Assessment of Anthropogenic Impact on the Environmental Flows of Semi-arid Watersheds: The Case Study of the Lower Jordan River

Abstract

The escalation in hydrological alteration of rivers on a global scale, potentially causing environmental degradation, initiated the establishment of the Environmental Flow Assessment science where the quality and quantity of water required for ecosystem conservation is determined and taken into consideration. The Lower Jordan River (LJR) Basin has gone through massive exploitation of its scarce water resources in the last half century: man-made stream regulations and diversions have drastically affected the LJR’s natural flow regime and degraded its water quality. This research aims to investigate the continuous degradation of water flow in the LJR, by looking into its past natural temporal and spatial flow variability. River flow data were obtained for years 1921–2011. Both natural and regulated flow regimes were examined. The software tool ‘Indicators of Hydrologic Alteration’ (IHA) was used for daily flows’ comparisons. The IHA tool results show significant changes in rates of base flows and frequency and magnitude of extreme flow events, between pre-impact and post-impact periods. According to our results, in order to mitigate these flow alterations, a relocation of 100 MCM/year of fresh water to the LJR river system is needed, which will be used to: fortify its depleted base flow; generate two yearly flood events; and introduce four additional high flow pulses. This reallocation would enable a mimicking of the LJR’s natural variability of flow at a relatively minimal amount of water. This research constitutes a first step towards understanding the LJR’s hydrological natural conditions. Its findings could be very useful when weighing different rehabilitation options for the LJR and other anthropogenic impacted semi-arid basins.