Operation Modeling for Tendaho Reservoir Using HEC-Ressim
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Date
2010-12
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Addis Ababa University
Abstract
In this study it has been intended to develop operation modeling for Tendaho reservoir using
HEC-ResSim software. The input data considered for the model are daily inflow, monthly
irrigation and environmental diversion flow requirements, monthly reservoir surface evaporation
and Tendaho dam and reservoir physical data.
The reservoir operation modeling has been done for two inflow source options. These are
upstream and Tendaho station inflow source options. In the upstream inflow source option the
ten years (1992-2001) daily flow records of Awash River at Adaitu and Mille River at Mille
Bridge have been routed to the reservoir. Moreover, for the ungauged catchments downstream of
the hydrological gauging stations considered, daily flows were generated using SCS-CN method.
However, in the Tendaho gauging station inflow source option, the ten years daily flows of
Tendaho gauging station has been used as source of inflow to the reservoir.
The SCS-CN method was calibrated for the ungauged catchments using five years (1992-1996)
flow data transferred from the Logiya catchment and areal rainfalls computed from Adaitu,
Mille, Bati and Dubti stations. The method was then validated using another five years (1997-
2001) data. The parameter considered was the CN.
For the two inflow source options considered, operation modeling has been made for three
spillway gate setting alternatives: Low level (1m), Average level (4m) and Maximum level
(6.9m) gate openings. Incase of the upstream inflow option the maximum reservoir releases are
282.35m3/s, 937.98m3/s and 1015.40m3/s for low level, average level and maximum level gate
settings respectively. Incase of Tendaho inflow the maximum reservoir releases are 259.82m3/s,
267.73m3/s and 349.11m3/s for low level, average level and maximum level gate settings
respectively. The irrigation outlet releases are similar for the three gate setting alternatives in
both inflow options.
The wet season reservoir operation rule curves have been developed for the minimum gate
opening alternative of both the inflow options. Following the ten years wet season pool level
curves, three Operation Guide Curves have been developed. These are Upper Bound Guide
Curve, Lower Bound Guide Curve and Average Guide Curve.
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Keywords
Bound Guide Curve and Average