Kalamazoo County Drain Commissioner
STORMWATER MANAGEMENT RULES
DESIGN STANDARDS FOR STORMWATER MANAGEMENT FACILITIES
SETTLEMENT BASIN (DIRECT SURFACE WATER DISCHARGE)
1. Direct discharge to a surface water will only be allowed in circumstances where a waterbody is confined with no outlet.
2. The basin (square feet of water surface) shall be sized to capture particles greater than 5 microns, which is about 90% of particles in urban runoff. Basin size shall be determined by percentage of drainage area as defined in the following table.
Basin Sizing for 5 Micron Particle Control
| Land Use | % of Total Drainage Area |
| Freeways | 2.8% |
| Industrial | 2.0% |
| Commercial | 1.7% |
| Institutional | 1.7% |
| Residential | 0.8% |
| Open Space | 0.6% |
Table 3
3. Minimum basin volume shall be determined using 0.5 inches of runoff per impervious acre of the total drainage area.
4. Minimum basin depth shall be four feet from the water surface.
5. Maximum outflow from the sediment basin shall be determined by the equation:
Qout = A x 43,560 sq. ft2/acre x V
Where
A = Required surface area basin size (acre)
V = Settling velocity needed to achieve 5 micron control (0.000023 ft/sec)
6. The minimum outlet pipe size shall be 4 inches in diameter regardless of the area calculated.
7. The overflow spill way shall be designed utilizing the Weir formula for the design flow of the basin inlet storm sewer pipe.
8. A minimum of 1 foot freeboard is required.
9. Flooding easements are required from adjoining property owners who may be affected by additional discharge.
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