[Ord. 759, 3/8/1993, § 801]
The drainage/stormwater management (hereafter referred to as
D/SWM) Plan shall consist of maps and a narrative prepared under the
direction of a professional engineer registered in Pennsylvania with
experience in D/SWM. The D/SWM plan shall include the following items:
A.
A narrative including a general statement of the project, the date
the project is expected to begin and end, a description of existing
and proposed conditions, ownership and maintenance of facilities and
conclusions.
B.
A 7 1/2 minute USGS topographic map, or equivalent, showing
the project location and its total watershed(s) and additional maps,
as necessary, to clearly show the delineation of all drainage areas,
both onsite and offsite, used in all computations for all stormwater
management facilities and all storm drainage facilities.
C.
Project mapping showing existing and proposed facilities such as
lots, streets, parking areas, drainage facilities, erosion control
facilities, areas of cut and fill, limits of earth disturbance and
stormwater management facilities.
D.
Project mapping showing existing and proposed topographic features
as follows:
(1)
Contours at two foot intervals except in areas where the slope
is greater than 15 in which case the contour interval shall be five
feet.
(2)
Boundary lines of the project area.
(3)
Drainage on the project and adjoining properties including floodplains,
floodways, streams, lakes, ponds and easements.
E.
Calculations for all drainage and stormwater management facilities.
[Ord. 759, 3/8/1993, § 802]
1.
General. The following design criteria are presented as the minimum
acceptable standards available at the time this Chapter was adopted.
New and innovative procedures are encouraged and shall be permitted
on a case-by-case basis by the Town Engineer/Consultant.
2.
Drainage.
A.
Design Storm. All drainage facilities shall be designed to safely
convey the ten-year storm. More stringent criteria may be required
where the above criteria will aggravate existing problems or create
new problems.
B.
Peak Flow. The rational method shall be used for drainage areas up
to 1 1/2 square mile. However, extreme care should be used for
watersheds with areas greater then 1/2 square mile, times of concentration
greater than 60 minutes or flow paths that include channel storage
or diversions. For drainage areas greater than 1/2 square mile, other
hydrologic methods should be considered such as the SCS soil cover
complex method.
C.
Rainfall. Design rainfall shall be determined using the Pennsylvania
Department of Transportation intensity-duration-frequency curves for
Region Four as follows:
(1)
Rational Method. The appropriate time of concentration and return
period shall be used to determine the rainfall intensity.
(2)
Soil-Cover-Complex Method. The Soil Conservation Service Type
II twenty-four-hour rainfall distribution shall be used with the following
rainfall depths:
|
Return Period
|
24 Hour Rainfall
| |
|
2 year
|
3.0 inch
| |
|
10 year
|
4.6 inch
| |
|
25 year
|
5.5 inch
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|
100 year
|
7.4 inch
|
E.
Time of Concentration. The methods found in Chapter 3 of TR-55 (Reference 1) shall be used to compute times of concentration. The length of flow path for sheet flow shall not exceed 150 feet and the length of flow path for shallow concentrated flow shall not exceed 1,000 feet.
F.
Allowable Spread of Water. The maximum allowable spread of water
on streets is 1/2 of a travel lane.
G.
Pipe Design. At a minimum, pipe capacities shall be computed using
both the Manning Equation for full flow capacity and the Inlet Control
Nomographs in Hydraulic Design Series 5 (Reference 2). For inlets,
the maximum headwater elevation must be less than the top of grate
or top of road. For culverts, the headwater/diameter ratio must be
less than or equal to 0.125. Complete outlet control calculations
shall be required for special circumstances such as high tailwater
conditions, long runs of pipe, excessive bends and other losses, etc.
H.
Inlet Spacing. The maximum spacing of inlets is 450 feet. On curbed
sections, a double inlet shall be placed at the low point on sag vertical
curves with an inlet on each side of the low point at a distance not
to exceed 100 feet or where the grade is two-tenths feet above the
low point.
3.
Stormwater.
A.
Design Storm. The maximum peak rate of runoff for the proposed conditions
shall not exceed the maximum peak rate of runoff for the existing
conditions for the two-, ten-, and twenty-five-year storms. More stringent
criteria may be required where the above criteria will aggravate existing
problems or create new problems.
B.
Hydrographs. Hydrographs shall be calculated using the following
methods:
|
Drainage Area
|
Method
| |
|---|---|---|
|
Less than 10 acres
|
Modified Rational Method
| |
|
10 to 20 acres
|
Modified Rational Method or SCS Soil Cover-Complex Method
| |
|
Greater than 20 acres
|
SCS Soil Cover-Complex Method
|
C.
Rainfall. Refer to subsection (2)(C).
D.
Runoff Coefficient. Refer to subsection (2)(D).
E.
Time of Concentration. Refer to subsection (2)(E).
F.
Routing. The design of the facility shall be verified by routing
the proposed two-, ten-, twenty-five-, and one-hundred-year hydrographs
through the facility using the storage indication method or modified
Plus method.
G.
Emergency Spillway. An emergency spillway must be provided to safely
pass the 100 storm with one foot of freeboard between the maximum
pool elevation and the top of the dam.
H.
Riser Pipe. The riser pipe shall be designed to withstand buoyancy
forces if it becomes clogged.
I.
Fencing. Any ponds with slopes steeper than three to one shall be
enclosed by a chain link fence not less than four feet in height.
J.
Pond Bottom. The minimum slope of any surface on the bottom of any
pond shall be 1 1/2%. Also, low-flow channels shall be constructed
from any pipe or swale leading into the pond to the principal spillway.
K.
Access. All facilities shall have access roads, gates and easements
where necessary.
[Ord. 759, 3/8/1993, § 804]
1.
General. Following are the minimum acceptable construction standards.
Other standards will be accepted on a case-by-case basis by the Town
Engineer/Consultant.
2.
Drainage and Stormwater.
A.
Pipe.
(1)
Pipes shall be constructed in accordance with the specifications
as set forth in the Pennsylvania Department of Transportation, Publication
408, as amended. (Reference 3)
(2)
Pipes, trenching and backfill shall be in accordance with RC-30
of Roadway Construction Standard Drawings. (Reference 4)
(3)
Pipe thickness and reinforcement shall be in accordance with
approved engineering calculations. Minimum pipe gauge for C.M.P. shall
be 16 gauge.
(4)
Pipe sizes shall be in accordance with that shown on approved
drawings. Minimum pipe size for drainage facilities shall be 15 inches
in diameter for onsite collection. Pipes utilized for upstream conveyance
of offsite flows shall have a minimum size of 18 inches.
(5)
Pipes shall be constructed and set to line and grade as shown
on approved drawings.
(6)
Pipes shall be inspected by the Town Engineer/Consultant or
his agent prior to backfilling.
B.
Inlets.
(1)
Inlets shall be constructed in accordance with the specifications
as set forth in the Pennsylvania Department of Transportation, Publication
408, as amended, and as detailed on the Roadway Construction Standard
Drawings (RC-34).
(2)
Inlet tops shall be precast concrete top units with a ten-inch
hood or equivalent in order to place inlet in a two sump condition,
and shall be compatible with type of curbing installed.
(3)
All inlets shall have weep holes placed at the appropriate elevations
to completely drain the subgrade prior to placing the base course
and surface course.
(4)
Inlets shall be inspected by the Town Engineer/Consultant or
his designated agent after completion of all work.
C.
Manholes.
(1)
Manholes shall be constructed in accordance with the specifications
as set forth in the Pennsylvania Department of Transportation, Publication
408, as amended, and as detailed on the Roadway Construction Standard
Drawings (RC-39).
(2)
Manholes shall be inspected by the Town Engineer/Consultant
or his designated agent after completion of all work.
D.
Miscellaneous Structures and Facilities. Miscellaneous structures
and facilities shall be constructed in accordance with Pennsylvania
Department of Transportation Publication 408 and Roadway Construction
Standards where applicable.
[Ord. 759, 3/8/1993, § 804]
Compliance with this Chapter does not preclude the need to obtain
other permits and approvals as required by the Town, Columbia County,
the Columbia County Conservation District, the Commonwealth of Pennsylvania,
the Federal government and other agencies. Other permits and approvals
may include an erosion and sedimentation pollution control plan, earth
disturbance permit, water obstruction and encroachment permit, dam
safety permit, submerged lands license agreement, §§ 401
and 404 of the Clean Water Act, and others. The most stringent of
all pertinent requirements shall apply.
[Ord. 759, 3/8/1993, § 805]
Prior to the granting of final approval of the D/SWM by the
Town, the applicant shall either provide for the dedication of the
permanent facilities to the Town or have a written agreement providing
for the ownership and maintenance of said facilities.
A.
Facilities Dedicated to Town. It shall be the Town's responsibility
to maintain any facilities that are dedicated to the Town. Upon construction
of the facilities which the developer or owner wishes to dedicate
ownership to the Town and before their acceptance by the Town, the
applicant shall provide to the Town an amount determined by the Town,
which at a rate of 6% per annum, will provide sufficient interest
income per year to cover the annual maintenance of such facilities,
which the developer or owner wishes the Town to accept for future
maintenance.
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Example:
| ||
|
Maintenance $250 per year = $4,166.67 deposit.
| ||
|
Maintenance $500 per year = $8,333.33 deposit.
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Prior to the Town approving the final D/SWM plan upon which
the facilities are shown for dedication to the Town, the developer
or owner shall provide to the Town satisfactory surety as approved
by the Town Solicitor to ensure the payment of the said required maintenance
amount at the completion of construction and prior to acceptance by
the Town Engineer/Consultant.
|
B.
Facilities Maintained by Private Entity.
(1)
In cases where permanent facilities are owned by a private entity
such as homeowners' association, such entity shall be responsible
for maintenance. In this case, a legally binding agreement between
the entity and the Town shall be made providing for maintenance for
all permanent facilities, including the inspection by the Town of
all such facilities deemed critical to the public welfare, annually
and after each major flood event.
(2)
If the Town determines at any time that any facility has been
eliminated, altered or improperly maintained, the entity shall be
advised of corrective measures required and given a reasonable period
of time to take necessary action. If such action is not taken by the
entity, the Town may cause the work to be done and lien all costs
against the entity.
C.
Facilities Maintained by Individual Lot Owners. When the facilities
are located on individual lots, and when they are the responsibility
of that landowner to maintain, a description of the facility or system
and the terms of their required maintenance shall be recorded with
the deed to the property.
D.
If the Town determines at any time that any facility has been eliminated,
altered or improperly maintained, the owner of the property shall
be advised of corrective measures required and given a reasonable
period of time to take necessary action. If such action is not taken
by the property owner, the Town may cause the work to be done and
lien all costs against the property.
[Ord. 759, 3/8/1993, § 806]
1.
Stormwater management facilities located in close proximity to Fishing
Creek and the Susquehanna River may be waived in order to facilitate
drainage prior to stream flooding. All conveyance facilities between
the project and the stream must have adequate capacity to safely pass
the proposed twenty-five-year storm or they must be improved to pass
the proposed twenty-five-year storm.
2.
Any proposed activity regulated by or subject to the stormwater requirements
of this Chapter which would create 10,000 square feet or less of additional
impervious cover shall not be required to adhere to the stormwater
provisions in § 22-802(3)(A) of this Part. Development which
is planned to occur in stages or phases will be considered in its
entirety for the purposes of determining exemption. Semi-pervious
areas shall be considered as impervious for purposes of this exemption.
Waivers shall not be provided for any diversion of watercourses or
watersheds.
3.
Where, owing to special conditions, a literal enforcement of the
provisions of this Part will result in unreasonable hardship, the
Town, on the recommendation of the Town Engineer/Consultant and Zoning
Officer, may make such reasonable variance thereto or waiver thereof
as will not be contrary to the public interest and so that the spirit
of this Part shall be observed and substantial justice done. A request
for a variance or waiver shall be submitted in writing by the applicant
to the Zoning Officer setting forth the grounds and all facts relied
upon by the applicant.
