Article IV. Stormwater Management Criteria
4.1 Minimum Control Requirements
A. The minimum control requirements established in this section and the Design Manual are as follows:
(1) The Town of Easton shall require that the planning techniques, nonstructural practices, and design methods specified in the Design Manual 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 Ordinance 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; and
(2) The Town of Easton shall require that the overbank flood protection volume for the 2-year and 10-year frequency storm events be used to design BMP’s according to the Design Manual; and
(3) Where conditions in a downstream conveyance system prohibit the proper discharge of the 10 year pre-developed flow, the Town Engineer may require additional onsite stormwater measures to reduce the allowable 10 year postdeveloped flow in order to improve the function of the conveyance system; or require the improvement of an off-site conveyance system; and
(4) For sites within the Tanyard Branch sub-watershed, the 10 year post-developed site discharge at each study point shall not exceed the 2 year pre-developed site discharge for each respective study point; and
(5) Onsite storm drain conveyance systems for public streets shall be designed to convey the 10 year post developed flows. The allowable gutter spread for roadways shall be 8 feet or half the lane width adjacent to the curb, whichever is smaller.
B. Alternate minimum control requirements may be adopted subject to Administration approval. The Administration shall require a demonstration that alternative requirements will implement ESD to the MEP and control flood damages, accelerated stream erosion, water quality, and sedimentation. Comprehensive watershed studies may also be required.
C. 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.
4.2 Stormwater Management Measures
The ESD planning techniques and practices and structural stormwater management measures established in this Ordinance and the Design Manual shall be used, either alone or in combination in a stormwater management plan. A developer shall demonstrate that ESD has been implemented to the MEP before the use of a structural BMP is considered in developing the stormwater management plan.
A. ESD Planning Techniques and Practices.
(1) The following planning techniques shall be applied according to the Design Manual to satisfy the applicable minimum control requirements established in section 4.1 of this Ordinance:
(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 percent 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
(i) Any practices approved by the Administration.
(2) The following ESD treatment practices shall be designed according to the Design Manual to satisfy the applicable minimum control requirements established in Section 4.1 of this Ordinance:
(a) Disconnection of rooftop runoff;
(b) Disconnection of non-rooftop runoff;
(c) Sheetflow to conservation areas;
(d) Rainwater harvesting;
(e) Submerged gravel wetlands;
(f) Landscape infiltration;
(g) Infiltration berms;
(h) Dry wells;
(j) Rain gardens;
(l) Enhanced filters; and
(m) Any practices approved by the Administration.
(3) The use of ESD planning techniques and treatment practices specified in this section shall not conflict with existing State law or local ordinances, regulations, or policies. The Town of Easton shall modify planning and zoning ordinances and public works codes to eliminate any impediments to implementing ESD to the MEP according to the Design Manual.
B. Structural Stormwater Management Measures.
(1) The following structural stormwater management practices shall be designed according to the Design Manual to satisfy the applicable minimum control requirements established in section 4.1 of this Ordinance:
(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 Town of Easton.
(4) Proprietary stormwater structures utilized for underground stormwater management, i.e. Stormtech® or RainTank,™ shall be on the Administration’s approved list and installed per the manufacturer’s specifications. All performance criteria specified in the Stormwater Design Manual shall be met by such devices.
C. ESD planning techniques and treatment practices and structural stormwater management measures used to satisfy the minimum requirements in section 4.1 of this Ordinance must be recorded in the land records of Talbot County and remain unaltered by subsequent property owners. Prior approval from the Town of Easton shall be obtained before any stormwater management practice is altered.
D. 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 Design Manual and all subsequent revisions and are approved by the Administration. Practices used for redevelopment projects shall be approved by the Town of Easton.
E. For the purposes of modifying the minimum control requirements or design criteria, the owner/developer shall submit to the Town of Easton 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 an existing development, dam, highway, structure, or natural point of restricted streamflow. The point of investigation is to be established with the concurrence of the Town of Easton, downstream of the first downstream tributary whose drainage area equals or exceeds the contributing area to the project or stormwater management facility.
4.3 Specific Design Criteria
The basic design criteria, methodologies, and construction specifications, subject to the approvalof the Town of Easton and the Administration, shall be those of the Design Manual.