Mini check dams only solution to solve water woes

During summer season, shortage of water supply to Mangaluru city and the industries has become a regular feature for the last few years. This year too, due to poor monsoon, the inflow in River Nethravathi, which is the main source of water to the city, has already drastically reduced.

The city’s daily drinking water requirement is around 36 MGD, which is equal to 0.163 million cubic meter a day. The present requirement of MRPL and SEZ is around 15 MGD, equal to 0.063 million cubic meter per day. Further, the requirement of towns, villages and farmers residing on the banks of downstream side of river Netravathi is approximately assessed around 0.07 million cubic meter per day.

Thus, the total requirement of water below Uppinangady up to Mangaluru city during the lean season comes to around 0.30 million cubic meter per day. This requirement has to be met from the main two storage reservoirs of Thumbe and AMR barrages during the summer season when the inflow in the river becomes negligible.

The storage in the newly constructed Thumbe dam up to 5.00 metre is around 7.50 million cubic meter. However, due to siltation and sand deposit, the available water for pumping is around 7 million cubic meter. The storage capacity of AMR dam of the Greenko Power Company is around 14.5 million cubic meter.

Deducting the dead storage of 0.25 million cubic meter, the available water for drinking water supply of Mangalore city, MRPL, SEZ and the requirement of farmers is 14.25 million cubic meter. There is also some additional storage of water in the upstream side of power producing companies, namely Sagar Power and Disha Power, which is estimated around 1.25 million cubic meter.

Thus, the total storage of water available during summer is around 22.5 million cubic meter. Considering around 1 million cubic meter for evaporation loss, the net storage available in the above barrages will be 21.5 million cubic meter.

The inflow in River Nethravathi normally during this period used to be around 40 to 50 cubic meter per second. But this year it has drastically come down to around 15 cubic meter per second at AMR dam site. The requirement of water to the city, MRPL, SEZ, towns, villages and farmers is 0.3 million cubic meter per day, equal to 3.5 cubic meter per second.

The flow is likely to become negligible by end of January 2017 and from there onwards, the stored water in the barrages is the only source of water if no unseasonal rainfall takes place during the lean period.

Hence, it is necessary to review the water availability by around January 20, 2017, by the authorities concerned and take necessary action to see that availability of water to the city is made available at least once in two days instead of daily supply.

Future course of action

The city is fast growing and has been already declared as Smart City. The population is likely to double in the next 10 years. On the other hand, River Nethravathi is the only source of water for the city and the industries.

Though there is plenty of water available in the river, there are no major dams/barrages constructed across the river to store sufficient water for usage of the same during lean season, as construction of major dams is ruled out in view of uprooting of huge population and submersion of vast area of land.

The only solution is building series of mini check dams of height of around 10 meter across River Nethravathi, Kumaradhara and Phalguni rivers for storing water.

Alternatively, as it will take time and involves huge expenditure for the government, the four mini hydel projects allotted to private companies in the Kumaradhara River basin must be forced to complete their power projects within two to three year.

This will ensure that sufficient storage of water will be available in their barrages during the lean season so as to release the same to Thumbe dam for the future requirement of water.

(The writer is former director, Karnataka Power Corporation)