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More than 1,500 local governments across 40 states have enacted this type of utility, including the cities of Detroit, Ann Arbor and Birmingham.
Stormwater begins as rain or snowmelt that flows over land rather than seeping into the ground. It flows over hard surfaces (impervious surfaces) such as roofs, driveways, and walkways, as well as pervious surfaces such as grass, gardens, and woodlands into the city’s combined sewer system. The more hard surface (impervious surface) on your property, the more stormwater runoff is contributed to the sewer system.
This drainage flows into the same underground pipes as sewage and must be treated at the Great Lakes Water Authority (GLWA) wastewater treatment plant before it can be released back into the environment.
The City of Royal Oak is billed by the Oakland County Water Resources Commissioner for the conveyance and treatment of combined sewage at GLWA.
Lawns and vegetation have a limited ability to absorb water based on site specific conditions. Once saturated or frozen, water can no longer be absorbed into landscaped areas. Often, only a limited amount of impervious surface areas can be directed to an impervious area before its ability to absorb the additional water is diminished.
Buildings, garages, sheds, houses, etc. are hard surfaces that directly shed stormwater off their roofs. These surfaces eliminate large impervious areas where water can infiltrate.
Pavements like concrete and asphalt are designed to drain stormwater to a low point to prevent ponding on the surface. Water does not infiltrate standard pavements.
Standard brick pavers are typically installed over compacted base material, and the joints in between the pavers are also filled in with compacted material. These act similar to pavements, and typically do not allow any stormwater to infiltrate.
Gravel materials used for parking, roads, driveways and walkways is tightly compacted, and does not allow for infiltration. Water will always find the path of least resistance, and will tend to run downhill over compacted gravel rather than infiltrate into the underlying soils.
While stormwater may be contained within pools during a rain storm, the pool itself does not allow water from other parts of the property to soak into the soil. When the pool is drained, the stormwater that was collected will be sent to the sewer system. Considering pools as impervious surfaces is consistent with many other stormwater utilities throughout the country.
For billing purposes, stormwater charges will be based on the amount of hard surface on your property. Hard surfaces within the city’s right of way (roads, boulevards and sidewalks) are not included in your property’s hard surface area.
The hard surfaces of a property will be measured using high-resolution aerial photography. This will provide the basis for the quarterly bill. Due to the possibility of error using aerial photography, each property’s hard surface area was reduced by 100 square feet before calculating the stormwater utility charge.
Newly-developed properties will have their hard surface area determined using the approved site plan. Property owners will have the opportunity to appeal the measurement. In these cases, the property owner can provide their own measurement and submit it to the city for review.
The diagram above shows impervious areas of the property above in gray and pervious areas in blue.
The hard areas (shown in gray in the example above on the right) of a property will be calculated to the square foot and are billable.
The area in yellow (the sidewalk and street right-of way) are non-billable.
A stormwater utility covers the critical service of carrying stormwater runoff away from properties, conveying it within the city’s combined sewer system to treatment facilities and ultimately discharging it to the Detroit River. Properly operated stormwater infrastructure prevents flooding and backups, expensive repairs, and pollut