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Transcript of SURAT FLOOD-2006
-LOCATON OF SURAT AND UKAI
-SALIENT FEATURES OF UKAI DAM
VARIOUS DATA RELATED SURAT FLOOD-2006
-FLOOD HISTORY AT SURAT
-SCENARIO OF FLOOD DURING AUGUST-2006
-FLOOD PREVENTION PLANS
IT WAS A PREVENTABLE DISASTER
-REASONS FOR FLOOD-2006
-WHAT COULD HAVE BEEN DONE..?
- WHY UKAI AUTHORITIES DID NOT RELEASE 3 LAKH CUSECS FROM 1ST AUGUST..?
-Surat city is situated at the delta region of river Tapi (India).
-The river Tapi is originating from a mountain Satpuda and flowing through three states Maharastra, Madhya Pradesh and Gujarat.
-The river Tapi is merging to the Arabian Sea at about 15 kms away from Surat city.
-Ukai dam controls the flow of water and water level in the river Tapi, which is 100 kms away from Surat city.
-The dam is constructed at Ukai, Tal: Songadh, Dist: Surat. It is constructed for irrigation purpose mainly and also served the purpose of flood control, generation of hydropower and supply of industrial and drinking water.
1) Flood history at Surat
2) Scenario of flood during August-2006
3) Flood reduction plans
IT WAS A PREVENTABLE DISASTER
Reasons for Flood-2006
SALIENT FEATURES OF UKAI RESERVOIR
-Location : Songadh, Surat district
-River : Tapi
-Catchment Area : 62 225 sq km
Gujarat : 1 337 sq km (2.15 %)
Maharashtra 51 254 sq km (82.37 %)
Madhya Pradesh 9 634 sq km (15.48%)
-Design flood discharge : 49 490 cumecs (1.75 million cusecs)
-Year of completion : 1972
-Gross storage capacity : 8.511 BCM
-Live storage capacity : 7.092 BCM
-FRL : 105.16 m (345 ft)
-Riverbed level : 47.87 m (157.05 ft)
-Installed power generation capacity : 905 MW
1) Desilting from Reservoir
Due to silting in the reservoir the dead storage capacity of dam has been reduced. The average rate of silting is 1 ft. per year. It is difficult to completely remove mud and silt from the reservoir, however silt removal devices can be installed to minimize the silting effects.
2) Increasing the carrying capacity of river Tapi
The effective waterway of river Tapi has been reduced over years due to silting. The dredging of river in certain reaches and other suitable measures can be implemented to increase the carrying capacity of the river.
3) Construction of flood protection wall
It is necessary to provide flood protection wall on both the banks of river Tapi to protect the residential areas. The existing flood protection wall may not be sufficient in respect of length and height as well as it is in a damaged condition.
4) Recharge of groundwater
It is necessary to construct widely spread groundwater recharge wells after proper planning and design in the flood affected area, which can absorb some portion of the flood water. The recharged water will also be useful for increasing the groundwater storage, improving the quality of groundwater and control of sea water intrusion.
5) Spreading of flood water on saline Soil
It is also proposed to divert the floodwater to the existing saline soil areas outside the city. Such a diversion is possible by construction of suitable diversion channels. The diverted water will serve the purpose of reclamation of saline soil through leaching.
1) Heavy rainfall in upstream catchment area
As we can see from the salient features of the Ukai dam, 97.85 % of the catchment area upstream from the dam site is in Maharashtra and Madhya Pradesh over 81.3 % in Maharashtra alone. Rainfall in the Tapi basin talukas in Maharashtra was more than 25 mm, during June 1, 2006 to August 14, 2006. We can see that such instances were spread all over July & Aug ‘06. It is clear from these figures that Ukai was going to get large inflows in the days to come and there was sufficient actionable information available with the Gujarat water resources dept to release water from Ukai Dam in July itself.
2) Ukai reservoir level
When we compared the Ukai reservoir levels just before the monsoon and at the end of July for the last four years, we were surprised to find that the levels at Ukai dam were the highest this year in last four years, both with respect to the level just before the monsoon and also at the end of July, as is clear from the table below.
3) Water released from Ukai reservoir
It is disturbing to know that even as late as on Aug 6 evening, the water releases from Ukai reservoir were just 254780 cusecs when the level had already built up to 102.57 m, that is reservoir was 83.6% full at 5.528 BCM live storage. A day earlier the releases were shockingly low at 23640 cusecs. This was when during the eight days preceding this, all the talukas of Nandurbar district had received over 25 mm rainfall at least for 4-5 days including an instance of 260 mm rainfall in a day and seven instances when rainfall was over 100 mm. Surgana taluka in Nashik was also getting similar pattern of rainfall.
A Nationwide independent enquiry should be set up on the issue of floods in India this year, particularly those from the sudden releases of dams all over India. With proper use of water in the reservoir before the monsoon and timely releases of water from the dams, many of these disasters could have been avoided or damages substantially reduced.
-Transparency in Dam operations
The inflows, outflows, levels, storages, reservoir operation rules and disaster management plans at all reservoirs should be routinely made public on daily basis.
Surat city (India) situated at the tail end of river Tapi is subjected to moderate to heavy floods frequently due to heavy rainfall in the catchment area. Study of floods at Surat city has been made in this paper. To minimize the effect of flood at Surat city, certain preventative measures have been suggested. A flood reduction plan has been prepared and discussed in this paper which mainly includes curative measures. The aspects of diversion of flood water to other rivers and construction of flood detention ponds are discussed in details.
What could have been done?
Had the Ukai dam authorities released 300000 cusecs of water starting from Aug 1, the reservoir level at Ukai would have been reduced by over 3 BCM by the morning of Aug 6 and the level of water at the dam would have been 94.2 m (about 2.34 BCM storage). After this even with all the additional water coming in, continued outflow of 3-4 lakh cusecs would have been sufficient to ensure that reservoir does not get full and there would have been no big flood disaster in Surat district.