Remote Sensing Based Assessment of Water Resource Potential for Lake Tana Basin
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Date
2007-04
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Addis Ababa University
Abstract
1. Remote sensing techniques have been applied to augment
estimation of hydrologic variables. Thus rainfall, evaporation, flooded
zone delineation and runoff estimation has been carried out. TRMM
monthly rainfall products were employed in rainfall gap filling
techniques, the satellite estimates were first validated against observed
ground station records and results indicated good correlation, average
of 81%. Combination equation (Energy balance-mass transfer) is used
to determine gridded potential evapotranspiration from the sub-basin
by making use of MODIS 16 days Albedo products. Spatial extent and
amount of water on flood plains during wet seasons of the year has also
been determined by making use of spot NDVI temporal images through
calibrating with high resolution SAR and optical images. Furthermore,
land use/land cover information is extracted from Landsat imagery and
existing data of land cover has been updated. Using the update land
cover information spatial Curve Number (CN) map was developed.
Runoff estimation, using SCS method and a soil water balance
simulation using WatBal model, was then carried out in order to
determine the runoff from un-gauged catchments and the results from
the two models were compared. Results indicated that the soil water
balance simulation model gave better correlation with the observed
than the SCS method. Therefore, runoff estimation from un-gauged
catchments was carried out using the soil water balance simulation
techniques. Lake water balance simulation was finally carried out using
continuity equation within simulation time span of 1998 to 2003
considering the variables, i.e. inflow estimation form the contributing
catchments, the improved evaporation estimation; the rainfall data
obtained incorporating TRMM images and water lost in the flood plains
due to evaporation. Simulation results were compared with the Lake
Tana Storage computed using the recorded Lake water surface
elevation. The six year average results indicated that out of the total of
7,688 MCM estimated runoff from the catchments 3.59% is lost in the
flood plains due to evaporation. Similarly, out of the 10,574 MCM
inflow to the lake (net runoff plus rainfall over lake area) 5,110 MCM is
lost through evaporation from the lake surface, 5,012 MCM is outflow
from the lake to the head of main Abbay river. Average reduction in
reservoir storage was computed to be 330 MCM. Therefore, the
remaining 1414 MCM is assumed to be seepage loss and other unaccounted
losses from the system
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Keywords
Tana ;basin