Hydro-morphological characteristics using flow duration curve, historical data and remote sensing: Effects of land use and climate

Ecohydrological changes in large rivers of the world result from a long history of human dimensions and climate. The increasing human population, intensified land use, and climate change have led to a decline in the most critical aspect of achieving sustainable development, namely, that of water resources. This study assessed recent hydromorphological characteristics of the tropical Tana River in Kenya using flow duration curve, and geospatial techniques to gain a better understanding of human impacts over the last two decades and their consequences for new development projects. The results show that all extremal peak, low, and mean discharges exhibited significant increasing trends over a period of 17 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 flows and low flows respectively. Dominant flow was observed to be higher for the current decade than the previous decade, representing a rise of the dominant stream flow by 33%. The assessment of four morphologically active sites at the downstream reach showed channel adjustments which support the changes in the flow regimes observed. The channel width increased by 8.7 and 1.9% at two sites but decreased by 31.5 and 16.2% for the other two sites under study during the time period. The results underscore the contribution of other main human modifications, apart from regulation, such as increased water abstraction and inter basin transfer, up-stream land use and anthropogenic climate change to assess the ecohydrological status in this river basin. Such stream flow regime dynamics may have implications on water resource management, riverine environments, and development of new water projects.