General design standards shall:
A. Provide protection for buildings from stormwater damage by directing
stormwater runoff away from the building via land grading adjacent
to the building.
B. Handle existing off-site runoff through the development by installing
adequate conveyance systems to accommodate the design storms as specified
herein.
C. Ensure that surface water flows that become concentrated occur in
a conveyance system of adequate capacity as specified herein.
D. Collect concentrated on-site runoff and convey the runoff from the
point of discharge into the common natural watercourse of the drainage
area, or to such other point approved by the Town. Transport stormwater
runoff for up to twenty-five-year frequency storms to the designated
stormwater management facility by means of adequate conveyance systems.
E. Maintain or improve the flow characteristics for runoff leaving the
site.
F. Seek to conform post-development grading to existing topography and
protect designated resource areas on the site to the maximum practical
extent.
The ground on which structures are located shall be graded to
carry stormwater runoff away from the buildings and dispose of it
without causing water to pond, except in approved designated areas.
Land grading shall comply with the following specific standards:
A. Minimum protective slopes around a dwelling. Grading of pervious
areas for a minimum distance of eight feet away from any building
shall slope perpendicularly away from the building toward areas designated
to accept runoff. The minimum slope in this area shall be 16 feet
horizontal to one foot vertical (16:1) (net differential in grade:
0.50 of a foot). Lesser slopes or shorter distances may be approved
in specific cases where application of these requirements is not feasible
and where an alternative method of foundation protection is provided
to the satisfaction of the Town. If the sloped area is greater than
eight feet in length, the slope may be reduced. However, the net differential
in grade must be at least 0.5 of a foot and provide a slope of at
least 2.00%.
B. Maximum protective slopes around a dwelling. In grading of pervious
areas for a minimum of four feet from the foundation of any building,
the slope shall not be steeper than four feet horizontal to one foot
vertical (4:1). The maximum man-made slope at any place on a developed
lot shall not be steeper than two feet horizontal to one foot vertical
(2:1), and any man-made slope steeper than three feet horizontal to
one foot vertical (3:1) shall be designed according to the applicable
provisions of the Delaware Erosion and Sediment Control Handbook,
to ensure slope stability and minimize maintenance requirements.
C. Driveways. The maximum grade slope shall be 8%. Driveways sloping
toward buildings shall be graded to a low point located at least eight
feet from the building with a minimum vertical elevation difference
of 0.50 foot between the elevation at the building and the low point.
The low point shall be graded to drain away from the building.
D. Fill slopes. The toe of slope on any fill steeper than four feet
horizontal to one foot vertical (4:1) on any individually developed
lot must be maintained at a minimum of two feet from the nearest property
line.
E. Retaining walls. Construction details must be provided for all retaining
walls greater than two feet in height. Retaining walls in excess of
four feet exposed height shall be located as far as necessary from
the property line to accommodate structural components. In addition,
retaining walls more than three feet exposed height shall be designed
according to the International Building Code, and calculations sealed
by a professional engineer registered in the State of Delaware shall
be submitted for review and approval by the Town.
F. Minimum slopes. The minimum slope, beyond the protective slope shall
be 5/10% on impervious surfaces, 1% on all other pervious surfaces.
When acceptable to the Town, the grade on pervious surfaces may be
reduced to 5/10, provided that soil testing and assessment by a qualified
professional are provided to ensure adequate infiltration potential
is available through all layers of the soil horizon and that the local
water table characteristics are amenable to such practices. It must
be demonstrated that the lesser gradient is adequate to drain the
lot without detrimental effect upon buildings or upon essential uses.
Conditions that result in standing water for in excess of 24 hours
are not acceptable, except in areas where delineated wetlands are
shown on the lot.
An overall lines and grades approval shall be required prior
to approval of the subdivision or land development application.
A. Approval phases.
(1) Phase 1. The first phase of this approval shall be a detailed drainage
design with calculations showing that full development of the upstream
basin has been considered in sizing all drainage structures associated
with the development. The drainage calculations and drainage plans
shall be submitted to the Town for review. At the option of the applicant,
a single plan satisfying drainage and lines and grades may be submitted.
(2) Phase 2. The second phase of this approval shall be the submission
and approval by the Town of a detailed lines and grades plan. The
grading plan shall be signed and sealed by the engineer or land surveyor.
B. Required information. The scale of the lines and grades plan shall
be sufficient to provide the following in a clear and legible manner:
(1) Contours or existing grades at intervals of not more than one foot.
If the average slope of the site is less than 1%, contour intervals
shall be 1/2 foot. Contours lines shall be supplemented with spot
elevations sufficient to determine high points, low points and to
determine that there is adequate slope throughout the site.
(2) Location of house, structure and accessory buildings on each lot.
(3) Identification of each lot by number.
(4) Elevations shall be based upon the USC and GS (United States Coast
and Geodetic Survey) data. The type of data and the location of the
benchmarks shall be indicated on the submission.
(5) The final grade elevations or contours of the proposed finished grades
shall be shown, including all drainage swales.
(6) Location of drainage outfall if any drainage is not to a street.
(7) Indication of the type of sanitary system to be used by the structure,
i.e., county sanitary sewer; also, the method and by whom this system
will or has been approved.
(8) Indicate where applicable the one-hundred-year flood line, either
storm or tidal, with elevation of said lines to be shown.
(9) Complete metes and bounds data on the property with bearings and
lengths of all lines including all necessary easements.
Before granting a certificate of occupancy, an as-built survey
plan must be submitted to the Town and reviewed by the Town Engineer
for conformance with the approved site grading plan. The Town must
approve the individual lot as-built plan before issuance of a certificate
of occupancy for said property.
In addition to any inspections performed by the Sussex Conservation
District, the Town may periodically inspect the sites of land-disturbing
activities for which permits have been issued to determine if the
activities are being conducted in accordance with the plan and if
the measures required in the plan are effectively controlling erosion
and sedimentation.