Quaggas and Gators: Effects of Invasive Species Dreissena Rostriformis Bugensis (Quagga Mussel) and Alternanthera Philoxeroides (Alligator Weed) On Groundwater Replenishment Operations and Selected Mitigation Measures to Protect Replenishment in SoCA

When designing or operating groundwater replenishment (spreading) facilities, many factors must be considered to minimize obstacles to replenishment.  Factors commonly considered include frequency and location of maintenance activities along water conveyance channels, and blending requirements for mixed water sources (e.g., recycled and imported water).  Less commonly considered are other factors such as invasive species; however, these can also impact replenishment operations.
Quagga mussel (Dreissena rostriformis bugensis) and alligator weed (Alternanthera philoxeroides) are two invasive species which have been detected in Southern California.  Both species can affect the ability of spreading facilities to obtain, transport or recharge water into underlying aquifers.  This paper presents an overview of the two species, their potential impacts to groundwater replenishment, detections and impacts to date, and efforts by the following Southern California water resource agencies to minimize future impacts.
The Water Replenishment District of Southern California (WRD) manages two of the most utilized groundwater basins in Southern California, the Central and West Coast Groundwater Basins (CWCB).  The CWCB were adjudicated in the 1960s to limit groundwater production and stabilize declining groundwater levels.  Since that time, natural recharge has been supplemented through artificial replenishment activities, including replenishment at spreading grounds.  WRD purchases water for these activities, owns and operates several replenishment-related facilities, and works closely with owners and operators of other such facilities within the District.
The Los Angeles County Department of Public Works (LACDPW) owns and operates the majority of replenishment facilities in Los Angeles County.  Their Rio Hondo Spreading Grounds (RHSG) and San Gabriel River Spreading Grounds (SGRSG) are the primary locations for artificial replenishment in the CWCB.  An average of 125,000 acre-feet of water (consisting of imported, recycled and local water) is conserved between the RHSG and SGRSG each year.  WRD and LACDPW work closely together and with other agencies to maximize replenishment at these grounds.