Topanga Lagoon

GENERAL

Source

Site Mouth of Topanga Canyon

Map Topanga 7.5' USGS quadrangle

Location Los Angeles County just east of the City of Malibu, partially within Topanga State Beach.

Contacts Los Angeles County, Department of Beaches and Harbors, 310-305-9503

Resource Conservation District of the Santa Monica Mountains, 310-455-1030

Santa Monica Bay Restoration Project, 213-266-7516

Approximate Wetland Acreage 2.1
1

Approximate Historic Acreage Not specified

Ownership Owner Acres Source

Los Angeles County Acreage refers to the entire state beach, all of which is south of Hwy 1. 31 2

Private Upstream of Hwy 1 Not specified 1

LAND USE

Source

Land Use Designation The area north of Hwy 1 between Old Malibu Road and Topanga Canyon Blvd is designated Commercial in the 1986 County of Los Angeles General Plan; the area south of Hwy 1 is State Park.
9

Onsite Use Hwy 1 crosses the creek mouth. The area south of Hwy 1 is within Topanga State Beach; the creek corridor north of Hwy 1 is undeveloped.
1, 7, 2

Historic Use No information specific to the lagoon. The Santa Monica Mountains watershed as a whole followed a pattern of native american homelands giving way to vast spanish ranches, with urban development picking up after WWII.
1

Adjacent Use The surrounding beach area south of Hwy 1 is part of Topanga State Beach; there is a parking lot on top of the coastal bluff immediately east of the creek. North of Hwy 1 there is scattered residential and commercial development atop the creek banks and coastal terrace, including Topanga Canyon Road which follows the east side of the canyon.
2, 7

Historic Adjacent Use Reference documents summarized changes in the Santa Monica Mountains watershed as a whole; since the early 1800's land uses have shifted from native american homelands to vast spanish ranches, with urban development beginning in earnest after WWII. The steep mountain terrain slowed urbanization of this area relative to the broader coastal plains of Los Angeles.
1

HYDROLOGY

Source

Tidal Influence Lagoon system described as intermittent, forming behind a beach berm after seasonal rains. An informal arrangement between County Parks and the Department of Fish and Game allows the County to breach the berm on a restricted basis to prevent flooding.
1, 2, 6

Watershed Area 18 square miles
2

Tributaries and Flow Tributary Flow Source

Topanga Creek Flows are intermittent, seasonal; the peak flow rate at the mouth of the lagoon for a 50-year rainfall was calculated in 1993 to be 25,200 cfs (model assumed burn conditions and an undeveloped watershed). The Creek is described as "notorious for flooding". The creek bed is natural for most of its length, however in the lower reaches where development has occurred, the bed has been lined with boulders and concrete, and the banks have been sandbagged. 3, 2, 1, 11

Dams None
1

Other Sources No storm drains empty into Topanga Creek.
1

WATER QUALITY

Source

General 1993 study reported absence of sewer hookups for many residences along the creek; the effect on water quality was not quantified. Included in draft 1996 list of impaired water bodies in the LA Region, selected standards exceeded for lead. Beneficial Uses are: nav, rec1, rec2, comm, est, wild, rare, migr, spwn, and wet.
1, 4, 5

Dissolved Oxygen (DO) April 1996 - February 1997, samples taken approximately semi-monthly, 1.5 miles upstream of the mouth found concentrations from 7.1 to 8.8 mg/l. The temperature range was 11-24 C.
12

Water Salinity April and May readings 1.5 miles upstream of the mouth were both 1.0 ppm. The lagoon is described as brackish and a 1993 study reported marine vegetation in the lower creek.
3, 1, 12

Sedimentation No quantitative data located, but several instances of severe bank erosion near the mouth of the creek were noted in a 1993 report.
1

SOIL

Source

Soil Gaviota-Millsholm association; soils of this classification are moderately deep and well-drained.
1

Habitat Acres Vegetation

Riparian 2.1 1993 - Dominated by western sycamore, alder, willow and mulefat; giant reed*, bamboo*, and nasturtium* also established. 1

ANIMAL USE

Source

Birds No data located

Fish No data located

Benthic Invertebrates No data located

Insect No data located

Other Wildlife No data located

Special Status Species No data located

OUTLOOK

Source

Enhancement Status A conceptual enhancement plan was prepared for the site in 1993 as part of the Santa Monica Bay Project. It had not been implemented as of Fall, 1996. A 1993 watershed management study (see watershed management) includes recommendations for construction policies to promote streambank stablilization and calls for establishment of a riparian revegetation program and the restoration of a functional estuary at the mouth.
1, 10

Watershed Management The Topanga Creek Watershed Management Study was prepared by a citizens advisory committee in April 1996, at the direction of the Los Angeles County Board of Supervisors. This plan proposes a variety of measures for reducing peak flow runoff, erosion, sedimentation,and flood hazard while protecting riparian habitat, infrastructure and existing development. The Creek is also within the watershed of the Santa Monica Bay, a National Estuary and subject of a comprehensive restoration plan. A major focus of the plan is the reduction of point and nonpoint pollution in the watershed.
8, 10

Pressure Development in the floodplain and atop streambanks, bank erosion, off-road creek crossings, lack of sewer hook-ups, exotic vegetation.
1

SOURCES

1 Romberg Tiburon Centers and Philip Williams and Associates. 1993. Wetland Inventory and Restoration Potential, Santa Monica Bay Watershed. 111 pp. Report prepared for the Santa Monica Bay Restoration Project identifying potential wetland restoration projects at: the Ballona wetlands complex, Lower Topanga Canyon, Malibu Lagoon, Upper Medea Creek, and Trancas Lagoon. The discussion includes a history of land use in the watershed and the effects on wetlands. It also describes the current extent of wetlands based on mapping of aerial photographs. Conceptual restoration plans for the 5 sites outline existing conditions, identify opportunities and constraints as well as goals and objectives and estimate implementation costs.

2 County of Los Angeles Department of Beaches and Harbors. 1986. Resource Inventory: Las Tunas, Topanga and Will Rogers State Beaches. ~ 200 pp. Documents the cultural and natural resources of Las Tunas, Topanga, and Will Rogers State Beaches. It describes the topographic, climatic, hydrologic, and geologic settings for each site (resources described are all oceanside of Hwy 1) as well as general descriptions of habitats and wildlife expected or observed. Aesthetic, cultural and recreation resources are also identified. The inventory is based on field visits and existing information.

3 Wetlands Research Associates. 1990. Port of Los Angeles Local Wetland Mitigation Program. ~ 80 pp. Prepared for the Port of Los Angeles, this report provides brief descriptions of 13 sites in coastal LA County in terms of their physical attributes, habitat quality, and opportunities and constraints for enhancement. Sites included are: Zuma Beach, Malibu Lagoon, Topanga Canyon, Oxford Flood Control Basin, Venice Canals, Ballona Lagoon, Ballona Wetlands, Del Rey Lagoon, El Segundo Dunes, Madrona Marsh, Sanitary District Wetland, Machado Lake, and Cabrillo Tidal Salt Marsh. In addition, slightly expanded (7-8 pp) evaluations of enhancement opportunities and feasibility are provided for Del Ray Lagoon, Machado Lake, and Zuma Beach.

4 California Regional Water Quality Control Board, Los Angeles Region. 1994. Water quality control plan Los Angeles Region. 200 pp., plus appendices. The plan designates beneficial uses and associated water quality objectives for inland surface waters, ground waters, coastal waters, and wetlands for the Los Angeles and Santa Clara River Basins. It includes a discussion of applicable policies and statutory requirements and identifies measures for achieving water quality objectives. It also describes ongoing monitoring and assessment programs.

5 Los Angeles Regional Water Quality Control Board. 1996. Water Quality Assessment and Documentation. Approx 100 pp. A list of waterbodies in the Los Angeles and Ventura County coastal watersheds that do not or are not expected to attain water quality standards after application of required technology-based controls. It includes a description of the methods and criteria used in the assessment. 303(d) lists are prepared as part of the Water Quality Assessment of the State's major waterbodies, and meet a requirement of section 303(d) of the federal Clean Water Act.

6 Gregory Woodell, Los Angeles County Department of Beaches and Harbors. Personal Communication, October 3, 1996.

7 Department of Water Resources. 1993. Aerial Photograph. Section 2, Flight Line 58-5. 1:12,000 aerial photograph of the coast showing lower Topanga Creek, taken April 14, 1993.

8 Santa Monica Bay Restoration Project. 1994. Public summary of the Santa Monica Bay Restoration Plan. 68 pp. Public information document describing the restoration planning effort in the Bay. It explains the values of the aquatic and wetland resources and how they are affected by activities in the watershed. It also provides a summary of current resource conditions and describes the strategy and specific actions for improving and protecting Bay health.

9 Wayne Zimmer. Los Angeles County Department of Regional Planning. Personal communication, October 22, 1996.

10 Topanga Canyon Floodplain Management Citizens' Advisory Committee. 1996. Topanga Creek Watershed Management Study. 13 pp. and appendices. Prepared for the Los Angeles County Board of Supervisors. This study was prepared by the a citizens' advisory committee to the Los Angeles Board of Supervisors to develop alternative strategies for limiting flood hazards in the watershed. This master plan makes specific recommendations for policies and additional research that would result in reduced peak runoff, erosion, sedimentation and flood hazard, while protecting riparian habitat, and existing development. Appendices include an evaluation of the method used by the Los Angeles Department of Public Works to calculate flood risk, a monetary valuation of the stabilizing function of riparian vegetation, and documentation of the plan's consistency with local land use plans.

11 Los Angeles County Department of Public Works. 1993. Topanga Canyon Floodway 50-year frequency rainfall Q's cfs, preliminary map. A preliminary map showing calculated peak flows in Topanga Creek where it is joined by each sub-drainage, for a 50-year frequency rainfall. The calculation assumes a completely undeveloped, burned watershed. The boundary, existing and proposed drains, debris basins, and watercourses of the Topanga watershed are also shown on the 1:1000 scale map.

12 Hafner, Nancy, Santa Monica Mountains Conservancy. Personal communication, February, 1997. Unpublished water quality data. 1 pp. Listing of temperature, D.O. and salinity readings taken 1.5 miles upstream of the mouth of Topanga Creek, between April,1996 and February, 1997. Total and fecal coliform, pH and nutrients were also sampled as part of an overall water quality analysis and Master's thesis investigation.

Webmaster: wetlands@resources.ca.gov

GENERAL			Source
Site	Mouth of Topanga Canyon
Map	Topanga 7.5' USGS quadrangle
Location	Los Angeles County just east of the City of Malibu, partially within Topanga State Beach.
Contacts	Los Angeles County, Department of Beaches and Harbors, 310-305-9503
	Resource Conservation District of the Santa Monica Mountains, 310-455-1030
	Santa Monica Bay Restoration Project, 213-266-7516
Approximate Wetland Acreage	2.1		1
Approximate Historic Acreage	Not specified
Ownership	Owner	Acres	Source
	Los Angeles County Acreage refers to the entire state beach, all of which is south of Hwy 1.	31	2
	Private Upstream of Hwy 1	Not specified	1


LAND USE			Source
Land Use Designation	The area north of Hwy 1 between Old Malibu Road and Topanga Canyon Blvd is designated Commercial in the 1986 County of Los Angeles General Plan; the area south of Hwy 1 is State Park.		9
Onsite Use	Hwy 1 crosses the creek mouth. The area south of Hwy 1 is within Topanga State Beach; the creek corridor north of Hwy 1 is undeveloped.		1, 7, 2
Historic Use	No information specific to the lagoon. The Santa Monica Mountains watershed as a whole followed a pattern of native american homelands giving way to vast spanish ranches, with urban development picking up after WWII.		1
Adjacent Use	The surrounding beach area south of Hwy 1 is part of Topanga State Beach; there is a parking lot on top of the coastal bluff immediately east of the creek. North of Hwy 1 there is scattered residential and commercial development atop the creek banks and coastal terrace, including Topanga Canyon Road which follows the east side of the canyon.		2, 7
Historic Adjacent Use	Reference documents summarized changes in the Santa Monica Mountains watershed as a whole; since the early 1800's land uses have shifted from native american homelands to vast spanish ranches, with urban development beginning in earnest after WWII. The steep mountain terrain slowed urbanization of this area relative to the broader coastal plains of Los Angeles.		1


HYDROLOGY			Source
Tidal Influence	Lagoon system described as intermittent, forming behind a beach berm after seasonal rains. An informal arrangement between County Parks and the Department of Fish and Game allows the County to breach the berm on a restricted basis to prevent flooding.		1, 2, 6
Watershed Area	18 square miles		2
Tributaries and Flow	Tributary	Flow	Source
	Topanga Creek	Flows are intermittent, seasonal; the peak flow rate at the mouth of the lagoon for a 50-year rainfall was calculated in 1993 to be 25,200 cfs (model assumed burn conditions and an undeveloped watershed). The Creek is described as "notorious for flooding". The creek bed is natural for most of its length, however in the lower reaches where development has occurred, the bed has been lined with boulders and concrete, and the banks have been sandbagged.	3, 2, 1, 11
Dams	None		1
Other Sources	No storm drains empty into Topanga Creek.		1


WATER QUALITY			Source
General	1993 study reported absence of sewer hookups for many residences along the creek; the effect on water quality was not quantified. Included in draft 1996 list of impaired water bodies in the LA Region, selected standards exceeded for lead. Beneficial Uses are: nav, rec1, rec2, comm, est, wild, rare, migr, spwn, and wet.		1, 4, 5
Dissolved Oxygen (DO)	April 1996 - February 1997, samples taken approximately semi-monthly, 1.5 miles upstream of the mouth found concentrations from 7.1 to 8.8 mg/l. The temperature range was 11-24 C.		12
Water Salinity	April and May readings 1.5 miles upstream of the mouth were both 1.0 ppm. The lagoon is described as brackish and a 1993 study reported marine vegetation in the lower creek.		3, 1, 12
Sedimentation	No quantitative data located, but several instances of severe bank erosion near the mouth of the creek were noted in a 1993 report.		1


SOIL			Source
Soil	Gaviota-Millsholm association; soils of this classification are moderately deep and well-drained.		1
Habitat	Acres	Vegetation
Riparian	2.1	1993 - Dominated by western sycamore, alder, willow and mulefat; giant reed, bamboo, and nasturtium* also established.	1


ANIMAL USE			Source
Birds	No data located
Fish	No data located
Benthic Invertebrates	No data located
Insect	No data located
Other Wildlife	No data located
Special Status Species	No data located


OUTLOOK			Source
Enhancement Status	A conceptual enhancement plan was prepared for the site in 1993 as part of the Santa Monica Bay Project. It had not been implemented as of Fall, 1996. A 1993 watershed management study (see watershed management) includes recommendations for construction policies to promote streambank stablilization and calls for establishment of a riparian revegetation program and the restoration of a functional estuary at the mouth.		1, 10
Watershed Management	The Topanga Creek Watershed Management Study was prepared by a citizens advisory committee in April 1996, at the direction of the Los Angeles County Board of Supervisors. This plan proposes a variety of measures for reducing peak flow runoff, erosion, sedimentation,and flood hazard while protecting riparian habitat, infrastructure and existing development. The Creek is also within the watershed of the Santa Monica Bay, a National Estuary and subject of a comprehensive restoration plan. A major focus of the plan is the reduction of point and nonpoint pollution in the watershed.		8, 10
Pressure	Development in the floodplain and atop streambanks, bank erosion, off-road creek crossings, lack of sewer hook-ups, exotic vegetation.		1


SOURCES
1	Romberg Tiburon Centers and Philip Williams and Associates. 1993. Wetland Inventory and Restoration Potential, Santa Monica Bay Watershed. 111 pp. Report prepared for the Santa Monica Bay Restoration Project identifying potential wetland restoration projects at: the Ballona wetlands complex, Lower Topanga Canyon, Malibu Lagoon, Upper Medea Creek, and Trancas Lagoon. The discussion includes a history of land use in the watershed and the effects on wetlands. It also describes the current extent of wetlands based on mapping of aerial photographs. Conceptual restoration plans for the 5 sites outline existing conditions, identify opportunities and constraints as well as goals and objectives and estimate implementation costs.
2	County of Los Angeles Department of Beaches and Harbors. 1986. Resource Inventory: Las Tunas, Topanga and Will Rogers State Beaches. ~ 200 pp. Documents the cultural and natural resources of Las Tunas, Topanga, and Will Rogers State Beaches. It describes the topographic, climatic, hydrologic, and geologic settings for each site (resources described are all oceanside of Hwy 1) as well as general descriptions of habitats and wildlife expected or observed. Aesthetic, cultural and recreation resources are also identified. The inventory is based on field visits and existing information.
3	Wetlands Research Associates. 1990. Port of Los Angeles Local Wetland Mitigation Program. ~ 80 pp. Prepared for the Port of Los Angeles, this report provides brief descriptions of 13 sites in coastal LA County in terms of their physical attributes, habitat quality, and opportunities and constraints for enhancement. Sites included are: Zuma Beach, Malibu Lagoon, Topanga Canyon, Oxford Flood Control Basin, Venice Canals, Ballona Lagoon, Ballona Wetlands, Del Rey Lagoon, El Segundo Dunes, Madrona Marsh, Sanitary District Wetland, Machado Lake, and Cabrillo Tidal Salt Marsh. In addition, slightly expanded (7-8 pp) evaluations of enhancement opportunities and feasibility are provided for Del Ray Lagoon, Machado Lake, and Zuma Beach.
4	California Regional Water Quality Control Board, Los Angeles Region. 1994. Water quality control plan Los Angeles Region. 200 pp., plus appendices. The plan designates beneficial uses and associated water quality objectives for inland surface waters, ground waters, coastal waters, and wetlands for the Los Angeles and Santa Clara River Basins. It includes a discussion of applicable policies and statutory requirements and identifies measures for achieving water quality objectives. It also describes ongoing monitoring and assessment programs.
5	Los Angeles Regional Water Quality Control Board. 1996. Water Quality Assessment and Documentation. Approx 100 pp. A list of waterbodies in the Los Angeles and Ventura County coastal watersheds that do not or are not expected to attain water quality standards after application of required technology-based controls. It includes a description of the methods and criteria used in the assessment. 303(d) lists are prepared as part of the Water Quality Assessment of the State's major waterbodies, and meet a requirement of section 303(d) of the federal Clean Water Act.
6	Gregory Woodell, Los Angeles County Department of Beaches and Harbors. Personal Communication, October 3, 1996.
7	Department of Water Resources. 1993. Aerial Photograph. Section 2, Flight Line 58-5. 1:12,000 aerial photograph of the coast showing lower Topanga Creek, taken April 14, 1993.
8	Santa Monica Bay Restoration Project. 1994. Public summary of the Santa Monica Bay Restoration Plan. 68 pp. Public information document describing the restoration planning effort in the Bay. It explains the values of the aquatic and wetland resources and how they are affected by activities in the watershed. It also provides a summary of current resource conditions and describes the strategy and specific actions for improving and protecting Bay health.
9	Wayne Zimmer. Los Angeles County Department of Regional Planning. Personal communication, October 22, 1996.
10	Topanga Canyon Floodplain Management Citizens' Advisory Committee. 1996. Topanga Creek Watershed Management Study. 13 pp. and appendices. Prepared for the Los Angeles County Board of Supervisors. This study was prepared by the a citizens' advisory committee to the Los Angeles Board of Supervisors to develop alternative strategies for limiting flood hazards in the watershed. This master plan makes specific recommendations for policies and additional research that would result in reduced peak runoff, erosion, sedimentation and flood hazard, while protecting riparian habitat, and existing development. Appendices include an evaluation of the method used by the Los Angeles Department of Public Works to calculate flood risk, a monetary valuation of the stabilizing function of riparian vegetation, and documentation of the plan's consistency with local land use plans.
11	Los Angeles County Department of Public Works. 1993. Topanga Canyon Floodway 50-year frequency rainfall Q's cfs, preliminary map. A preliminary map showing calculated peak flows in Topanga Creek where it is joined by each sub-drainage, for a 50-year frequency rainfall. The calculation assumes a completely undeveloped, burned watershed. The boundary, existing and proposed drains, debris basins, and watercourses of the Topanga watershed are also shown on the 1:1000 scale map.
12	Hafner, Nancy, Santa Monica Mountains Conservancy. Personal communication, February, 1997. Unpublished water quality data. 1 pp. Listing of temperature, D.O. and salinity readings taken 1.5 miles upstream of the mouth of Topanga Creek, between April,1996 and February, 1997. Total and fecal coliform, pH and nutrients were also sampled as part of an overall water quality analysis and Master's thesis investigation.