WORKSHOP ITEM - Robert Therres, Public Service Manager/Public Works Director
Title
EASTSIDE PARK DRAINAGE ISSUES
Background
Staff was directed by Council at a previous meeting to investigate resident concerns over tree cutting debris in the storm water ponds and general drainage issues at Eastside Park and the neighborhood rear yards across the street in 4600 block of 107th Ave NE.
The rear yards of the property owners who expressed concerns are part of the storm water system for the D Erickson neighborhood which was constructed in the mid 80’s. The rear yards, which are in a drainage and utility easement, act as a drainage basin for the storm sewer system in the neighborhood. According to record drawings, the storm sewer outlet pipe elevation for this basin was originally designed to be approximately 6 inches higher than the lowest elevation of the rear yard basin area. The storm sewer outlet pipe for the basin crosses under 107th Avenue and empties into a pond system in Eastside Park. This pond system outlets into a small ditch which joins with a branch of County Ditch 53-62 right where it crosses under I 35W and travels north.
Public works storm water personnel inspected the area and storm water system and observed the following on the day of inspection:
1) There is no evidence of any tree cutting recently. In talking with one of the property owners, they said it was done years ago and the kids threw the branches in the pond. Public Works will work to clean up what can be accessed.
2) The flared end section (FES) in the back yard, which serves as the outlet for the drainage basin, had ¼ of an inch of water in it and was flowing north to the pond in Eastside Park. The portion of the rear yard drainage basin that still had standing water had approximately 4 inches of water standing.
3) The final outlet on the west end of the East Side Park pond system is clear and open with about 1 inch of water standing in the FES.
4) The bottom of the culvert that serves as the final outlet of the East Side Park pond system is rusted clean through the entire length of the culvert. The culvert is still functioning properly but this will be added to the list to be changed out this year.
5) There is some sediment build up in areas of the ponds but it is not affecting overall drainage patterns. A pond survey for these ponds was completed in 2016 and the elevations of the pond bottom do not indicate significant sediment buildup or loss of pond volume that needs to be addressed at this time.
6) The storm system is operating as designed with no obstructions or blockages present.
Staff was contacted by the one of the property owners on Tuesday April 25, 2017 requesting a meeting to discuss the issues with drainage of their rear yards and East Side Park. A meeting was held Thursday April 26, 2017 and staff discussed the water issues in the backyards, basements and Eastside Park with the property owners.
Prior to the meeting, staff reviewed the plat and drainage area as well as reviewed historic aerial photography of the area. The historic aerial photos appear to show the backyards to be a wetland which would be consistent with why this area was chosen to be a drainage basin. The development was platted in 1985 prior to the Minnesota Wetland Conservation Act which was passed in 1991 so developers weren’t required to delineate the wetlands
Staff explained to the property owners how the entire system functions. It was stated that there were unique issues last year further downstream that caused the extensive water ponding in the rear yards and that the basement water issue was unrelated to the rear yard water issue. Rice Creek Watershed will be modifying the outlet structure near Home Depot this fall which was a contributing factor to last year’s issues. The design of the storm basin and outlet means that there can be a few inches of water standing until it infiltrates into the ground and during times of high groundwater, it may not infiltrate. This is entirely consistent with what likely happened in the wetland prior to development.
Staff discussed some options with the property owners to help mitigate the amount of standing water and they are as follows:
1. Stop mowing the backyards and allow the wetland vegetation to grow and absorb more of the water
2. Remove any landscaping that could be taking up the drainage capacity
3. Reduce or stop irrigating their lawns during wet periods
4. Position downspouts away from their back yards if possible or provide for longer distance to drain and infiltrate.
5. Complete a wetland delineation review to determine where the wetland boundary is and if the area could be excavated to create a deeper pond to concentrate the remaining water in one place.
A wetland boundary review has been scheduled for Wednesday May 10, 2017 with staff and an Anoka Conservation District Wetland Specialist. Once the wetland boundary review has been completed, the next steps will be to discuss the results and potential options with the property owners.
Once weather conditions allow, staff will work to remove some of the downed trees and vegetation in Eastside Park and start the process to remove and replace the downstream culvert that has rusted out.