Global mapper 15.0: A comparative software tool in the design of open channel drainage systems

Abstract

This research aimed at computing peak flow discharge using state-of-theart technology for watershed analysis to design a suitable open channel to minimize the effects of flood hazard during and after rainfall in an environment. A comprehensive topographical survey data obtained by Shuttle Radar Topographic Mission was employed in this study. The result of the survey shows that both the maximum and minimum elevation at 61.9 m and 51.1 m, respectively, and the mean slope of the area was 0.012. Watershed analysis of the study area was carried out using the Global Mapper15.0. The result shows that the parameters obtained such as the mean area of the sub-catchments is 1.43 ha, the mean length of channel flow is 99.33 m, the mean length of overland flow is 111.81 m, mean upstream elevation for overland flow is 63.30 m, mean downstream elevation for overland flow is 62.37 m and mean downstream elevation for channel flow is 61.12 m. The intensity duration frequency curve of the catchment was developed and a return period of 25 years was used to obtain an average rainfall intensity of 218.81 mm/hr. The peak discharge was obtained as 2.01 m3 /s using rational formula due to the area of the watershed being less than 80 hectares. Finally, several design parameters for the modeled rectangular channel were calculated. The result indicated that the width of the channel is 0.80 m and the depth of the channel is 1.0 m. The developed modeled channel has a design capacity of 2.03 m3 /s which is greater than watershed peak discharge 2.01 m3 /s. The size of the modeled channel was compared with the size of the existing channel and the result revealed that the existing drain was insufficient to carry the discharge from the catchment area due to its design capacity of 0.91m3 /s. It is recommended that the dimension of the existing drain should be increased to meet with the dimension of the modeled drain and a discharge point (safe outlet) should be provided.