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.

Pervious Surface versus Hard Surface

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 example above shows a parcel with a house, garage, deck (with pavement below) and areas of brick, gravel and concrete pavement.	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 pollution of natural waterways. While the city currently operates a combined sewer system, the method of funding this operation and the associated costs for treatment has been determined to be outdated by current standards. The city’s proposed stormwater utility will proportionally bill users for their use of the system and will encourage activities that promote better stormwater management and lessen the burdens of the system, making the existing infrastructure more adaptable to severe rain events.

The city used low-altitude, high-resolution aerial photography to determine the hard surface area on each property. The city will perform aerial flyovers every three years to update the hard surface database.

Using aerial photography is the best possible way to measure each property’s individual hard surface area. However, mapping of aerial photographs does have a degree of inherent error. The hard surface area on each property was therefore reduced by 100 square feet to account for error in the measurements.

The image below is an example of aerial photography. The area outlined in blue represents the hard surface area. The pop-up block indicates the Billable Hard Surface Area of this property is 91,215 sq. ft. 

To view your property go to: https://royaloak.maps.arcgis.com/apps/webappviewer/index.html?id=88ea895ad7f34bdb885f3994d431f972

Royal Oak has a "combined" sewer system, which means that all the stormwater from rain and snow is mixed with all the sanitary sewage from private sewer leads into one pipe. Parts of the city do have separate stormwater pipes and sanitary sewer pipes, but these all ultimately drain to the same county drain and are combined. This means that the city has to pay to treat all the sewage AND stormwater that enters the system.

Roads and public rights-of-way maintained by the city are exempt from the stormwater utility fee because they function as part of the stormwater collection and conveyance system. City-owned properties such as parks and parking lots are subject to the stormwater utility fee.

While stormwater is a result of rain and snowmelt, the stormwater fee is not related to how much rain falls on your property, but rather the facilities used to manage stormwater such as sewers, manholes, catch basins and wastewater treatment. The more hard surface a property has, the more it uses the stormwater system components.

The settlement was based upon language in the Drain Code that requires the city to bill for its portion of the debt on the Kuhn RTF on an ad valorem basis. However, billing for stormwater costs based upon the amount of stormwater that a property contributes to the stormwater system is more rational and more equitable than billing for stormwater costs based upon the amount of water consumed at that property.