Water Retention, Seepage and Evaporation Losses
The rate of seepage loss adopted for the seepage loss calculations is 25 x 10-6 MLD/m2 (million liters per day per square meter). This rate of seepage is estimated using a mathematical modeling study carried out by Physical Research Laboratory, Ahmedabad. The model considered characteristics of the Sabarmati River passing through Ahmedabad - approximately from Vasna Barrage up to Subhash Bridge. The evaporation loss calculations are based on evaporation rates recommended by Water Resources Research Foundation, Ahmedabad. These are based on data from the Agro-Climatic Atlas of India, 1978.
Water Retention and the Fatehwadi Irrigation Scheme
At present, following the monsoon, water retained upstream of the Vasna Barrage is released into the Fatehwadi Canal (which has a total discharge capacity of 45.3 cumecs) for irrigating the Fatehwadi Command Area. If water is to be retained through out the year - up stream of the Vasna Barrage - it is imperative that an alternative way of irrigating the Fatehwadi Command Area be identified. following are two viable alternatives.
Using Water from the Narmada Main Canal for irrigating the Fatehvadi Command Area
Using Treated Water from the Proposed Sewage Treatment Plants for the Ahmedabad Urban Area to Irrigate the Fatehvadi Command Area
Replenishing Water
It is proposed that, at the very least, through out the year the depth of water at Subhash bridge should be 1 m ( which it will be in the first week of October). To ensure this, as discussed above, first of all it will be necessary to eliminate the requirement of irrigating the Fatehwadi Command Area by using water retained by the Vasna Barrage. Secondly it will be necessary to replenish seepage and evaporation losses to the extent that water depth at Subhash Bridge remains 1 m. The following discusses various options for replenishing water in the river.
Using Water from the Narmada Main Canal
Using Water released from the Dharoi Dam
Using Treated Sewage Water (Soil Aquifer Treatment, SAT):
Ground Water Recharge:
The combination of city owned and private tube-wells is depleting the supplies resulting in rapid drop of 2 m per year in the water table. This pattern of water consumption is obviously unsustainable in the long run.The construction of embankments will make it possible to retain water till the top of Vasna Barrage. Retaining water in the river will have a positive effect on the recharging of ground water aquifers and considerably decrease the presently rapid fall in the water table in the city area.
