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If the watershed is small, you can use the Rational Method to calculate the design flow rate. If the area is large or you need hydrographs for designing a detention basin, the Flood Control District can calculate the hydrographs for you. You need to request a HYDRO6 submittal package. There is a fee for the District to calculate the flows for you. Contact Public Works Hydrology staff at (925) 313-2000 or email us and they can email the HYDRO6 instructions and submittal package to you. You may also purchase the submittal package at the front counter of the Public Works Department office at 255 Glacier Drive, Martinez, CA 94553.
Find your project location on the Mean Seasonal Isohyet Map that can be found in the Public Works Hydrograph Standards webpage and determine the mean seasonal rainfall for your site. Then, use the 25-year Precipitation Duration-Frequency-Depth Curve found at the same link. Find 24-hours (1-day) on the x-axis, go up parallel to the y-axis on the graph to the mean seasonal rainfall for your site. Go horizontal parallel to the x-axis to the y-axis to read off the rainfall depth for the 25-year 24-hour storm.
POCs are pollutants that impair waterways which are commonly found in urban run-off. They include Total Suspends Solids (TSS), sediment, bacteria (fecal coliform) and pathogens, heavy metals (e.g., lead, zinc), oil and grease, polyaromatic hydrocarbons (PAHs), synthetic organics (pesticides, PCBs), nutrients (fertilizers), oxygen demanding substances (vegetations, pet waste), and litter.
BMPs are devices or control measures for managing stormwater run-off. They include structural drainage inlet protection like catch basin inserts, gravel bags and straw waddles as well as operational controls like training, good housekeeping, adequate spill response and proper material handling and storage.
All of the land that drains to a common receiving body of water. In Contra Costa County we have 32 watersheds, several of these share boundaries with Alameda County. Watersheds are commonly named for the waterway or water body they flow to.
An illicit discharge is any non-stormwater discharge or discharge to the storm drain system that is not composed entirely of rain or precipitation run-off.
Call 911 or the Sheriff’s Dispatch (925) 646-2441 to report an illegal discharge going on right now. Call (925) 313-2236 to report an illicit discharge that has taken place in unincorporated County or call 1 (800) NO-DUMPING to report an illicit discharge that occurred in other cities/towns in Contra Costa County.
An NOI is a “Notice of Intent’ application to be included in one of CA’s General Stormwater Discharge Permits. If you are a commercial or industrial facility covered by certain NAIC code like chemical manufacturing or vehicle servicing, you may be required to file an NOI for inclusion in CA’s General Permit for Industrial Facilities. If you disturb soil of more than 1 acre you may be required to file an NOI for inclusion in CA’s General Construction permit. If you are a point source discharger like an industrial facility you may be required to apply for an individual NPDES permit. If you are a municipality that owns/maintains an MS4 you may be required to apply for a Municipal Stormwater Discharge NPDES permit.
C.3 refers to Provision C.3 of the County’s NPDES Permit, which was added to the Permit in 2003. This provision requires stormwater runoff from projects creating and/or redeveloping at least 10,000 square feet of impervious surface to treat stormwater runoff with permanent stormwater management facilities, and requires projects creating and/or redeveloping to design such facilities to control runoff rates and volumes (in addition to treatment). Projects that are not required to comply with C.3 still implement permanent stormwater controls to the maximum extent practicable.
NPDES stands for the National Pollutant Discharge Elimination System. It’s a permitting program required under the U.S. Clean Water Act for discharges to surface waters of the U.S. In CA, USEPA has delegated its authority to implement the NPDES Program to CAL/EPA’s State Water Resources Control Board (SWRCB) who in turn manages the NPDES Program via five Regional Water Quality Control Boards (RWQCBs). In Contra Costa County, two RWCQBs oversee our County’s discharges to the Bay and the Delta, the San Francisco Bay and Central Valley RWCQBs, respectively.
The County Title 9 (Title 9: 911-2.010) sets the design storm based on the watershed area draining to the creek of drainage facility as follows:
A Stormwater Pollution Prevention Plan (SWPPP) is a document that describes how a project will prevent pollution during the construction process. This document details how erosion will be prevented and how sediment will be controlled, as well as how other construction-related pollutants, such as concrete dust and fluids from construction equipment, will be prevented. SWPPPs, which are required under the California Construction General Permit, must be submitted for projects disturbing at least 1 acre of soil, and for certain projects involving less earthwork but pose special threats to water quality. Smaller projects also are required to implement adequate erosion and sediment controls.
A Stormwater Control Plan (SWCP) is a document that details permanent storm water management facilities (such as bioretention areas) that will be incorporated into development projects to treat storm water runoff and control runoff rates and volumes after the construction process is completed. SWCPs are required for projects that must implement permanent storm water management facilities to comply with C.3 of the NPDES Permit.
A point source, also termed ‘end of pipe’ discharge, is a discharge from a defined, discrete conveyance like an outfall coming off an industrial property. The US Clean Water Act was enacted to stop point source discharges like sewage and industrial chemicals to our waterways.
Today, non-point source pollution is the primary contributor of pollutants to our waterways. It comes from a variety of diffuse sources like atmospheric deposition, automotive leaks, and brake pad dust, fertilizer and pesticide use, construction, agriculture, mining and fecal waste. Pollutants from these sources are picked up by urban run-off and deposited into our surface waters impairing their beneficial uses.
Municipalities are required to educate residents and inspect business in storm water pollution prevention practices.
Both the Contra Costa Clean Water Program and the County Watershed Program (CWP) are tasked with ensuring compliance with the Municipal Stormwater National Pollutant Discharge Elimination System (NPDES) Permit.
The NPDES permit is issued to the Clean Water Program, which is a collaboration between the County (represented by the County Watershed Program), the 19 incorporated cities and towns in the County, and the County Flood Control and Water Conservation District (“Co-Permittees”).
The Clean Water Program (www.cccleanwater.org) has its own staff that interacts with regulatory and elected officials, and provides guidance to the Co-Permittees. The Co-Permittees benefit from these collaborative efforts which the individual jurisdictions time and money. Ultimately, however, each jurisdiction is individually responsible for administering the NPDES permit within the bounds of its jurisdiction.
Operationally, the County Watershed Program is a program within the Flood Control Division of the County’s Public Works Department. CWP is responsible for ensuring compliance with the NPDES permit in the unincorporated areas of the County.
Storm drain systems include the gutter, drainage inlets, catch basins, piping and the waterways they convey storm water to in order to prevent flooding of our streets. Stormwater flows through these conveyances directly to receiving waterbodies such as the Delta and Bay without being treated. Storm drain systems are also often referred to as MS4s or Municipal Separate Storm Sewer Systems. Sanitary sewers transfer wastewater from our homes and businesses to wastewater treatment plants for primary, secondary or tertiary treatment prior to being discharged to receiving waterbodies via outfall pipes or reclaimed for irrigation purposes.
Easements provide the Public Works Department and Flood Control District with land rights for construction, reconstruction, maintaining and accessing its drainage facilities and for other related purposes. Some access easements are not used regularly but must be kept clear for potential future use. An easement allows the property owner use of the property as long as it does not interfere with easement rights.
No permanent structures or encroachments will be permitted or constructed within or over any drainage easement. This includes, but is not limited to:
- fill slopes- retaining walls- fencing- sheds- landscaping
Any such obstructions will be removed as necessary for maintenance and access purposes and will not be repaired or replaced (Title 0; 914-14.010).
During business hours, call Public Works Maintenance Division at (925) 313-7000 or email Public Works Maintenance. Visit the Public Works Request Services webpage for other ways to report flooding or other service requests. If it is an emergency after hours, call the Sheriff's dispatch at (925) 646-2441.