FLOODPLAIN RECHARGE AND SUBSURFACE STORAGE OF WATER

In California, climate change is increasing winter runoff and hence reducing water volumes that can be captured by surface reservoirs during the critical April through July time frame. This study investigates a way to compensate for loss of surface storage through floodplain recharge projects that would capture excess flood flows and store the water beneath the Central Valley floor. Though the Central Valley aquifers offer significant storage space that could be used to capture and retain flood waters, floodplain recharge mechanisms and feasibility of accomplishing enough recharge to mitigate California’s diminishing water storage problem have not been investigated. In this study, the variably saturated parallel numerical model, ParFlow, is used to estimate the timing and volume of floodplain recharge into a heterogeneous alluvial aquifer underlying the Cosumnes River in Sacramento County, California. In order to investigate the possibility of using geologic preferential flow paths to promote more efficient floodplain recharge to the aquifer, various scenarios are examined, including a comparison between complete inundation of the floodplain and inundation of a selected sub-section of the floodplain overlying high-permeability material. Results of the simulations will indicate the value of managed floodplain recharge as a tool to mitigate the state’s water storage crisis and to restore groundwater levels in over-drafted basins.