Reservoir storage variations from hydrological mass balance and satellite radar altimetry

Abstract

Knowledge of storage variations in reservoirs and lakes is important for water resources planning and use. In developing countries where lakes may be poorly gauged and water quantity data sparse or unavailable, a simple and cost-effective method of estimating storage would be useful for reservoir operation and management. In this study, we showed how to estimate reservoir storage by combining hydrological mass balance and remotely-measured lake levels. Water levels measured by ERS/ENVISAT and Topex/Poseidon satellite altimeters in Kainji reservoir, Nigeria, were first compared with ground-measured levels. The resulting time series plot and high determination coefficient for both data sets (R2 = 0.93 and 0.95 respectively) showed that altimetric levels can complement gage data for this reservoir. Reservoir storage was then estimated from gage and altimetric lake levels using a storage-level curve generated by performing a simple water balance. The resulting correlation and root-mean-square errors between storage estimated from altimetry and water balance suggest that storage may be directly determined from satellite-measured levels. These results have far-reaching implications for water resources monitoring and quantification in ungaged lakes and the methodology could revolutionize conventional techniques of computing volume changes even in gaged reservoir. Key words: reservoir storage, satellite altimetry, Africa water resources, Kainji Lake, storage curves, lake volume, reservoir operation.