Hydro-Morphological Characteristics Using Flow Duration Curve, Historical Data and Remote Sensing: Effects of Land Use and Climate

Abstract

Ecohydrological changes in large rivers of the world result from a long history of humandimensions and climate. The increasing human population, intensified land use, and climate change haveled to a decline in the most critical aspect of achieving sustainable development, namely, that of waterresources. This study assessed recent hydromorphological characteristics of the tropical Tana River inKenya using flow duration curve, and geospatial techniques to gain a better understanding of humanimpacts over the last two decades and their consequences for new development projects. The results showthat all extremal peak, low, and mean discharges exhibited significant increasing trends over a period of17 years. Dam construction represents a 13% reduction of the maximum discharge and a 30% decrease inlow flows, while post-regulation hydrological changes indicated an increase of 56 and 40% of high flowsand low flows respectively. Dominant flow was observed to be higher for the current decade than theprevious decade, representing a rise of the dominant streamflow by 33%. The assessment of fourmorphologically active sites at the downstream reach showed channel adjustments which support thechanges in the flow regimes observed. The channel width increased by 8.7 and 1.9% at two sites butdecreased by 31.5 and 16.2% for the other two sites under study during the time period. The resultsunderscore the contribution of other main human modifications, apart from regulation, such as increasedwater abstraction and inter basin transfer, up-stream land use and anthropogenic climate change to assessthe ecohydrological status in this river basin. Such streamflow regime dynamics may have implicationson water resource management, riverine environments, and development of new water projects.