Estimating water loss from the Renoster River, Free State province, South Africa
Date
2006-11-17T08:04:59Z
Authors
Brown, Fred Herman
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Abstract
The Renoster River is a minor left-bank tributary of the Vaal River located some 120 km
south-west of Johannesburg in the Free State Province of South Africa. The river is dammed
by the Koppies Dam, which divides the river into upper and lower basins. No water is
released directly from the Koppies Dam into the Renoster River channel except as a
protective measure during natural flooding events. Irrigation releases are made through a
separate canal system.
The lower Renoster River was modeled as a series of channels, crossing four quaternary
catchments. Hydraulic routing was used to estimate potential flow losses for discrete flow
events. Out-of-bank flow was found to occur when flow exceeded 300 m3/s. A Pitman monthly
rainfall-runoff hydrologic model was used to model longer term historical streamflow data and
associated losses.
Flow losses for individual flood events along the lower Renoster River were found to vary
between 3% and 17%. For a longer term constant flow regime, losses can be expected to
range between 10% and 40%. Based on both the hydraulic and hydrologic models, the
primary cause of flow loss was found to be evaporation, with insignificant transpiration and
transmission losses.
For eighty years flow in the lower Renoster River has been artificially controlled. Within that
time period the river has adjusted itself to the imposed anthropogenic flow regime. Water
losses associated with planned releases into the lower Renoster River can be minimized by
using a high discharge rate, to a maximum of 300 m3/s, combined with larger volumetric
flows. Evaporation losses can be significant, and release strategies will need to take this into
consideration.
Description
Faculty of Engineering
School of Civil and Enviromental Engineering
9308302w
fredb@ananzi.co.za
Keywords
Hrydranlic Model, Koppies dam, Pitman model, Water loss, Renoster River