Author(s): H. M. V. V. Herath; R. G. A. B. Dayananda; M. M. G. D. Madakumbura; W. M. S. Priyankara; S. B. Weerakoon
Linked Author(s): Viraj Vidura Herath Herath Mudiyanselage
Keywords: WRF; HEC-HMS; Flood warning
Abstract: Polgolla barrage has been constructed across the Mahaweli River to divert part of Mahaweli water to the North Central Province of Sri Lanka while harnessing hydro-electric power. Polgolla reservoir has only an active capacity of 3.404 MCM (2013 September) and its gate operation is extremely important to manage flood water levels in the reservoir and the river upstream during flood inflows. Early flood warning system for the Polgolla reservoir is useful to plan gate operation ahead of the flood arrival to the reservoir. The study was carried out to model anticipatory reservoir flood levels based on the downscaled rainfall forecast in the catchment using WRF model (Weather Research and Forecasting model). WRF model is a numerical weather prediction and atmospheric simulation system designed for both research and operational applications. WRF model was calibrated for forecasting rainfall in the Polgolla catchment by investigating the impacts of its physics options including microphysics schemes, cumulus parameterization schemes, land surface schemes, planetary boundary layer schemes, surface layer schemes and radiation physics schemes. WRF predictions were compared with the observed point rainfall data of selected gauging stations within the catchment. Observed point rainfall data were distributed to the same grid of WRF predictions by GIS based Inverse Distance Weighting (IDW) technique. After the comparison of WRF prediction with observed rainfall, a most appropriate physics combination was selected for rainfall prediction. The calibrated and validated WRF model was used to forecast rainfall over the Polgolla catchment. WRF model forecasted extreme rainfalls were used with calibrated HEC-HMS hydrological model to compute flood inflow to the polgolla reservoir. The copuled model is a useful tool for flood warning system for the Polgolla Barrage.