1. Background
Water resources projects have been given high priority in all developmental plans and a large number of dams/ reservoirs have been built since independence. The projects had a designed life span, which varied as per the terrain conditions. It has been observed over a period of time that the capacity of these projects (reservoirs) is reducing at a rate more than the designed rate. Silting is taking place at all the operating levels of reservoir and live as well as dead capacity of reservoir is getting reduced. Due to capacity reduction in live storage, sedimentation of reservoir is of great concern to all concerned with water resources development. Capacity evaluation of reservoir is necessary for all planning and operational purposes and it can be obtained through capacity surveys done at regular intervals. Remote sensing technique to calculate the present capacity of reservoir is found to be very useful in this context due to its synoptic and repetitive coverage. The surveys based on remote sensing data are faster, economical and more reliable.

Remote sensing data is used as a tool for regular monitoring of reservoirs. It calculates water spread areas at the time of satellite pass. Water spread area of the reservoir reduces with the sedimentation at different levels. The time interval for capacity calculation using remote sensing technique is fixed as once in five years for major reservoirs. To complete the analysis of this gigantic task in time bound mode, it is necessary to design a system, which will help the analyst to complete the task in an effective manner. To achieve this task, customisation of analysis package based on low cost technology was taken up.

2. Development using ENVI/IDL
ENVI (The Environment for Visualisation of Images) is an image processing system. ENVI was designed to address the needs of those who regularly use satellite and aircraft remote sensing data. ENVI provides comprehensive data visualisation and analysis for images of any size and any type - all from within an innovative and user friendly environment.

ENVI, along with its development tool IDL (Interactive Data Language) is used for development of this semi-automated package KSHAMTA for reservoir capacity estimation. IDL is used for customisation due to its complete, structured language that can be used both interactively and to create sophisticated functions, procedures and applications.