TOPANGA WATERSHED AND
LAGOON RESTORATION
FEASIBILITY STUDY

In order to establish the feasibility to restore Topanga Lagoon, it is necessary to evaluate the current physical processes at work throughout the watershed that impact the creek mouth, including flooding, sedimentation, hydrology, water quality, land use, wildfires, and impact of invasive exotics. This study will provide basic data used by all stakeholders, State Parks, LA County, Caltrans, UCLA, NRCS, and a consulting engineering firm to develop a comprehensive plan for action.

This comprehensive study is composed of the following 5 integrated segments. All of these segments will be incorporated into a GIS database that will allow for more detailed analysis of potential restoration options. Ultimately, a watershed assessment integrating the verified hydrologic model ( including rainfall/runoff, peak storms, etc.) with erosion and sediment transport and identified impacts on water quality from point and non-point sources will be completed using the appropriate computer model.

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

1.  Feasibility Study Design, Integration and Hydrologic Analysis

An integrated, comprehensive watershed and lagoon analysis is required in order to evaluate restoration possibilities within the context of existing watershed conditions. An RFP will be used to select a contractor to develop an integrated feasibility study using the data from on-going research, existing historical and digital resources, and 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 (already 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.

Pertinent references, scopes of work and additional background information will be available for review on the web via the Topanga Watershed Committee site found at www.TopangaOnline.com.

Water quantity under a variety of conditions plays a major role in defining creek and lagoon configurations. These parameters will be studied in several ways. The consultant will perform the following tasks to help answer this question.

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

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, 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.
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 both an ArcView GIS system and a watershed model such as AnnAGNPS, BASINS, etc.
5. Identify ways to integrate associated studies on erosion and sediment delivery, water quality and biological resources with the hydrologic analysis.
6. Provide an interim report presentation to the community presenting analysis of opportunities and constraints at the June 2001 Topanga Watershed Committee meeting, and a final presentation in December 2001.
7. Provide a summary report in both print and digital format to the RCDSMM no later than November 2001.

If possible, utilize either dyes or other tracers to identify the time it takes for water to move through the watershed under both saturated (winter) and dry (summer) conditions. Topanga Creek is characterized as an intermittent creek, and as such flows are interrupted during the warm summer months and continue below the surface of the channel bed. Movement of pollutants through the system is unknown. This will also help identify the contribution of ground water sources to the overall stream flow pattern. Another potential source of pollution is the contribution of the septic systems along Pacific Coast Highway to the north and west of the present lagoon/beach. If permission from landowners becomes available, tracer studies in this area are also important.

Additional flow monitoring will take place using current meters and/or an additional stream gage to measure contributions from major subdrainages during a rainfall event in the fall, and under saturated conditions towards the end of the rainy season.

3.  Sediment Study

In order to complete the field study of erosion and sediment delivery within the lower creek and lagoon, funding from this grant will provide for the additional sampling for erosion at several locations and correlation to sites monitored following the 1993 Old Topanga Fire. This work will be specifically contracted and coordinated with the associated Santa Monica Bay Restoration Project grant under the direction of Dr. Antony Orme and the RCDSMM.

4. Water Quality

The majority of water quality data (funded by 205j grant) is being collected weekly at 5 locations and monthly in an additional 10 locations throughout the watershed, with the lowest site located 2.2 miles upstream from Pacific Coast Highway. Additional data is collected by the City of Los Angeles at Topanga Beach, however no data is collected directly from the lagoon itself.

Therefore samples will be taken in the lagoon itself according to the methodology of the larger water quality study. Samples will be sent to the lab monthly to measure total and fecal coliform bacteria, E. coli, total suspended solids. Samples will also be taken following the first 3/4" storm event and towards the end of the rainy season following a storm event when the lagoon entrance is still open. Samples will be taken by wading knee deep into the lagoon by the concrete wing wall found on the east side near the lifeguard tower. On site data regarding water temperature, salinity, dissolved oxygen, pH, and turbidity will be taken at the time each sample is collected. Tests for nitrogen — N, ammonia-N, phosphates and conductivity will be done according to the procedure identified in the QA/QC Plan filed for the 205j grant.

5. Integrated Information Management

All of the data collected for this project will be integrated into a comprehensive GIS based watershed analysis that will allow queries to better understand how the physical, chemical and biological components of the watershed interact. This work will be completed by the GIS technician with assistance from the NRCS, NPS, Caltrans and LA County.

Using historic aerial photos, topographic maps and the US Coast Series 1877 survey map, overlays will be generated using GIS. With the help of 3D and Spatial Analyst, the changes in channel and lagoon configuration over time should become more visible, allowing evaluation of the impacts of current anthropogenic constraints on the creek and lagoon. An RFP will be prepared to ensure that the subcontractor has the necessary GIS skills to complete the project.

As it becomes available, data and other resources will be posted on the Topanga Watershed site at www.TopangaOnline.com.

6. Project Oversite and Community Liaison

Any potential restoration plan will need the complete support of a host of involved landowners, agencies and the general public. The key to developing this support is for a coordinated on-going dialog relating information gathered to the community during the entire process. This effort will be integrated into the overall project coordination and administration by the staff of the RCDSMM.

Technical and Landowner Advisory Committee

In order to keep all parties actively involved in the evaluation of restoration possibilities, a Technical and Landowner Advisory Committee will be convened. Early in the project, they will review and comment upon the Requests for Proposals (RFP’s) that will be prepared by the RCDSMM for contractors to bid on the hydrological, water movement, GIS and integrated components of the study.

As data is gathered and GIS overlays become available, the Committee will convene as needed to review the progress of the project, provide input on data analysis and consider the implications of the information learned.

Upon completion of the data collection and analysis, the Committee will review the Final Project Report for accuracy and completeness.

They will host a community meeting in June 2001 and late Fall 2001 to share the results of the study and discuss the alternatives for restoration options identified.

Members of the Technical and Landowner Advisory Committee will include, but not be limited to, qualified representatives of the following:

Caltrans

CA Dept. of Parks and Recreation

Los Angeles Athletic Club and/or the American Land Conservancy

Los Angeles County Dept. of Beaches and Harbors

Los Angeles County Dept. of Public Works — Watershed Division

Santa Monica Mountains Conservancy

Topanga Creekside Homeowners Assoc.

Topanga Watershed Committee

CA Coastal Commission

CA Coastal Conservancy - Southern CA Wetlands Recovery Project

CA Dept of Fish and Game

Heal the Bay

Los Angeles Regional Water Quality Control Board

National Marine Fisheries Service

National Park Service —Santa Monica Mountains National Recreation Area

Natural Resources Conservation Service

Resource Conservation District of the Santa Monica Mountains

Santa Monica Bay Restoration Project

Surfrider Foundation

Topanga Canyon Floodplain Management Citizen’s Advisory Committee

US Fish and Wildlife Service

Get project up and running.

1.1. Acquire necessary field equipment, historical photos, background data.

1.2. Develop Requests for Proposals and solicit bids.

1.3. Convene the Technical and Landowner Advisory Committee.

1.4. Establish data collection locations for hydrologic and sediment studies (sediment traps, flow meters, water markers, lagoon parameters).

1.5. Compile necessary historic aerial photos, digitize and georeference.

1.6. Set up data collection system tied to existing GIS database.

1.7. Generate additional overlays for each study as needed.

1.8. Begin input of volunteer rainfall data, and coordinate with LA County data.

1.9. Review Hec-2 analysis done by LA County and NRCS.

1.10. Input historic creek channel configurations for analysis.

1.11. Assemble necessary ancillary data on stream flow, water quality, etc.

On-going data gathering, input and analysis.

2.1 Install field equipment and begin weekly monitoring during the rainy season and monthly monitoring during the dry season.

2.2 Weekly (or monthly depending on rainfall) data collection for sediments and water movements.

2.3 Digitize and geo-reference all geomorphological resources.

2.4 Complete GIS analysis of historic channel conditions.

2.5 GPS all field locations and create GIS overlays.

2.6 Monitor lagoon conditions weekly (or monthly depending on rainfall).

7. Collect water quality samples in lagoon monthly.
8. Track water movement and flow rates.

2.9 On-going data input and management for all subsets of the study.

2.10 Provide continuous updates to the Topanga Watershed Committee and the community via the local newspaper and web site.

2.11 Solicit community input into the study process via the Watershed Committee.

1. Begin data collection for instream habitat and fish survey, if funded by CDFG.

Preliminary results shared with community.

3.1 Geomorphological Mapping showing historical channel and lagoon changes completed and maps prepared for review.

3.2 Town Hall Community Meeting led by the Technical and Landowner Advisory Committee to provide maps showing evolution of the creek and lagoon, preliminary data on limiting factors and design constraints.

Seek community input on restoration actions including but not limited to: restoring the lagoon and wetlands, recreational possibilities, visitor center needs, habitat enhancement, exotic invasives removal, streambank restoration actions, etc.

Complete water year data collection, input and analysis.

4.1 Complete water year data collection and finalize input and analysis.

4.2 Circulate data and community generated design concerns to NRCS and LA County DPW for evaluation.

4.3 Generate alternatives analysis of potential restoration actions.

4.4 Draft Final Report prepared complete with maps and preliminary results of all hydrologic, sediment, water quality, etc analysis.

Complete the project.

5.1 Present comprehensive restoration plan at the annual Topanga Watershed Committee State of the Watershed meeting.

5.2 Final Report submitted - An integrated, conceptual restoration plan with specific recommendations and design constraint parameters for restoring the lagoon and lower Topanga Creek will be ready for use as an RFP for designing the implementation specifications. This feasibility study will complete the background research needed and incorporate community participation. Implementation is not dependent on acquiring the LAACO property, but could begin on Topanga Beach.

3. Begin next phase of preliminary design work with grant from Southern CA Wetlands Recovery Project.