Role of sar data in water body mapping and reservoir sedimentation assessment

Abstract

Reservoir sedimentation is the major problem, due to it every year the reservoir capacity is lost to considerable amount. Surveying for assessment of the reservoir by conventional approach is time and money consuming. Geospatial technology provides ample opportunity in this field through the availability of high resolution satellite data from sensors such as Sentinel, Indian Remote Sensing Satellite, Landsat, and SPOT have been used to calculate the water spread area of the reservoir. However, due to presence of cloud in most of the optical data during onset of monsoon, the water spread at the lowest reservoir level could not be mapped. In turn the revised capacity or sedimentation is generally assessed between either below full reservoir level (FRL) or above maximum draw down level (MDDL). Nowadays, the microwave synthetic aperture radar (SAR) data at reasonable spatial resolution is available freely in public domain. Moreover, microwave data has capability to penetrate cloud and the information below cloud can easily be retrieved. To overcome the issues related to optical data, in the present study, the reservoir sedimentation for Ghataprabha reservoir was estimated using SAR data. Sentinel-1A data was used to delineate the water spread area for the water year of 2016-17. The original live storage capacity (1974) was estimated to be 1434.14Mm3 at FRL 662.940m by the authorities using the hydrographic survey during the commissioning of the reservoir in the year 1974. The live storage capacity was found out to be 1366.14Mm3 at FRL, however, as per original elevation-area-capacity curve the live capacity is around 1262.404Mm3 at 660.50m. Estimated live storage capacity from Remote sensing approach (2016-17) was assesses as 1182.5Mm3 at 660.51m. The storage capacity has reduced from 1262.40Mm3 (1974) to 1182.51Mm3 i.e. around 171.732Mm3. As per present analysis the rate of sedimentation is around 4Mm3/yr. It was realized that using the SAR microwave data, the revised capacity of the reservoir from its near MDDL to FRL could be assessed through remote sensing approach.