Town of St. Michaels, MD Stormwater Management Criteria

The minimum control requirements established in this chapter and the Stormwater Design Manual are as follows:

The use of ESD planning techniques and treatment practices must be exhausted before any structural SMP is implemented. Stormwater management plans for development projects subject to this chapter shall be designed using ESD sizing criteria, recharge volume, water quality volume, and channel protection storage volume criteria according to the Stormwater Design Manual. The MEP standard is met when channel stability is maintained, predevelopment groundwater recharge is replicated, nonpoint source pollution is minimized, and structural stormwater management practices are used only if determined to be absolutely necessary.

(2)

For sites that discharge to closed storm drain systems or nontidal open ditch systems, management control of the two-year and ten-year-frequency storm events to predevelopment rates shall be provided. This requirement may be waived if the requirements of § 281-11E of this chapter are satisfied.

Stormwater management and development plans, where applicable, shall be consistent with adopted and approved watershed management plans or flood management plans as approved by the Maryland Department of the Environment in accordance with the Flood Hazard Management Act of 1976, as it may be amended from time to time.

The ESD planning techniques and practices and structural stormwater management measures established in this chapter and the Stormwater Design Manual shall be used, either alone or in combination, in a stormwater management plan. The owner or licensed engineering representative shall demonstrate that ESD has been implemented to the MEP before the use of a structural SMP is considered in developing the stormwater management plan.

Environmental site design planning techniques and practices.

(1)

The following planning techniques or some combination thereof shall be considered and, where appropriate, applied according to the Stormwater Design Manual to satisfy the applicable minimum control requirements established in § 281-10 of this chapter:

(a)

Preserving and protecting natural resources;

(b)

Conserving natural drainage patterns;

(c)

Minimizing impervious area;

(d)

Reducing runoff volume;

(e)

Using ESD practices to maintain 100% of the annual predevelopment groundwater recharge volume;

(f)

Using green roofs, permeable pavement, reinforced turf, and other alternative surfaces;

(g)

Limiting soil disturbance, mass grading, and compaction;

(h)

Clustering development; and/or

(i)

Any other practices approved by the Administration.

(2)

The following ESD treatment practices shall be designed according to the Stormwater Design Manual to satisfy the applicable minimum control requirements established in § 281-10 of this chapter:

(a)

Disconnection of rooftop runoff;

(b)

Disconnection of nonrooftop runoff;

(c)

Sheet flow to conservation areas;

(d)

Rainwater harvesting;

(e)

Submerged gravel wetlands;

(f)

Landscape infiltration;

Infiltration berms;

Dry wells;

Micro-bioretention;

Rain gardens;

Swales;

Enhanced filters; and

(m)

Any practices approved by the Administration.

(3)

Requirements in the Town's Zoning Code or in other Town ordinances regulating development will not excuse implementation of ESD to the MEP. As the Town implements this stormwater management chapter, the Commissioners will evaluate provisions in the Town Zoning Code[1] or other ordinances or development requirements as necessary or appropriate in order to eliminate or mitigate impediments to implementing ESD to the MEP according the Stormwater Design Manual.

[1]

Editor's Note: See Ch. 340, Zoning.

Structural stormwater management practices.

(1)

The following structural stormwater management practices shall be designed according to the Stormwater Design Manual. In accordance with § 281-11A(1) and (2), these or any other structural practices shall be employed only after implementing ESD to the MEP and the stormwater management requirements of § 281-10 have not been met.

(a)

Stormwater management ponds. The outer slope from the rim of any embankment to preconstruction grade shall not be steeper than 10:1;

(b)

Stormwater management wetlands;

(c)

Stormwater management infiltration;

(d)

Stormwater management filtering systems; and

(e)

Stormwater management open channel systems.

(2)

The performance criteria specified in the Stormwater Design Manual with regard to general feasibility, conveyance, pretreatment, treatment and geometry, environment and landscaping, and maintenance shall be considered when selecting structural stormwater management practices.

(3)

Structural stormwater management practices shall be selected to accommodate the unique hydrologic or geologic regions of the Town.

(4)

Proprietary stormwater structures utilized for underground stormwater management shall be approved by the Administration and installed per the manufacturer's specifications. All performance criteria specified in the Stormwater Design Manual shall be met by such devices.

Environmental site design planning techniques and treatment practices and structural stormwater management measures used to satisfy the minimum requirements in § 281-10 of this chapter must be recorded in the land records of the county and remain unaltered by subsequent property owners. Prior approval from the enforcement authority shall be obtained before any stormwater management practice is altered.

Alternative ESD planning techniques and treatment practices and structural stormwater measures may be used for new development runoff control if they meet the performance criteria established in the Stormwater Design Manual and all subsequent revisions and are approved by the Administration. Practices used for redevelopment projects shall be approved by the enforcement authority.

For the purposes of modifying the minimum control requirements or design criteria, i.e., increasing the allowable post peak flow above the predeveloped discharge, the owner/developer shall submit to the enforcement authority an analysis of the impacts of stormwater flows downstream in the watershed. The analysis shall include hydrologic and hydraulic calculations necessary to determine the impact of hydrograph timing modifications of the proposed development upon a dam, highway, structure, storm drain, culvert or natural point of restricted stream flow. The point of investigation is to be established with the concurrence of the enforcement authority, downstream of the first downstream tributary whose drainage area equals or exceeds the contributing area to the project or stormwater management facility.

Stormwater management facilities and practices generally shall not be open to the public and, when not located on a privately owned residential or commercial lot, shall be protected against intrusions by the public. The purpose of this provision is to protect the public and the integrity of the stormwater management facility.