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Parametrization of the Snyder Unit Hydrograph Method for Arid Regions

Author(s): Luminda Gunawardhana; Ghazi A. Al-Rawas

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Abstract: Wadi-flow in arid regions tends to be dominated by rapid responses attributed to occasional extreme rainfall events. This study developed a method, which can be easily adaptable by practitioners at sub-catchment levels, especially when the focus area is ungauged, for estimating unit hydrograph (UH) at reasonably finer time scales. Observed wadi-flow at 5-minutes interval and rainfall measurements at 1-minute interval were analyzed at 10major watersheds in Sultanate of Oman. The deconvolution method was applied to derive the unit hydrographs from wadi-flow and excess rainfall. Key catchment characteristics such as the watershed area, length of the main wadi and the length to the centroid of the catchment area were derived from DEM data. The whole study area was then divided to 515 sub-catchments with various shapes and sizes. A strong relationship was found between the wadi length and the length to the centroid of the catchment area (R2> 0.87). This relationship was then adopted to simplify the classical Snyder method to determine UHs. Moreover, several parameters of the Snyder method were calibrated to the arid environment by matching the peak-flow, lag-time and time-widths at 75,50, and 30% of the peak-flow of 10-min and 1-hr UHs with physical characteristics of the watersheds. All developed relationships were validated with independent rainfall events. Results indicate that the calibrated parameters in these arid watersheds are quite distinct from those suggested for other regions of the world.


Year: 2018

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