San Juan Creek

San Juan Creek begins high in the Santa Ana Mountains southwest of Lake Elsinore, at the head of the steep and narrow San Juan Canyon, at roughly in elevation where Morrell Canyon Creek, draining the western Elsinore Mountains and southernmost Santa Ana Mountains, has its confluence with Bear Canyon Creek. From there, it flows steeply down a rocky gorge over rapids and waterfalls. San Juan Canyon forms the mountain pass for California State Route 74 (the Ortega Highway), which connects San Juan Capistrano to Lake Elsinore and the Inland Empire. San Juan Falls, a cascade, and the Ortega Falls are located along the headwaters of the creek. The creek then flows generally southwest through a canyon, receiving Hot Springs Creek and Cold Springs Creek from the right, and Lucas Canyon Creek from the left. At Caspers Wilderness Park, the San Juan Canyon opens up into a fairly wide valley in the foothills of the Santa Ana Mountains. This reach of San Juan Creek is underlain by thick alluvial deposits and is still used for farming and grazing. It is joined by Bell Canyon from the right, and Verdugo Canyon Creek from the left. Trampas Canyon enters from the left and Cañada Gobernadora and Cañada Chiquita enter from the right. The creek flows through residential Rancho Mission Viejo, crosses under Interstate 5, and enters a concrete flood control channel, turning south and receiving El Horno Creek on the right. It receives its largest tributary, Arroyo Trabuco, from the right, then flows south toward the Pacific Ocean. The creek forms a fresh water lagoon at the northern end of Doheny State Beach, which overflows into Capistrano Bay during periods of high flow. Tributaries All direct tributaries of San Juan Creek, from mouth to source, are listed. The list also includes streams that join major tributaries. • Arroyo Trabuco • Oso Creek • La Paz Channel • Tijeras Canyon Creek • Live Oak Canyon Creek • Hickey Canyon Creek • Rose Canyon Creek • Falls Canyon Creek • Holy Jim Canyon Creek • El Horno Creek • Cañada Chiquita • Cañada Gobernadora • Wagon Wheel Canyon Creek • Trampas Canyon • Verdugo Canyon • Bell Canyon (Bell Creek) • Crow Canyon Creek • Dove Canyon Creek • Fox Canyon Creek • Lucas Canyon Creek (mouth of San Juan Canyon) • Aliso Canyon Creek • Cold Springs Canyon • Hot Spring Canyon • Chiquito Spring Creek • Lion Canyon Creek • Bear Canyon Creek (head of San Juan Canyon) • Morrell Canyon Creek • Long Canyon Creek • Arroyo El Cariso • Decker Canyon Creek ==Geology==

The San Juan Creek watershed is crossed by a complex network of seismic fault zones, with streams tending to form canyons along fault traces. The Cristianitos fault (Cristianitos) runs northeast-southwest along Oso Creek, passing offshore south of the mouth of San Juan Creek. The Mission Viejo fault zone parallels the Cristianitos but ends much farther south, in San Diego County. The first recorded earthquake in the area partially destroyed Mission San Juan Capistrano in 1812 (which had been built only six years before), killing forty people in the adobe chapel when it collapsed. Other major quakes occurred in 1862, 1933 and 1938. ==Hydrology and groundwater==

The U.S. Geological Survey (USGS) measured the discharge of San Juan Creek in the city of San Juan Capistrano for two periods, from 1928 to 1969 and from 1969 to 1985. Stream flows for the earlier period are considerably different from the later period due to increased volumes of urban runoff. For 1928–1969, the average discharge was , and the peak flow was on February 25, 1969. During the 1969–1985 period, the average flow was , and a peak flow of was recorded on March 4, 1978. After 1985, the USGS stopped measuring discharge but continues to monitor water level in real-time at the La Novia Street bridge. According to the city of San Juan Capistrano, the largest flood of record occurred on January 11, 2005 with an estimated discharge of . According to the California State Water Resources Control Board (1977) the San Juan Creek Groundwater Basin has a total volume of roughly . Natural groundwater recharge in the San Juan basin is estimated at per year. This amount has been reduced due to extensive urbanization of the lower watershed which results in more water running off to the Pacific Ocean. However, water from irrigation run-off and other human activities is responsible for recharging an additional per year. The Christianitos and Mission Viejo fault zones split the watershed into distinct "Upper" and "Lower" groundwater basins. The groundwater mostly lies in alluvium, which ranges from a depth of in the lower elevations to almost none in the high elevations. Although San Juan Creek contains water for most of the year, it is highly seasonal, with strong flows during the wettest months of January through March, and shrinking to a trickle during the other months. In poor rain years, the stream can often dry up completely in its lower reaches. The total natural (unimpaired) surface outflow from the San Juan basin into the Pacific is estimated at per year. Agricultural and urban runoff significantly increased the average outflow, to as of 1993. The maximum annual outflow is . Although the use of local surface water and groundwater is increasing, local groundwater levels have not been affected significantly by human use, due to the relatively high natural recharge rate. However, the U.S. Army Corps of Engineers considers many levees in the San Juan Capistrano area to be inadequate for handling the 100-year flood, and that such a flood would cause $149 million of property damage. ==Watershed==

The San Juan Creek watershed covers in south Orange County and a very small portion of Riverside County. The Santa Ana Mountains occupy most of the north, east and south parts watershed, while the San Joaquin Hills border the watershed on the southwest. Along with San Juan Creek, the two largest tributaries – Trabuco and Bell Creeks – both originate in the Santa Ana Mountains. Although more than half of the watershed is undeveloped land, it also includes parts of the cities of Dana Point, Laguna Hills, Laguna Niguel, Mission Viejo, Rancho Santa Margarita, San Clemente, San Juan Capistrano, and the unincorporated communities of Trabuco Canyon (near Rancho Santa Margarita) and Rancho Mission Viejo (east of San Juan). There are four main alluvial river valleys in the watershed. The San Juan Creek valley occupies the south portion of the watershed; the heavily urbanized lower (southwest) portion is located in the cities of San Juan Capistrano and Dana Point, while the largely rural (northeast) portion extends well into the foothills of the Santa Ana Mountains. The Arroyo Trabuco valley forms a large alluvial plain called "Plano Trabuco" in the north part of the watershed (part of suburban Rancho Santa Margarita). The Oso Creek valley is narrower, running south through Mission Viejo and Laguna Hills, and is mostly urbanized. The Bell Creek valley is the least urbanized of the four, being mostly located in the Cleveland National Forest, Starr Ranch Preserve and Caspers Wilderness Park. There are 19 other major tributaries in the watershed. The California Department of Water Resources includes San Juan Creek in the San Juan Hydrologic Unit, which includes the coastal watersheds of Aliso Creek, Salt Creek, Prima Deshecha Cañada, Segunda Deshecha Cañada, and San Mateo Creek, which share a similar range of elevations and climate. Elevation in the Hydrologic Unit ranges from sea level to at Santiago Peak (the headwater of Holy Jim Creek, a tributary of Arroyo Trabuco). The climate is Mediterranean, with hot, dry summers and cool, wet winters. Almost all the precipitation occurs between October and April; the average rainfall is , although mountain areas often receive higher amounts. San Juan Creek receives extra runoff from agriculture, urban areas, and other human sources, resulting in unnatural dry season flows ==Ecology==

San Juan Creek was originally rich in riparian zones and other types habitat in both its upper and lower watershed, with wetlands totaling over historically in the lower reaches, before urban development began in the 1950s. Only 0.3 percent of those wetlands remain. Recent efforts of stream conservation have been in the planning stage including habitat conservation plan work. There are sixteen prominent vegetation zones in the San Juan watershed, which include riparian vegetation, montane woodlands, coastal sage scrub and chaparral. Riparian vegetation is found along the banks of free-flowing streams with a measurable flow for at least several months out of the year. These include most of San Juan Creek, upper Arroyo Trabuco, Cañada Gobernadora, Bell Canyon, and other headwater streams, as well as scattered patches along Oso and El Horno creeks. Forests are present at high elevations, and also occur in close proximity to waterways. Coastal sage scrub is found on south-facing hillsides, while chaparral is found on higher-elevation hillsides and mesas. There are also a number of rare plant communities along rock outcroppings and vernal pools. However, introduced plant species, such as giant reed, castor bean, and tobacco tree, are rapidly spreading along streams. Giant reed has taken over huge areas of wetlands, swamps and riparian zones along the creek and its tributaries, although in recent years the county has taken steps toward eradicating it from San Juan Creek and other nearby streams. Historically, the San Juan watershed supported up to 12 invertebrate species, 5 fish species, 12 amphibian species, 35 reptile species, 143 bird species, and 42 mammal species, which benefited from the diverse vegetation communities present. Some streams and ponds host federally listed endangered/threatened species such as tidewater goby, fairy shrimp, and California red-legged frog. Federally listed bird species include least Bell's vireo, California gnatcatcher, California least tern, and southwestern willow flycatcher. Other listed species include Pacific pocket mouse and Quino checkerspot butterfly. As urbanization continues to increase in the San Juan watershed, most sensitive species have been pushed back to the foothills, mountains, and agricultural/ranching areas of the watershed. The loss of riparian habitat along the lower of San Juan Creek and much of Trabuco and Oso Creeks due to channelization has also reduced steelhead habitat. However, in 2003 the California Department of Fish and Game reported three sightings of steelhead in a large stream pool along Trabuco Creek, immediately downstream of a drop structure that channels the creek beneath Interstate 5. In response, the Department of Fish and Game lobbied Caltrans to build a fish ladder at the structure, but it has not yet been implemented, due to concerns about structural stability of the I-5 bridge and the presence of a nearby natural gas pipeline. ==History==

Indigenous peoples Before the 18th century, the San Juan Creek watershed was mostly Acjachemen territory, which extended from Aliso Creek in the north to San Mateo Creek in the south, a distance of roughly . Most of the population lived along the two major streams in the area, San Juan and San Mateo Creeks, as well as Arroyo Trabuco. The Acjachemen lived in villages along San Juan Creek, including villages on the main stem of San Juan Creek, the largest being Putiidhem, which was the mother village of the people, as well as Sajavit and Piwiva, while Huumai was located on the tributary Cañada Gobernadora. The Acjachemen diet usually consisted of fruits, acorns, grains, and some meat, while they practiced little agriculture. Shell middens indicate that they also harvested shellfish from the coast. Native peoples in this area are not known to have built permanent structures in this area or significantly influenced the natural environment. On the return journey to San Diego, the party used the campsite again, on January 20. In 1776, Father Junípero Serra founded Mission San Juan Capistrano on a site close to the creek (possibly near the Cañada Gobernadora confluence), and the creek was named after the mission. The first site was abandoned due to lack of water, although some historical accounts suggest the creek once had a perennial flow. The origin of the name of Oso Creek (Spanish: "Bear Creek") is not known. Many of the creeks in the watershed have names of Spanish origin, which were most likely named by the Spanish conquistadors a long time before the area was annexed by the United States. The breakwater prevented the occurrence of a large surf break phenomenon, colloquially known as "Killer Dana", in the bay. When Killer Dana disappeared, water circulation in the bay decreased. As polluted runoff from San Juan Creek continues to flow into the bay, it is trapped for extended periods of time. At Doheny State Beach, 850,000 annual visitors are exposed to potential health risks from high bacteria levels in the water. During floods in the 1990s, an almost-sheer waterfall appeared on Arroyo Trabuco in northern San Juan Capistrano, threatening the foundations of a railroad bridge. The drop required quick reinforcement with grouted riprap. With an average gradient of 29 percent, it has become a major barrier to migrating fish and other riverine organisms, and thus isolates aquatic environments in upper Arroyo Trabuco from the rest of the San Juan watershed. ==River modifications==

Although the San Juan Creek watershed is less heavily developed than other coastal Orange County watersheds, extensive works have been constructed to control floods, reduce erosion, and provide reclaimed water for irrigation. A growing amount of urban runoff flows into the creek and its tributaries, creating a dry season "nuisance flow". Historically, only San Juan Creek and Arroyo Trabuco were known to contain water for most or all of the year. Runoff has caused Doheny Beach to rank in the ten most polluted beaches of California. The Santa Margarita Water District is currently proposing a new reservoir in Verdugo Canyon, another tributary of San Juan Creek, to collect and store reclaimed water. The lower of San Juan Creek are channelized between levees, from a point immediately upstream of the Interstate 5 bridge to Doheny Beach. Arroyo Trabuco is only channelized for several hundred yards above its confluence with San Juan Creek. Oso Creek is the most heavily modified, flowing in an artificial channel for almost its entire length. Bell Creek and other eastern tributaries have retained their natural characteristics. The USACE describes the San Juan and Arroyo Trabuco levees as providing a "fairly high level of protection currently", There are also seven drop structures on Oso Creek, mostly built of riprap. There are no such specifically constructed structures on San Juan Creek itself. ==List of crossings==

This is a list of major crossings of San Juan Creek, proceeding upstream of the mouth. • State Route 1 (Pacific Coast Highway) • Camino Las Ramblas • Stonehill Drive • Metrolink Orange County Line & Amtrak Pacific Surfliner • Camino Capistrano • Interstate 5 (San Diego Freeway) • State Route 74 ("Lower" Ortega Highway) • Antonio Parkway • Nursery Road • State Route 74 ("Middle" Ortega Highway) • State Route 74 ("Upper" Ortega Highway) ==See also==

• Shaffer, Chris. The Definitive Guide to the Waterfalls of Southern and Central California. Shafdog Publications, 2005. ==External links==