February, 2011

Storm Drainage Design and Technical Criteria Manual - Updated July, 2008

Douglas County worked cooperatively with Arapahoe County, the City of Centennial, the City of Lone Tree, the Town of Castle Rock and the Urban Drainage and Flood Control District (UDFCD) to revise and update the Storm Drainage Design and Technical Criteria Manual. A goal of the group is to draw on the cumulative experience and perspectives of the local governments and UDFCD representatives and to develop some consistency in design criteria among the participating local governments in Arapahoe and Douglas Counties. In addition, the cooperation allowed for the local governments to use available funding more efficiently and to share additional funding that was provided by the UDFCD.

Introduction to Phase II Stormwater Program

Managing storm drainage is an integral component of a comprehensive package of public services. Stormwater runoff is a valuable resource if handled wisely, with increased water supply volumes and enhanced open space quality being just two of the benefits. Inadequate stormwater management can result in flooding, infrastructure and property damage, excessive soil erosion, degraded open space, unacceptable water quality in potable water supply reservoirs and other water bodies with decreased recreational and/or fish and wildlife values, and excessive financial burdens placed upon Douglas County due to flood damage repairs or increased operation and maintenance costs.

The primary function of storm sewer systems, including natural channels, is the collection, conveyance, and storage of stormwater runoff. In a watershed-based approach to urban stormwater management, the municipal separate storm sewer system, or MS4, including both structural (e.g., pipes, inlets, and outlets) and natural drainage ways, is a critical structural component. The MS4 serves multiple functions, such as storm drainage facilities, areas for recreation, and for open space and biodiversity conservation. While all of these aspects are important and need to be addressed as part of a comprehensive stormwater management program, the hydraulic function of the overall MS4 takes precedence.

Douglas County is committed to taking a proactive role in managing stormwater runoff in the County as part of the overall goal of providing quality services to its citizens. Based upon legislation by the U.S. Environmental Protection Agency (EPA), through the National Pollutant Discharge Elimination System (NPDES) Program requirements of the Federal Clean Water Act, and regulations promulgated by the Colorado Department of Public Health and Environment (CDPHE) – Water Quality Control Division (WQCD) in their Stormwater Phase II Program, Douglas County is a Stormwater Phase II permittee (beginning in March 2003) and, as such, must take the lead role in stormwater and drainage way management within the unincorporated areas of the County.

Objectives

As an integral part of Douglas County’s vision of providing its citizens with the highest quality services at the best value, with respect to stormwater management, the County will, to the maximum extent practicable:

• Safeguard the public welfare through the proper collection, conveyance, and storage of stormwater runoff in a non-damaging and non-life threatening manner.
• Ensure compliance with all applicable water quality regulations related to stormwater runoff, including and in particular, both the WQCD’s Stormwater Phase II Program and the Cherry Creek Reservoir and Chatfield Reservoir Control Regulations, respectively.
• Ensure that all County MS4 facilities are functioning and well maintained, including applicable open channels (i.e., stable physical characteristics).
• Ensure sound management and regulation of County floodplains, particularly with respect to Federal Emergency Management Agency requirements.
• Protect the overall water quality of the County’s water resources.
• Provide healthy and diverse natural habitats for flora and fauna in applicable drainage ways and County open spaces.
• Integrate recreational opportunities and facilities into drainage way planning, where feasible.