[Ord. 00075, 4/14/2014, § 17-301]
1.
Preparation of a SWM site plan is required for all regulated activities, unless preparation and submission of the SWM site plan is specifically exempted according to § 17-502 or the activity qualifies as a small project.
2.
No regulated activities shall commence until the Borough issues unconditional
written approval of a SWM site plan or stormwater permit. The Borough's
approval shall not constitute a warranty by the Borough to the owner,
developer or any third party that the plan or permit is in conformance
with the laws of this commonwealth or this chapter.
3.
SWM site plans approved by the Borough, in accordance with § 17-505, shall be on site throughout the duration of the regulated activity.
4.
The Borough may, after consultation with DEP, approve measures for
meeting the state water quality requirements other than those in this
chapter, provided that they meet the minimum requirements of, and
do not conflict with, state law including, but not limited to, the
Clean Streams Law. The Borough shall maintain a record of consultations
with DEP pursuant to this subsection. Where an NPDES permit for stormwater
discharges associated with construction activities is required, issuance
of an NPDES permit shall constitute satisfaction of consultation with
DEP.
5.
For all regulated activities, erosion and sediment control and stormwater
management BMPs shall be designed, implemented, operated, and maintained
to meet the purposes and requirements of this chapter and to meet
all requirements under Title 25 of the Pennsylvania Code and the Clean
Streams Law. Various BMPs and their design standards are listed in
the Erosion and Sediment Pollution Control Program Manual (E&S
Manual),[1] No. 363-2134-008 (March 2012), as amended and updated,
and the BMP Manual.
[1]
Editor's Note: See Part 10, Reference 9.
6.
Developers have the option to propose a Regional Stormwater Management Plan or participate in a Regional Stormwater Management Plan developed by others. A Regional Stormwater Management Plan may include off-site volume and rate control, as appropriate and supported by a detailed design approved by the Municipality in accordance with Subsection 4. A Regional Stormwater Management Plan must meet all of the volume and rate control standards required by this chapter for the area defined by the Regional Stormwater Management Plan, but not necessarily for each individual development site. Appropriate agreements must be established to ensure the requirements of this chapter and the requirements of the Regional Stormwater Management Plan are met.
7.
Unless prohibited by Akron Borough.
8.
Zoning Ordinance [Chapter 27] or any ordinance which regulates construction and development within the areas of the Borough subject to flooding, and any other applicable requirements of the Floodplain Management Act, stormwater management facilities located in the floodplain are permitted when designed and constructed in accordance with the more strict provisions of Chapter 27 of the Akron Borough Code of Ordinances and the BMP Manual, regulatory requirements and the requirements of this chapter.
9.
Impervious Areas.
A.
The measurement of impervious area shall include all of the impervious
areas in the total proposed development even if development is to
take place in stages or phases.
B.
For development taking place in stages or phases, the entire development
plan must be used in determining conformance with this chapter.
C.
Any areas designed to initially be gravel or crushed stone shall
be assumed to be impervious.
10.
All regulated activities shall include such measures as necessary
to:
A.
Protect health, safety, and property.
B.
Meet the water quality goals of this chapter by implementing measures
to:
(1)
Protect and/or improve the function of floodplains, wetlands,
and wooded areas.
(2)
Protect and/or improve native plant communities including those
within the riparian corridor.
(3)
Protect and/or improve natural drainageways from erosion.
(4)
Minimize thermal impacts to waters of this commonwealth.
(5)
Disconnect impervious surfaces by directing runoff to pervious
areas, wherever possible.
11.
The design of all stormwater management facilities over karst shall
include an evaluation of measures to minimize adverse effects.
12.
Infiltration BMPs shall be spread out, made as shallow as practicable,
and located to maximize use of natural on-site infiltration features
while still meeting the other requirements of this chapter. Infiltration
BMPs shall include pretreatment BMPs unless shown to be unnecessary.
13.
Infiltration BMPs intended to receive runoff from developed areas
shall be selected based on suitability of soils and development site
conditions and shall be constructed on soils that have the following
characteristics:
A.
A minimum depth of 24 inches between the bottom of the facility and
the limiting zone, unless it is demonstrated to the satisfaction of
the Borough that the selected BMP has design criteria which allow
for a smaller separation.
B.
A stabilized infiltration rate sufficient to accept the additional
stormwater load and drain completely as determined by field tests
conducted by the applicant's professional designer.
14.
The calculation methodology to be used in the analysis of volume and peak rates of discharge shall be as required in § 17-305.
15.
A planting plan is required for all vegetated stormwater BMPs.
A.
Native or naturalized/noninvasive vegetation suitable to the soil
and hydrologic conditions of the development site shall be used unless
otherwise specified in the BMP Manual.
B.
Invasive vegetation may not be included in any planting schedule.
[See invasive plants in Pennsylvania by the Department of Conservation
and Natural Resources (DCNR).]
C.
The limit of existing, native vegetation to remain shall be delineated
on the plan along with proposed construction protection measures.
D.
Prior to construction, a tree protection zone shall be delineated
at the dripline of the tree canopy. All trees scheduled to remain
during construction shall be marked; however, where groups of trees
exist, only the trees on the outside edge need to be marked. A forty-eight-inch
high snow fence or forty-eight-inch high construction fence mounted
on steel posts located eight feet on center shall be placed along
the tree protection boundary. No construction, storage of material,
temporary parking, pollution of soil, or regrading shall occur within
the tree protection zone.
E.
All planting shall be performed in conformance with good nursery
and landscape practice. Plant materials shall conform to the standards
recommended by the American Association of Nurseryman, Inc., in the
American Standard of Nursery Stock.
16.
Areas proposed for infiltration BMPs shall be protected from sedimentation
and compaction during the construction phase to maintain maximum infiltration
capacity. Staging of earthmoving activities and selection of construction
equipment should consider this protection.
17.
Infiltration BMPs shall not be constructed nor receive runoff from
disturbed areas until the entire contributory drainage area to the
infiltration BMP has achieved final stabilization.
18.
A minimum ten-foot wide access easement shall be provided for all
stormwater facilities with tributary areas equal or greater than 1,000
square feet and not located within a public right-of-way. Easements
shall provide for ingress and egress to a public right-of-way.
19.
Drainage easements shall be provided where the conveyance, treatment,
or storage of stormwater, either existing or proposed, is identified
on the SWM site plan. Drainage easements shall be provided to contain
and convey the one-hundred-year frequency flood.
20.
The Borough may require additional stormwater control measures for
stormwater discharges to special management areas including, but not
limited to:
A.
Water bodies listed as "impaired" on Pennsylvania's Clean Water
Act 303(d/305(b)) Integrated List.
B.
Any water body or watershed with an approved total maximum daily
load (TMDL).
C.
Critical areas with sensitive resources (e.g., state designated special
protection waters, cold water fisheries, carbonate or other groundwater
recharge areas highly vulnerable to contamination, drainage areas
to water supply reservoirs, source water protection zones, etc.)
21.
Roof drains and sump pumps shall be tributary to infiltration or
vegetative BMPs. Use of catchment facilities for the purpose of reuse
is also permitted.
22.
Nonstructural BMPs shall be utilized for all regulated activities
unless proven to be impractical.
[Ord. 00075, 4/14/2014, § 17-302]
1.
Volume control BMPs are intended to maintain existing hydrologic
conditions for small storm events by promoting groundwater recharge
and/or evapotranspiration as described in this section. Runoff volume
controls shall be implemented using the design storm method described
in paragraph .A below, or through continuous modeling approaches or
other means as described in the BMP Manual. Small projects may use
the method described in paragraph .B to design volume control BMPs.
A.
The design storm method is applicable to any size of regulated activity.
This method requires detailed modeling based on site conditions.
(1)
Do not increase the post development total runoff volume for
all storms equal to or less than the two-year twenty-four-hour storm
event.
(2)
For modeling purposes:
(a)
Existing (predevelopment) non-forested pervious areas must be
considered meadow in good condition.
(b)
When the existing project site contains impervious area, 20%
of existing impervious area to be disturbed shall be considered meadow
in good condition in the model for existing conditions.
(c)
The maximum loading ratio for volume control facilities in Karst
areas shall be 3:1 impervious drainage area to infiltration area and
5:1 total drainage area to infiltration area. The maximum loading
ratio for volume control facilities in non-Karst areas shall be 5:1
impervious drainage area to infiltration area and 8:1 total drainage
area to infiltration area. A higher ratio may be approved by the Borough
if justification is provided. Hydraulic depth may be used as an alternative
to an area based loading ratio if the design hydraulic depth is shown
to be less than the depth that could result from the maximum area
loading ratio.
B.
Volume Control for Small Projects.
(1)
At least the first one inch of runoff from new impervious surfaces
or an equivalent volume shall be permanently removed from the runoff
flow — i.e., it shall not be released into the surface waters
of this commonwealth. Removal options include reuse, evaporation,
transpiration and infiltration.
D.
Storage facilities, including normally dry, open top facilities,
shall completely drain the volume control storage over a period of
time not less than 24 hours and not more than 72 hours from the end
of the design storm. Any designed infiltration at such facilities
is exempt from the minimum twenty-four-hour standard, i.e., may infiltrate
in a shorter period of time, provided that none of this water will
be discharged into waters of this commonwealth.
E.
Any portion of the volume control storage that meets the following
criteria may also be used as rate control storage:
(1)
Volume control storage that depends on infiltration is designed according to the infiltration standards in § 17-301.
(2)
The volume control storage which will be used for rate control
is that storage which is available within 24 hours from the end of
the design storm based on the stabilized infiltration rate and/or
the evapotranspiration rate.
F.
Volume control storage facilities designed to infiltrate shall avoid
the least permeable hydrologic soil group(s) at the development site.
[Ord. 00075, 4/14/2014, § 17-303]
1.
Rate control for large storms, up to the one-hundred-year event,
is essential to protect against immediate downstream erosion and flooding.
A.
Match Pre-development Hydrograph. Applicants shall provide infiltration facilities or utilize other techniques which will allow the post-development one-hundred-year hydrograph to match the pre-development one-hundred-year hydrograph, along all parts of the hydrograph, for the development site. To match the pre-development hydrograph, the post development peak rate must be less than or equal to the pre-development peak rate, and the post development runoff volume must be less than or equal to the pre-development volume for the same storm event. A shift in hydrograph peak time of up to five minutes and a rate variation of up to 5% at a given time may be allowable to account for the timing affect of BMPs used to manage the peak rate and runoff volume. "Volume control" volumes as given in § 17-302 above may be used as part of this option.
B.
Where the pre-development hydrograph cannot be matched, one of the
following shall apply:
(1)
For areas not covered by a release rate map from an approved
Act 167 Plan:
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Post development discharge rates shall not exceed the predevelopment
discharge rates for the two-, ten-, twenty-five-, fifty-, and one-hundred-year
twenty-four-hour storm events.* If it is shown that the peak rates
of discharge indicated by the post development analysis are less than
or equal to the peak rates of discharge indicated by the predevelopment
analysis for two-, ten-, twenty-five-, fifty-, and one-hundred-year,
twenty-four-hour storms,* then the requirements of this section have
been met. Otherwise, the applicant shall provide additional controls
as necessary to satisfy the peak rate of discharge requirement.
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* A twenty-four-hour SCS type II storm or an IDF curve rational method storm. See Table 17-3-1 in § 17-305.
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(2)
For areas covered by a release rate map from an approved Act
167 Plan:
|
For the two-, ten-, twenty-five-, fifty-, and one-hundred-year
storm events,* the post development peak discharge rates will follow
the applicable approved release rate maps.
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* A twenty-four-hour SCS type II storm or an IDF curve rational method storm. See Table 17-3-1 in § 17-305.
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C.
Normally dry, open top, storage facilities shall completely drain
the rate control storage over a period of time less than or equal
to 24 hours from the peak one-hundred-year water surface design elevation.
D.
A variety of BMPs should be employed and tailored to suit the development
site. The following is a partial listing of BMPs which can be utilized
in SWM systems for rate control where appropriate:
(1)
Decreased impervious surface coverage.
(2)
Routed flow over grass.
(3)
Grassed channels and vegetated strips.
(4)
Bioretention areas (rain gardens).
(5)
Concrete lattice block or permeable surfaces.
(6)
Seepage pits, seepage trenches or other infiltration structures.
(7)
Rooftop detention.
(8)
Parking lot detention.
(9)
Cisterns and underground reservoirs.
(10)
Amended soils.
(11)
Retention basins.
(12)
Detention basins.
(13)
Other methods as may be found in the BMP Manual.
E.
Small projects are not required to provide for rate control.
[Ord. 00075, 4/14/2014, § 17-304]
1.
Runoff from impervious areas shall be drained to pervious areas within
the development site, unless the site has 85% or more impervious cover
and is a redevelopment,[1] in which case the portion of the site that discharges
to pervious areas shall be maximized.
[1]
Editor's Note: See Part 10, Reference 10.
2.
Stormwater runoff from a development site to an adjacent property
shall flow directly into a natural drainageway, watercourse, or into
an existing storm sewer system, or onto adjacent properties in a manner
similar to the runoff characteristics of the pre-development flow.
3.
Stormwater flows onto adjacent property shall not be created, increased,
decreased, relocated, or otherwise altered without written notification
of the adjacent property owner(s) by the developer. Such stormwater
flows shall be subject to the requirements of this Borough, including
the establishment of a drainage easement. Copies of all such notifications
shall be included in SWM site plan submissions.
4.
Existing on-site natural and man-made SWM facilities shall be used
to the maximum extent practicable.
5.
Stormwater runoff shall not be transferred from one sub-watershed
to another unless they are sub-watersheds of a common watershed that
join together within the perimeter of the development site and the
effect of the transfer does not alter the peak discharge onto adjacent
lands.
6.
Minimum floor elevations for all structures that would be affected
by a basin, other temporary impoundments, or open conveyance systems
where pending may occur shall be two feet above the one-hundred-year
water surface elevation. If basement or underground facilities are
proposed, detailed calculations addressing the effects of stormwater
ponding on the structure and water-proofing and/or flood-proofing
design information shall be submitted for approval.
7.
All stormwater conveyance facilities (excluding detention, retention,
and wetland basin outfall structures) shall be designed to convey
a twenty-five-year storm event.* All stormwater conveyance facilities
(excluding detention, retention, and wetland basin outfall structures)
conveying water originating from off site shall be designed to convey
a fifty-year storm event.* Safe conveyance of the one-hundred-year
runoff event* to appropriate peak rate control BMPs must be demonstrated
in the design.
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* A twenty-four-hour SCS Type II storm or an IDF curve rational
method storm.
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8.
Erosion protection shall be provided along all open channels, and
at all points of discharge. Flow velocities from any storm sewer may
not result in erosion of the receiving channel.
[Ord. 00075, 4/14/2014, § 17-305]
1.
Any stormwater runoff calculations involving drainage areas greater
than 200 acres and time of concentration (Tc) greater than 60 minutes, including on- and off-site areas, shall
use generally accepted calculation techniques based on the NRCS soil-cover
complex method.
2.
Stormwater runoff from all development sites shall be calculated
using either the modified rational method, a soil-cover-complex methodology,
or other method acceptable to the Borough. Table 17-3-1 summarizes
acceptable computation methods. It is assumed that all methods will
be selected by the design professional based on the individual limitations
and suitability of each method for a particular development site.
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Table 17-3-1
Acceptable Computation Methodologies for Stormwater Management
Plans
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|---|---|---|
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Method
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Method Developed by
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Applicability
|
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TR-20 (or commercial computer package based on TR-20)
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USDA NRCS
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Applicable where use of full hydrology computer model is desirable
or necessary.
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Win TR-55 (or commercial computer package based on TR-55)
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USDA NRCS
|
Applicable for land development plans within limitations described
in TR-55
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HEC-1/HEC-HMS
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U.S. Army Corps of Engineers
|
Applicable where use of full hydrologic computer model is desirable
or necessary
|
|
Rational method (or commercial computer package based on rational
method)
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Emil Kuichling (1889)
|
For development sites less than 200 acres, Tc<60 min. or
as approved by the Borough
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EFH2
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USDA NRCS
|
Applicable in rural and undeveloped areas subject to the program
limits
|
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Other Methods
|
Varies
|
Other methodologies approved by the Borough
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3.
If the SCS method is used, Antecedent Moisture Condition 1 is to
be used in areas of carbonate geology, and Antecedent Moisture Condition
2 is to be used in all other areas. A type II distribution shall be
used in all areas.
4.
If the rational method is used, the National Oceanic and Atmospheric Administration (NOAA) Atlas 14 data (see Subsection 2 above) or PennDOT Publication 584 "PennDOT Drainage Manual," 2008 Edition, or latest, shall be used to determine the rainfall intensity in inches per hour based on the information for the five through 60 minute duration storm events.
5.
Hydrographs may be obtained from NRCS methods such as TR-55, TR-20,
or from use of the "modified" or "unit hydrograph" rational methods.
If "modified" or "unit hydrograph" rational methods are used, the
ascending leg of the hydrograph shall have a length equal to three
times the time of concentration (3xTc) and
the descending leg shall have a length equal to seven times the time
of concentration (7xTc) to approximate an SCS
Type II hydrograph.[1]
[1]
Editor's Note: See Part 10, Reference 11.
6.
Runoff calculations shall include a hydrologic and hydraulic analysis
indicating volume and velocities of flow and the grades, sizes, and
capacities of water carrying structures, sediment basins, retention
and detention structures and sufficient design information to construct
such facilities. Runoff calculations shall also indicate both predevelopment
and post-development rates for peak discharge of stormwater runoff
from all discharge points.
7.
For the purpose of calculating pre-development peak discharges, all
runoff coefficients, both on-site and off-site, shall be based on
actual land use assuming summer or good land conditions. Post-development
runoff coefficients for off-site discharges used to design conveyance
facilities shall be based on actual land use assuming winter or poor
land conditions.
8.
Criteria and assumptions to be used in the determination of stormwater
runoff and design of management facilities are as follows:
A.
Runoff coefficients shall be based on the information contained in
Appendix 17-B-1 and 17-B-2 if the actual land use is listed in those
appendices. If the actual land use is not listed in these appendices,
runoff coefficients shall be chosen from other published documentation,
and a copy of said documentation shall be submitted with the SWM site
plan.
B.
A sample worksheet for calculating Tc is provided
in Appendix 17-B-4. Times of concentration (Tc) shall be based on the following design parameters:
(1)
Sheet Flow. The maximum length for each reach of sheet or overland
flow before shallow concentrated or open channel flow develops is
150 feet. Flow lengths greater than 100 feet shall be justified based
on the actual conditions at each development site. Sheet flow may
be determined using the nomograph in Appendix 17-B-3, or the Manning's
kinematic solution shown in the sheet flow section of Worksheet No.
1 in Appendix 17-B-4.
(2)
Shallow Concentrated Flow. Travel time for shallow concentrated
flow shall be determined using Figure 3-1 from TR-55, Urban Hydrology
for small watersheds, as shown in Appendix 17-B-5.
(3)
Open Channel Flows. At points where sheet and shallow concentrated
flows concentrate in field depressions, swales, gutters, curbs, or
pipe collection systems, the travel times to downstream end of the
development site between these design points shall be based upon Manning's
equation and/or acceptable engineering design standards as determined
by the Municipal Engineer.
C.
The developer may use stormwater credits for nonstructural BMPs in
accordance with the BMP Manual. The allowable reduction will be determined
by the Borough.
D.
Peak rate control is not required for off-site runoff. Off-site runoff
may be by-passed around the site provided all other discharge requirements
are met. If off-site runoff is routed through rate control facilities,
runoff coefficients for off-site discharges used to design those rate
control facilities shall be based on actual land use assuming winter
or poor land conditions.
9.
Times of concentration shall be calculated based on the methodology
recommended in the respective model used. Times of concentration for
channel and pipe flow shall be computed using Manning's equation.
Supporting documentation and calculations must be submitted for review
and approval.
[Ord. 00075, 4/14/2014, § 17-306]
1.
In order to protect and improve water quality, a riparian corridor
easement shall be created and recorded as part of any subdivision
or land development that encompasses a riparian corridor.
2.
Except as otherwise required by Chapter 102, the riparian corridor
easement shall be measured to be the greater of the limit of the one-hundred-year
floodplain or 35 feet from the top of streambank (on each side).
3.
Minimum Management Requirements for Riparian Corridors.
A.
Existing native vegetation shall be protected and maintained within
the riparian corridor easement.
B.
Whenever practicable invasive vegetation shall be actively removed
and the riparian corridor easement shall be planted with native trees,
shrubs and other vegetation to create a diverse native plant community
appropriate to the intended ecological context of the site.
4.
The riparian corridor easement shall be enforceable by the Borough and shall be recorded in the Lancaster County Recorder of Deeds Office, so that it shall run with the land and shall limit the use of the property located therein. The recorded easement shall be superior to all liens of record and the easement shall be on such form as the Borough Council may adopt, from time to time, by resolution. The easement shall allow for the continued private ownership and shall count toward the minimum lot area as required by zoning, unless otherwise specified in Chapter 27 of the Borough of Akron Code of Ordinances.
5.
Any permitted use within the riparian corridor easement shall be
conducted in a manner that will maintain the extent of the existing
one-hundred-year floodplain, improve or maintain the stream stability,
and preserve and protect the ecological function of the floodplain.
7.
Septic drainfields and sewage disposal systems shall not be permitted
within the riparian corridor easement and shall comply with setback
requirements established under 25 Pa Code, Chapter 73.
[Ord. 00075, 4/14/2014, § 17-307]
Attached hereto as Appendix 17-D is a certain "design templates"
for purposes of administering the technical provisions of this chapter.
Council of the Borough of Akron reserves the right, from time to time
by resolution, to amend the design templates. The use of the design
templates shall not in any way reduce the requirements of this chapter
as it relates to the matter of design, the use of BMPs and the standards
of maximum extent practical as contained in this chapter. This design
templates provides specifications for design professionals and municipalities
to use in administering the provisions of the ordinance.
The use of the design templates are mandatory, unless a waiver
is granted by Council (however, no waiver shall be given that effects
the BMPs). The standard for modification of a design template shall
be the same as the standard for a waiver of a standard in a subdivision
and land development plan under the Pennsylvania Municipalities Planning
Act.
[Ord. 00075, 4/14/2014, § 17-308]
In the case of the construction of one or more new residential
dwelling units, the stormwater management plan shall include calculations
and facilities to insure that, as to each dwelling, the standards
of this Part 3 allow an additional 250 square feet of impervious surface
above that calculated and designed for the proposed dwelling and its
appurtenances, so that each subsequent property owner may have the
ability to erect a utility shed not in excess of 250 square feet without
additional planning.
