Author(s): T. A. J. G. Sirisena; S. M. C. K. Subasinghe; V. Dharmadasa; D. E. N. Senarathne; D. P. L. Ranasinghe; K. D. W. Nandalal; K. Raveenthiran
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Keywords: Demodara concrete gravity dam; Design flood hydrographs; Environmental flow; Probable maximum flood (PMF); Sediment yield
Abstract: A dam construction generally follows various stages like planning and designing with associated detailed studies. Hydrological investigations are the preliminary studies which shall be carried out and they are highly important during the design process. This study focused carrying out of necessary hydrological investigations, such as estimation of Probable Maximum Flood (PMF), design flood hydrographs corresponding to storm events with different return periods (2yr, 5yr, 10yr, 50yr, 100yr, and 1000yr) and estimation of the environmental flows and sediment yield related to the design of proposed Demodara dam. The rainfall hyetographs were developed for SCS Type IA distribution and the estimation of flood flows was done based on characteristics of the drainage basin (MIKE 11 RR, Unit Hydrograph Method). The recommended flood hydrographs for spillway design and stability check of dam structure (100yr design flood and PMF) are 304 m 3 /s and 980m 3 /s, respectively. The environmental flow of 0.08m 3 /s was recommended based on the developed Flow Duration Curves at the Demodara dam location. Based on the reservoir water balance study, the reservoir is capable to release 0.272 m 3 /s peak flow amount of water approximately at a 80%successive rates. The observed critical periods are June–Sep and the month of March in a year. Further, sediment yield of 12,990m3/yr at the reservoir location has been estimated and it is necessary to provide a guideline to decide sluice gate operations for sediment removal.
Year: 2016