Title: Description of the Application
Course: Volume determination of lake Tana using bathymetry and altimetry

Lakes and reservoirs are important as a source for fresh water and sustain activities such as agriculture, fisheries and recreation. In periods of drought, the rural population in most semi-arid environments rely heavily on small reservoirs to sustain their livelihoods. Water stored in these reservoirs allows for all year-round irrigated agriculture and ensures that domestic water shortages are reduced during dry periods. In order to manage the water effectively for competing uses, the actual storage of these reservoirs need to be accurately estimated (Annor, et al., 2009).

To get an idea of the (near real time) volumes stored in (small) lakes and reservoirs relations can be established between lake / reservoir area and volume or between lake / reservoir level and volume. In the first case time series of satellite data can be used to derive the lake extent. The boundaries of the lakes at various extent can be transformed into iso lines. The challenge is to link these iso lines to absolute elevation or bathymetric values in order to estimate the volume changes.

This challenge can be overcome when use is made of altimeter observations (Sulistioadi et. al., 2015). As from September 1992 altimeter observations from different instruments are available. Currently more lakes / reservoirs and rivers are monitored using altimeters. In this way absolute water levels have become available over time.