Workshop Item: 1 - Robert Therres, Public Services Manager
Title
RECOMMENDATIONS FOR APPROVING STORM DRAINAGE TREATMENT IN NEW DEVELOPMENTS
Background
Rule changes for treating storm water runoff which have come from both watershed districts and the Minnesota Pollution Control Agency are requiring an increased focus on using infiltration practices where feasible. As a result, the City is now seeing an increase in the amount of infiltration features being proposed on new developments. Many times this is not an issue but on smaller 5 to 10 acre developments some developers are proposing placing storm water treatment facilities such as swales and infiltration basins in drainage and utility easements in the rear yards to maximize the number of buildable lots in the development (see the attachment for an example). In many cases, the new developments utilize these rear yard facilities for treatment or infiltration of public street runoff by routing the storm sewer to an outlet in the rear yards. This in turn means these storm water treatment facilities are public and will need to be maintained by the City. The result is high maintenance costs combined with unhappy residents.
Infiltration basins are of particular concern as they are likely to require more frequent maintenance than storm water ponds or swales. This maintenance includes such things as removing areas of sediment deposits, plant maintenance, and restoration of infiltration rates by removing and replacing soils that have become less permeable over time. In addition, infiltration basins are not always suitable places to grow turf grass, which many property owners desire to have in their back yard.
Swales in rear yards are less of a maintenance issue but are still a concern for future resident complaints of drainage problems in their back yards.
Staff is concerned that placing these storm water treatment facilities such as swales and infiltration basins in rear yards may cause future issues with:
· Property owners who complain to the City of wet areas or standing water in their back yard.
· Property owners who alter or remove the storm water treatment facility or infiltration basin, requiring the City to restore it to its original design.
· Difficult maintenance access to rear yards as residents install sheds, fences, landscaping, etc. in their yards.
Because the requirements for infiltration and storm water runoff treatment are not going away, there needs to be somewhere for developers to put these features. Alternatives to rear yards might include placing them in a drainage and utility easement on an outlot which is turned over to the City, installing a regional facility to handle multiple small developments or placing them within public right of way. Some potential positives and negatives of each are as follows:
· Require all infiltration facilities to be located within an outlot covered by a drainage and utility easement which is adjacent to public right of way.
o Provides the best maintenance access.
o Can be planted with native grasses and other plants which require less maintenance than rain gardens.
o Eliminates complaints of wet yards or standing water in yards.
o Will likely result in the developer losing one or more buildable lots.
· Require underground infiltration facilities
o Eliminates wet yards or standing water.
o Depending on location (right of way, outlot, rear yards), ease of maintenance access will vary.
o May not work in all areas
· Require regional infiltration facilities.
o Most efficient method for areas where small 5-10 acre developments are clustered in an area.
o May require the City to be the lead in constructing these types of regional facilities.
o May be difficult to anticipate how future development will occur and thus may not eliminate the need for infiltration features on future small developments in the area.
o May not be feasible in many cases due to geography, securing easements from property owners, or many other reasons.
· Require all infiltration facilities be located within the right of way.
o Would likely be constructed as rain gardens.
o Provides for greatly improved maintenance access versus rear yards.
o Property owners may still complain of wet yards or standing water.
o Initial establishment of the rain garden will require maintenance for the first two years but will require minimal maintenance after that.
o Some homeowners may find the looks of the infiltration basins in front of their homes to be objectionable.
Discussion
· How does the Council feel about the practice of storm water runoff being directed from public right of way to drainage and utility easements on residential lots?
· Are there some types of public storm water treatment facilities that should or should not be allowed to be located within easements on residential lots? All treatment facilities will require maintenance; some will require more frequent maintenance than others.
· The problematic treatment facilities in residential yards seem to be those that have temporary ponding water during storms or wet periods. It is recommended that any rear yard storm water facility that receives street water runoff is not of a type that will result in temporary ponding or storage of the water. Permanent pools such as storm water ponds are generally acceptable.
· It is recommended that Council give staff direction on this topic and staff will come back before Council with a draft policy for Council review.