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Friends of Corte Madera Creek




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Topics discussed on this page include: Location, Rainfall and Streamflow, Flooding, Plants and Animals in the Watershed, Development History, Land Management, Problems in an Urban Watershed

(View Relief Map [49K] )
Shown here: San Anselmo and Mount Tamalpais

San Anselmo-Mt. Tamalpais The Corte Madera Creek watershed is located in the eastern urbanized corridor of Marin County, California, and reaches from San Francisco Bay into the foothills of Mount Tamalpais, in the Coast Range. It is bounded on the west by a steep, forested ridge running northwest from the East Peak of Mt. Tamalpais (elevation 2,571 ft) to Pine Mountain and then north-northeast to White's Hill (elevation 1,430 ft).

San Anselmo and Fairfax creeks rise along these ridges and drain steep upland areas onto relatively steep and narrow valley flats; these creeks combine as San Anselmo Creek in the town of Fairfax. San Anselmo Creek then flows southeast through Ross Valley, bounded by a sandstone ridge running southeast. Several intermittent tributaries rise on the grassland and grass-oak woodland-covered hills along the northern and eastern edges of the basin. Sleepy Hollow Creek joins San Anselmo Creek in San Anselmo near Saunders Avenue. Ross Creek is a major tributary descending from the northern flank of Mount Tamalpais to join San Anselmo Creek in Ross. The channel is called Corte Madera Creek from the Ross Creek confluence to San Francisco Bay Estuary, and for a mile of its length it is encased by a concrete-lined channel. It drains into a tidal salt marsh at Kentfield, and then into San Francisco Bay near Corte Madera. Larkspur Creek and Tamalpais Creek are the only major tributaries to Corte Madera Creek that enter downstream from the concrete channel. Corte Madera Creek has approximately 29 named tributaries, with an aggregate length of approximately 44 miles. In addition to these streams, Phoenix Lake, which covers 28 acres, is located above Ross, and is an impoundment of Ross Creek.

For more information:
LocationMap.pdf (91.1 KB)
Streams.pdf (76 KB)
WatershedMap.pdf (448 KB)

Rainfall and Streamflow
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Shown here: Ephemeral stream near Fairfax

Fairfax Waterfall The average annual rainfall for the period October 1979 through September 1996 measured by Roy Farrington Jones on Olive Avenue in Ross was 49.33 inches. The lowest rainfall during that period was 28.29 inches in water year 1990 (October 1989 through September 1990) and the highest, 90.75 inches during water year 1983.

Average annual rainfall at the Marin Municipal Water District gage at Lake Lagunitas for the period 1875 to 1995 was 52.63 inches. Although this gage is not within the watershed, it is representative of rainfall in Kentfield, Ross, and San Anselmo. The lowest value during that period was 19.70 inches for water year 1924; the highest, 112.15 inches for water year 1890.

Between 1951 and 1993, the U.S. Geological Survey maintained a stream gage just upstream of the Lagunitas Road Bridge in Ross. Since 1993, the Marin County Department of Public Works has gathered data at the gage. Between 1951 and 1993, the lowest flows occurred July through September 1977 when the stream was dry. The highest flows occurred in early January 1982, when the peak flow within the channel was 6000 cubic feet per second.

For more information:
Discharge.pdf (44 KB)

Fairfax Flooding Flooding
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Shown here: Bolinas Avenue, Fairfax, January 1982

Between 1914 and 1960 there were twelve damaging floods of the valley floor or about one flood every four years. Since 1960 damaging floods have occurred less frequently for several reasons, including better creek maintenance, construction of a concrete channel in Kentfield and Ross, and the fact that 14 out of the 38 years were relatively dry with rainfall between 42% and 75% of the average. Even so, the largest and third largest floods of record occurred during this time, in January 1982 and March 1983. The flood of January 3-5, 1982 was the largest on record and caused considerable damage in San Anselmo, Ross, Kentfield, and Larkspur. Flood water 4 to 5 feet deep flowed down Poplar and Kent avenues with enough force to move cars. On February 2, 1998, just as water began to come out of the channel at the Lagunitas Road bridge and at Granton Park, the rain eased up and the water level dropped. A flood on December 31, 2005 reached levels only slightly below those of the 1982 flood, and has spurred town and county officials to initiate an ambitious program to reduce future flooding. Many creekside homeowners have raised their houses to reduce damage from future flooding.

For more information:
History of Flood Management

Spotted Owl

Harvest Mouse

Rainbow Trout

Plants and Animals in the Watershed
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Shown here: Northern spotted owl, salt harvest mouse, juvenile rainbow trout

The natural communities of the watershed reflect the variety of local soil types, drainage patterns, elevations, slope, and orientations to sun and wind. The following natural communities are found in the watershed: Northern Coastal Scrub, Chaparral, Grasslands, Coastal Salt Marsh, Freshwater Marsh, Vernal Marsh (Seasonal Wetland), Coastal Riparian Forest, Valley Oak Woodland and Oak Savannah, Coast Live Oak Woodland, and Mixed Evergreen Forest. A number of rare plant species are found in or adjacent to our watershed, especially where serpentine is exposed. There is substantial urban and suburban development within the watershed, so habitats in the watershed also include suburban gardens, urban parks and roadsides.

Our watershed provides habitat to species that have adapted well to urban and suburban development, including mule deer, raccoon, opossum, skunks, numerous birds, and a variety of reptiles and amphibians. Mountain lions, coyotes and river otters are occasional visitors. The federally endangered California clapper rail and salt marsh harvest mouse and the threatened northern spotted owl occur in the watershed.

Over the years, sightings of adult steelhead (Oncorhynchus mykiss), coho salmon (O. kisutch) and Chinook salmon (O. tshawytscha) have been reported for the Corte Madera Creek watershed. These fish migrate from the ocean to spawn in the shallow headwater streams where they hatched, although pairs of Chinook salmon seen in 2001and 2003 were probably strays from the Sacramento River. Coho salmon sightings in winter were quite common up to the 1970s, when degradation of its habitat ended spawning runs; in some years during the 1950s spawning fish were so plentiful on the Drake High School campus that students could gather them up. Unlike coho and Chinook salmon, steelhead survive spawning, returning immediately to the ocean, so are not often seen as adults. However summer surveys of pools continue to record them in fair numbers, especially in upper San Anselmo and Cascade creeks in Fairfax. Among the many consequences of urbanization that have diminished the steelhead run, the construction of the mile-long concrete channel in Ross and Kentfield was the most dramatic: in 1971, immediately after the channel's completion, steelhead was still the dominant species by number in Ross, while surveys conducted in 1973-1975 showed that it had been relegated to a minor species. Steelhead is classified as a threatened species under the federal Endangered Species Act, and this status provides leverage for improving creek habitat in our watershed, to the benefit of all species. (Some members of the species O. mykiss, the same species as steelhead, spend their entire lives in freshwater, in which case they are called rainbow trout. It is possible that some of the adult fish found in Corte Madera Creek watershed are rainbow trout.)

For more information:
Fish&Wildlife.pdf (204 KB)
FisheriesES.pdf (52KB)
NatCommPlants.pdf (290 KB)
PlantID InvasivePlants.pdf(332 KB)
PlantID Native Shrubs and Vines.pdf
PlantID Native Trees.pdf (52KB)
San Anselmo Creeks Survey (pdf)

Kent Home Development History
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Shown here: The Kent home, built in 1873; photo courtesy Ross Historical Society

"A tract of park-like land, shaded by ancient trees with a sparkling stream running through it" was how Dr. Taliaferro described Ross Valley in 1849. The Coast Miwok practice of burning grasslands, and subsequent Mexican cattle ranching, had suppressed the growth of shrubs under the large oaks of the valley floor and created the scene he encountered. Soon, logging and increasingly intensive livestock grazing made their mark. Redwood and Douglas-fir forests were clear-cut for lumber; oak woodland was harvested for firewood and tan bark; intervening grassland was grazed or cut for hay; and brickworks operated at Larkspur and on the San Quentin peninsula. The bulk of the produce was shipped to San Francisco, via Larkspur and Ross Landing in today's Kentfield.

By 1900 small communities were forming the nuclei of Corte Madera, Larkspur, San Anselmo, and Fairfax, served by a railroad from Sausalito, and the valley was dotted with grand landscaped estates. The population grew slowly until the opening of the Golden Gate Bridge in 1937; growth accelerated in the post-Word War II housing boom, and by the 1950s the last dairies in Sleepy Hollow and in the Sorich Creek basin had been closed. The lower reaches of the watershed have mostly been developed; parts of the remaining areas have been set aside as parks and nature reserves. Intermediate elevations are characterized by low-density residential development. The upper reaches of the watershed are dedicated to recreation and domestic local water supply. The areas where large development projects can occur are very few, but in-fill development and redevelopment of existing residential and urban areas is continual.

Land Management and Regulatory Authority
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Shown here: View from Azalea Hill, managed by the Marin Municipal Water District, after a rare snowfall; the Marin Cricket Club playing in Piper Park, Larkspur; Marta's Marsh, Corte Madera; Corte Madera Creek passing through Greenbrae

Entities with land management responsibility over the watershed include: State Department of Parks and Recreation; California Department of Fish and Game; Golden Gate Bridge and Transportation District; Marin Municipal Water District; Marin Community College District; Marin County Open Space District; and Marin County Parks Department. There are several public school districts that enjoy considerable freedom from local jurisdiction, although they are expected to follow state and federal regulations protecting natural resources and air and water quality.

Azlea Hill

Piper Park

San Anselmo-Mt. Tamalpais

San Anselmo-Mt. Tamalpais

Land use falls into five broad categories:

1. Open Space or Resource Protection: Marin Municipal Water District manages a significant part of the upper reaches of the southern and western sides of the watershed. All or part of eight Open Space Preserves managed by the Marin County Open Space District are in the watershed; these areas are also in the upper reaches of the watershed. Sorich Ranch Park is managed by the Town of San Anselmo. A small part of Mount Tamalpais State Park is within the watershed. The California Department of Fish and Game manages the Corte Madera Ecological Reserve, located south of the Ferry Terminal along San Francisco Bay.
2. Developed Parks: Creekside Park, including the multi-use path along the creek, is a county park located in Kentfield; the path reaches from the Ferry Terminal into the Town of Ross. Deer Park in Fairfax is also a county park. Local communities maintain several parks within the watershed, nearly all of which are along creeks: Peri Park in Fairfax; Faude, San Anselmo Memorial, Creek, and Robson-Harrington parks in San Anselmo; Ross Common; Piper, Dolliver, Magnolia, Hamilton, Bon Air Landing, Niven, and Remillard parks in Larkspur; and Town, San Clemente, and Granada parks in Corte Madera.
3. Schools: Three high schools and numerous middle schools and elementary schools are near streams. Corte Madera Creek passes through the College of Marin Kentfield campus. Public schools are not under local planning jurisdiction.
4.Suburban Development:
Private property is under the jurisdiction of the incorporated communities of Corte Madera, Fairfax, Larkspur, Ross, and San Anselmo or the County of Marin.
5. Urban Development: This is a mixture of private and public property and includes residential and commercial uses.

Regulatory authority for biological resources is held by the California Department of Fish and Game and three federal agencies: U.S. Army Corps of Engineers, U.S. Fish and Wildlife Service, and NOAA Fisheries. Agencies dealing with water resources include the Environmental Protection Agency, California Environmental Protection Agency, and California Water Resources Control Board (both the Division of Water Rights and the Regional Water Quality Control Board). Some kinds of activities may involve the San Francisco Bay Conservation and Development Commission and/or the State Lands Commission. The State Department of Water Resources Division of Dam Safety has jurisdiction over repairs or changes to the dam at Phoenix Lake.

Regulations that apply state-wide and that are implemented by state and federal agencies include the Clean Water Act, the federal Endangered Species Act, the California Endangered Species Act, and the California Native Plant Protection Act. Marin County and each of the incorporated communities within the watershed have some planning and land use tools that can be used to protect the integrity of the watershed. They may include such things as setbacks for development along drainages, policies for the protection of large trees, or other measures implemented at the discretion of local jurisdictions.

Jurisdictions with land use and planning authority within the watershed include the State of California, Marin County, and the incorporated communities of Corte Madera, Fairfax, Larkspur, Ross, and San Anselmo.

For more information:
Community Map.pdf (251KB)

Problems in the Urbanized Watershed
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Shown here: American egret

Urbanization not only affects habitat in obvious ways-for example, direct loss of habitat, channelization of streams, degradation of water quality, and dewatering of streams-but it can also affect habitat in more subtle ways by altering and disrupting ecosystem processes that can have unintended impacts to aquatic ecosystems through increased flooding, channel erosion, landslides, and aquatic habitat destruction. It is impossible to separate the overlapping and interrelated impacts of urbanization; however, the following broad categories are used to provide more detail. Friends of Corte Madera Creek Watershed addresses all of these issues in its work.

Alteration of Natural Vegetation

Urbanization causes severe and permanent alteration of the natural vegetation when the vegetation is removed or converted to lawns and ornamental plants. In upland areas urbanization contributes to erosion and altered drainage, often reducing infiltration and increasing surface runoff. Impacts are particularly severe in riparian corridors, that under natural conditions are extremely rich in wildlife. Vegetation is commonly removed to increase the visibility of and access to streams and to allow the installation of landscaping and structures near the tops of stream banks. Loss of riparian vegetation reduces inputs of beneficial nutrients, recruitment of large woody debris, and stream-bank stability and increases the input of sediment and other pollutants in runoff by reducing the filtering effect of vegetation. It also leads to an increase in stream temperature by removing much of the overhead canopy. In spite of these impacts, what remains of our creek corridors constitutes a refuge for native trees and wildlife on the valley floor.

Disrupted Hydrological Processes and Reduced Stream Complexity
Shown here: Abandoned home at the former Marin Town and Country Club, Fairfax

Abandoned home Construction and landscaping near streams is often followed by the installation of retaining walls and other hard structures intended to protect or enlarge developed areas. In downtown San Anselmo, buildings hang over San Anselmo Creek and foundations rest on the creek bed. The course of Fairfax Creek was changed and it was buried in a culvert, apparently to provide more buildable area near the center of town. This results in severely constricted streams with disrupted or altered hydrological and riparian processes. Furthermore, in developed areas, much of the surface soil is covered by impervious surfaces (buildings, parking lots, roads), which increase peak flows and change channel characteristics. These changes increase the maximum discharge associated with floods and increase the frequency of flooding.

San Anselmo Creek, like many degraded urban streams, has a relatively uniform bed, with few pools or riffles, exposed near-vertical banks downcut by several yards, chronic high sediment loads, is deficient in woody debris, and has severely reduced numbers of aquatic organisms compared to nearby undeveloped streams.

Clearing of vegetation, compaction of soil, installation of roads and other impervious surfaces, and direct interception of subsurface flows by drains damage watershed hydrology. Impervious areas increase winter peak flow and block infiltration into the soil. This results in a reduced groundwater storage and lower summer base flows.

Impaired Water Quality

Urban non-point source pollution includes heavy metals, pesticides, bacteria, organics (oil and grease), dirt, and nutrients. In urbanized streams, the type and quantity of nutrients can change significantly. The important function of large woody debris and leafy detritus in providing nutrients in natural streams is taken over by excessive nutrient loading from sewage and runoff from roads and landscaped areas. The principal effect of excess nutrients upon a stream is the stimulation of algae and other aquatic plant growth, such as can be seen in the lower reaches of Corte Madera Creek during the spring and summer. Water quality testing in our watershed shows high concentrations of E. coli in some locations, especially in the summer. In tidal reaches, Enteroccocus concentrations do not meet the standard for water contact recreation. The San Francisco Bay Regional Water Quality Control Board has listed Corte Madera Creek as impaired because of high diazinon levels.

In 1999, fish biologist Alice Rich placed thermographs at several locations in the creek. During the monitoring, which took place between March and September, she observed elevated temperatures throughout the watershed. The warmest water, which became lethal to young steelhead, was in the upstream end of the concrete flood control channel. Sleepy Hollow Creek had water temperatures during the summer that were generally satisfactory in shaded pools. Several habitat changes caused by urbanization can affect stream temperatures. Loss of riparian vegetation and increased channel width increase the area of unshaded stream surface area, and reduced water depths further contribute to heat loss or gain, increasing diurnal temperature fluctuations. Stream temperatures in urban areas may also be indirectly affected by changes in hydrology, channel morphology, and microclimate. Lower summer base flows resulting from reduced infiltration can also contribute to higher water temperatures.

Barriers to Fish Passage
Shown here: Downstream view of the fish ladder and concrete channel behind Ross Post Office

Ross Channel
Urban development is characterized by high road densities, and the resulting bridges, culverts, and other structures constrain channels and impede fish migration in a variety of ways. The most significant barrier to passage for fish in our watershed is the concrete flood control channel in Kentfield and Ross. It is a velocity barrier for spawning steelhead at high flows because the resting pools are inadequate and it is a thermal barrier to smolts as they swim to the ocean. Other barriers include a very long culvert under downtown Fairfax and various poorly designed fish ladders, weirs, and small dams throughout the watershed. Areas of high temperature and poor water quality can also present barriers to passage.

For more information:
BarriersCMC.pdf (135KB)

Degraded Biological Diversity and Habitat Suitability
Shown here: Isolated section of creek in downtown San Anselmo

Isolated Creek
The abundance and diversity of aquatic organisms are greatly altered by urban impacts. The key to protecting and restoring urban streams appears to be reducing the imperviousness of surfaces associated with urban development, and protecting channel integrity and riparian vegetation. It has been observed that stream quality impairment is first observed when watershed imperviousness reaches 15% of the total watershed, and becomes severe at 30%. For stream ecosystems containing self-sustaining steelhead populations, some experts recommend that watershed imperviousness should not exceed 10%. At this level, creek flows are not radically changed, and minor pollutants can be filtered out by vegetation and soil. (The figure for the Corte Madera Creek watershed has not yet been determined.) Reducing the amount of runoff and minimizing landscape disturbance also can reduce urban impacts to habitat quality.

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Articles relating to topics covered on this page may be found in Creek News.

Photo in logo: View from Corte Madera to San Quentin Peninsula.

All use of text and photographs for other than personal purposes is prohibited without permission from Friends of Corte Madera Creek Watershed.

All photographs © Charles Kennard unless otherwise credited.

Web site design by Karen Peterson, San Anselmo.

Friends of Corte Madera Creek Watershed
PO Box 415 Larkspur, CA 94977
415-456-5052 (voice) / 415-456-4992 (fax)