections.
Stream Crossings. Centerline and offset profiles for the crossing shall extend 5 ft. above the limits of extreme high water on each side of the channel and sufficiently beyond the limits of the proposed structure. Sufficient length of the profiles on stream crossings is important as they are used as valley sections for hydraulic modeling.
Grade Crossings. Centerline and offset profiles for the crossing shall extend sufficiently beyond the limits of the proposed structure. See EPG 7220.127.116.11.4 Additional Information for Grade Separations and EPG 718.104.22.168.5 Additional Information for Railroad Crossings for minimum extents.
22.214.171.124.4 Widening Existing Bridges
Bridge surveys for widening existing bridges include the same survey information as that required for new structures. In addition, certain information regarding the existing structure is required. If the existing structure was not constructed by the state, the bridge survey includes complete details of the existing structure to the extent required to structurally analyze its loading capacity. If the existing structure was constructed by the state, these details are not necessary. The bridge survey for widening the existing structure includes accurate ties to the existing bridge from the survey centerline. For multiple box culverts, classified as bridges, the bridge survey includes the flow line elevation and the top slab elevation for the existing structure. For span type structures, the bridge survey includes elevations along the existing bridge floor at 5 ft. intervals along the centerline and curb lines on each side, along with elevations of the bridge seats at all bents, and, if practical, the elevation of the top of the footings. Where deck replacement is necessary on steel beam or girder bridges, bottom of top flange elevations for each stringer or girder for each substructure unit are required. Locations where elevations are taken on existing bridges must be clearly described on the bridge survey sheets. Stationing at existing bridge ends and at the centerline of each intermediate bent or pier is also required.
126.96.36.199 Grade Separation
Surveys for grade separation structures, both railroad and highway, include offset profiles to beyond the limits of the structure along the centerline on which the structure is to be constructed. This is in addition to profiles and cross sections along the survey centerline and the centerline of the crossroad. Additional requirements for offset profiles are discussed later in this article. Surveys at railroads include a profile of the top of rail or rails to at least 200 ft. from the survey centerline measured normal to the survey centerline. Top of rail profile elevations are obtained at intervals not exceeding 50 ft. Profiles are required for each railroad track at multiple track crossings. Profiles are required for each rail where the top of rail elevation differs. Where structures cross existing pavements, the survey includes profiles along the existing pavement at the centerline and at the edges of pavement for at least 50 ft. outside the structure. Profile elevations are obtained at intervals not exceeding 25 ft. Cross-sections may be obtained at interval not exceeding 25 ft. along the existing pavement in lieu of the profiles. Contours are required for grade separation structures only where the natural ground elevation differs by more than 10 ft. within the limits of the proposed structure and the bridge skew angle exceeds 50 degrees. Where contours are required they extend radially approximately 500 ft. from the point of intersection. Contours and/or cross sections are obtained by photogrammetry on photogrammetric surveys. All other information is obtained by field methods.
188.8.131.52 Stream Crossings
In order to provide the best possible structural design, it is imperative that the bridge survey be completed as fully and accurately as possible. Consultation with the Bridge Division early in the project to answer questions or resolve issues is encouraged. Bridge surveys require the following minimum information:
- Stream meander, man-made features, and contours extending at least 1000 ft. up and down the valley from the proposed bridge location;
- Centerline and offset profiles;
- Stream bed profile;
- Two typical channel sections;
- Description of and section under existing bridges if applicable;
- Extreme high water elevation, date of occurrence, and estimated frequency;
- Ordinary high water elevation;
- Extreme low water elevation;
- A survey for any necessary channel changes or channel cleanouts;
- Photographs depicting the character of the site; and
184.108.40.206.1 Coordination of Survey
Care is exercised to insure that the valley sections, profiles, and channel change surveys do not conflict with the stream meander survey, contours, and other survey data.
220.127.116.11.2 Use of Photogrammetry
On conventional surveys all bridge survey information is obtained in the field. On photogrammetric surveys all bridge survey information is obtained in the field except man-made features, stream meander, channel sections, water elevations and channel change surveys. Photogrammetric methods may be utilized to obtain stream crossing data. A contour interval of 2.0 ft. will provide adequate accuracy for hydraulic design. If water is present in the stream when aerial photographs are taken conventional survey methods must be used to obtain the streambed profile and portions of channel sections below the water surface. Prior to aerial photography, the district will determine the locations of valley sections from topographic maps. The valley sections are to be located on suitable maps to aid in obtaining sufficient aerial photographic coverage of the location. Generally it is more economical to use photogrammetric methods. Typical channel sections, profiles, water elevations and sections under an existing structure must be acquired in the field. If methods of photogrammetry cannot be used, the use of GPS or a total station EDM may be used. All angles are turned in a clockwise direction from the backsight. A complete set of notes is necessary to provide a complete record of the bridge survey, and for checking if necessary.
18.104.22.168.3 Field Notebooks
A plat sheet is drawn in the field to a scale of 1" = 100' (1:1000). The alignment, stream meander, man-made features including any buildings near extreme high water elevation, valley and channel sections, contours, north point, direction of flow, and datum are drawn on this sheet in the field. A complete set of notes containing the data plotted on this sheet is included in the field notebooks. If an electronic data collector is used, the field drawing and manual notes are not required.
22.214.171.124.4 Stream Meanders
The stream meander should be accurately located since it determines the structure location. The meander shall be plotted a minimum of 1000’ upstream and downstream of the structure location, and extend from the furthest upstream valley section to the furthest downstream valley section. Where the stream has both a high bank and a low bank, both are located and indicated on the plat sheet (use a solid line for the high bank and a dashed line for the low bank).
126.96.36.199.5 Extent of Contours
The typical contour interval is 2 ft. and extends to at least 1000 ft. up and down the valley, and to 5 ft. above extreme high water elevation. Contours are taken up and down the valley for this distance measured along the valley, not along the stream meander.
188.8.131.52.6 Streambed Profiles
Location The profile is taken along the thread of the stream with the distance measured along the general centerline of the stream. With the exception of certain situations (i.e, drainage ditches) care is exercised to avoid placing the profile centered between the banks.
Streambed profiles shall extend at least 1000 ft. upstream and downstream from the proposed crossing and extend from the farthest upstream to the farthest downstream valley sections. When stream bed profiles are required on confluent streams, the streambed profile limits for the tributary stream extends to the confluence of the streams. If there is a change in the slope of the streambed profile within this distance, the profile limits are extended.
The streambed profile is equated to the survey centerline and extends from station 0+00 downstream to upstream.
Water Surface Profile
When the stream is flowing, the profile of the water surface is also indicated since it provides an accurate hydraulic gradient.
184.108.40.206.7 Valley Sections
The layout of valley sections varies with stream size, slope, meander and other factors. As such, the guidance presented here considers a typical crossing of a natural stream. Additional guidance should be sought at multiple structures in the same floodplain, severe bends, deeply incised channels, drainage ditches, high skews, most stream junctions and other atypical locations. The Bridge Division can provide assistance in determining locations for the valley sections. This should be discussed with Bridge Division personnel as early in scoping/design as possible.
Location for Structures
A minimum of three valley sections are required, one upstream and two downstream of the proposed structure. The ideal location for valley section placement for creation of a hydraulic model is upstream and downstream of the disturbance to flow caused by the structure and roadway fill.
- Initial Placement of Valley Sections
- Initial placement of the upstream and the first downstream valley section should be based on a 1:1 contraction ratio (upstream) and a 2:1 expansion ratio (downstream) from the streamside end of the roadway fill to the limit of the 100-yr floodplain. The slope of the contraction and expansion lines should be based on 100-yr flood flow path. For locations without an existing structure or when the replacement structure may be shorter, the origin of the expansion line may be moved closer to the bank of the channel. Initial placements should be adjusted as specified below.
- Final Placement of Valley Sections
- Upstream Valley Section – The upstream valley section is used to help determine the upstream water surface elevation and the flow velocity entering the bridge. Placement should be in a location representative of the average floodplain width upstream in the vicinity of the bridge and should not be placed at an excessively wide location in the floodplain or at junctions with tributaries. The location of the section should remain either at or upstream of the intersections of the Expansion lines and floodplain limits after any location or orientation adjustments are made. Orientation adjustments may be needed when the channel flow is not parallel to the 100-yr flood flow. (See Valley Section Orientation for details).
- First Downstream Valley Section – The first downstream valley section is used to establish the water surface elevation and flow velocity downstream of the bridge which is used to calculate the energy loss through the bridge caused by the bridge and roadway fill. Placement should be in a location near the initial section that provides a natural constriction. If a natural constriction does not exist, the section should be placed at a location representative of the average floodplain width downstream in the vicinity of the bridge and should not be placed at an excessively wide location in the floodplain or at junctions with tributaries. The location of the section should remain either at or downstream of the intersections of the expansion lines and floodplain limits after any location or orientation adjustments are made. Orientation adjustments may be needed when the channel flow is not parallel to the 100-yr flood flow. (See Valley Section Orientation for details).
- Second Downstream Valley Section – The second downstream valley section is used to establish a starting water surface elevation and flow velocity for the hydraulic model. Placement should be in a location downstream of the final location of the first downstream valley section within a range of 0. 5 to 1.0 times the distance between the roadway centerline and the final location of the first downstream valley section (measured along the 100-yr flood flow path) that provides a natural constriction. If a natural constriction does not exist the section should be placed at a location representative of the average floodplain width downstream in the vicinity of the bridge and should not be placed at an excessively wide location in the floodplain or at junctions with tributaries. Orientation adjustments may be needed when the channel flow is not parallel to the 100-yr flood flow (see Valley Section Orientation below for details).
- Valley Section Orientation
- Valley sections are taken through the entire valley including the stream channel and floodplain at right angles to both the channel and 100-year flood flows. To conform to right angles, the valley section may be "doglegged" so the first leg is at right angles to one side of the valley, the second leg is at right angles to the channel, and the third leg is at right angles to the opposite side of the valley. For hydraulic modeling purposes if the angle of the stream flow is within 15° of the 100-year flood flow it may be considered to be at a right angle and doglegging the valley section is unnecessary.
Valley Section Locations at Junctions
Stream junctions near bridges are relatively common. Below are some generalized cases for determining if valley sections are needed:
- Small Tributaries – For bridges over the main channel with a small tributary entering either upstream or downstream of the bridge, additional valley sections will not be required when the drainage area of the tributary is less than 20% of the drainage area of the main channel.
- For bridges over small tributaries near larger channels, valley sections will be required. The Bridge Division can provide assistance in determining locations for these valley sections.
- Larger Tributaries – The Bridge Division can provide assistance in determining locations for these valley sections.
For each surveyed valley section obtain the distance along the channel meander from the roadway centerline. The valley sections are tied to the survey centerline.
Valley sections extend to at least 5 ft. above the extreme high water elevation, and outside the limits of the 100-yr floodplain.
The stationing along the valley section is established from left to right looking downstream.
The type of ground cover should be indicated to assist office personnel in the establishment of Manning's "n" value.
220.127.116.11.8 Typical Channel Sections
Typical channel sections are obtained within 300 ft. of the survey centerline both upstream and downstream. These sections are not precisely tied to the survey centerline but the survey field book indicates the approximate distance from the survey centerline to where the sections are taken.
The stationing for the typical channel sections is established from left to right looking downstream.
The typical channel sections extend to the top of the high bank of the stream or, in the case where the stream bank is also the side of the valley; the sections extend to 5 ft. above extreme high water.
18.104.22.168.9 Existing Bridges
In addition to other required sections, a section showing the entire waterway below extreme high water for existing structures crossing the stream being surveyed is required if they are within the limits of the obtained stream bed profile. A complete detail section is taken under the existing structure with a general description of the structure along with the elevation of extreme high water at the existing structure.
22.214.171.124.10 Extreme High Water Elevation
An extreme high water elevation is obtained for the centerline profile, either by observation of visible high water marks or by conferring with maintenance personnel or local residents. If sufficient information is available to make an accurate determination, extreme high water elevations are obtained for each of the valley sections. The location and elevation of the high water elevations are included in the survey notes while the location is tied to the survey centerline or base lines. The best procedure is to obtain information from local residents and then confirm this information by observation. Quite often local residents may exaggerate, or the high water elevation remembered by them will be far beyond the flood frequency to which the structure is to be designed. Particular care is exercised in obtaining this information since it is used as the basis for laying out the proposed structure. If any doubt exists as to high water marks reported to the survey party, give location and elevation of all such marks and in every case give dates of occurrence. Survey personnel are encouraged to mark and record, for future reference, high water elevations for at least all major streams during or immediately after floods.
126.96.36.199.11 Ordinary High Water Elevation
An ordinary high water elevation is obtained for each bridge survey. The ordinary water elevation is defined by the Corps of Engineers as: “a line on the shore established by the fluctuations of water and indicated by physical characteristics such as a clear natural line impressed on the bank, shelving, changes in the character of soil, destruction of terrestrial vegetation, the presence of litter and debris, or other appropriate means that consider the characteristics of the surrounding areas”.
188.8.131.52.12 Low Water Elevation
A low water elevation at the centerline profile is necessary for streams that are generally never dry. The low water elevation is defined as “the lowest water elevation during a year of normal rainfall”. This information is used to establish the datum for structure excavation. Including this data with the bridge survey is always necessary.
184.108.40.206.13 Channel Surveys
Proposed channel change surveys are always included for each bridge survey. The channel change survey consists of alignment, profile, and cross sections. On photogrammetric surveys the channel change profile and cross sections and/or contours are furnished by photogrammetry. If no channel change is necessary, the existing channel is surveyed, including cross sections 300 ft. upstream and downstream for use in computing earthwork quantities for any necessary cleanout of the existing channel.
Photographs documenting the site characteristics are necessary. They are taken in an overlapping manner to provide a 360° panoramic view at or near the proposed stream crossing. Photographs are also taken to show the channel, banks, and streambed both upstream and downstream of the proposed structure, as well as the waterway through the existing structure. If the existing roadway is overtopped at extreme high water, photographs are provided showing the roadway on both sides of the existing structure. If land use or stream characteristics are significantly different at upstream or downstream valley sections, additional photographs documenting these conditions are provided. Additional photographs are also used to provide information on other site-specific conditions, including any nearby improvements that may be affected by flooding or changes in stream velocity.
220.127.116.11.15 Bridge Survey Report Form
Pages 1, 2, 3 and 4 of the Bridge Survey Report Form are partially completed in the field to supplement the bridge survey. Certain information included on this form cannot be obtained in the office, such as a complete, accurate description of the stream channel and valley as required to describe their hydraulic characteristics. This information is used in the hydraulic calculations for the structure(s) and should receive careful consideration, both in the field and in the office. Survey notes for bridge surveys are recorded in accordance with previously mentioned requirements.
18.104.22.168.16 Triangulation at Large Streams
Triangulation may be necessary to project the survey centerline across larger streams where it is not practical to make a direct measurement across the stream. Since the distance across the stream and, in turn, the length of structure is determined by the triangulation, the base lines are surveyed and the angles measured to at least the same accuracy as required for the survey centerline. Increased accuracy for the base line survey may be required for large streams and where the length of the base line is short in relation to the distance across the stream. The base line is established in relation to the survey centerline and to a length that will cause the interior angles of the triangle to be as near to 60 degrees as possible. Base lines are established on both sides of the stream, and the triangulation is computed from both directions as a check on all surveys. The survey field book includes notes for the base line survey, a record of the angles, and the computations for the triangulation. Electronic distance measuring equipment can be used for direct measurement of stream crossing distances.
22.214.171.124.17 Multiple Structures
Multiple structures in the same floodplain work as a system and changes to the hydraulic capacity of one structure in this system affects backwater elevations, flow velocity, scour potential, etc. at all the structures in the system. Bridge surveys are provided for each structure being replaced and should be tailored to that structure, but the bridge survey data is developed based on the system of bridges and not each individual structure even if only one structure in the system is being replaced.
For multiple structures, in the same floodplain, all items in EPG 238.3 are required for the Bridge Survey(s) with the following modifications:
Multiple Defined Channels
A streambed profile is provided for all structures, including overflow structures that have a defined channel, even if that structure is not being replaced.
A streambed profile is not required for overflow structures that do not have a defined channel. When only the overflow structure is being replaced, the bridge survey is still developed based on all structures that are in the floodplain. Streambed profiles are provided for all other structures in the floodplain that have a defined channel.
238.3.37 Contacts with Property Owners
Prior to a request for a survey the designer sends a letter to property owners located along the proposed roadway improvement. The District Right of Way office will supply the designer with a list of property owners and their addresses. The survey party chief will contact property owners and/or occupants, if conveniently possible, prior to entering a property as a matter of respect and to promote good public relations. The survey party chief explains in general the proposed improvement, explains in layman terms how the survey will proceed, and requests the consent of the owner and/or occupant to proceed with the survey. Should the owner and/or occupant refuse to allow the survey party chief to enter the property the project development engineer is immediately advised of the situation. They will handle the case beyond this point. The survey party will not enter any property when consent to enter has been refused until further advised by the project development engineer. The survey party chief will advise the owner and/or occupant that the survey is made a step at a time and the party will be passing through the property several times to complete the work. These numerous visits are not an indication that mistakes have been made. If the survey is a photogrammetric survey the owner and/or occupant must understand the placement and purpose of ground control targets. The public is never given questionable information by the survey party. It is much better to say, "I do not know" than to impart false information. A letter may be sent to property owners in lieu of other means of contact
238.3.38 Survey Property Damage
During the process of making surveys, it may become necessary to trim crops or trees; or be involved in other circumstances that may involve property damage related to obtaining survey information. When property damage does result due to activities of the survey party, it is the responsibility of the survey party chief to complete a General Liability Claim Report should the property owner make a damage claim. If circumstances of the property damage are questionable, a letter of explanation will be sent to the Design Division prior to submitting the property damage release and report form to fiscal services. The property owner must be contacted prior to the cutting of crops or trees. The survey party chief must inform the property owner of the need for, and the extent of, the required damage.
238.3.39 Traffic Safety
Survey parties are to utilize the equipment and procedures available to provide the maximum level of safety for their personnel and the traveling public. When working on the road, appropriate signing is used as a minimum guide for traffic safety. When working on the outside shoulder one "Survey Crew" sign is placed on that shoulder, preceding the work by 200 ft. in urban areas and 500 ft. in rural areas. When working in the median, "Survey Crew" signs are used facing both directions. When working outside the outside shoulder line signing is not normally used. The major factors bearing on the protection to be used in each situation are:
- Volume of traffic
- Highway geometrics
- Duration of operation
- Exposure to hazards
- Weather (or road conditions)
Warning signs are placed at appropriate minimum distances. Field conditions will control the actual placement of signs and channelizers. The individual in charge of the survey party has the responsibility to see that the necessary safety precautions are taken. Safety vests are to be worn by all members of the survey party while working on the right of way. Where signs are used they are to be placed prior to beginning work and at locations having adequate approach visibility. Channelizers are to be used as needed. Personnel using stop-slow paddles are positioned as needed to provide the best direction of traffic and safety for working personnel. Personnel must be instructed concerning the importance of staying alert, being courteous to motorists, and the fact that the responsibility for the lives of the party and traveling public are in their hands. The department publication "Safety Rules and Regulations" gives additional traffic control information. Trucks with top mounted flashers may be used to provide additional protection for personnel by blocking the lane or parking on the shoulder. Two-way radios may be used to handle traffic where two way operation over a single lane is maintained without visible contact between personnel.
The required degree of accuracy for conventional surveys is shown in the following table. The survey party is responsible for obtaining at least this degree of accuracy, through the proper adjustment and care of instruments and equipment and the method of making measurements.
|Levels||0.05 ft. x Sq. Root Dist.(miles)|
238.3.41 Recording accuracy
Single measurements are recorded to the accuracy shown in the following table.
|SURVEY RECORDING ACCURACY|
|Levels||0.01 ft. Bench Levels, Turns, etc.|
0.01 ft. on Concrete
0.1 ft. All Others