Stormwater Management Facilities
All local jurisdictions in the State of Maryland are required to have stormwater management (SWM) laws that are consistent with State SWM regulations and are approved by the Maryland Department of the Environment (MDE). The result is that SWM regulations have only minor variations from jurisdiction to jurisdiction, with most of those being where a particular jurisdiction has chosen to be more restrictive than MDE recommends. The Annapolis SWM regulations are codified as Chapter 17.10 in the Annapolis City Code.
The SWM section of the Adequate Public Facilities regulations - Chapter 22.30 - of the City Code - exceeds the requirements of 17.10 in that downstream natural and man-made stormwater conveyance structures must be identified and shown capable of handling a volume of stormwater equivalent to a 10 year storm. If not, they must be repaired or replaced. If natural stream channels are deteriorated, the developer must repair them as a condition of approval for the project. Further, 22.30 defines a study impact area as from the proposed development to the next tributary downstream. Currently, the City has the latitude to define the study area on a case by case basis, but typically a developer is required to provide computations for the first 500 feet downstream.
Following is Chapter 22.30, Stormwater Management, of the Adequate Public Facilities ordinance:
The goal of adequate stormwater management facilities is to assure that all public and private stormwater infrastructure as installed within a receiving drainage area is capable of handling a 10-year storm as calculated prior to installation. Consideration will be given to any existing or proposed infrastructure within the study impact area downstream of the point of discharge.
There are no exemptions.
- A development passes the test for adequate stormwater management facilities if in the scheduled completion year of the development:
- On-site stormwater management - The on-site stormwater management facility installed by the developer is capable of managing and conveying through and from the property the design flow of storm water runoff originating in the development to an acceptable outfall that discharges directly to surface waters or via man-made or natural stormwater conveyance systems capable of handling a 10-year storm without resulting in erosion, sedimentation, or flooding of the receiving channel and downstream properties.
- Off-site stormwater management - The off-site stormwater management facilities are capable of conveying the design flow of stormwater runoff to an acceptable outfall that discharges directly to surface waters or via man-made or natural stormwater conveyance systems capable of handling a 10-year storm. The outfall must be in a stable, non-eroded condition and the discharge must be at a non-erosive velocity. If an outfall is not considered to be "adequate" in its preconstruction state, then it must be repaired as part of construction to meet adequacy standards. Review and approval of outfall adequacy may also be subject to review and approval by the Anne Arundel County Soil Conservation District.
- The developer has a designed and approvable mitigation plan and has received a waiver to on-site stormwater management pursuant to Section 17.10.120. Mitigation consists of the construction or funding of improvements to offsite facilities by a developer that increase capacity or safety on each facility that is below the minimum standard in the study impact area so that the capacity or safety of the facility after construction of the development will be equal to or greater than if the development had not been constructed. A mitigation plan shall be approved by the Director of Public Works and the Director of Neighborhood and Environmental Programs.
- The criteria for determining that the stormwater management facilities are capable and adequate for conveyance of the stormwater runoff as described above shall be developed as prescribed in the design manual entitled the 2000 Maryland Stormwater Design Manual, Volume I and II, and any amendments, as published by the State of Maryland Department of the Environment, Water Management Administration, and in accordance with Chapter 17.10 of the Annapolis City Code.
- Study Impact Area. The study impact area limits shall be to a point of investigation which is defined as the confluence with the next tributary downstream from the proposed development of the tidal waters of a tributary of the Chesapeake Bay.