Simulation of Subsidence Mitigation Effects on Island Drain Flow, Seepage, and Organic Carbon Loads on Subsided Islands Sacramento–San Joaquin Delta

• Main Authors: Steven J. Deverel, David A. Leighton, Christina Lucero, Timothy Ingrum
• Format: Article in Journal/Newspaper
• Language: English
• Published: eScholarship Publishing, University of California 2017
• Subjects: subsidence; sustainability; groundwater; water quality; Environmental sciences; GE1-350; Delta Island
• Online Access: https://doaj.org/article/aabaa20846af45de882d651a91113f43

https://doi.org/10.15447/sfews.2017v15iss4art2 In light of desired implementation of subsidence mitigation practices on Delta islands and perceived need for evaluation tools, we developed groundwater and solute transport models and we attempted to answer the following questions. 1. How do the groundwater flow and drainage systems interact to influence island drainage volumes and drain dissolved organic carbon (DOC) concentrations and loads? 2. How will future subsidence impact drainage volumes and loads and seepage onto islands? 3. How will land-use changes to mitigate subsidence affect seepage and drain flow and loads? 4. How can water-quality impacts from drainage and restoration and rice cultivation on Delta islands be minimized? We utilized hydrologic and geochemical data and modeling to answer these questions. Subsided Delta island hydrology is dominated by subsurface processes. Seepage and siphoned irrigation water recharge groundwater which flows to drains. Drainage water containing DOC derived from oxidation of organic soils is discharged to adjacent channels. We analyzed the effects of subsidence mitigation through simulation of mosaics of rice and palustrine wetlands with varying hydrologic management on a representative subsided island (Twitchell Island). These alternative land uses reduce seepage onto islands and thus contribute to increased levee stability. However, most scenarios resulted in increased drain flow and DOC loads. Reducing drain flow is essential to reducing DOC loads relative to the business-as-usual scenario and can be accomplished through hydrologic controls that reduce drain flow on the islands.