Existing Water Supply

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The primary sources of water in the LA River are wet weather runoff originating from direct precipitation on the watershed, and dry weather inputs from the watershed including incidental urban runoff, and groundwater upwelling.

The dominant source of dry weather flow is recycled water discharge from the Donald C. Tillman Water Reclamation Plant (DCTWRP), LA Glendale Water Reclamation Plant (LAGWRP), and Burbank Water Reclamation Plant (BWRP) and much of this flow originates from waters that are imported from outside the watershed of the LA River. Imported water is generally referred to as water brought into the region from the Colorado River, Sacramento-San Joaquin River Delta, and the Eastern Sierras. Water imports in the early 20th century reduced the river’s importance as a municipal water supply. Water uses/losses along the river consist of evaporation, evapotranspiration, limited infiltration that recharges underlying groundwater basins, and discharge into the Pacific Ocean.

Groundwater pumping from underlying groundwater basins, managed by the Upper LA River Area (ULARA) Watermaster and the Water Replenishment District of Southern California (WRD), provides many beneficial uses along the river system. Beneficial uses of the surface flows of the river include habitat in the Glendale Narrows region, significant bird habitat in the lower reaches between river miles 9 and 3, and recreation in several locations including the Sepulveda Basin and Glendale Narrows.

Hydrologic Drivers

Groundwater Basins

Water is a scarce and valuable resource in drought-prone Southern California. In the greater LA basin (composed of the LA River, San Gabriel River, South Santa Monica Bay, Ballona Creek, Malibu Creek, and Dominguez Channel/LA Harbor watersheds), water supply consists of approximately 57% imported water, 34% groundwater, and 9% sourced from recycled water and local surface water.¹ There is an urgent need and regional desire by the major water suppliers in the greater Los Angeles Basin to increase reliability by improving local water supply and possibly decreasing the LA Basin’s reliance on imported water.² ³ ⁴ ⁵ ⁶

The LA River presents an opportunity to develop and diversify local water resources through capture of wet and dry weather flows and recharging local groundwater basins for extraction at a future time.

Water Supply Portfolio

Less than 50% of the region’s water supply is from local sources.

The water flowing in the LA River supports many uses. These can include wetland and freshwater habitat, recreational uses, and municipal and industrial supply. It can be developed to further enhance habitat and recreation along the river system and can be used as a source water for municipal and industrial uses integrated into the portfolio of existing source waters. Use of the river flows for groundwater recharge is particularly attractive because the groundwater basins have reliable water storage that allows use of the LA River supplies not when they occur, but when they are most needed. Dry weather flow is attractive as source water because facilities built to use the supply would be operated at a relatively consistent and manageable rate resulting in a high use factor for capital investment.

However, the consistent rate of these dry weather flows makes them suitable for sustaining a large number of competing uses including public trust needs and, and thus the suitability of dry weather flow as a groundwater recharge supply is uncertain. Wet weather flow diversions show promise as these flows that are largely wasted today have a much lower potential for alternative uses. Wet weather diversions require overcoming the technical challenges associated with temporary detention of large water volumes, water treatment under fluctuating flow conditions, and river diversions under flow conditions greater than baseflow. However, these technical challenges may be overcome, resulting in high use potential of the water once it is recharged into the groundwater aquifers.