reservoir

Reservoir operation under variable climate : case of Rozava Dam,

Zimbabwe

Objective

1. To investigate if there is evidence of climate change occurrence at local scale with respect to rainfall and temperature

2. Apply modeling techniques to investigate the performance of Rozva Dam

3. Predict the impact of reduce inflow on reservoir operation, based on climate change study

Flow chartHydro-climatic data

Trend analysis

Estimation demand

Modeling

Model validation

Check scenario 1

Check scenario 2

Check scenario 3

conclusions

Hydrology

• Medium size dam • Water supply and irrigation purpose • Rainfall – 700 mm/yr (November to April )• Evaporation – 2000 mm/yr• Irrigation efficiency – 60%• Environment flow - 5% of available water

Characteristics of Rozva dam

Analysis of hydro-climatic Data

• Climatic data (Rainfall, Temperature) – Meteorological Department and Zimbabwe Climate Change Office

• Trend analysis

Rsp = Spearman’s rank – correlation coefficient

D = difference between the rankings

)1(

61

21

2

nn

DR

n

i isp

Estimation of agriculture demand

• FAO CROPWAT 8.0 software used

• IWRgross= gross irrigation water requirement

• Etc= crop evapotranspiration

• Pe = effective precipitation • n = irrigation efficiency

ec

gross

PETIWR

Rozva river system

Modeling techniques

• WAFLEX model are use – Easily modified to suit local condition – Based on continuity equation– Applying model to simulate the reservoir response

to simulate the reservoir response to different water demand scenarios on monthly time step

Scenarios

• Current system operation• 50% reduction in runoff and accommodating

projected increased demands • Improve irrigation efficiency with climate

change impacted inflows

Results and analysis • Rainfall

– Trend at 5% insignificant level– Rsp = -0.82

Temperature

Irrigation water requirements

Model validation

Scenario 1 • Current Water Demand and Inflow– 100% satisfaction level for current demand

Scenario 2(a)

• Climate Change effects leading to 50% inflow reduction and current Demands

Scenario 2(b)

• Climate Change effects leading to 50% inflow reduction and Projected increased Demands

• In 2030, maximum shortage of 19% for downstream user

Scenario 3• Change in irrigation technology

Conclusions

• No significant change in climate but variability• Currently have much water for satisfied all

demand • When 75% inflow reduces and projected

increased demand at that time 19% shortage for downstream users

• Reduces downstream shortage by using more efficient irrigation technology