Application of Morphometric Analysis and Thiessen Method for a Geo-Hydrological Study Using GIS Techniques: Case of the Mpanda Watershed, Northwestern Burundi

The morphometric parameter analysis of a drainage watershed and spatial rainfall distribution over a basin play an important role to understand the hydrological behaviour of a watershed. A quantitative analysis of morphometric parameters of Mpanda watershed and its sub-watersheds has been carried out using Geographical Information System (GIS) techniques. Morphometric parameters for that watershed and its sub-watersheds were evaluated from three perspectives: watershed geometry, watershed shape, and drainage network in order to establish a relationship with hydrological characteristics of the basin. Based on geometry and shape parameters, the Mpanda watershed and its sub-watersheds have moderate elongated to very elongated shapes, which results in limited peak flood development at the watershed outlet. The watershed is a fifth order basin and the first order streams dominate the basin (±50 %). The development of stream segments in the study area is affected by rainfall and groundwater discharge. The mean bifurcation ratio indicates geological heterogeneity, higher permeability and lesser structural control. The drainage density and stream frequency indicate that the watershed has permeable subsurface material, good vegetation cover, causing more infiltration of water and recharging groundwater aquifers. The average rainfall calculated using Thiessen method for a period of 20 years over the entire Mpanda watershed is 1341 mm. The basin can be separated in two sub-basins and it can be observed that the upper basin receives almost twice the rainfall recorded in the alluvial plain basin. The results of this study provide information on morphometric characteristics and spatial rainfall distribution that can serve as a basis to improve planning, and management of watershed resources.