Sourya Kharb
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VISION AND PLANNING
To store State's 25% average annual surface water resources by constructing 30 km long dam across the Gulf of Khambhat. This reservoir will store about 10,000 MCM of surface water and will be the the world’s largest fresh water reservoir in sea.
Benefits
·World’s largest man made fresh water reservoir in the sea.
·Highest importance and priority to irrigation and drinking water for Saurashtra and Central Gujarat regions.
·The Reservoir will have the storage more than double the Sardar Sarovar (Narmada Reservoir) capacity.
·10.54 lakh ha land in 39 talukas of 6 districts of Saurashtra region will get irrigation benefit facility including rejuvenation of rivers. More than 60 existing dams will get permanently filled up with water.
·Wind and solar energy will be generated which can also be used for lifting fresh water from the reservoir to the canal.
·Bhavnagar port will get revived which will result into speedy development of the region.
·There will be large saving in travel time and fuel due to reduction in distance by about 200 km between Bhavnagar to Surat-Mumbai.
·Saline ground water of coastal area of Saurashtra & Central Gujarat will get converted into fresh water with reduction in soil salinity.
·Substaintial improvement in ground water quality as well as soil salinity of coastal area of Saurashtra & Central Gujarat.
·About 2 lakh ha land along the periphery of the reservoir will be opened up for development towards value-based land utilization.
·Enhanced benefit of world class industrial estate like Dahej and Dholera will be available to Bhavnagar/Saurashtra region.
The State of Gujarat with a population of 50 million (year 2000) is situated on the West Coast of India. It has a geographical area of 1, 96,000 sq.km (19.6 Mha) and the cultivable area of 12.36 Mha. The average annual rainfall, confined to 3 months of the monsoon season, is 760 mm which is highly variable both in space and time, the southern part receiving 2500 mm of rainfall while the northern portion including Kachchh and the Saurashtra peninsula receiving rainfall of 300 to 450 mm. Intra-state rivers are small with very low and highly variable flows. Every 3rd year is a drought year in Saurashtra, North Gujarat and Kachchh region. Monsoon waters are required to be stored in reservoirs for use in the lean nine months of the year. The ground waters are saline and contain harmful proportions of fluorides and nitrates in large parts of the State. The limited utilizable ground water has been over exploited over the past 3 to 4 decades and ground water tables are presently going down rapidly by as much as 3 meters every year in North Gujarat and Kachchh regions. In recent past Gujarat has faced it’s most severe droughts in the years 1987 and 2000.
Historical Background:
The Gulf of Khambhat was identified as a promising site for tidal power generation by UNDP Expert, Mr. Eric Wilson in the year 1975. In 1988-89 a reconnaissance report was prepared for the dam across the Gulf of Khambhat. The report concluded that, assuming sound foundation conditions, the closure of Gulf was technically feasible.
Kalpasar Project Transformed:
A project thus conceived initially as a tidal power project was transformed as tidal power cum fresh water supply project providing large multipurpose benefits. It is in fact a project envisaging total multipurpose development of the Gulf of Khambhat. It is proposed to build a dam across the Gulf of Khambhat connecting Ghogha in Bhavnagar and Hansot in Bharuch Districts. The reservoir formed will be sub-divided into (a) Tidal basin and (b) Fresh water basin. This would provide benefits of tidal power generation, as well as use of large quantities of fresh water. This unique concept has, in no small measure, contributed to the economic viability of the Mega Project. The scope and size of the project would perhaps exceed that of any other similar project in the world.
Dam height:
The height of the closure works is not determined by reservoir water level, as is the case in river valley storage reservoirs, but by the water level conditions at the sea side of the KALPASAR reservoir.
The crest level of the dam has been assessed at GTS + 13 m to prevent overtopping of the dam during extreme sea level and wave conditions. As a consequence, the maximum dam height corresponds to 53 m at the deepest part of the dam alignment, where the bottom level is at GTS-40m.
Scope and Size of Project:
The pre-feasibility study and six specific studies have shown that the project is technically and economically viable and detailed feasibility study needs to be taken up.
The project planning and designs as well as the nature and quantum of benefits have undergone several changes and now the project has emerged as a mega-multi-purpose project.
Closure method:
A maximum acceptable flow velocity during closure of 6 m/s has been adopted in order to keep the handling of rock manageable. The maximum acceptable flow velocity occurs when the width of the opening of the Gulf at the location of the dam alignment is reduced to 10 km. Further narrowing of the opening leads to exceedance of the maximum acceptable flow velocity. As a consequence, the last 10 km need to be closed suddenly. Such sudden closure is achieved by placing, over a length of 10 km, gated caissons which can be closed suddenly by lowering the gates.
Bottom protection is needed over the whole dam alignment to prevent local scour during construction.
The adopted closure method is a proven concept. The immense scale of the Khambhat closure works justify the development of new technologies that could lead to a more economic construction method. In this stage of the project preparation, however, a definite confirmation of the technical viability of the closure of the Gulf of Khambhat can only be given on the basis of tried out closure concepts.
Plan of Action:
In keeping with the planned completion schedule of the Kalpasar Project, before end of second decade of the Millennium, it is essential that the detailed feasibility report is completed with the latest technology through a high international standard within the next 3-4 years. This, including the bankable project proposal, has to be prepared after carrying out various detailed and comprehensive investigations. These would include geotechnical assessments and explorations, topographical and bathymetric surveys, marine observations and analysis for the determination of design height of the sea waves, silt content in tidal waters as well as intensive data concerning the Arabian Sea tides.
The Government of Gujarat has now taken up the task of preparation of the full scale feasibility report for which action plan has been prepared. All these activities will be taken up on hand with the help of the expert groups of both National and Internationals.
Estimated Cost:
The cost is approximately Rs.54,000 cores for single tidal basin options and Rs.47,800 cores for double tidal basin option at 1999 price level. The cost of the Kalpasar dam and tidal power works is estimated as Rs.44,301 cores and Rs.38,124 cores for single basin and double basin respectively at 1999 price level.
Costs of closure works:
The total costs of the closure works have been estimated at Rs 19,253 Cores. This cost includes 20 % miscellaneous and unforeseen, and also Rs 500 Cores for engineering, investigations and administrative costs for project preparation and management. Ship lock and spillway are also included at the rate of Rs 340 Cores and Rs 1,285 Cores respectively.
Function of kalpasar project:
Area of reservoir:
2070 km2 (fresh water lake)
872 km2 (Tidal Basin)
Possible of storage water:
Live storage of reservoir: 12247 Mm3
Gross storage of reservoir: 16791 Mm3
Dead storage of reservoir: 4544 Mm3
The canal capacity:
Canal capacity is 425 cumecs (15,000 cusecs).
Tidal power can be gained in both of these cases:
Tidal power to be gained. Single basin - 5880 MW (Installed)
Double basin - 1680 MW (Installed)
Cost of tidal power generation:
Cost of tidal power generation. Single basin - Rs 44301 (Rs.in cores)
Double basin - Rs 38124 (Rs.in crores)
Flow in the canal by gravity or intermediate pumping proposed:
In the total canal length of about 660 km, flow is by gravity as well as 13 lifts of about 10 m with total lift of @ 110 m.
How many pumping stations:
13 Pumping station at Chainage (km) 0.0, 7.2, 85.5, 87.0 , 88.8, 90.0, 91.2, 110.0, 209.0, 308.0, 407.0, 506.0
Water is planned to flow for irrigation-water supply-industrial use:
Sr.No. Water planning mm3
1. Irrigation 5461
2. Drinking W/s 900
3. Industrial use 500
4. Firming up of existing Irrigation projects. 430
DEVELOPMENT POTENTIALS
Water availability for irrigation and water supply:
Once the closure works are completed, the saline water body within the reservoir will be replaced by the fresh waters entering into KALPASAR. The desalinization period has been assessed at 4 years when the KALPASAR reservoir is used for fresh water storage only. When part of the reservoir is used for tidal power generation, this period is reduced substantially. With 500 km2 tidal power basin the fresh water reservoir can be used 2 years after the closure of the Gulf.
The volume of the KALPASAR reservoir between the maximum and minimum allowable reservoir levels of respectively GTS + 4 m and GTS - 6 m amounts to 16,585 Mm3.The average yearly inflows of fresh water totals 12,552 Mm3.
Tidal energy:
All alternatives, except the "fresh water only" option, achieve the objective of making use of the tidal power potentials in the Gulf of Khambhat. The extent, to which use is made of this potential, depends merely on the amount of power installed. This is maximum in the "tidal power only" alternative and minimum in the combined alternative with 1,500 MW installed.
Dam alignment:
Geophysical and geotechnical surveys have shown that foundation conditions north of the Narmada river mouth can be considered fit for dam construction. The soil conditions south of the Narmada estuary are influenced by deposits of the river and are less suitable for the construction of closure works.
The hydraulic conditions do not change significantly if the closure dam is constructed immediately north of the Narmada mouth or some 20 km more to the north. Shifting the dam alignment to the north reduces, however, the storage capacity of the reservoir.
Dam construction in the proximity of the Piram Island has been rejected because the deep channels flanking the island have prohibitive impact on the construction costs.
The selected dam alignment is located between Gogha on the Saurashtra bank and Luhara Point, south of Dahej on the eastern bank of the Gulf. From Luhara Point the dam is extended across the Bharuch Channel of the Narmada estuary towards the island of Alia Bet. The dam alignment continues along the southern outline of the island and crosses the secondary branch of the Narmada estuary near Hansot.
The length of the closure of the Gulf of Khambhat between Gogha and Luhara Point amounts to 28.9 km, the dam closing the Narmada estuary hs a length of 34.0 km.
Dam elements
The works for the closure of the Gulf of Khambhat including the Narmada estuary consist of the dam body itself, of which 10 km is provided with closure caissons, a spillway, and a navigation lock.
The spillway comprises 65 discharge openings with a width of 17 m each and a sill level at GTS - 11 m. The discharge openings are provided with 17 m high radial gates. The spillway allows the passage of the Narmada PMF in combination with the simultaneous occurrence of 50% of the sum of the PMF's of the remaining tributaries entering into the KALPASAR reservoir, without causing flooding of the reclaimed areas on the edge of the reservoir. In a worst case scenario in which the all PMF's occur simultaneously, still over 5 m freeboard is left at the reservoir side of the dam.
A ship lock with length 200 m and a width of 35 m, with sill level at GTS - 10 m, is incorporated in the dam. This lock allows for ships of approximately 50,000 DWT to pass the dam under all tidal and reservoir level conditions. The lock is to be used for construction purposes and for maintaining the accessibility of existing ports after finalization of the closure works. A second ship locks allowing ships of approximately
20,000 DWT to enter the tidal basin is envisaged if tidal power development is incorporated in the development alternative.
Water availability for irrigation and water supply:
Once the closure works are completed, the saline water body within the reservoir will be replaced by the fresh waters entering into KALPASAR. The desalinization period has been assessed at 4 years when the KALPASAR reservoir is used for fresh water storage only. When part of the reservoir is used for tidal power generation, this period is reduced substantially. With 500 km2 tidal power basin the fresh water reservoir can be used 2 years after the closure of the Gulf.
The volume of the KALPASAR reservoir between the maximum and minimum allowable reservoir levels of respectively GTS + 4 m and GTS - 6 m amounts to
16,585 Mm3. The average yearly inflow of fresh water totals 12,552 Mm3. For the assessment of this volume the situation has been taken that the development of the Narmada river basin has been completed according to the directions of the
Narmada Water Disputes Tribunal, while only 10 % of the Gujarat share of the
Sardar Sarovar Project 'spill' is allocated to KALPASAR.
The demand for KALPASAR water for domestic and industrial use in Saurashtra has been set at 1,387 Mm3 per year on the long term (year 2060). When this demand is met with 100 % reliability, then a total yearly volume of 6,100 Mm3 can be made available
For irrigation at 75 % reliability.
Land reclamation:
The Gulf of Khambhat is surrounded by salinity affected soils covering an area of almost 400,000 ha. By creating the fresh water KALPASAR reservoir, sufficient water will become available for a sustainable agricultural development of these salt affected areas.
Most of the salinity affected areas are planned to be irrigated by Mahi waters or from the Sardar Sarovar Project through the Narmada canal. The area that is left to be reclaimed and irrigated within the KALPASAR scheme amounts to 119,100 ha only. With the KALPASAR concept proven to be feasible, the use of both KALPASAR and SSP waters needs to be optimized in order to improve the output of both systems.
In the economic evaluation of the KALPASAR scheme, it is assumed that land reclamation will take place at a rate of 10,000 ha per year.
Agriculture will be the principal use of the reclaimed areas. It is anticipated that some 60 % of the reclaimed area will be used for agriculture, this corresponds to some 70,000 ha net or 80,000 ha gross.
Socio-economic criteria
Investment costs:
The cost of the construction of closure works, not including power works, would be as follows for the different alignments:
- alignment of "fresh water only" and combined alternatives: Rs 19,597 Crore
- alignment "tidal power only" alternative: Rs 13,857 Crore
- northern dam alignment: Rs 13,950 Crore
The inclusion of power works in the different alignments carries additional costs that have been valued at Rs 3.17 Crore per MW power on the average. The power works have a major impact on the total investments.
Consequently, lowest investment costs (Rs 19,597 Crore) are related to the "fresh water only" alternative. The highest investment costs (Rs 34,961 Crore) are related to the "5,000 MW" alternative.
It is anticipated that further investigations and research in closure techniques may result in savings on the costs of closure works.
Environmental aspects:
Sustainability KALPASAR reservoir
From the environmental studies it is concluded that the viability of the KALPASAR project essentially is related to the willingness and capability to upgrade the water quality in the rivers flowing into the reservoir. This upgrading can be achieved either by treating the effluents, by relocation of industries and/or by diverting (treated) effluents towards the part of the Gulf that remains open. Part of these measures are essential in the without KALPASAR scenario also. The additional costs to be allocated to KALPASAR for making the project sustainable are difficult to estimate.
However, assuming that the essential measures for improvement of the water quality in the without KALPASAR situation have been taken, the additional measures for KALPASAR sustainability are not the same for all alternatives.
The additional measures are basically related to the maintenance of an acceptable water quality in the fresh water reservoir. Therefore, it is estimated that the "tidal power only" alternative will not require additional measures from a sustainability point of view.
The quality of the water stored in the fresh water basin of the "northern dam alignment" alternative is more severely threatened by the Sabarmati river then the fresh water basins belonging to the southern alignment alternatives. It is anticipated, therefore, that the sustainability of the northern dam alternative will require more additional measures than the other fresh water or combined alternatives.
For comparison sake, the alternatives with the Narmada included have been rated neutral, while the "tidal power only" and the northern alignment alternatives have been given a positive and negative value respectively.
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