Modelling and Forecasting Awassa Lake Level Fluctuation
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Date
2007-03
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Addis Ababa Universty
Abstract
Lake Awassa is located in the central main Ethiopian rift valley. The Lake is important
water resource in the study area and is used for irrigation, municipal and domestic water
supplies as well as recreational purposes. Beside its importance, the level of the lake has
changed dramatically over the past two decades. Because of this, the lake has attracted
considerable attention in recent years especially when the lake flooded the surrounding
area including Awassa town which is established adjacent to the lake. Fundamental for
understanding the lake level fluctuation requires knowledge of the lake's water balance
and its response to human induced and climatic changes in the hydrologic regime.
The present study develops a water balance forecast model for Lake Awassa. The model
uses annual values of surface runoff (gauged and ungauged), evaporation, precipitation
and groundwater outflow to simulate past lake levels. For this reason, the model was
calibrated using multiple linear regressions and ARIMA model fit using SPSS software.
The calibrated model was verified and used to forecast future lake level based on various
selected applications and assumptions.
The model result shows that the surface runoff and evaporation accounts about 81% and
38% in short term lake level fluctuation but in long term lake level fluctuation
precipitation and evaporation accounts 45% and 73%respectively. This is mainly the
result of land use/cover changes which causes the runoff to increase and evaporation to
decrease. If this continues the lake would be a treat to the surrounding area and the town
might be at risk if remedial measures are not considered.
Although the environmental implications of a given lake level are beyond the scope of
this study, the model provides an essential tool for water policy and management
decisions in the Awassa catchment.
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Keywords
Awassa Lake