Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Feasibility of Thermal Restoration by Groundwater Additions in the Middle Fork John Day

Auteur : Hale, Abigail E.

Université de soutenance : Oregon State University

Grade : Master of Science (M.S.) 2021

Résumé partiel
Survival of ecological systems pivot on critical moments. In the arid John Day Basin of Eastern Oregon, extensive restoration of the stream and floodplain focused on supporting salmon has been ongoing for the past 20 years, but recurring short periods of extreme temperature increase and low flows result in mortality of salmonids before spawning. Temperature stress during extreme events may be alleviated by strategically adding cooler groundwater to the stream. The feasibility of groundwater additions is here examined in hydrologic, economic, and socio-political terms for the Middle Fork of the John Day. Based on thermal mixing equations, adding between 0.03 and 0.14 cubic meters per second of water at 10°C lowers MFJD stream temperatures by several degrees. Previous studies suggest that as much as 75% of thermal benefits exist at 1 km downstream (Hall et al., 2020) providing thermal refugia for salmonids. To completely isolate drawdown impacts from pumping, wells to access water must be placed a minimum of 220 meters away from streams. This would limit potential declines in flow to the wet season (October to January). A physically based model of potential streamflow decline indicates that even if well were placed within the hydraulically connected region, that declines in stream flow are on the order of 1% of what is added to the stream by pumping. However, legal structures of water resources in Oregon limit the use of such methods in headwaters with narrow floodplains and less studied aquifers. Oregon legislation protects areas hydraulically connected to streams, especially in designated core salmonid habitat, by limiting water use development within a quarter mile of a stream channel. Because the groundwater is intended for instream benefit of threatened and endangered salmonids, limited use may be permissible although such a project in Oregon has not been implemented before

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