Changes in River Channel form and Geometry below Dam Reservoir in Karadua Catchment, Katsina State, Nigeria

This paper studied the effects of dam on the downstream changes in river channel form and geometry below dam reservoir in karadua catchment, katsina state, Nigeria.

The objective of the study includes assessing the changes in river form and geomorphic characteristics of the downstream River Karadua as a result of dam and reservoir operations following the construction of Zobe Dam. The method used for computing cross-sectional area was simply by obtaining Bankfull width and depth of the stream by dividing the width into 10 equal intervals based on the technique outlined by Gregory and Wailings (1973).Using Topographical maps alongside the remotely sensed images, Global Land Cover Facility (GLCF) MSS+1978/79 and spot-4 Imagery 2008 were used to study changes on stream length, sinuosity and channel shifting which was undertaken mainly by comparing the old and new imageries of the study area. The result shows a slight variation in cross-sectional area because the greater value of the mean width at above dam reach was counterbalance by the greater value of mean depth at below dam reach. The significant variation was only obtained between mean width and average mean depth of the channel reaches. Channel morphology from the cross-sectional information indicates two main morphological changes. The first is the narrowing of the channel below the Dam, abandoning the former storm channel and creating an incised channel. The second is vertical cutting and deepening of the channel. These all together bring about lateral displacement of the active channel and flood plains. Alteration of the river morphology will therefore, hinder the much dependence of the populace on the river for sustenance in the study area.

Keywords: River, Geometry, Reservoir, Catchment, Karadua Katsina.