Talbot County, MD Stormwater Management Criteria

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

Planning techniques, nonstructural practices, and design methods specified in the Design Manual shall be used to implement ESD to the MEP. The use of ESD planning techniques and treatment practices must be exhausted before any structural BMP 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 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)

Control of the two-year or ten-year frequency storm event may be required according to the Design Manual if the County Engineer determines that additional stormwater management is necessary because historical flooding problems exist or are anticipated.

(3)

Without limitation of the foregoing, the County Engineer may require more than the minimum control requirements specified in this chapter if hydrologic, topographic or stream channel conditions warrant.

Alternate minimum control requirements may be adopted subject to County and Administration approval if alternative requirements will implement ESD to the MEP and control flood damage, accelerated stream erosion, water quality, and sedimentation. Comprehensive watershed studies may also be required.

The ESD planning techniques and practices and structural stormwater management measures established in this chapter and the Design Manual shall be used, either alone or in combination in a stormwater management system. A developer shall demonstrate that ESD has been implemented to the MEP before the use of a structural BMP is considered in developing a stormwater management system.

ESD planning techniques and practices.

(1)

The following ESD planning techniques shall be incorporated into the stormwater management plan as necessary to satisfy minimum control requirements established in § 164-4.1 of this chapter to:

(a)

Preserve and protect natural resources;

(b)

Conserve natural drainage patterns;

(c)

Minimize impervious area;

(d)

Reduce runoff volume;

(e)

Maintain 100% of the annual predevelopment groundwater recharge volume;

(f)

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

(g)

Limit soil disturbance, mass grading, and compaction; and

(h)

Cluster development.

(2)

The following ESD treatment practices shall be incorporated into the stormwater management plan as necessary to satisfy minimum control requirements established in § 164-4.1 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; and

Enhanced filters.

The guide shall be used for evaluation and selection of ESD planning techniques and treatment practices. Also, the Guide details the interrelationship between the planning and zoning development review process and the review and approval of stormwater management plans.

(4)

ESD planning techniques and practices or treatment practices not specified in this § 164-4.2A may be considered if approved by the Administration and allowed by the County Engineer.

(5)

The use of ESD planning techniques and treatment practices specified in this section shall not conflict with existing state or local law or local ordinances, regulations, or policies.

Structural stormwater management.

(1)

The following structural stormwater management practices shall be incorporated into the stormwater management plan as necessary to satisfy the minimum control requirements established in § 164-4.1 of this chapter:

(a)

Stormwater management ponds;

(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 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 County.

A stormwater maintenance and inspection agreement incorporating the approved stormwater management system shall be recorded in the County land records. A stormwater management system shall remain functional and shall be unaltered by subsequent property owners. Prior approval from the County Engineer shall be obtained before any stormwater management system is altered.

Alternative ESD planning techniques and treatment practices and structural stormwater measures may be used to control runoff from new development if they meet performance criteria established in the Design Manual and are approved by the Administration and allowed by the County Engineer. Practices used for redevelopment projects shall be approved by the County Engineer.

To modify any minimum control requirement or design criteria, an applicant shall submit an analysis of the impact of stormwater flows downstream to the County Engineer. 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, or natural point of restricted stream flow. The point of investigation shall be established, with concurrence of the County Engineer, downstream of the first downstream tributary whose drainage area equals or exceeds the contributing area to the project or stormwater management facility.