Regional Detention Program
The Washington State Department of Ecology Stormwater Management Manual for Western Washington (SMMWW) prescribes nine minimum technical requirements for new development, re-development and land disturbing activities.
Minimum Requirement Number 7 requires flow control for projects which add or replace 5,000 square feet of new plus replaced hard surface area, or convert ¾ acres or more of vegetation to lawn or landscaped area, or convert 2.5 acres of more of native vegetation to pasture.
Flow Control Exemption
Due to local soil limitations, the City of Longview petitioned Ecology for a flow control exemption for projects within the geographic boundary of CDID #1’s system. Projects exempt from Minimum Requirement Number 7 must address flow control by attenuating the post-developed peak discharge rate to the pre-developed rate for the 25 year, 24 hour storm event or provide mitigation such as a fee-in-lieu for use of regional detention.
Regional Detention Basin
In 2002, CDID #1 constructed a Regional Detention Basin for the purpose of retaining and detaining stormwater runoff until it can be discharged to the Columbia River via CDID #1 conveyances.
The Regional Detention Basin allows landowners and developers the option to purchase non-exclusive use of offsite detention capacity as an alternative to constructing and maintaining privately owned detention facilities.
Determine whether your project is eligible for this program based on its proximity to the Regional Detention Basin and existing conveyances to ensure unrestricted flow. Eligibility for regional detention is defined by the Regional Detention Facility Service Area (PDF).
Contact us for a pre-application meeting to verify there is sufficient volume remaining in the Regional Detention Basin to meet the needs of your project, and to determine if any additional analysis or improvements will be required to ensure unrestricted flow.