Excess silt undermining potential of irrigation projects

Cause for concern:The catchment area of Satnala medium irrigation project in Jainad mandal of Adilabad district, falls under the hilly region of Narnoor mandal too.-Photo: S. Harpal Singh  

The decimation of forests in the district over the years has had a lasting impact on almost all the irrigation projects by way of losing the storage capacity. There has been no survey with regard to the extent of silt deposits in the reservoirs, but engineers concede that the phenomenon has reduced the potential of the projects.

Built in mid 1940s across the Kademvagu stream, the Kadem dam, now in Kadem mandal, was the first major irrigation project in the district. The meticulously conducted surveys with regard to silt curves and other factors like rainfall all along the stream also became a benchmark for future projects, of which there were a dozen of medium irrigation facilities.

When the survey for Kadem dam was conducted in 1930s, the area had a thick forest cover which apparently had the engineers calculate much lesser amount of silt flowing into the stream. The situation, nevertheless, changed drastically, but all the projects which were subsequently built, including Mathadivagu in Tamsi mandal and Gaddennavagu project in Bhainsa mandal constructed in the last decade, were designed based on the Kadem parameters.

Since 1970s, the loss of forest cover on the hills and in the plains has been rapid which has increased the flow of silt into the respective hill streams. This silt eventually gets deposited on the bed of the reservoir killing its storage capacity.

Take for instance the case of Satnala medium irrigation project in Jainad mandal. Its catchment area falls completely under the hilly region of Narnoor mandal too.

The utility value of the project is declining rapidly as it irrigates only about 5,000 acres against a contemplated 24,000 acres ayacut, also because of the steady decrease in its storage capacity. The reservoir dries up beyond its one tmc dead storage level due to the worrisome phenomenon.

The case of Vattivagu project in Asifabad mandal is much more glaring. Much of the soil excavated from the Dorli open cast coal mines is being washed into the reservoir.

Some of the projects have silt ejectors or scour sluices constructed, but these gates were never operated which eventually got obliterated. The SRSP in the neighbouring Nizamabad district and Kadem dam itself are a prime example of the silt ejecting facility gone abegging and their capacities reducing by nearly 30 tmc and 2 tmc against 120 tmc and 7.5 tmc respectively.

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Printable version | Oct 22, 2021 4:52:45 PM |

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