Can restored floodplain connectivity lead to greater baseflow in a semi-arid, multi-use watershed?

Climate change and land use have disconnected floodplains across the Western US, shifting many historically perennial streams into intermittent flow regimes. Disconnection is expected to intensify with further decreases in snowpacks and increases in drought frequency. The Upper Crooked River (UCR; Oregon, USA) is no exception, with low flows < 1 cfs (28 L/s) in 17 of the past 20 years despite average peak flows > 1,500 cfs (42,000 L/s). Diverse stakeholders agree that intermittent flows threaten multiple uses of the UCR (e.g., critical wildlife habitat, working lands), but potential solutions are debated. It is unclear whether floodplain reconnection can restore perennial flow regimes, and if so, under what climatic and geologic conditions. That is, can reconnected floodplain aquifers detain high flows in the spring that slowly percolate back to the river to maintain baseflow through the summer? We quantified the potential baseflow contribution of floodplain aquifers that are currently disconnected along the UCR. First we tracked groundwater levels over time in a floodplain transect in which one side was artificially inundated and the other side was not. Second, we analyzed soil cores for relevant aquifer properties. We found many areas with potentially meaningful baseflow contributions from deep (i.e., > 2 m) unsaturated zones and high specific yields. Other areas had less potential due to smaller unsaturated depths or specific yields. The artificially inundated field was saturated within 11 days and water levels subsequently declined over approximately 90 days. The maximum potential baseflow from the total floodplain area (1,200 ha) could exceed 10 cfs (280 L/s) for 90 days. However, evaporation or additional abstraction could account for much of the aquifer drawdown and are still being investigated. We place our results in the context of stream restoration potential as compared to other interventions for baseflow recovery (e.g., altered irrigation practices, upland management).