1.0 recommendations from appendix a
A2.1-1 Establish a policy that limits stormwater runoff and sedimentation from new development to that which occurs over naturally existing terrain under all conditions.
A2.1-2 Establish a policy of using a broader spectrum of soil conditions to perform runoff comparisons between the developed and undeveloped site.
A2.2.1-1 Use shoulder fill that can not be easily eroded away.
A2.2.1-2 Cease dumping loose soil over embankments.
A2.2.2-1 Preserve and enhance the function of the existing riparian vegetation.
A2.3-1 Establish practices which make reduction of peak flow runoff an important element in the selection of a grading and brushing procedure.
A2.3-2 Minimize the removal of existing mature vegetation.
A2.4.-1 Provide identification and protection of sites particularly vulnerable to erosion or obstruction in the Watershed Management Plan.
A2.4-2 Require that projects which alter the stream flow characteristics document their impact on downstream properties and mitigate any significant increases in flood hazard and environmental degradation.
A2.5-1 An annual monitoring program that identifies dumping sites prior to the rainy season and ensures debris removal is needed. Also a program for removal of large pieces of natural debris is needed.
A.2.6-1 New designs and approaches are needed that preserve the natural setting of the watercourses while providing slope stability.
A3.1.2-1 Require DPW to do a comparative analysis of CRS credit points for the proposed Topanga Creek Watershed Management Plan and the Proposed Topanga Floodway Ordinance.
A3.1.3-1 Rely on the present federal, state and local regulations to appropriately mitigate unsafe conditions (e.g., repetitive loss or substantially damaged buildings) within the floodplain.
A3.2-1 An amendment should be made to the Local Annex to the State FHMP to incorporate the Topanga Creek Watershed Management Plan.
A3.3-1 Adopt the Topanga Creek Watershed Management Plan, which would provide protection for life and property, the existing community and the creek environment.
A3.3-2 Use a more rigorous approach to define the boundaries of the 100 year floodplain (e.g., as described in Section 1.1.3 of Appendix C).
A3.4.2-1 Adopt an environmentally sensitive watershed management approach to flood hazard reduction, which is vital to protect life, property, and the riparian habitat.
A3.4.2-2 Rescind Floodways in lower Topanga, Garapito, Red Rock and Santa Maria creeks and immediately implement the Topanga Creek Watershed Management Plan.
A3.4.2-3 Ensure that the ability to protect existing property by modest and effective means is preserved through employing structures, such as gabion flood walls, that do not create downstream impacts.
A3.4.2-4 Adopt the California DWR Model Floodplain Management Ordinance using FEMA minimum standards.
A3.5.1-1 Establish a Watershed Management Committee including representatives of all agencies with jurisdiction within the creek floodplain to establish a common set of development standards and Best Management Practices.
A3.5.2-1 Assess flood hazard to the County bridges along Topanga Canyon Boulevard and Old Topanga Canyon Road, and make appropriate emergency plans where required.
A3.5.2-2 Flood Hazard mitigation regulations should be applied alike to private property owners and public agencies.
A3.5.2-3 Use a broader range of options in the CRS program to reduce the flood hazard in order to benefit both public and private owners.
A3.5.3-1 Pre-peak discharges should be evaluated using best estimate models rather than the worst case models used currently.
A3.5.3-2 Downstream property should be protected from increases in runoff due to upstream developments.
A3.5.4-1 Continue to require that the Fire Department review and approve landscape and fuel modification/vegetation management plans for all new developments and major remodels. No fuel modification plans should be approved that require greater than 30' vegetation clearance on slopes >3:1 (33%)..
A3.5.4-2 Require that the Fire Department and the Regional Planning Department evaluate all fire safety factors that affect the ability of a development site in the Santa Monica Mountains to survive a wildfire including: proximity to downhill slopes; time and distance from fire services; and adequate road access to and from the major roads that provide emergency ingress and egress to the site.
A3.5.4-3 Provide recommendations on zoning and code changes to the Board of Supervisors to allow comprehensive site evaluation of fire safety by the Planning Department, to be implemented in conjunction with the fuel modification guidelines.
2.0 recommendations from appendix c
C1.1.2-1 Employ detention basins to reduce peak flow runoff.
C1.1.2-2 Develop criteria for the siting and construction of detention basins. The primary purpose of these criteria is to insure that the impact of the basins on the riparian habitat is minimal.
C1.1.2-3 Employ ponds to mitigate the increase in peak flow runoff and sedimentation engendered by the development of small parcels (e.g., grading a building site, building a house) and additions to existing residents and businesses (e.g., paving).
C1.1.2-4 Develop a funding mechanism for building detention basins.
C1.1.2-5 Assess exisitng serendipitous detention basins in Topanga (i.e., those formed by road fill of a side canyon) as to their present and long term potential to act as detention basins. Priortize the importance of each basin to flood hazard mitigation. Insure that these serendipitous detention basins are not destroyed by culvert upgrades and infilling.
C1.1.3-1 Ensure that all drainage plans specify that runoff is delivered to a natural drainage channel or public drainage device at non-erosive velocities with the fine sediments retained on-site.
C1.1.3-2 For those properties having impervious paving that exceeds the areas given in Table C-3, any increases in peak flow runoff and sedimentation (i.e., over the unpaved condition) are to be mitigated on site.
C1.1.3-3 Where clear cutting or disking is used to remove brush over an area exceeding the limits specified in Table C-3, any additional runoff and sedimentation, which is generated over that due to hand brushing techniques, is be mitigated on site.
C1.1.3-4 Grading, road building, and any other practice which disturbs an area of soil over the limits specified in Table C-3, should demonstrate that any additional peak flow runoff and sedimentation (i.e., over the undeveloped condition) is mitigated and retained on site.
C1.1.3-5 Protect trees and vegetation from harmful practices to reduce runoff and sedimentation, and increase absorption of rainfall.
C1.1.3-6 Develop regulations that endorse the basic notion that passing whatever runoff a particular property generates onto its downstream neighbors is no longer an acceptable practice.
C1.1.3-7 Assess a proportional fee to fund costs of off-site flood hazard mitigation (e.g., detention basins).
C1.1.3-8 Evaluate current grading standards and inspection procedures and develop standards and practices that will effectively prevent any sediment transportation from construction sites.
C1.1.3-9 Require that all new roads with either cut or fill slopes shall be replanted or retained to prevent erosion.
C1.1.3-10 Develop a road management program for both public and private properties to correct existing adverse conditions at major sites of road induced slope erosion by constructing remedial drainage improvements, slope plantings or retaining structures.
C1.2-1 Adopt the recommendations of the TCWMP to implement the policies of the local area plans.
C1.3-1 Create a hydrologic watershed model that identifies undersized or poorly located/designed structures and provides guidelines for replacement.
C1.3-2 Prepare a survey of the existing major hydraulic structures so that significant deficiencies may be identified and a plan made for their remediation.
C1.3-3 Develop a set of general designs for embankment stabilization, flood walls, and other devices that may be needed to lessen the flood hazard at a particular location. These designs are to be specifically related to the situations encountered in Topanga, require little maintenance, and be consistent with the protection of the environment.
C1.3-4 Discourage the use of concrete in the floodplain or along creek banks. Where grouted rip rap exists, replacement with more appropriate materials should be made over time.
C1.3-5 Erosion control should be performed only with porous materials that allow the infiltration of runoff. Energy dissipaters should be used to ensure that water velocities remain low.
C1.3-6 DPW should incorporate into its capital improvements program the replacement of undersized bridges.
C1.3-7 Create an emergency warning and evacuation system for those bridges and major roadways where a substantial public safety hazard exists. This is especially important for the Topanga Elementary School.
C1.3-8 Assign the WMC the responsibility of insuring that flood hazard protection at one location does not increase the flood hazard at another.
C1.3-9 Allow a lesser standard than the 50-year design storm where site conditions warrant. The need for the lesser standard must be demonstrated by a professional engineer and approved by the County.
C1.4-1 Coordinate the Topanga Creek Watershed Management Plan with the Santa Monica Bay Restoration Plan and the Malibu Creek Watershed Council, particularly as they relate to stream protection and land use practices in the Santa Monica Mountains.
C2.1-1 Adopt a Santa Monica Mountains Community Standards District to implement the development standards of the TCWMP.
C2.2-1 Establish sufficient slope setbacks for new structures for fire protection; prohibit ridgetop development; allow only limited vegetation clearance on slopes greater than 3:1 (30' or less). All fuel modification and fuel management plans required under Section 11.702(a) of the Fire Code shall comply with these standards.
C2.2-2 Require development setbacks from oak and riparian habitats.
C2.2-3 Prohibit alteration of stream channels or floodplains; prohibit development within floodplains; require development setbacks from stream courses.
C2.2-4 Establish and implement a cooperative program for clearing stream obstructions.
C2.2-5 Establish BMPs for any work in stream courses and adjoining habitat areas.
C2.2-6 Prohibit any increase in the rate of peak runoff from new development.
C2.2-7 Control erosion and sedimentation. Retain sediment and runoff on-site. All drainage must be conveyed and released in a non-erosive manner at nonerosive velocities into natural channels or to an approved public drainage device.
C2.2-8 Establish maximum limits on the amount of grading allowed.
C2.2-9 Establish maximum limits on the amount of impervious surfaces allowed.
C2.2-10 Provide plans to control runoff and erosion from roads/driveways. All cut and fill road slopes must be replanted or retained to prevent slope erosion.
C2.2-11 Protect water quality by monitoring and regulating the location of septic systems.
C2.2-12 Prohibit new development where inadequate road access exists for emergency ingress and egress to the main roadways of Pacific Coast Highway, Mulholland Highway, Topanga Canyon Boulevard, and Old Topanga Canyon Road.
C2.2-13 Land use density in undeveloped areas of core habitat should be low, 5-40 acres/unit. Infilling should be allowed in existing developed neighborhoods where infrastructure is adequate. Land use density shall be determined by a development constraints matrix and be consistent with all of the land use policies.
C.3.0-1 Require a pre-design constraints analysis to identify site-specific hazard mitigation problems prior to design.
C4.0-1 Perform a baseline water quality study and monitor changes yearly.
C4.0-2 Identify the major sources of pollution and develop realistic programs to address them.
C4.0-3 Develop an anti-dumping campaign, focusing on rewards, heightened public education, signing, and a hot-line to reduce this form of pollution. Pursue grant money to fund these efforts.
C5.1-1 Disseminate information to all affected property owners as recommended by the CRS Repetitive Loss Plan (see Appendix A, Section 3.1.2) including: the design manual for retrofitting flood prone residential structures; information on elevating residential structures; the handbook on flood emergency and residential repair; and information on flood-proofing techniques and systems.
C5.1-2 Distribute brochures with ìuser friendlyî information on water quality, vegetation management, flood hazard reduction, maintenance of slope stability, etc.
C5.1-3 Publish a series of articles in the Messenger newspaper on the watershed plan.
C5.1-4 Coordinate volunteers to provide hands-on implementation of BMP's.
C5.1-5 Establish demonstration sites for detention basins and holding ponds
C5.1-6 Have experts address community meetings.
C5.1-7 Identify who is to be called when a problem is identified, establish a response time, and create a list of agreed-upon possible responses.
C5.1-8 Clearly define who is responsible for what actions.
C5.1-9 Establish a twice annual monitoring schedule to identify problems before and after the rainy season.
C5.1-10 Hold an annual public meeting to discuss watershed management concerns.
C5.1-11 Establish an appeal process to address conflicts that arise due to proposed remedial actions.
C5.2-1 Compile annually a list of flood hazards and sites of potential slope failure.
C5.2-2 Identify appropriate solutions to the hazards and have the solutions approved by relevant agencies (i.e., Coastal Commission, US Fish and Wildlife Service, Calif. Department of Fish and Game, US Army Corps of Engineers, etc.).
C5.3-1 Use only non-erodable approved materials to construct fills, backfills, embankment stabilizations, and road shoulders.
C5.3-2 Prohibit importation of any fill debris material from outside of the watershed.
C5.3-3 Prohibit placement of any materials within the protected zone of a tree, or a minimum of 10 feet from the trunk.
C5.4-1 Design hardscape to preserve and enhance vegetation whenever possible.
C5.4-2 Limit use of grouted concrete rip rap only to those areas where gabions, bio-engineering efforts, etc. are not possible.
C5.4-3 In compliance with the Los Angeles County Oak Tree Protection Ordinance, any work done within the protected zone of an oak or any other trees within 50 feet of a stream bank should be done by hand. No stockpiling of dirt or equipment should be permitted within the protected zone of the tree(s).
C5.4-4 Tunneling under roots rather than cutting them should be the standard. Any roots exposed during construction should be protected by wet burlap and reburied as soon as possible. Any cuts should be clean and smooth.
C5.4-5 Creation of soil or asphalt berms to direct road run-off should avoid direct contact with tree trunks.
C5.4-6 Removal of understory vegetation, or burying such vegetation under permanent rip-rap or culverts should be prohibited except under exceptional conditions.
C5.4-7 Documentation of existing riparian vegetation should be performed prior to any grading activities.
C5.4-8 Use of methods encouraging re-establishment of stream vegetation should be preferred over concrete or rip-rap retaining walls.
C5.4-9 The services of a consulting biologist/arborist should be sought prior to and during both the design and implementation phases of all projects. Specified monitoring following completion of construction is also recommended.
C.5.4-10 Require analysis with the hydrologic model prior to installation of any streambank hardscape to identify any impacts that could alter channel capacity or stream flow dynamics and to identify potential downstream impacts.
C5.5-1 Remove any large debris that could create a flood hazard by obstructing the creek channel.
C5.5-2 Plan strategic placement of boulders on a stream-wide basis to reduce stream velocity during peak flow.
C5.5-3 Require that plants and animals be protected during any construction within or adjacent to the stream channel.
C5.6-1 Reduce impacts by coordinating line clearance pruning among all concerned agencies.
C5.6-2 Prohibit topping (cutting trees straight across without regard to branch structure).
C5.6-3 Apply directional pruning and crown reduction as pruning standards. Use ISA standards for pruning.
C5.6-4 Prohibit pruning between January and April in order to protect nesting raptors.
C5.7-1 Replace caissons, concrete retaining walls, and other support structures in accordance with BMPs to protect stream resources and prevent downstream impacts by altering flow dynamics. Use hydrologic model to estimate impacts.
C5.8-1 Establish and maintain a revegetation program in order to encourage quick re-establishment of riparian vegetation.
C5.8-2 Create a list of appropriate species for planting under utility wires in order to reduce problems related to tree/utility line interactions.
C5.9-1 Develop a program to eradicate giant cane (Arundo donax), castor bean (Ricinus communis), periwinkle (Vinca minor), tree tobacco (Nicotania glauca), German ivy (Senecio sp.). and Algerian ivy (Hedera sp.).
C5.10-1 Prevent illegal dumping by limiting vehicle access, placing appropriate signage, imposing and enforcing penalties (fines, misdemeanor offense).
C5.11-1 Reduce flood hazard and catastrophic erosion and sedimentation by carrying out controlled burns.
C6.0-1 Seek a variety of grants to fund restoration programs and basic research necessary to implement the watershed management plan. Major issues include: water quality analysis, sediment and erosion control analysis, embankment stabilization methods, tree inventory, biological inventory, exotic plant eradication, and restoration of the Topanga Creek estuary.
C7.0-1 Develop an early warning system through the EOC that can provide an accurate assessment of potential flood hazards in Topanga Canyon. Tie this system into the weather service and the real time data collected by the various government agencies.
C7.0-2 Develop a system whereby the major commuter routes can be closed to non residents when the potential flood hazard exceeds a designated threshold.
C7.0-3 Incorporate into the TCWMP the findings and recommendations of the Comprehensive Disaster Management Plan based on the wildfire prototype project currently being developed at the Center for the Study of the Environment at UC Santa Barbara.
3.0 recommendations from appendix M
M1.2-1 Develop a procedure for computing ìbest estimateî values of Q so that comparison studies may evaluate the effect of proposed developments and runoff mitigation measures for a range of storm conditions (e.g., saturated and unsaturated soils, burned/unburned watershed, 1/5/25-year storms and the Capital storm).
M1.2-2 Use runoff coefficients which reflect the consequence of our proposed watershed management plan. These coefficients should either reflect what is presently the case or be lowered to reflect the mitigation efforts of the proposed plan. These efforts are described in Appendix C, Section 1.3.
M1.2-3 Develop an estimate of the actual recurrence interval associated with Countyís 50-year design storm. This is needed so that the decision makers and the public have a clear notion of the standard they are being held to.
M1.2-4 More data is needed concerning the effects on the runoff coefficient from grading, vegetation and fire.
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