EVALUATING PEAK RUNOFF HYDROGRAPHS FOR OYUN RIVER CATCHMENT IN KWARA STATE USING GIS AND REMOTE SENSING TECHNIQUES
The power of Geographic Information System and Remote Sensing techniques was used in this work, to determine the required hydrological characteristics of Oyun basin in Kwara State. Both primary and secondary data were used; the primary data are the field coordinates of prominent features in the study area while the secondary data were the administrative maps, satellite imagery, SRTM (Shuttle Radar Topographical Mission) raster data and rainfall data for the study area. The GIS techniques of data analysis used comprised of overlay operation, digital terrain modeling (DTM), spatial query operations and map calculation operations. The rainfall data was fitted using Gumbel distribution to obtain basin discharges for four selected return periods. Snyder's method was used to obtain the unit hydrograph ordinates these ordinates were used in conjunction with the discharges to generate rainfall excesses for the respective return periods while the rainfall excesses were convoluted to obtain the predicted peak runoff(storm) hydrographs for each of the selected return periods. The outcome of this research showed that Oyun river watershed had the following hydrological characteristics; Catchment area is 827 square kilometers, main river length is about 83.57 km, length from Centroid to outlet is 43•24km, average basin slope is 0.01464 , the peak discharges of the basin for 5years, 25years, 50years and ioovears are 129ml/s/cm, 184.4 m3/s/cm, 207.3 m3/s/cm and 230 m3/s/cm, while the corresponding predicted storm hydrographs were 457.12M3/S ,793.32 M3/S ,941.70 M3/S and 1088.70 M3/S respectively.
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