Stormwater Management Manual
REQUIREMENTS FOR SUBMITTALS
This section identifies the information to be submitted for review of plans for drainage and flood control features.
All of the information listed does not apply in every case, but review will proceed much faster if the necessary information is provided and is complete. Incomplete submittals will require subsequent submittals with additional information.
It is suggested that questions regarding the omitted or need for particular information should be discussed with City, County or District staff in advance.
PRELIMINARY PLAN OF DEVELOPMENT
A preliminary plan of development is one prepared prior to receiving discretionary approvals. These include tentative maps, specific plans and environmental reports.
- A narrative report stating the goals, assumptions, and design concepts underlying the drainage system and including, at minimum, the information listed below. Additional information may be required as appropriate depending upon the size and complexity of the project.
- A vicinity map showing the location of the project area in relationship to well-known features
- A topographic map of the watershed containing the area being studied and upstream watershed areas. (Maps at a 1 inch to 800 feet scale map are available from the County Department of Public Works)
- A table indexed to the watershed map which indicates drainage area, soil and cover types, land use, pervious infiltration rates, impervious areas and design flows for both pre-development and post-development conditions.
- A description of the hydrologic methods used and identification of any extraordinary hydrologic conditions and how they were treated.
a) Design criteria tabulation for 10-year and 100-year storm runoff
b) Peak discharge computations for pipe sizing
c) Peak discharge computations for 100-year runoff
d) Assumptions as to upstream storage
- A description of mitigations proposed or required.
- A description of any special design features, such as storage basins, including the underlying design concepts
- A map of the area to be served. The map generally should be at a scale of 1 inch to 100 feet or 1 inch to 50 feet, having 2-foot contours, except where local governmental requirements modify this interval
- A layout of the area to be drained showing:
a) Streets and street names and street drainage flow direction
b) Irrigation ditches
c) Conflicting utilities (if necessary)
d) Drainage basin and sub-basins
e) Storm sewer layout with sizes and storm inlet locations
f) Cross-gutter locations and open drainage ways
g) Layout of major drainage system showing flows and directions
h) Scale and North Arrow
i) Signature blocks for review approvals
j) Location map and subdivision names
- Profiles of streets, utilities, and drainage components. The drainage profile shall also show inlet elevations and hydraulic grade lines
- Location and elevation of the outfall point of the storm drainage system for the planned project
- Typical street cross sections
- At the discretion of the approving agency, a plan, including funding, for operation and maintenance of facilities.
Improvement plans are those submitted subsequent to discretionary approval of a project. Typically, improvement plans include construction drawings.
A narrative report shall be provided stating the goals, assumptions, and design concepts underlying the drainage system and include, at minimum, the information listed below. Additional information may be required as appropriate depending upon the size and complexity of the project.
The following sections cover specific requirements of final construction drawings and specifications for drainage systems. A complete review of utilities, property locations, and other items which may affect construction of the system must also be provided, including, but not limited to:
- Subdivision plats, section lines, and corners, utility easements, highway right-of-ways, and any other property data.
- As-built drawings of existing streets or highways wherever would affect design or construction.
- Records of existing utilities, pipelines, and structures both above and below ground. Data which are incomplete or questionable should be checked by field survey.
- Size, construction, material, invert elevations, area served and type of development.
A field survey may be necessary to supplement design maps to locate utilities, test hole locations, and other items not accurately located on the maps.
Mapping for use in final design shall be of sufficient accuracy to enable horizontal locations to be set within 0.1 foot and elevations within 0.01 foot. Elevation datum shall be USGS unless other datum is specifically required. Horizontal control shall be tied to state grid coordinates and section corners to allow matching of maps for different projects.
When alternate types of materials are considered, hydraulic design profiles must be shown for each material to verify that both are acceptable.
Plans and Maps Formats
- Title block (lower right-hand corner preferred), Scale, Name of Professional Engineer or firm, Professional Engineer's Seal
- Statement as to Specifications
- Approval spaces with date spaces, Date and Revisions, Drawing numbers
Drainage Area Plan
- North Arrow
- Contours (maximum 2-foot intervals)
- Location & elevation of USGS bench marks
- Property lines, Boundary lines (counties, districts, tributary area)
- Streets and street names & approximate grades with width
- Subdivision (name and location by section)
- Irrigation ditches
- Proposed piping and open drainage ways
- Existing drainage structures and ways including flow directions
- Drainage sub-basin boundaries, Easements required
- Proposed curbs and gutters and gutter flow directions
- Proposed cross pan and flow directions, inlet location and inlet sizes
- Critical minimum finished floor elevations for protection from 100-year storm runoff
- North Arrow, Property lines and ownership or subdivision information
- Street names and easements with width information
- Test hole locations and log
- Existing utility lines (buried), location and depth water, gas, telephone, storm drainage, irrigation ditches sanitary sewers
- Vertical and horizontal grids with scales
- Ground surface existing and proposed
- Existing utility lines where crossed
- Pipes, plan showing stationing profile, grades, inlet and outlet details size, lengths between manholes and type
- Manhole details (station number and invert elevations)
- Typical bedding detail
- Open channels plan showing stationing, profile, and grades typical cross section, lining details
Special structures (manholes, head walls, trash racks, etc.) plan, elevation, details of design and appurtenances
The following information regarding storage basin shall be submitted with a stormwater management plan.
- A narrative description of the design goals, methods, criteria and assumptions. The description shall also address the choice of location and potential for joint use.
- Design Data, including:
a) objective outflow
b) inflow hydrograph
d) discharge-stage data
e) watershed parameters (slope, area, etc.) reflected in the inflow hydrographs
f) inflow hydrographs
g) storm routings
h) routings summary (in tabular form)
i) drawdown time
j) expected sedimentation rate
k) soils and geotechnical report
- Maps and Drawings
a) location map showing watershed boundaries.
b) basin drawings basin drawings should show plan and vertical views along with dimensions of all structures and features.
d) basin bottom slopes
e) low flow channel
f) trash racks
h) maintenance access
Soil and Geotechnical Report Requirements
A soil and geotechnical report may be required at the discretion of the approving agency and would include:
- Site geology including bedding, foliation, fracture, joint, fault and land slide plane attitudes.
- Seismic conditions including fault locations and potential seismic surface movements respective loadings and parameters of seismic shaking.
- Potential impact of reservoir loading on geologic structure should be evaluated.
- Detailed descriptions, locations, and logs of all field explorations.
- Field and laboratory tests and analysis descriptions and results.
- Ground water table elevation and analysis of near surface groundwater movement.
- Recommended design parameters including, but not limited to, the following for the dam and its natural abutments and slopes adjacent reservoir areas:
a) Lateral earth loadings
b) Shear strengths
c) Bearing capacities
e) Slope stability analysis when saturated and during rapid drawdown conditions
f) Sieve analysis
g) Sand equivalents
h) Liquefaction analysis and if appropriate; mitigation
i) Seismic Seiche analysis
j) UBC Chapter 70
- Special design and construction recommendations including, but not limited to the following:
a) Foundation preparation requirements
b) Suitability of materials for embankments (gradation, sand equivalent, etc.) and abutments
c) Compaction methods and minimum requirements
d) Seepage and piping control provisions
e) Potential for settlement
f) Necessity of impervious core or shear key
g) Erosion control of abutment
h) Seismic considerations - Minimum design factors of safety are:
| ||Without Seismic ||With Seismic|
|Embankment, abutment and adjacent slope stability|
FLOODPLAIN ANALYSIS WITH HEC-2 OR HEC-RAS
- Plan view with:
a) Cross section locations with bank stations
b) Maximum extent of inundation (floodplain)
- Cross section plots with:
a) Bank stations
b) Mannings n values
- Profile view with:
a) Water surface
b) Energy grade line
c) Invert elevations
d) Bridges with low chord and roadway elevations
- HEC-2 or HEC-RAS input on a diskette with an explanatory narrative describing goals, methods and major assumptions.