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

Abstract

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.

Effects of Extreme Hydrologic Regimes on Juvenile Chinook Salmon Prey Resources and Diet Composition in a Large River Floodplain

“…Climate change projections specific to the San Francisco Bay-Delta predict warming air and water temperatures (aggravating water supply stress by 10-20%) and increased flooding (flows and frequency; Cloern et al 2011;Dettinger et al 2015). Flood management, such as levee setbacks with riparian habitat restoration and managed floodplains (e.g., bypasses), could also aid in reducing flood risks and aquifer recharge to benefit salmon food webs and protect valuable infrastructure (Merenlender and Matella 2013;Matella and Merenlender 2015). Over the last 20 years, riparian habitat restoration has occurred in the upper two-thirds of the Sacramento River (~3% increase between 1988 and 2009), but to the best of our knowledge, the Yolo Bypass represents one of the few riparian corridors bridging the lower Sacramento River and north Delta.…”

Stakeholder-led science: engaging resource managers to identify science needs for long-term management of floodplain conservation lands

“…In ungaged areas, remotely sensed data are being increasingly used to understand temporal inundation dynamics (Ward et al 2014, Thomas et al 2015. Spatially-explicit inundation information can be linked to known species responses to identify suitable habitat for species of interest (Jacobson et al 2011) and evaluate changes in habitat availability under different management and climate change scenarios (Matella and Merenlender 2015). Two-dimensional hydrodynamic models have been employed to identify appropriate species to plant in restoration planning (Leyer et al 2012).…”

Connectivity as an emergent property of geomorphic systems

“…longitudinal, lateral, and vertical connectivity), explaining the efficiency of sediment transfer relationships within catchment systems (see also Fryirs et al, 2007a, Fryirs et al, 2007b. In bio-geomorphic floodplain systems, the four dimensions of connectivity provide a framework to examine hydrologicmediated exchanges of organisms, nutrients, carbon, and energy (Zeug et al, 2005;Opperman et al, 2010;Kupfer et al, 2014;Matella and Merenlender, 2015).…”