Aliso Creek

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Aliso Creek
Aliso Creek flows past a bridge, showing distinctive riprap. A few storm drains and the tip of a drop structure, one of two of its kind on the creek, are seen in the distance. This picture was taken in medium to high flow.
Country	USA
State	California
Region	Orange County
Length	20 mi (32 km)
Watershed	35 sq mi (91 km²)
Discharge at	Aliso Beach
- maximum	4,760 cu ft/s (135 m³/s)
- minimum	2-6 cu ft/s (2 m³/s)
Source	Santa Ana Mountains
Mouth	Laguna Beach, California
Major tributaries
- left	Wood Canyon Creek, Aliso Hills Channel
- right	English Canyon Creek, Sulphur Creek

Aliso Creek ("Alder Creek") is a stream that flows through central Orange County in southern California. Originating from the foothills of the Santa Ana Mountains, inside the Cleveland National Forest, it winds about 20 miles west to the Pacific Ocean. The upper and lower sections of the creek are reserved as open space, while its central part flows through several cities , as well as flowing through Laguna Beach before emptying into the sea. The creek is polluted with storm drain runoff and treated sewage.

[edit] Characteristics

Aliso Creek receives water from an approximately 30.4 square mile (78.9 square kilometer) drainage basin, as well as receiving water from smaller tributaries such as Wood Canyon Creek, Sulphur Creek, and the Aliso Hills Channel. The creek flows through parts of the cities of Lake Forest, Aliso Viejo, Laguna Niguel, and Mission Viejo. The cities decrease the amount of rainfall that soaks into the ground, and thus more water enters the creek. (Urban runoff.) Along its course, it flows over at least 20 drop structures, ranging from 1-10 feet tall, that affect upstream and downstream travel of fish and other wildlife. Its volume can range from an average dry season flow of 2-6 cfs (most if not all of which is storm drain outflow) to an astonishing recorded peak of 2,850 cfs during the storm of 2/17 to 2/25/2005, and a maximum peak of 4,760 cfs during the storm of 10/24 to 10/29/2004. For at least 50% of its length, it either flows in a narrow, concrete flood control channel or surrounded by riprap walls. In its lower portion it flows through Aliso and Wood Canyons Wilderness Park.

[edit] Water quality

Aliso Creek contains high amounts of bacteria and chemical pollutants including E.coli. Close to 500,000 gallons of raw, untreated sewage have been dumped by Aliso Creek onto Aliso Beach, the creek's outlet. Recently, however, storm drain discharge into Aliso Creek have been monitored closely and two have been fitted with treatment system to reduce the amount of pollutants entering the creek. Surprisingly, Aliso Creek is not even the most polluted in Orange County but nearby Oso Creek and Arroyo Trabuco, as well as San Juan Creek after its confluence with Trabuco, are the most polluted.