The hydro-geomorphic response of the ephemeral lower Nahal Tzalmon stream to experimental flow releases towards replenishment of the Sea of Galilee, NE Israel

The Sea of Galilee’s western watershed includes the Lower and Upper Galilee subregions in northern Israel. Nahal Tzalmon stream (110 km 2 ) is one of the major gravel-bed channels draining those subregions into the lake. The study focus was to monitor the immediate effects of introducing “hungry water” from the newly mega-project of the “Reverse National Water Carrier” (RNWC). The project was designed to convey desalinated water from the Mediterranean coastal desalination plants through a 5 km open channel into the lower Nahal Tzalmon stream in order to replenish the Sea of Galilee. During a 2-day experimental flow releases with three different peak flow discharges, the hydrologic and geomorphic outcomes were documented. The three flow releases showed significant discharge attenuation (67–39 %) due to the large transmission losses over a dry bed (91 %) that was significantly reduced when the alluvium was moist (52 %) or wet (30 %). The suspended sediment concentrations and yields were low compared to natural flow events but also when compared to other Mediterranean streams. Bedload transport under the hydrological conditions of the experiment did not cause a major disruption to the armored channel bed. A conceptual model is proposed for the new hydrologic-geomorphic conditions the RNWC offers for channel restoration, making the stream a prominent perennial tributary to the Sea of Galilee. • A 2-day flow experiment demonstrated the hydro-geomorphic capabilities of desalinated water release in a natural setting. • High transmission losses occur over a dry alluvium and decrease over wet or moist alluvium. • Flow releases with a short pause in between them may connect downstream and behave as a single hydrograph flow event. • Suspended sediment concentrations and volumes were low compared to natural flows and to other Mediterranean streams. • Bedload transport during the experiment was minor suggesting the disruption to the armored channel bed was almost negligible.