A.
The minimum control requirements established in this section and
the Design Manual are as follows:
(1)
The Town requires 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 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 and ten-year frequency storm event is required
according to the Design Manual and all subsequent revisions if the
Town determines that additional stormwater management is necessary
because historical flooding problems exist and downstream floodplain
development and conveyance system design cannot be controlled.
(3)
The Town may require more than the minimum control requirements specified
in this chapter if hydrologic or topographic conditions warrant or
if flooding, stream channel erosion, or water quality problems exist
downstream from a proposed project.
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.
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
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 § 133-9 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
(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 § 133-9 of this chapter:
(a)
Disconnection of rooftop runoff;
(b)
Disconnection of nonrooftop runoff;
(c)
Sheetflow to conservation areas;
(d)
Rainwater harvesting;
(e)
Submerged gravel wetlands;
(f)
Landscape infiltration;
(g)
Infiltration berms;
(h)
Dry wells;
(i)
Micro-bioretention;
(j)
Rain gardens;
(k)
Swales;
(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 will, with due consideration
given to public safety issues, 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 § 133-9 of this chapter:
(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.
C.
ESD planning techniques and treatment practices and structural stormwater management measures used to satisfy the minimum requirements in § 133-9 of this chapter must be recorded in the land records of the county and remain unaltered by subsequent property owners. Prior approval from the Town 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.
E.
For the purposes of modifying the minimum control requirements or
design criteria, the owner/developer shall submit to the Town 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, or natural point
of restricted streamflow. The point of investigation is to be established
with the concurrence of the Town, downstream of the first downstream
tributary whose drainage area equals or exceeds the contributing area
to the project or stormwater management facility.
The basic design criteria, methodologies, and construction specifications,
subject to the approval of the Town and the administration, shall
be those of the Design Manual.
