The required detention volume is based on the different in runoff volume generated during the pre-developed and post-developed condition for the 100 year, 24 hour event. Participants wanting to purchase regional detention capacity should submit a stormwater report, signed and dated by an engineer licensed in Washington state, or other licensed professionals if appropriate.
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The current purchase price for regional detention capacity is $3.19 per cubic foot of stormwater runoff. It is a one-time non-refundable fee.
The option to buy regional detention capacity is available to anyone. However, in order to be eligible, your project must be located such that discharge from your site will reach CDID #1’s Regional Detention Basin using existing conveyances. Primary and most secondary ditches with unrestricted flow are available for direct discharge. Some of our secondary ditches may have to be improved or hydraulically modeled to demonstrate sufficient flow in order to be considered eligible. Discharges to small ditches and finger drains are not eligible for regional detention. The participant is responsible for the cost of any additional analysis or improvements required to determine eligibility, if needed.
CDID #1’s Regional Detention Basin was constructed with an original storage capacity of 480,000 cubic feet of volume. As of January 2020, approximately 200,000 cubic feet of remaining storage volume is available to purchase.
Design storm data is defined by of the City of Longview Stormwater Manual for the Longview-Kelso urbanized area (see Appendix C). Rainfall intensity for the 100-year storm is 0.26 inches per hour, and the total rainfall depth for the 100-year, 24-hour event is 6.17".