Geography and topography of South Coast Hydrologic Region
Alluvial groundwater basins and subbasins in the South Coast Hydrologic Region

The South Coast hydrologic region of California is one of the 10 major hydrologic regions of the state as identified by the California Department of Water Resources. The South Coast hydrologic region has a surface area of about 11,100 sq mi (29,000 km2), and includes all of Orange County, major portions of Los Angeles, Riverside, San Bernardino, San Diego, and Ventura counties, and a small portion of Santa Barbara County.[1] The state-defined South Coast hydrologic region is roughly equivalent to the federally-defined Southern California Coastal water resource subregion. The South Coast hydrologic region has 78 state-recognized alluvial groundwater basins and subbasins.

Significant geographic features include the Transverse Ranges and the Peninsular Ranges. Major rivers in the region include the Los Angeles River, San Gabriel River, San Diego River, San Luis Rey River, Santa Ana River, Santa Clara River, Santa Margarita River, and Ventura River.

The climate in the region ranges from Mediterranean to subtropical steppe. Annual precipitation in the region ranges from more than 40 in (1,000 mm) in the mountains to less than 10 in (250 mm) in some valleys, with an overall average of 17.6 in (450 mm) for the region.

Alluvial groundwater basins in the South Coast hydrologic region

The South Coast hydrologic region overlies an aquifer with a number of identified alluvial groundwater basins and subbasins. An alluvial groundwater basin is essentially the top level of an aquifer, above less-permeable rocks below, such as limestone and shale.[2] Alluvium (from Latin alluvius, from alluere 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings.[3]

Alluvial groundwater basin[1] State basin code[1] Basin priority Surface area (acres)[4] Well yield (gpm) Maximum[4] Well yield (gpm) Average[4] Notes
Upper Ojai Valley groundwater basin 4-1 3,800 200 50
Ojai Valley groundwater basin 4-2 Medium 6,830 600 383
Ventura River Valley groundwater Basin 4-3 12,710
Santa Clara River Valley groundwater basin 4-4 High
Acton Valley groundwater basin 4-5 8,270 1,000 140
Pleasant Valley groundwater basin 4-6 Medium 21,600 1,000
Arroyo Santa Rosa Valley groundwater basin 4-7 Medium 3,740 1,200 950
Las Posas Valley groundwater basin 4-8 Medium 42,200 750
Simi Valley groundwater basin 4-9 12,100 394
Conejo Valley groundwater basin 4-10 28,900 1,000 100
Coastal Plain of Los Angeles groundwater basin[5] 4-11 High
San Fernando Valley groundwater basin 4-12 High 145,000 3,240 1,220
San Gabriel Valley groundwater basin 4-13 Medium 154,000 4,850 1,000
Tierra Rejada groundwater basin 4-15 4,390 1,200 172
Hidden Valley groundwater basin 4-16 2,210
Lockwood Valley groundwater basin 4-17 21,800 350 25
Hungry Valley groundwater basin 4-18 5,310 28
Thousand Oaks Area groundwater basin 4-19 3,110 39
Russell Valley groundwater basin 4-20 3,100 25
Malibu Valley groundwater basin 4-22 613 1,060 1,030
Raymond groundwater basin 4-23 High 26,200 3,620 1,880
Coastal Plain of Orange County groundwater basin 8-2 High 224,000 4,500 2,500
Upper Santa Ana River valley 8-3
Elsinore groundwater basin 8-4 25,700 5,400
San Jacinto groundwater basin 8-5 High 188,000
Hemet Lake Valley groundwater basin 8-6 16,700 820 196
Big Meadows Valley groundwater basin 8-7 14,200 120 34
Seven Oaks Valley groundwater basin 8-8 4,080
Bear Valley groundwater basin 8-9 Medium 19,600 1,00 500
San Juan Valley groundwater basin 9-1 Medium 16,700 1,000
San Mateo Valley groundwater basin 9-2 2,990
San Onofre Valley groundwater basin 9-3 1,250
Santa Margarita Valley groundwater basin 9-4 Medium 626 1,980
Temecula Valley groundwater basin 9-5 High 87,800 1,750
Cahuilla Valley groundwater basin 9-6 Medium 18,200 500
San Luis Rey groundwater basin 9-7 Medium 37,000 2,000 500
Warner Valley groundwater basin 9-8 24,000 1,800 800
Escondido Valley groundwater basin 9-9 2,890 190 50
San Pasqual Valley groundwater basin 9-10 Medium 4,540 1,700 1,000
Santa Maria Valley groundwater basin 9-11 12,300 500 36
San Dieguito Creek groundwater basin 9-12 3,560 1,800 700
Poway Valley groundwater basin 9-13 2,470 200 100
Mission Valley groundwater basin 9-14 7,350 1,000
San Diego River Valley groundwater basin 9-15 Medium 9,890 2,000
El Cajon Valley groundwater basin 9-16 7,160 300 50
Sweetwater Valley groundwater basin 9-17 5,290 1,500 300
Otay Valley groundwater basin 9-18 6,830 1,000 185
Tijuana groundwater basin 9-19 7,410 2,000 350
Batiquitos Lagoon Valley groundwater basin 9-22 741 Batiquitos Lagoon
San Elijo Valley groundwater basin 9-23 883 1,800
Pamo Valley groundwater basin 9-24 1,500
Ranchita Town Area groundwater basin 9-25 3,130 125 22
Cottonwood Valley groundwater basin 9-26 3,850
Campo Valley groundwater basin 9-27 3,550 <40
Potrero Valley groundwater basin 9-28 2,020
San Marcos Area groundwater basin 9-32 2,130 60

See also

References

  1. 1 2 3 "Bulletin 118 (South Coast, Chapter 6)" (PDF). This article includes material published by the U.S. state of California that is believed to be in the public domain.
  2. ↑ US EPA, OLEM (2015-06-25). "Section 8: Ground Water - Aquifers". www.epa.gov. Retrieved 2023-03-20.
  3. ↑ Jackson, Julia A., ed. (1997). "alluvium". Glossary of geology (Fourth ed.). Alexandria, Virginia: American Geological Institute. ISBN 0922152349.
  4. 1 2 3 "Antelope Valley Watermaster" (PDF).
  5. ↑ California (1961). Planned utilization of ground water basins: Coastal Plain of Los Angeles County. Appendix A, Ground water geology. Bulletin ;no. 104, Appendix A. Sacramento.{{cite book}}: CS1 maint: location missing publisher (link)
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