Table 1. Maximum Pre-Development Runoff Curve Numbers
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---|---|---|---|---|
Runoff Curve Number
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Hydrologic Soil Group
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A
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B
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C
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D
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Woodland
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30
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55
|
70
|
77
|
Grassland
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39
|
61
|
71
|
78
|
Cropland
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55
|
69
|
78
|
83
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Trees and Brush
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Trees and brush may be permitted on slope surfaces
or berms.
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Stump Removal and Sprout Prevention
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Stumps of trees should be removed so vegetation
can be established and the surface mowed. Stumps can either be removed
by pulling or with machines that grind them down. All woody material
should be removed to about 6 inches below the ground surface. The
cavity should be filled with well-compacted soil and grass vegetation
established.
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Stumps of trees in riprap areas that cannot usually
be easily pulled or ground down can be chemically treated so they
will not continually form new sprouts. Certain herbicides are effective
for this purpose and can even be used near water supply reservoirs
if applied by licensed personnel. These products should be painted,
not sprayed, on the stumps. Other instructions found on the label
should be strictly followed when handling and applying these materials.
Only a few commercially available chemicals can be used along shorelines
or near water.
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Landscaping
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Vegetation shall be examined regularly, at least
twice a year during the first two growing seasons. Stunted growth
of pond vegetation or growth and excessive invasive species indicate
that increased maintenance and intervention will be necessary.
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Native landscaping prairie area shall be managed
by hand removal for invasives during the first 2-3 years of the growing
season in order to become well established. Burning, cutting, or selective
herbicide for management of invasives and woody species should take
place as needed on a two-year cycle after the third growing season.
Emergent and submergent vegetation around the perimeter of the pond
areas shall be inspected annually and any non-native and invasive
species be removed. Herbicides should not be used near open water
areas.
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Structural Inspection and Maintenance
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After construction and site grading are complete,
the pond should be checked by the City Engineer for correct design
depth and volume. If sediment has deposited during construction or
site grading, the pond shall be re-excavated.
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The annual inspection by the City Engineer and/or
maintenance of the following items shall include inspection of:
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•
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Pond inlets and outlets for structural integrity and blockage,
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•
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Riprap at pipe and culvert outlets for placement, integrity,
and effectiveness,
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•
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Inspection of berms for cracks, excessive settlement, or seepage.
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Sediment Removal (Dredging)
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This component includes monitoring of the levels
of the sediment on an annual basis. When the sediment in the forebay
(or the main basin) reaches a depth of two feet, the material shall
be removed so that the original volume of the permanent pool is maintained.
In general, pond dredging is expected to occur once every 10 to 15
years. The following practices help ensure dredging is not warranted
prematurely:
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•
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Construction site erosion control,
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•
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As-built survey of the pond at time of completion,
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•
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Successful re-vegetation and/or restoration of pond surroundings.
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Nuisance Waterfowl Control
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Nuisance waterfowl control is generally achieved through the
use of upland or shoreland buffers consisting of un-mowed tall vegetation.
The buffer zone can be mowed in the early summer of the second full
growing season. Refer to Appendix "F" of the City of Franklin Storm
Water Management Plan Update dated December 2002 by Bonestroo, Rosene,
Anderlik and Associates.
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Debris and Obstructions
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It is important to regularly remove any accumulation of debris,
which may act to block the primary outlet, the trash rack leading
into the outlet pipe, or the outlet pipe itself. If any of these items
become obstructed, a rise in the pond level could occur, creating
undue stress and endangering the slopes and berms. In addition, debris
can promote deterioration of the slopes through abrasive actions.
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Animal Burrows
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Animal burrows provide a seepage path for water through the
berms. Concentrated seepage can result in slope failure. All burrows
should be filled in with soil or grout, topped, and seeded for erosion
protection and live trapped and removed if necessary.
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Riprap
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Maintenance of riprap areas should be relatively minor. Any
displaced riprap should be replaced. This may be occurring near the
water surface, when ice accumulation can move riprap.
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Riprap is placed over geotextile fabric. Roots from vegetation
may act to compromise this fabric, thereby reducing its effectiveness.
Therefore, all vegetation in riprap areas should be removed using
methods described in subd. (3).
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