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.
A. 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;
(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
(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;
(e)
Submerged gravel wetlands;
(3)
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.
B. 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.
C. 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.
D. 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.
E. 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.
The design, methodologies, and construction specifications,
subject to the approval of the County Engineer, shall be as specified
in the Design Manual and this chapter.