San Juan Creek
|San Juan Creek|
|San Juan River|
Hikers ford San Juan Creek below the hot springs, February 2008.
|Name origin: Named for Mission San Juan Capistrano by Spanish conquistadors in the 1700s.|
|Regions||Orange County, Riverside County|
|- left||Lucas Canyon Creek, Verdugo Canyon Creek, Trampas Canyon Creek|
|- right||Lion Canyon Creek, Hot Springs Canyon Creek, Cold Spring Canyon Creek, Bell Canyon Creek, Cañada Gobernadora, Cañada Chiquita, Horno Creek, Trabuco Creek|
|Source||head of San Juan Canyon, at the confluence of Morrell Canyon Creek with Bear Canyon Creek, Santa Ana Mountains|
|- elevation||1,690 ft (515 m)|
|Mouth||San Juan Lagoon, Doheny State Beach, Dana Point|
|- elevation||0 ft (0 m)|
|Length||29 mi (47 km)|
|Basin||133.9 sq mi (347 km2)|
|Discharge||for Doheny Beach|
|- average||75 cu ft/s (2 m3/s)|
|- max||33,650 cu ft/s (953 m3/s)|
|- min||0 cu ft/s (0 m3/s)|
San Juan Creek, also called the San Juan River, is a 29-mile (47 km) stream in Orange County, California that consists of a catchment basin encompassing 133.9 square miles (347 km2). Its mainstem rises in the Santa Ana Mountains, in the Trabuco Ranger District of the Cleveland National Forest. From there it runs parallel to the Ortega Highway as it winds west and south through San Juan Canyon, where it is joined by numerous small tributaries, and is joined by Trabuco Creek, its main branch as it passes through San Juan Capistrano. It flows into the Pacific Ocean at Doheny State Beach. Once out of the foothills, San Juan Creek flows through the city of San Juan Capistrano where groundwater flow direction generally is from the northeast to the southwest. Groundwater in this basin at the San Juan Capistrano reach is considered good. Recent efforts of stream conservation have been in the planning stage including habitat conservation plan work.
Historically, the San Juan Creek watershed was inhabited by the Acjachemen, now Juañeno Indians. The Juañeno received their current name from Spanish conquistadors in the 1770s, who built Mission San Juan Capistrano very near San Juan Creek, giving it its name. After the Spanish settlement, development in the watershed continued to grow and pollution of the creek has increased. The construction of Dana Point Harbor in 1960 increased the pollution of San Juan Creek at its mouth, posing an increasing danger to visitors of Doheny State Beach. In the late 1990s and early 21st century, floods destroyed many river control structures in the San Juan watershed, and the risk of floods continues to grow.
Although the San Juan watershed was formerly rich in biodiversity, with sixteen major plant communities and hundreds of species of birds, invertebrates, mammals, and others, the watershed is projected to be 48 percent developed by the year 2050. Many reaches of open land in the San Juan watershed are now heavily developed, and urban runoff coming from residential communities is taking an increased toll on the creek and its tributaries. Although the mainstem San Juan Creek does not have any water diversions or dams, its tributaries are heavily affected, most notably Trabuco and Oso Creeks.
- 1 Course
- 2 Geology
- 3 Watershed
- 4 History
- 5 River modifications
- 6 Stream crossings
- 7 See also
- 8 References
- 9 Works cited
- 10 External links
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 1,690 feet (520 m) 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 downhill over riffles and waterfalls, and paralleling California State Route 74, here known as the Ortega Highway, as it winds through the rocky gorge. It drops over San Juan Falls, a 15-foot (4.6 m) cascade, then crosses under an arch bridge that carries the Ortega Highway. It is joined by Hot Springs Creek and Cold Springs Creek on the right bank, while Lucas Canyon Creek meets it on the left.
Once out of the mountains, San Juan Creek proceeds to meander through a broad and shallow farming and ranching valley underlain by thick alluvial deposits. The creek swings west to receive Bell Canyon on the right, from several residential communities that overlook, but do not border, it. 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 then crosses under Interstate 5, and enters a flood control channel, turning south and receiving El Horno Creek on the right. It receives its largest tributary, Trabuco Creek, on the right bank, then continues south and east to the Pacific Ocean. Before it reaches the sea, however, it enters a lagoon at the northern end of Doheny State Beach, which occasionally spills into Capistrano Bay.
All direct tributaries of San Juan Creek, from mouth to source, are listed. The list also includes streams that join major tributaries.
Rocks and topography
The geology of the San Juan Creek watershed is complex, but can be described as having many seismic fault zones, with streams tending to follow these fault zones where canyons have formed, and having extremely erosive soils. The alluvial floodplain of San Juan Creek tends to have very deep concentrations in lower reaches and are said to be poorly drained. Soil types in the San Juan watershed can be divided into the Metz-San Emigdio, Sorrento-Mocho, Myford. Alo-Bosanko, Cieneba-Anaheim-Soper, and Friant-Cieneba-Exchequer associations, in order from most level to steepest. Sedimentary bedrock composes many hillsides in the San Juan watershed, and poses a landslide danger during earthquakes, severe erosion or other events that may cause failure of hillside stability.
There are also several seismic faults within the watershed. These include a fault line (Cristianitos) running along Oso Creek northeast-southwest, passing offshore 7 miles (11 km) south of the mouth of San Juan Creek, as well as another fault zone (Mission Viejo) that parallels the Cristianitos but ends far more south, in San Diego County. In summary, the San Juan watershed can be considered as being bisected by two faults, running through its approximate center. The first recorded earthquake in the area partially destroyed Mission San Juan Capistrano in 1812, followed by others in 1862, 1933 and 1938.
The uplift of the San Joaquin Hills, a small coastal mountain range generally following the Pacific coast of Orange County, created a physical barrier for streams flowing off the Santa Ana Mountains. But by the Wisconsinian Glaciation, an enormous climate change helped solve that problem. During the Wisconsinian Glaciation, a period of time that lasted from about 70,000 to 10,000 years ago, glaciers and ice sheets moved south from Canada into the northern United States, radically altering the climate of the entire continent. The arid Southern California climate was supplanted by a temperate rainforest climate that would receive rainfall in excess of 80 to 90 inches (2,000 to 2,300 mm) per year. San Juan Creek and other streams along the South Coast became powerful rivers that cut their way through the San Joaquin Hills, but this condition reverted by the end of the period. Several wet periods did occur throughout the Ice Age, but the Wisconsinian was the largest.
Hydrology and groundwater
Groundwater in the San Juan Creek basin, also referred to as the "San Juan Creek Groundwater Basin", has a total volume of roughly 900,000 acre feet (1.1×109 m3). (California State Water Resources Control Board, 1977.) Natural groundwater recharge in the San Juan basin is estimated to be roughly 160,000 acre feet (200,000,000 m3) per year historically, mostly from precipitation. This amount has been reduced due to extensive development of the lower segment of the watershed, which is continuing to reduce the amount of open ground that can potentially serve in groundwater recharge. Artificially sourced water from irrigation and other uses is responsible for recharging roughly 37,500 acre feet (46,300,000 m3) annually. The watershed is essentially split into half by the Christianitos and Mission Viejo fault zones, which result in the division of the "Upper" and "Lower" groundwater basins. The groundwater mostly lies in alluvium, which ranges from a depth of 200 feet (61 m) in the lower watershed to mostly none in the upper reaches of the watershed.
Historically, the total surface outflow from the San Juan basin into the Pacific was calculated at 5,200 acre feet (6,400,000 m3) annually. Increasing urban development, resulting in increased runoff from irrigation and other sources, brought the annual outflow to 7,800 acre feet (9,600,000 m3) as of 1993. The maximum annual yield is 9,000 acre feet (11,000,000 m3). Although water from San Juan Creek, tributaries and basin groundwater are increasingly used for a limited amount of agricultural and municipal purposes, the annual yield from the watershed is continually increasing. As the groundwater recharge rate of the watershed is relatively high, it is safe to assume that groundwater levels will recover quickly from human use and human-induced pollution.
Due to the lower amount of urbanization in the San Juan watershed as compared with other watersheds in the county, the 100-year flood inundation risk is also significantly lower than that of most of the nearby watersheds. It has been calculated that a 100-year flood in the watershed would only affect a roughly 0.5 mi (0.80 km) wide area for the lower reaches of San Juan Creek inside San Juan Capistrano, while for Trabuco Creek, only a 0.2 mi (0.32 km) wide area would be affected, mainly due to severe downcutting. A fact of note is that the failure of the earthen Trampas Canyon Dam (in Trampas Canyon, 2 miles (3.2 km) upstream of San Juan Capistrano) would actually create a floodwave slightly larger than that of the 100 year flood that would race down San Juan Creek to its mouth. However, many levees in the San Juan area are still inadequately suited to a 100 year flood, regardless of the extent.
The Santa Ana Mountains occupy most of the north, east and south parts of the approximately 133.9-square-mile (347 km2) San Juan Creek watershed, while the San Joaquin Hills and one of their small subranges border the watershed on the southwest, east, and northwest. The three major tributaries, San Juan, Trabuco and Bell Creeks, all originate in the Santa Ana Mountains. There are four main alluvial river valleys in the watershed, drained by San Juan, Trabuco, Oso and Bell Creeks. The San Juan Creek valley occupies the south portion of the watershed, running roughly south before spreading wider near the coast, and running northeast until it turns sharply to the southeast to meet the Pacific Ocean at the city of Dana Point. The Trabuco Creek valley runs west from the northeasternmost portion of the watershed, then gradually becomes wider in a section called the Plano Trabuco then it joins the smaller, urbanized valley of Oso Creek, which runs primarily south. The combined valley then runs southward to merge with the San Juan Creek valley in San Juan Capistrano. The Bell Creek valley is narrower, beginning a few miles south of Trabuco Canyon, California, and running in an almost perfectly straight southward course to San Juan Creek, which at this point is shortly out of the uppermost reach of its watershed, San Juan Canyon. There are 19 other major creeks in the watershed, including Tijeras Canyon Creek and El Horno Creek, both of which drain parts of the foothills of the Santa Ana Mountains.
San Juan Creek is considered as part of the 500-square-mile (1,300 km2) San Juan Hydrologic Unit, which is a coastal region running from central-south Orange County to the north extent of San Diego County, which borders Orange County on the south. The hydrologic unit also covers the watersheds of Aliso Creek, Salt Creek, Prima Deshecha Cañada, Segunda Deshecha Cañada, and San Mateo Creek, in order from north to south. Elevation above sea level ranges from 0 to 5,700 feet (0 to 1,700 m), and precipitation in the hydrologic unit ranges from 12 to 16 inches (300 to 410 mm) annually. Except for San Mateo Creek, all of the other streams in the unit have a relatively developed watershed. San Juan Creek receives extra runoff from agriculture, urban activities, commercial irrigation, and other human-induced sources, which creates an extra unnatural flow (consisting of urban runoff and agricultural return flows). This runoff is often polluted by trash, heavy metals, and oil received while running over pavement, and pesticides and fertilizer if draining farmland. A specific point of concern in the watershed is Oso Creek. A Southern California environmentalist, Michael Hazzard, said after diving into Upper Oso Creek Reservoir to retrieve an outboard motor:
I spent three days diving to retrieve an outboard motor and my skin broke out in hives and boils and my gallbladder suffered and I later had six operations over a 21⁄2-year period.
San Juan Creek was originally rich in riparian zones and other habitats in both its upper and lower watershed, with wetlands totaling over 300 acres (1.2 km2) historically in the lower reaches, before the rapid population explosion of Orange County began. There are 16 major vegetation zones in the watershed. Currently, the total wetland acreage in the watershed is 3 acres (0.012 km2), or one percent of the historic total. In 1987, just five bird species were confirmed in the watershed, while for fish, benthic invertebrates, and certain insects there were no confirmed observations, in part due to insufficient site coverage. Steelhead trout have recently been observed in the creek and its tributary, Trabuco Creek. A further reason for the decline of creek habitat and wildlife is mainly due to invasive plant and animal species, including giant reed (Arundo donax) and many sport fishes, such as bluegill and striped bass. However, a notable aspect of the creek water is while a sample taken at the creek mouth in January 1995 had a temperature of 13.8oC (56.84 degrees Fahrenheit), many creeks along the Orange County coast have much higher temperatures.
The USGS operated two stream gauges on San Juan Creek in the city of San Juan Capistrano, one from 1929 to 1969 and the second from 1970 to 1984. For the former gauge, the highest recorded peak flow during that period was 22,400 cubic feet per second (630 m3/s) per second on 25 February 1969, with a gauge height of 5.6 feet (1.7 m). The second highest peak flow during that period was 13,000 cubic feet per second (370 m3/s) on 2 March 1938, presumably at the peak of the Los Angeles Flood of 1938. For the more recent stream gauge, the highest recorded flow was 14,700 cubic feet per second (420 m3/s) on 4 March 1978, gauge height 17 feet (5.2 m). The second highest flow was 11,700 cubic feet per second (330 m3/s) on 20 February 1980, gauge height 15.43 feet (4.70 m). The highest flow recorded on San Juan Creek of all time, however, was not by a USGS stream gauge; the flow of 33,650 cubic feet per second (953 m3/s) was recorded on 11 January 2005.
Before the 18th century, San Juan Creek and its tributary, Trabuco Creek, had indigenous names, but these are thus far unknown. The land in the San Juan watershed was mostly Acjachemen Indian territory, which extended from Aliso Creek in the north to San Mateo Creek in the south, a distance of roughly 35 miles (56 km) north-south. Most of the population centered on the outfalls of the two large perennial streams in the area, San Juan and San Mateo Creeks, as well as Trabuco Creek.
Such inhabitants, who numbered roughly two thousand overall, were hunter-gatherers, living in small, semi-permanent villages beside or near perennial streams. There were five villages on the main stem, three of which were below the Trabuco Creek confluence, and four more in other parts of the watershed, mostly on Trabuco and Oso Creeks. Their diet usually consisted of fruits, acorns, and grains, and sometimes meat, while they practiced little agriculture. Shell middens indicate that they also harvested shellfish from the coast. Although natural disasters such as floods, drought, and wildfires occurred during that time, as they do today, the Juañeno did not affect the environment of the area in either a negative or positive way. No permanent structures were built in the San Juan watershed until the arrival of the Spanish.
In 1776, Father Junípero Serra founded Mission San Juan Capistrano on a site that was most probably close to the creek, and as a result, the creek takes its name from the mission. The first site, however, was abandoned due to lack of water, although the creek was known in historical accounts to be perennial. The mission was moved to a second site, where it now stands. The Acjachemen were dubbed the "Juañeno" by the Spanish, after the mission. The Spanish were among the first to create hydrological changes in the San Juan watershed, which included excavating irrigation channels, diverting water from streams, and channelizing and changing course of streams. Grazing animals, including cows, sheep and other livestock, began their prevalence during this period, destroying many native grasses and leaving the ecosystem unbalanced and prone to erosion.
The origin of the name of Trabuco Creek (Spanish: "Blunderbuss Creek", literally) stems from the Gaspar de Portolà expedition of 1769, during which a soldier lost a blunderbuss ("trabuco"), and the name became associated with the creek after that point. 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.
In 1812, a heavy earthquake severely damaged many of the structures built by the Spanish. The Great Stone Church at Mission San Juan Capistrano, which had been built only six years before, collapsed; over forty people were reported to have been killed.
Before urban development, the partially devastated lands caused by overgrazing during the Spanish period was still potentially capable of rebounding to their natural state. In 1964, the urban percentage was 3, while by 1988, it had increased to 18 percent. In the 1990s, the watershed was 32 percent urban, and the projected growth by 2050 is 50 percent. Many areas in the watershed now have no chance to revert to their natural state as long as human habitation continues.
20th century to present
In the late 1960s, the construction of Dana Point Harbor began very near the mouth of San Juan Creek. This harbor prevented the occurrence of a large surf break phenomenon, colloquially known as "Killer Dana", in the bay. With the disappearance of Killer Dana, water circulation in the bay decreased. Resultantly, as pollution from San Juan Creek continued to flow freely into the bay, it stayed there for a longer period of time in comparison with that if the harbor had never been built. The pollution problems are ongoing, posing problems at Doheny Beach, where the 850,000 annual visitors are threatened by the continuing pollution from San Juan Creek.
During floods in the 1990s, an almost sheer 30-foot (9.1 m) waterfall was rapidly scoured out of a steep earthen slope on Trabuco Creek, downstream of a railroad bridge and upstream of the Oso Creek confluence. This drop required quick reinforcement with grouted riprap, and still exists, with an average gradient of 29 percent before sheerly plunging into a murky stream pool. It still poses a major barrier to migrating fish and other riverine organisms, and thus isolates the lower few miles of Trabuco Creek from the relatively natural upper course.
In 1996, severe floods caused by heavy rainstorms in the San Juan watershed caused both San Juan and Trabuco creeks to overflow, destroying long sections of concrete lining near their confluence. The damage was chiefly caused by severe basal erosion, which led to subsequent failure of the concrete walls and levees. Once the concrete was breached, the bare earth underlying it was exposed to erosion, threatening a nearby residential community, but the floods receded before any serious harm was done. The failed sections were repaired with grouted riprap, which can still be seen today.
In early 2005, even more severe floods that also caused flooding along area streams such as San Diego Creek and Aliso Creek impacted the San Juan watershed, with an all-time highest flow of 33,650 cubic feet per second (953 m3/s) recorded on January 11. Although the floods did not exceed the San Juan Creek channel capacity of 58,800 cubic feet per second (1,670 m3/s), the west levee of the channel inside San Juan Capistrano nearly failed. Also in 2005, pumps were installed on Tick and Dove Creeks (tributaries of Bell Canyon, which flows into San Juan Creek) to remove urban runoff stemming from a 1,100-acre (4.5 km2) residential community on a nearby ridge. The pumps remove excess flow and divert it to storage basins for later use as reclaimed irrigation water.
In May 2009, it was announced that levee repairs along San Juan Creek would close a popular bikeway for up to two years, with repairs finished later in 2013. This spurred protests from many area residents who are common users of the path.
Although most streams in the San Juan watershed are less developed than those in the neighboring Aliso Creek and Salt Creek watersheds, San Juan, Oso and Trabuco Creeks have undergone an extensive series of modifications designed to control floods, reduce excessive erosion, and provide reclaimed water for irrigation. A growing amount of urban runoff flows into the creek and its tributaries, adding to the excessive perennial flow referred to often as a "nuisance flow" or "dry season nuisance flow". Historically, only San Juan and Trabuco creeks were known to be perennial, while most of the tributaries, except for spring-fed ones such as Holy Jim Creek, were ephemeral. Oso Creek was formerly ephemeral, but currently it can flow in excess of 100 cubic feet per second (2.8 m3/s) in up to ten percent of an year. Finally, the long series of human-made modifications to the creek have resulted in its mouth, Doheny State Beach, placing tenth in the most polluted beaches of California.
San Juan Creek is channelized for approximately 3.5 miles (5.6 km) from immediately upstream of the Interstate 5 bridge to the mouth. Trabuco Creek is only channelized for several hundred yards above its confluence with the larger stream. In sharp contrast is Oso Creek, which is channelized along nearly its entire length, while Bell Canyon Creek is free-flowing. Two large reservoirs, Upper Oso and Lake Mission Viejo, are built on Oso Creek, with a total storage capacity of roughly 7,500 acre feet (0.0093 km3). While Lake Mission Viejo is primarily for recreation, the 115-acre (0.47 km2) Upper Oso Reservoir collects Oso Creek water and diverts it for irrigation use, while any low-flow spillage that occurs over its dam is collected at a small downstream dam that feeds a pipe that pumps it back to the reservoir; in this way the Upper Oso Reservoir can be considered as a pumped-storage operation, although it does not produce hydroelectricity. A notable aspect of the reservoir is that it was vital in providing water to extinguish a large wildfire in October 2002. The dam is rockfill, 800 feet (240 m) long and 142 feet (43 m) high.
A few check dams exist on small upper tributaries of San Juan Creek, mostly inside the Cleveland National Forest, as well as a small, abandoned gabion structure lower on San Juan Creek. The structure, which was formerly a small dam, is now out of operation, but its roughly 3-to-4-foot (0.91 to 1.2 m) drop still poses a problem for migrating steelhead trout. There are a few water diversion weirs that exist on San Juan tributary streams to divert water for irrigation, ranching and limited municipal uses, but due to limited flows and polluted water, the usefulness of these structures are limited.
A number of drop structures, which are small dams used to control water velocity, exist on streams in the San Juan watershed, primarily also on Trabuco and Oso creeks. On Trabuco Creek, there are eight drop structures, mostly built of riprap. The largest are a 30-foot (9.1 m) cascade immediately downstream of a Metrolink bridge and a concrete drop structure at the terminus of a culvert that crosses underneath Interstate 5; however, neither is inventoried by the Orange County Flood Control Division. There are also about seven drop structures on Oso Creek, most of which are also built of riprap. The mainstem San Juan Creek does not have any notable drop structures, dams or water diversions.
As with channelization, levees are only found in the lower San Juan watershed. San Juan Creek is bounded with levees from upstream of Interstate 5 to very near its mouth at Doheny Beach, while Trabuco Creek has levees from upstream of Del Obispo Street (a continuation of the Ortega Highway) downstream to its mouth at San Juan Creek. Oso Creek has some raised banks, but it is not certain if those are levees. Smaller tributaries, such as El Horno Creek and Bell Canyon, do not have levees. Although the San Juan and Trabuco Creek levees are said to have a "fairly high level of protection currently", failure scenarios of levees in the San Juan watershed have been extensively studied, and they have been determined to possibly fail for a variety of reasons, some of which have already been demonstrated in the floods of 1996 and 2005. In response to the danger of another flood, work has begun on a new west-bank levee replacement that will finish in 2013.
||Aliso Creek||Trabuco Creek||Christianitos Canyon|
|Salt Creek||Prima Deshecha Cañada|
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