indicators of seawater intrusion - Seasidebasinwatermaster.org

FINAL DRAFTSECTION 2OVERVIEW OF SEAWATER INTRUSIONSeawater intrusion is a threat to many coastal groundwater basins along theCalifornia Coast. It has been observed and documented in a number ofgroundwater basins in both southern and central California.In general, groundwater in coastal basins flows from recharge areas in localhighlands towards discharge areas along the coast. In most undeveloped coastalgroundwater basins there is a net outflow of fresh water into the ocean.Seawater intrusion occurs when the outflow of freshwater ceases and seawaterflows into the groundwater basin from the ocean.In the simplest condition, seawater intrudes as a wedge beneath the freshgroundwater (Figure 1). This wedge shape is a result of seawater being denserthan freshwater.Figure 1: Seawater Wedge in a Simple Coastal Aquifer (from Barlow, 2003)In more complex, layered groundwater systems, the location of theseawater/freshwater interface may vary among the different aquifers. Such asituation is illustrated in Figure 2. Figure 2 shows a series of aquifers in blue,which transmit water easily. The aquifers are separated by a series of tanSeawater Intrusion Response PlanNovember 19, 2008 A-2