Hydrologic effects of tidal wetland restoration in the subsided Sacramento‐San Joaquin Delta,
California
,
United States
Steven Deverel, Marc Olds Abstract
Objective
The Dutch Slough Tidal Restoration project in the Sacramento‐San Joaquin Delta involves flooding of delta lands; however, concerns have been raised that such flooding will increase the hydraulic pressures on subsided adjacent islands and threaten levee stability. We thus examined the hydrological effects of the Dutch Slough Tidal Restoration project on an adjacent subsided island.
Methods
We collected hydrologic data in Dutch Slough, the flooded area on the Dutch Slough Emerson Parcel, and on adjacent and subsided Jersey Island before, during, and after the levee breach for tidal connection. We used these data to assess the groundwater level changes on Jersey Island resulting from the breach and to quantify the time lapses for the transmission of tidal signals to estimate the aquifer transmissive and storage properties for inputs to a groundwater flow model. We developed a groundwater flow model to simulate pre‐ and post‐breach conditions.
Results
Monitoring results revealed increased groundwater levels on Jersey Island coincident with the levee breach. The groundwater model successfully simulated pre‐ and post‐breach conditions. Modeling indicated that increased hydraulic conductivity of the coarse‐grained aquifer causes increased hydraulic heads on subsided islands adjacent to flooded islands. Model results also demonstrated that implementation of a managed marsh on Jersey Island prior to a breach would prevent increased levee under‐seepage force.
Discussion
Our results demonstrate the importance of assessing the potential for seepage and effects on levees on subsided delta islands adjacent to islands slated for tidal restoration and investigation of mitigation measures.