160-5 The hydro-geomorphic response of the ephemeral lower Nahal Tzalmon stream to experimental flow releases towards replenishment of the Sea of Galilee, NE Israel

Session: Advances in Fluvial Processes and Sediment Transport, Part I

Presenting Author:

Authors:

Abstract:

Following a severe prolonged drought (2013-2018) and a consequent decline in Sea of Galilee lake levels, Israel Water Authority decided to hydrologically connect the Mediterranean Sea desalination plants with the Sea of Galilee at the Rift Valley. This engineering mega-project was termed the “National Reverse Water Carrier”. While most of the desalinated water flow will run through large-diameter closed pipes powered by giant pumps and storage pools, the last 5 km of the project are designed to gravitational open channel flow through the lower ephemeral, gravel-bed Nahal Tzalmon, one of the western tributaries of the Sea of Galilee.

Three experimental discharge releases from the newly National Reverse Water Carrier during December 2022, provided a rare opportunity to monitor hydrology and sediment transport on a flashy ephemeral stream during small flows in a controlled environment. Channel geometry changes were minor, whereas changes in flow behavior over dry and wet bed associated with transmission losses were significant. In-channel movement of fine sediment into the lake and within reach gravel transport were monitored, but were small. These observations and measurements provided a first glimpse into the processes expected once the project becomes a regular management tool for the Sea of Galilee level.

Transmission losses were 91% over dry channel alluvium (1^st release) and decreased to 30-52% over wet alluvium (2^nd and 3^rd releases, respectively). Suspended sediment transport along the channel into the lake during the experiment was low (concentrations of 21-1423 mg/l), lower than during natural flows and low compared to other Israeli Mediterranean streams, with low sediment yields. Bedload transport measured using both painted tracers and basket samplers showed minor disruption to the armored gravel-bed. These flow releases can be used for channel restoration of lower Nahal Tzalmon, sustaining management of baseflows and natural hydrology, channel morphology, riparian vegetation and the aquatic fauna that will reestablish once the stream becomes perennial again.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9377

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