[Ord. No. 45,
§ 400, eff. 10-15-1973; Ord. No. 45-10, eff. 12-24-1998]
For township approval of storm sewer systems, the applicant
shall furnish to the township department of public works, a detailed
estimate of cost and two sets of storm sewer drainage and paving plans,
including the general plan for the system on which he desires approval,
specifications, detailed storm sewer design computations and drainage
area map indicating the various areas going into the points of inlet.
The department of public works shall collect the review fee and refer
the plan to the township engineer who shall check the estimate and
review the plans for conformity to standards set forth in this section,
and certify that they are consistent with the overall utility plans
of the township, after which they will comment on the plans conformity
with township standards and accepted engineering practices. The applicant,
after making any changes requested shall then submit two sets of the
revised plans to the township, for final approval. The township engineer
shall then review these revised plans for conformity to the comments
mentioned heretofore, and upon approval of such plans will retain
four copies for the township's records, and return five approved copies
to the applicant. The applicant shall obtain approval of the county
road commission and the county drain commissioner where applicable.
[Ord. No. 45,
§ 401, eff. 10-15-1973; Ord. No. 45-1, eff. 7-25-1980; Ord. No. 45-2, eff. 3-27-1986; Ord. No. 45-10, eff. 12-24-1998]
(a)
Storm drainage systems shall be designed for a ten-year storm. The
rational method (Q = CIA) for arriving at stormwater runoff shall
be used. The formula for rainfall intensity shall be:
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in which "T" is the time of concentration.
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Accepted C values for the rational method
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C Value
|
Cover
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|---|---|---|
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0.20
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Grassed (open)
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0.35
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Subdivision
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0.55
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Multiple
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0.90
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Commercial, Industrial, Office
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The township engineer reserves the right to assign higher "C"
values if the perviousness of the proposed development warrants.
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The consulting engineer shall submit a map outlining the various
areas, including off-site upstream areas, which drain to the points
of inlet used for design together with the storm sewer design computations.
This map shall include the proposed storm sewer layout and structure
numbering.
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In general, sufficient capacity shall be provided in the storm
sewer system to take upstream drainage from a fully developed, paved,
and sewered district area into the system.
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(b)
Where the hydraulic gradient is above the top of the sewer pipe,
the design elevation of the hydraulic gradient should be indicated
on the profile plan. In no case shall the hydraulic gradient exceed
one foot below the rim elevation.
(c)
Unless otherwise approved by the superintendent of the township sewer
department, manhole spacing for storm sewers shall be as follows:
|
Diameter of Sewer
(inches)
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Manhole Spacing
(feet)
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|---|---|---|
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12 to 30
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350
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36 and 42
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400
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|
48
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450
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54 and 60
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500
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66 and larger
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600
|
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A catchbasin and manhole may not be combined in a single structure
except that sump manholes on rear lot storm sewers carrying less than
two cubic feet per second (cfs) design flow may be used as a catchbasin.
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(d)
Unless otherwise approved by the superintendent of the township sewer
department, storm structures shall have a minimum diameter of four
feet.
(e)
All sets of plans which include plans for storm sewer shall include
the current township storm sewer detail sheets which shall be considered
an inseparable part of the plans when such plans are approved.
(f)
The following information shall be indicated on the storm sewer profile:
(1)
Length of run and type of sewer pipe between manholes.
(2)
Size and slope of sewer between manholes. Where possible, the
slope of the sewers shall provide a minimum velocity of 2.5 feet per
second velocity. The maximum allowable velocity in a storm sewer shall
not exceed eight feet per second.
(3)
Top elevation and diameter of all manholes and catchbasins.
(g)
Where possible, provide a minimum of three feet of cover from the
top of curb, road centerline, or proposed ground to the top of any
storm sewer. If the depth of cover to the top of the pipe is less
than three feet, C-76—class 4 pipe shall be used. All catchbasin
leads within a street shall be C-76—class 4 pipe, including
the leads to the manholes.
(h)
In general, catchbasins in paved areas shall be located as follows:
(1)
At the radius return of street intersections, 150 feet maximum
distance along the street between a high point and a corner catchbasin
is allowed when drainage is required to go around the corner.
(2)
At all low points in streets.
(3)
At intermediate points along the street such that there is maximum
of 600 feet of drainage draining to a catchbasin.
(4)
As required in parking lots and grass areas. Generally a maximum
tributary area of 25,000 square feet shall drain to catchbasins.
(i)
In general, catchbasins in nonpaved areas shall be located as follows:
(1)
In subdivisions field catchbasins shall be provided at all low
points in easements. Locate intercepting field catchbasins such that
not more than 300 feet of drainage runs into any one catchbasin other
than a low point catchbasin. A maximum of 600 feet of drainage is
allowed to run into a low catchbasin. Locate field catchbasins in
rear lot easement swale when such swale changed direction by more
than 45°.
(2)
Rear yard storm sewers shall be required in all subdivisions.
Catchbasins shall be placed at every other property corner so that
every lot directly abuts a catchbasin in at least one corner. Where
the distance between every other lot corner exceeds 350 feet or where
an intermediate low point exists, additional catchbasins shall be
installed at the intermediate lot corners and/or low point.
(3)
All catchbasins shall have lateral underdrain constructed as
shown on the township standard storm details.
(j)
Improved open drains may be permitted upon special circumstances
in accordance with article XVI.
(k)
Headwalls, inlet structures and end sections shall be placed as necessary.
End sections 18 inches and larger shall have prefabricated bar grates
on the end. Openings of the bar grates shall be constructed in accordance
with MDOT standards.
(l)
Lateral storm sewers shall be constructed to provide an outlet for
the footing drain sump pump discharge leads for each proposed building
site. Lateral storm sewers which provide for footing drain sump pump
discharge only shall be a minimum of 12 inches in diameter on a minimum
0.32% grade with manholes spaced a maximum of 350 feet.
(m)
Footing drain leads shall be connected to catchbasins. The lead shall
be constructed at a minimum depth of three feet on a minimum of 1.0%
grade. Leads and downspout connections shall be ductile iron when
located under pavement and less than 42 inches of cover exist. PVC
schedule 40 at all other locations or as approved by the township
water and sewer superintendent. The materials and methods of construction
shall be in accordance with the current township standards.
(n)
The township board has adopted resolutions prohibiting the installation
of landscape culvert enclosures in certain areas. The installation
of landscape enclosures shall be prohibited on the following streets:
Book Court, Pheasant Drive, Mallard Drive, Forbes Drive, Anchor Drive,
Sugar Bush Road, Sutton Road, and all streets on the lake side of
Jefferson Avenue.
(o)
Each condominium unit shall have a separate sump pump and sump lead
which connects directly to a catchbasin.
