All our developmental plans envisage high priority to water resources projects specially construction of reservoirs. Accordingly large numbers of reservoirs have been constructed in Maharashtra. These reservoirs on completion face the problem of sedimentation. The soil erosion is a natural process occurring in the river basin system. To account the soil erosion process, the sediment load is estimated while designing the dead storage of the reservoir. However, it has been found that the sediment also gets deposited in live storage, reducing the utilizable capacity. Evaluation of reduced live storage capacity is essential for assessing useful life of reservoir as well as for Irrigation scheduling. There are many methods of sediment load estimation. The remote sensing technique is effectively used mainly for live storage of the reservoir while Differential GPS based bathymetric technique can be used for entire storage. The remote sensing based sediment assessment in live storage of reservoir has proved to be most economical method. In Maharashtra this technique has been used since long.
In present paper an attempt is made to analyze the sedimentation surveys and rates in live storage capacity of reservoirs. The analysis is based on the available data of 28 reservoirs from different basins in Maharashtra. The live storages of these 28 reservoirs range from 27.476 Mm3 to 2677 Mm3. The sedimentation rate assumed for projects varies from 3.57 to 7.15 ha m/100 km2/year whereas the observed sedimentation rate in live storage of reservoir varies from 0.90 to 38.33 ha m/100 km2/year. This shows that actual sedimentation rate is much higher than the designed rate.
It is observed from the data that rate of sedimentation depends on 4 major factors namely rainfall quantity, size of catchment area, sedimentation period, reach of reservoir. The sedimentation rates from small catchments are found to be on higher side as compared to large catchments. Similarly the upper reach reservoirs are having less sedimentation in live storage than downstream region reservoirs. The sedimentation rate is more in early life of reservoir but go on reducing after 15–20 years. The rate is influenced by rainfall pattern. It increases rapidly for area having rainfall more than 2000mm.It is to sum up that the sedimentation rate is combined function of size of catchment area, rainfall, impoundment years, reach etc.
