20-11 Constant flow injections of desalinated water from the Reverse National Water Carrier into the ephemeral Lower Nahal Tzalmon and the Sea of Galilee with future implications for stream restoration, Lower Galilee, NE Israel

Abstract:

Here, we summarize seven months (October – May) of desalinated water flow injections into Ein Ravid Spring together with the main outflow of the Reverse National Water Carrier (RNWC) into Lower Nahal Tzalmon and the Sea of Galilee.  In contrast to the three flow experiments that lasted for only two consecutive days in late December 2022 (Bergman et al., 2025), the stable and continuous flow allowed to monitor the hydrology (hydrographs, transmission losses, water temperature and groundwater levels), turbidity and channel bed activity during constant conditions after the initial bores. The desalinated flow releases included 1000 m³/hr (0.28 m³/sec) from Ein Ravid Spring and 4000 m³/hr (1.11 m³/sec) from the main release site of the RNWC - a total of 5000 m³/hr (1.39 m³/sec). Once the flow stabilized downstream, the constant discharge attenuated to 3600 m³/hr (1.0 m³/sec) when reaching the lake, due to friction and transmission losses estimated at 28% of water volume loss. Air temperature, desalinated water temperature and stream temperature were correlated as the channel course is mostly exposed to solar radiation, riparian vegetation is currently missing and the flow cannot sustain a steady diurnal temperature which a healthy aquatic habitat would favor. Turbidity values were high (up to 9700 mg/l) during the first bores, but the constant flow completely cleared of mineral suspended sediment and was replaced by biological activity (algae) implying exhaustion and limited amounts of fines available on the bed surface and banks at baseflow. Bedload transport of sand up to 50 mm coarse gravel was minimal with transport distances up to 3-9 m according to painted tracers. Load captured by three basket bedload samplers was meager - probably associated with loose material up to coarse gravel but most of it was organic debris. The fine suspended sediment deposited in the alluvium consolidated the bed, the loose particles were transported and probably increased the shear stress needed for incipient bed motion for future flows. However, the bed was not actually disturbed in terms of scour and the channel morphology was not modified as no significant natural flow arrived from upstream during the entire hydrological year.

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