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Located in southern California, roughly between Los Angeles and San Diego, the Santa Ana Region continues to be one of the most rapidly growing areas of the State. While the region is geographically the smallest (nearly 3,000 square miles), of the nine regions, it boasts one of the largest populations (almost five million people) making it one of the most densely populated regions.
The climate of the Santa Ana Region is classified as Mediterranean: generally dry in the summer with mild, wet winters. The average annual rainfall in the region is about fifteen inches, most of it occurring between November and March. Much of the area would be near-desert were it not for the influence of modern civilization.
In very broad terms, the Santa Ana Region is a group of connected inland basins and open coastal basins drained by surface streams flowing generally southwestward to the Pacific Ocean.
The boundaries between California’s nine regions are usually hydrologic divides that separate watersheds, but the boundary between the Los Angeles and Santa Ana Regions is the Los Angeles County Line. Since that county line only approximates the hydrologic divide, part of the Pomona area drains into the Santa Ana Region, and in Orange County, part of the La Habra drains into the Los Angeles Region.
The east-west alignment of the crest of the San Gabriel and San Bernardino Mountains separates the Santa Ana River basin from the Mojave Desert, which is part of the Lahontan Basin (Region 6). In the south, the regional boundary divides the Santa Margarita River drainage area from that of the San Jacinto River, which normally terminates in Lake Elsinore.
Near Corona, the Santa Ana River has cut through the Santa Ana Mountains and flows down onto the Orange County coastal plain. The Pacific Ocean coast of the Santa Ana Region extends from just north of Laguna Beach up to Seal Beach and the Los Angeles County line. Other features of the coast include Newport Bay, Anaheim Bay-Huntington Harbour, and the major coastal wetlands areas associated with those bays.
Before this area was settled, it is thought that the Santa Ana River flowed from its headwaters in the San Bernardino Mountains to the Pacific Ocean throughout most of the year. The San Jacinto River, also a substantial surface stream, typically would have ended at Lake Elsinore, which acted as an inland sink. Once out of the sycamore-filled mountain canyon, these rivers meandered along in sandy streambeds, shaded by willows, cottonwoods, and live oaks, flows decreasing where water percolated, filling the groundwater basins, increasing where local geological features forced the groundwater to the surface. High groundwater made springs, swampy areas, marshes and bogs common.
Deep alluvial valley deposits made up large groundwater basins, both in the inland valleys and on the coastal plain, basins naturally full of fresh water. Along with its nearby tributaries, the Santa Ana River fed the Bunker Hill groundwater basin, the Colton and Riverside basins, and to a lesser extent, part of the Chino Basin. Streams in the San Gabriel Mountains recharged the Chino Basin. The San Jacinto River recharged a deep (over two thousand feet) graben, the San Jacinto groundwater basin, as it left the mountains, then several other basins in succession on its way to Lake Elsinore. When especially heavy rainfalls or a series of wet winters filled Lake Elsinore, overflows went down Temescal Creek to the Santa Ana River near Corona. The Santa Ana River entered Santa Ana Canyon and passed through the coastal mountains out onto the Orange County Plain, overlying another large, deep groundwater basin largely recharged by river flows. With the diversion of most of this natural surface flow for agricultural and domestic uses, creeks and rivers dried up, carrying only storm flows and runoff. Eventually, treated wastewater replaced some of the flows in some streams.
The most serious water-related problem in the Santa Ana River Basin at this time is water supply. This region now uses approximately twice as much water as is available from local sources. As a result, the quantity of water imported into this region each year now equals or exceeds the amount of ground and surface water utilized.
Unknown to most is that the Region’s Chino Basin once had the highest concentration of dairy animals in the world, with approximately 350 dairies and over 300,000 dairy cows in a 20 square mile area. While the number of Chino Basin dairies declined to 86 in 2015, historic land application of manure and process wastewater in the Chino Basin resulted in significant groundwater degradation due to high levels of total dissolved solids (TDS) and nitrate. In response to groundwater degradation, the Dairy General Permit prohibits land application of manure, process wastewater, and CAFO production area stormwater runoff in the Chino Basin. This area is now slowly yielding to urban development.
The Region is also addressing water quality issues through several Total Maximum Daily Loads (TMDL). Once a waterbody has been placed on category 5 of the 303(d) list of impaired waters, states are required to develop a Total Maximum Daily Load (TMDL) to address each pollutant causing impairment. A TMDL defines how much of a pollutant a waterbody can tolerate and still meet water quality standards. Each TMDL must account for all sources of the pollutant. TMDLs allocate allowable pollutant loads for each source, and identify management measures that, when implemented, will assure that water quality standards are attained.
Current TMDLs within the region include a TMDL for Total Phosphorus in the Big Bear Lake drainage basin. Middle TMDL’s for indicator bacteria in the Middle Santa Ana River and another in Newport Bay. Newport Bay has an additional TMDL Basin Plan amendments for the Newport Bay watershed TMDLs for selenium, organochlorines compounds, nutrients, and sediment and copper.
RESOURCES:
Santa Ana Regional Water Quality Control Board’s Website
www.waterboards.ca.gov/santaana/
www.waterboards.ca.gov/santaana/about_us/contact_us.html
- Santa Ana Region - Regional Boundaries Map
www.waterboards.ca.gov/santaana/about_us/regional_boundaries_map.html
- Santa Ana Region – Programs
www.waterboards.ca.gov/santaana/water_issues/programs/
Santa Ana River Basin Plan
www.waterboards.ca.gov/santaana/water_issues/programs/basin_plan/index.html
- Total Maximum Daily Loads (TMDLs)
www.waterboards.ca.gov/santaana/water_issues/programs/tmdl/index.html
Santa Ana Regional Water Quality Control Board Factsheet
www.waterboards.ca.gov/santaana/resources/docs/reg8_factsheet.pdf
Santa Ana Watershed Association
www.sawatershed.org/
Santa Ana Watershed Project Authority
https://sawpa.org/
SWAMP - Region 8 (Santa Ana) Monitoring Program
www.waterboards.ca.gov/water_issues/programs/swamp/monitoring/regional_monitoring_programs/region_8.html
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