Utilization of Catchment Morphometric Features to Estimate Design Peak Flow Ungauged Catchments: Insights Lake Tana Sub-Basin, Ethiopia

Abstract

A reliable estimate of design peak flow is one of the main and most frequently required engineering hydrology tasks. The necessity for estimating design peak flow is associated with civil engineering structures required for water storage, diversion, transport, and waterways crossings. The objective of this paper is to develop an alternative peak flow estimation model for the ungauged catchments using catchment morphometric features as input variables. Daily stream flow data from gauged catchments are collected and annual maximum daily flow series are extracted. At-site flood frequency analysis is used to estimate peak flow quantiles for 10, 25, 50, 100, and 200-year return periods. Based on previous similar experiences catchment area, longest stream length, channel slope, and catchment circularity ratio are selected as the most important catchment morphometric features for peak flow generation. Using GIS, the selected catchment morphometric features are quantified and regression analysis is applied to relate them with the quantiles. The result shows that Pearson type III, general extrem value, Log Normal, and general Pareto distributions are the best-fit probability distributions in the sub-basin. The regression analysis shows that design Peak flows have a very good degree of association with the catchment area, longest stream length, channel slope, and catchment circularity ratio with the coefficient of determination (R²) ranging from 0.962 to 0.993. The developed models can be used as alternative simplified means in estimating design peak flow for ungauged catchments in the Lake Tana sub-basin and other hydrologically homogeneous catchments.