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Scenarios for Restoring Floodplain Ecology Given Changes to River Flows Under Climate Change: Case from the San Joaquin River, California

Matella, M. K., Merenlender, A. M.
River research and applications 2015 v.31 no.3 pp. 280-290
Oncorhynchus tshawytscha, Pogonichthys, climate change, environmental health, floodplains, freshwater, habitats, models, planning, rearing, rivers, salmon, spawning, statistical analysis, stream flow, California, San Joaquin River
Freshwater ecosystem health has been increasingly linked to floodplain connectivity, and some river restoration efforts now overtly target reconnecting floodplain habitats for species recovery. The dynamic nature of floodplain habitats is not typically accounted for in efforts to plan and evaluate potential floodplain reconnection projects. This study describes a novel approach for integrating streamflow dynamics with floodplain area to quantify species‐specific habitat availability using hydraulic modelling, spatial analysis and statistical measures of flow regime. We used this hydro‐ecological modelling approach to examine the potential habitat for splittail (Pogonichthys macrolepidotus), Chinook salmon (Oncorhynchus tshawytscha) and their food resources under two restoration treatments and two climate change flow scenarios for a study site on San Joaquin River in California. Even with the addition of new floodplain through restoration efforts, the modelling results reveal only 13 streamflow events in the past 80 years had the magnitude and duration required for splittail spawning and rearing, and 14 events had flows long enough for salmon rearing benefits. Under climate change, modelled results suggest only 4–17% of the years in the rest of this century are likely to produce required flow‐related habitat conditions for splittail and salmon rearing along the study reach. Lastly, we demonstrate by simulating augmented reservoir releases that restoration of fish habitat will require a more natural flow regime to make use of restored floodplain and achieve the desired hydrologic habitat connectivity.