Channel protection detention is 24-hour extended detention of the post-developed 1-year 24-hour storm event. This feature is intended to reduce channel erosion. All sites with a flood detention basin should also provide the channel protection feature. The existence of nearby erosion problems will also necessitate channel protection detention.Appendix D-11 of the Maryland Stormwater Manual shall be used to calculate the channel protection storage volume and the orifice (outlet) size.
If a site is smaller than five acres, flood detention is not required, and nearby downstream erosion problems do not exist, then channel protection detention is not a site requirement. Additionally, redevelopment sites larger than five acres may be exempt, if certain criteria are met. (See Amendment No. 1 to MSD Rules and Regulations for a list of criteria.)
MSD will allow the storage provided by bioretention and porous pavement to be increased to meet channel protection detention criteria. This typically occurs on larger sites where channel protection is required, but flood detention basin is not. Additional information on this approach is provided in technology descriptions for bioretention and porous pavement.