Restoration Feasibility Study
and Hydrologic Analysis Of the
Topanga Lagoon and Topanga
Creek Watershed

December 2000


What kind of lagoon and watershed enhancement/restoration design will create a self sustaining lagoon that will improve water quality, assess and minimize flood hazard, restore habitat for steelhead trout and tidewater gobies, and maintain recreational opportunities, without changing the surf break?

The Resource Conservation District of the Santa Monica Mountains, under a grant from the Coastal Conservancy Southern California Wetlands Recovery Project is requesting proposals to prepare a comprehensive feasibility study of the potential for restoring the resources of the Topanga Lagoon and Topanga Creek Watershed. The purpose of this feasibility analysis is to identify and verify the physical characteristics of the existing creek and lagoon, and evaluate several possible restoration alternatives. The Feasibility Study must also outline a phased approach, including the necessary scope of work and budget to produce a sustainable lagoon/watershed restoration plan that can be implemented. The development and implementation of this restoration plan would be a subsequent, separately funded effort.

Many of the elements that would be integrated into the Feasibility Study have been completed or in progress. These include: water movement, water quality, biological resources, erosion and sediment delivery, as well as maps of the present and historic creek channel configurations. The work plan and results of these studies are available through the RCDSMM and/or online. (See references)

The hydrologic analysis needed for the Feasibility Study, however, has not yet been accomplished and is a major part of this RFP. Use of models that can evaluate both continuous storm events and more normal low flow conditions is expected. This information will allow planners to assess the natural and anthropogenic impacts in the watershed to determine the feasibility and potential design constraints impacting a restoration of the historic lagoon, which previously covered a much larger area.

Project Background

Water quantity under a variety of conditions plays a major role in defining creek and lagoon configurations. A clear understanding of how these parameters interact with other physical processes in the watershed is necessary prior to designing a potential restoration plan. The restoration of Malibu Lagoon failed to incorporate watershed wide constraints, and as a result has experienced consistent problems, which we hope to avoid in Topanga. By contrast, the Carpenteria Marsh - Ash Street Restoration conducted a more thorough evaluation of physical constraints which informed the design process and resulted in a functional system. Therefore, the purpose of this Feasibility Study is to identify and integrate the various components of the creek/lagoon system and develop a sustainable, functional design plan. (See references for additional information.)

Since 1990, residents of the Topanga Watershed have been studying the Los Angeles County hydrologic analysis in light of its impacts on designating floodways and effecting the historic properties along Topanga Creek in the upper watershed. Their work led to the development of the Topanga Creek Watershed Management Study, which identified inconsistencies in the County analysis and the need to verify the County results. The Topanga Watershed Committee was convened in 1998 to provide a forum for community education and discussion of voluntary actions residents could undertake to reduce flood risks, reduce downstream impacts from new development, develop more environmentally sensitive streambank protection measures, retain drainage, reduce erosion and sedimentation, improve water quality and holistically attempt to become better stewards of the watershed. A number of research projects providing baseline information about the watershed are either on-going or completed. (See references for additional information.)

Concurrently, the Santa Monica Bay Restoration Project, CA Department of Parks and Recreation, the Santa Monica Mountains Conservancy and the Santa Monica Mountains National Recreation Area identified restoration of the historic lagoon as a high priority to help improve water quality at Topanga Beach, increase access for endangered steelhead trout, and enhance habitat for endangered tidewater gobies. The Los Angeles County Department of Beaches and Harbors has expressed a willingness to consider restoration possibilities for the area it oversees on the south side of Pacific Coast Highway. The LA Athletic Club property to the north of Pacific Coast Highway is under option for sale as parkland, and if purchased, could provide additional restoration potential.

In Spring 2000, adult steelhead were once again found residing in Topanga Creek. Improving water quality at Topanga Beach has become increasingly important and a year long study of water quality indicated that the upper watershed is contributing very little, if any, to the problems with high coliform counts at Topanga Beach. Funding for the Lagoon Restoration Feasibility Study became available from the Coastal Conservancy and the Santa Monica Bay Restoration Project. It is now time to move forward.

Scope of Work

The consultant will perform the following tasks to help achieve the Project Objective.

  1. Develop an integrated feasibility study using the data from on-going research, existing present and historic resources, and perform any additional hydrologic analysis required to determine the feasibility for lagoon and watershed restoration.
  2. An integrated, comprehensive watershed and lagoon analysis is required in order to evaluate restoration possibilities within the context of existing watershed conditions. Data from on-going research, existing present, historical and digital resources are available. The Consultant will perform any additional hydrologic analysis required to determine the feasibility of lagoon and watershed restoration. Models will be selected that characterize continuous (potentially catastrophic) storm events, as well as calculate more common low flow conditions pertinent to the enhancement of the lagoon.

    Examples of potential models include: HEC-2 and HECRAS analysis (available from Los Angeles County Dept. of Public Works), Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) developed by EPA; Agriculture Nonpoint Source Model (AnnAGNPS) developed by NRCS; Stormwater Management Model (SWMM) from EPA; Hydrologic Simulation Program Fortran (HSPF) from EPA; Storage, Treatment, Overflow, Runoff Model (STORM) developed by the ACE Hydrologic Engineering Center and.

  3. Evaluate at least 3 scenarios of lagoon configuration within the present watershed context: a) the existing lagoon; b) if the lagoon area is expanded to include the filled area to the west of the creek, south of Pacific Coast Highway; and c) if the lagoon is expanded both west and north into both LA County and the current LA Athletic Club property.

Discuss the hydrological characteristics of the lagoon/watershed system and how these might change under each condition. Discuss tidal circulation potentials and how these designs might reduce flood hazard. Evaluate the role of the PCH bridge, as well as the possibility of lengthening the PCH bridge and how this could improve lagoon function.

The hydrological analysis may include, but not be limited to, the following components:

  1. Identify and perform a hydrological model for the watershed under each of the 3 scenarios that incorporates documented conditions and leads to the best estimates for evaluating the worst case conditions as well as more normal conditions, and long term viability of an enhanced/restored lagoon and watershed. Identify what factors are needed and critical parameters for achieving an enhanced/restored lagoon and watershed. Data available from either the RCDSMM or online includes: cross sections developed by the RCDSMM and/or LA County, run-off coefficients for saturated conditions, both Los Angeles County and volunteer generated rainfall data, and Los Angeles County stream gage data, historical photos and topos of Topanga Lagoon, water quality and sediment study data.
  2. Develop a model tying amount of runoff to land—use type and burn history. Develop a runoff and water balance model to identify volumes of water anticipated to flow into the lagoon under both burned and unburned conditions. Fire history is available as GIS overlay courtesy of the Los Angeles County Foresters and NPS.
  3. Evaluate the role of anthropogenic constraints (Topanga Canyon Blvd., Pacific Coast Highway and the bridge, fill areas, adjacent structures, etc.) on the creek and lagoon system.
  4. Provide digital data that can be integrated into an ArcView GIS system and watershed models such as AnnAGNPS, BASINS, etc.
  5. Integrate associated studies on erosion and sediment delivery, water quality and biological resources with the hydrologic analysis.


  1. Identify phased approach to achieving lagoon and watershed enhancement/restoration, including a scope of work and budget.

  2. Provide an interim report to the community presenting analysis of opportunities and constraints related to lagoon and watershed restoration at the June 2001 Topanga Watershed Committee meeting, and a final presentation in December 2001.

  3. Provide a summary report in both print and digital format to the RCDSMM no later than November 2001.


Pertinent references, previous and on-going research results, modeling parameters, and additional background information will be available for review on the web via the Topanga Watershed Committee site found at Additional materials are available by appointment at the RCDSMM, Topnaga, CA.


The Resource Conservation District of the Santa Monica Mountains has $55,000 to complete the tasks described above. The scope of work, methodology, or the scale of the project is somewhat negotiable; however, the maximum funding level is not negotiable.


Proposal Guidelines

Proposals of no more than 10 pages should contain the following items:

  1. A detailed description of the approach to be used to complete the tasks outlined in the scope of work. Explain how and why your approach will result in a viable restoration plan. Explain how your approach will integrate additional research such as erosion and sediment transport, water quality, and biological concerns. If necessary, identify any other work needed to complete a reliable feasibility study.
  2. A schedule of costs for each of the tasks listed under the scope of work. This should include project meeting and management costs.
  3. Proposed schedule for completion of each task.

6 Copies of Additional information required includes (no page limit):

  1. Descriptions of no more than five projects successfully completed by the consultant which are indicative of the ability to carry out this project.
  2. Name and qualifications of the project team to be assigned to the project.
  3. Names, addresses, and qualifications of subconsultant firms anticipated to be used on this project and a description of the types of tasks each subconsultant is expected to perform, if any.

Proposals must bear the signature of a principal authorized to enter into a contract.

12 copies of the initial proposal must be received by the Resource Conservation District of the Santa Monica Mountains on or before January 15, 2001, to be considered. Send proposals to:

The Resource Conservation District of the Santa Monica Mountains

122 N. Topanga Canyon Blvd.

Topanga, CA 90290

Attn: Rosi Dagit

Selection Procedure

The Resource Conservation District of the Santa Monica Mountains, in consultation with the Coastal Conservancy, and the Technical and Landowners Advisory Committee will select the consultant. The Selection Committee will meet in early February 20001.

Only the most qualified applicants will be interviewed, but all firms or teams that submitted proposals will be notified of their status by the RCDSMM. The basis of the selection will include relevant experience in watershed analysis and integrated biological/hydrological lagoon design, project understanding, and cost-effectiveness.


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