Stormwater Management Manual
III. MASTER PLANS
The regional master plan is regarded as one of the most cost effective means of achieving stormwater management goals. This chapter describes the concepts, elements, and requirements of regional plans.
Regional master plans identify the needs of a watershed or portion thereof and formulate plans, programs, and policies for effective stormwater management. The plans coordinate facilities and policies, and help assure that all effects of watershed changes are identified, including especially the cumulative effects of many small-scale changes.
Regional master plans are normally where major decisions are made as to: design assumptions and parameters; locations of structures; potential alternative uses of open channels; and requirements and locations of storage facilities.
Regional master plans play a particularly important role in a developing region by providing critical information and criteria for the coordinated planning and design of development projects in the watershed. In addition, appropriate on-site flood control facilities may be required, and offsite facilities are identified for which developers may be charged shares. Appropriate floodplain and watershed development policies and decisions are also identified. For example, development may be discouraged in areas subject to flooding, and natural drainage ways may be preserved.
1. Master plans will be prepared as soon as possible for each major drainage basin. The major basins in Western Placer County are:
- Auburn Ravine - in and below Auburn
- Auburn Ravine - vicinity of Lincoln
- Colfax - sphere of influence
- Coon Creek
- Doty Ravine
- Dry Creek Basin - from headwaters to County line
- Markham Ravine - vicinity of Lincoln
- North Auburn area
- Pleasant Grove Creek - from headwaters to County line.
2. Regional master plans will be prepared by the Placer County Flood Control District.
3. Each municipality in Placer County is responsible for detailed master plans in its jurisdiction. The District will coordinate the local plans to assure consistency with the regional plans.
4. Master plans are developed on the basis of priorities. The most pressing problems are not necessarily given the highest priority. A master plan of a basin in which development is just beginning might be simple, of low cost, and readily completed and most effective in terms of returns to the community.
Priorities for master plans are based on:
- frequency and severity of problems
- opportunity for accomplishing goals
- information base available
- manpower availability
5. The Placer County Flood Control District shall establish a format for master plan reports to achieve consistency in planning and facilitate coordination of efforts.
The District shall archive and maintain all pertinent data developed during the master plan process and make it available to all affected parties. This data would include maps, map overlays, reports, and hydrologic and hydraulic models.
C. Master Plan Elements
1. Goals, Concepts, and Criteria
The plan shall identify and describe the goals, concepts and assumptions of the plan and criteria to be used for evaluation.
It should also identify:
- basic flooding, erosion sedimentation and water quality problems in the region
- pertinent legal and regulatory issues, environmental concerns
- the relationship to other, regional drainage plans and to local general and specific plans for development.
a. Hydrologic Features The plan shall identify and describe the important hydrologic features of the watershed including:
- a watershed map with topography, including upstream areas, minimum 1:2000 scale
- major conveyances
- existing drainage structures and improvements
- soils map and description
- land use maps for existing and future conditions
- maps of areas subject to flooding, erosion, sedimentation
- locations of restrictions, such as road crossings
- estimates of channel capacities
- precipitation and flow frequency and magnitudes
- a summary of streamflow and precipitation data
- design flows at key points for existing and future conditions
Previous studies, including FEMA, Corps of Engineers, SCS and consultant studies and reports, shall be identified and considered.
b. Hydrologic Models A hydrologic model of the watershed is key to evaluating current and potential flow and flooding characteristics and evaluating potential mitigation measures.
The model shall represent all major conveyances and storage, control facilities and include all relevant control points. It shall be reasonably sensitive to watershed and conveyance changes in order to evaluate general development projects and proposed improvements to the drainage system. The model shall represent both present and ultimate watershed conditions. The hydrologic models shall conform with the criteria and standards specified in this manual. The hydrologic models shall be maintained as tools for readily evaluating proposed changes to the watershed. Maintenance includes periodic updates to reflect current conditions.
3. Facilities, Policies, and Programs The plan shall identify and provide cost estimates for the facilities, programs and policies which would alleviate or mitigate problems and quantify their effects to the extent feasible.
Evaluation of the alternative solutions shall be based on level of service cost, environmental effects, and potential for secondary use. Prioritization of recommended alternatives is an important step. The potential strategies could include:
a. Capital Improvements
Possible drainage improvements include major storm drain systems, detention or retention basins, and improvements to existing channels and road and railroad crossings.
Cost estimates for the improvements shall include right of way easements and engineering, maintenance and administrative costs as well as land and construction costs.
b. Floodplain Management Program
The delineation of 100-year floodplains is an important tool in the prevention of flood damages and may also support the availability of low-cost flood insurance under the National Flood Insurance Program administered by the Federal Emergency Management Agency (FEMA).
The evaluation and determination of the 100-year floodplain shall at least meet FEMA standards and criteria, but shall also consider the 100-year floodplain under ultimate conditions of development and the effects of flood fringe filling.
c. Flood Warning Systems
Flood warning systems can play an important role in reducing flood damages and saving lives.
d. Monitoring Program
A monitoring program is essential to maintaining and improving the performance of facilities and programs.
e. Operations and Maintenance Program
An ongoing operations and maintenance program is essential for an effective stormwater system. Channel maintenance can reduce flood damages by removal of floating debris which can clog or reduce the capacity of culverts and bridges. Channel maintenance can also include measures for the reduction of erosion at key locations.
Maintenance programs shall identify the elements to be maintained and the types and frequency of maintenance procedures required to accomplish maintenance goals.
Records of maintenance on similar elements would be useful in developing and evaluating a maintenance program.
4. Funding Program
The master plan shall include means of funding the construction, maintenance and administrative activities identified.
Alternative sources of funding include: development fees based on the subdivision Map Act or CEQA; utility fees; Mello-Roos Districts, County Service Areas; and assessment districts.
Basin Master Plans prepared by the Flood Control District shall be adopted by the affected jurisdictions and the Flood Control District Board of Directors in public meetings.
E. Distribution and Coordination
Copies of approved master plans shall be distributed to the Placer County Flood Control District and to the governmental jurisdiction in which the works are located. Copies shall also be sent to each governmental entity located downstream along the tributary waterways affected.