Construction Plans
General Requirements
- If other agencies having authority over the proposed development
have more stringent specifications than these rules and regulations
then the more stringent specifications will supersede.
- Submit three (3) sets of plans covering the entire area requesting
approval.
- Plan size shall be twenty-four (24) inches x thirty-six (36)
inches.
- The minimum scale to be used for all but the overall sheet shall
be 1" = 50’ (1" = 60’ or more not acceptable). The overall grading and
drainage plan shall have a minimum scale of 1" = 100’.
- Plans shall be sealed by a licensed Professional Engineer
registered in the State of Michigan.
- An overall plan shall be provided showing all phases of the
development, topography, total tributary area(s) and a general
indication of proposed improvements for the phase requesting approval.
- The plans must include the proprietor’s name, telephone number and
address.
- Each sheet in the plans shall have the following:
Designer’s name, telephone number and address
A proper engineer’s seal
At least one bench mark with a reference to the datum used
Sheet number, date and revision date
North arrow and bar or graphic scale
Existing structures, utilities and easements
Any inflow into a storage basin shall have a minimum fall of
eighteen (18) inches to the bottom of the basin (invert-bottom'18").
Grading And Drainage Plan
- Show all existing and proposed contours at a minimum of two (2)
foot intervals.
- Show flow arrows to designate runoff direction.
- Show inlet and manhole locations.
- Show erosion control measures.
- q Designate all 100 year floodplain levels with a heavy dashed
line. DEQ regulated floodplains usually are predetermined. All other
100 year floodplains will need be calculated. This includes
retention/detention basins and low areas that have no outlet.
- Show specifications for establishing vegetation in all areas
disturbed by construction. Seasonal limitations may require seeding
during the following spring. If this happens a silt fence will be
required in area prone to erosion.
- Show the entire tributary area boundary on this plan for each
stormwater storage area. Retention basins, detention basins and self
contained low areas all have their own tributary areas.
- Unless a special variance is granted as a result of extensive
engineering proof, no single retention basin tributary area shall be
larger than fifty (50) acres.
- Show flood routing information; designate what would happen if the
storm runoff conveyance systems were overloaded and backed up.
- Show locations of soil borings and provide soil boring logs. A
minimum of one boring per acre of storage basin is required. Borings
in the stormwater storage basin(s) must extend to at least two (2)
feet below the proposed bottom.
- Soil classifications using USDA terminology is required.
- Provide at least one bench mark with a datum definition.
- For all stormwater storage areas show the volume, top elevation,
bottom elevation inlet structure details, outlet structure
details and freeboard.
- Indicate on the plans where energy dissipation (rip-rap, gabions,
etc.) will be constructed.
- Inlets/manholes or intake structures shall be placed so that
surface road runoff does not travel more than 300 feet. Exceptions to
this rule will only be allowed if the project engineer provides proof
that the 1 year storm peak flow to a particular structure is < 1 cubic
foot per second (cfs).
- HDPE (High Density Poly Ethylene) smooth interior corrugated
plastic pipe may be used as long as it is installed according to the
pipe trench detail (Exhibit H) on Page 40 and is inspected during
installation by the project engineer. HDPE pipe may not be acceptable
under pavements if there is less than three (3) feet or more than
eight (8) feet of cover. Class III RCP (reinforced concrete pipe) and
CSP (corrugated steel pipe) gauge minimum are acceptable pipes for
storm sewer.
- Inlets, manholes, piping and end section shall be specified
according to Appendices C, D, E, F, G & H.
- Minimum pipe cover shall be eighteen (18) inches for twelve (12)
inch pipe and more as pipe size increases. The project engineer will
need to provide proof that the cover proposed is acceptable under
Calhoun County Road Commission specifications.
- If side slopes of a storage basin are steeper than 4 to 1 (4
horizontal to 1 vertical) or if the stormwater is one (1) foot or
deeper for more than twenty-four (24) hours a fence around the entire
basin is required. Any proposed fence must be shown on the grading
plan.
Construction Details And Specifications
If additional information describing the proposed construction is
necessary a detail sheet is recommended.
Retention Basins
1. On-site retention will be required of all subdivisions unless a
positive outlet is acquired to a natural stream approved by the DEQ or
to a county drain approved by the Drain Commissioner. Retention basins
can be man-made or natural. If the area is a wetland, a DEQ permit will
be required. All basins must utilize the following specifications.
2. Retention basins will be designed to hold a 100 year storm event
in a twenty-four (24) hour period. In Calhoun County this is five point
five (5.5) inches of rainfall within 24 hours.
3. To property size the basin the following items will be taken into
consideration:
a. Soil borings "required to groundwater".
b. Soil type.
c. Total tributary area.
d. Coefficiency runoff calculations of the tributary area.
e. Infiltration rate calculations.
f. Floodplain elevation for area.
g. Design of basin natural or constructed.
h. Basin must have eighteen (18) inches of fall from the invert of
the inlet pipe to bottom of basin. Bottom of basin has to be at least
one (1) foot above the seasonal high groundwater level set by project
engineer.
i. Evaporation is not considered.
j. Use of parking lots for retaining water is prohibited.
Detention Basin
A detention basin can be used when a suitable outlet can be obtained
that does not run water off from the development more than the
pre-development runoff.
Fencing
All drainage basins that are subject to water standing over 1 foot
deep for twenty-four (24) hours and/or less than 4 to 1 slopes shall be
fenced with approved fence. A sixteen (16) foot gate will be
provide at an approved location.
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Drain Commissioner
Several photos included in this 
