Update on plans for Wetland 114P Outlet

This case was presented at the October 18 Public Works Committee meeting.  Staff met with DNR staff after the meeting. Results of that meeting are reported in the Observations/ Alternates Section.

Wetland 114P is in the southeast quadrant of the City. It is an irregular shaped wetland with a mixture of narrow channels and wider basins.  The northern edge of the wetland touches Alpine Drive west of Nowthen Boulevard. It runs along the west edge of Ramsey Elementary, and passes under the Bridge on Sunwood Drive west of Krypton Street.  The wetland continues south between Krypton Street on the east and 147th Lane and Neon Street on the west.  The largest portion of the wetland is between Iodine Street and Potassium Street, north of 142nd Avenue. The outlet for Wetland 114P is a ditch and pipe off the northeast end of Junkite Street.  This ditch runs parallel to 142nd Avenue and enters the storm sewer system west of the intersection of 142nd Avenue and Dysprosium Street. The water stays in the pipe to the outfall to the Rum River in River's Bend Park.

This case is focused on the open water portion of the wetland bounded on the south by 142nd Avenue and on the north by 146th Avenue and on the east by Iodine Street and on the west by Neon and Postassium Streets.  The properties on the southeast quadrant of the wetland were platted as Ramsey Terrace in 1972.The properties on the east side of the wetland were platted as The Ponds of Ramsey in 2002. The properties on the southwest quadrant were platted in several phases commencing in 1992.

The County Ditch Law was passed by the legislature in the late 1880s.  This law allowed property owners adjacent to wetlands to band together and petition to construct a ditch through the wetland to drain the wetland and the adjacent properties to provide better growing conditions on the adjacent lands.  County DItch 43 was created in 1908.  It started in Wetland 114P where Alpine Drive touches it west of Sunfish Lake Boulevard. The City obtained plans for this ditch from Anoka county.  The plans run south and end south of the Sunwood Drive Bridge west of Krypton Street.  This is the north edge of the open water portion of Wetland 114P.  There is a channel with a pipe that forms the outlet of Wetland 114P. The City does not have a record of when the channel was constructed or the pipe installed.  It seems reasonable that the channel would have been constructed at the same time as Ditch 43 since a drainage ditch needs an outlet to be effective.  The outlet pipe and channel are off the north end of the Junkite Street cul-de-sac.

Trunk Sanitary sewer was extended along the east and north edges of Wetland 114P in the early 1990's.  The construction plans did not indicate a normal water level for the wetland.  Manhole rims were set to be above adjacent natural grade.

The City has received several emails over the years from residents adjacent to Wetland 114P.  The Minnesota DNR has been copied on some of the emails.  There were two different view points expressed in the emails.  The first was that the invert of the pipe was too low and the wetland was drying out.  The second was that the invert of the pipe was too high and there was potential for the wetland to flood basements. Pictures of the outlet from 2018 and 2022 are attached.  There was some water flowing through the outlet in 2018.  There is no water flowing in 2022 since rainfall totals are below normal.  

The City visited the site after a highwater email was received and observed that a beaver had constructed a dam over the outlet.  The notes from the City  workers that removed the dam indicate this appeared to be a natural dam, No man-made materials were observed.

The DNR provided information on their records for the normal water level of the wetland.  This information was used to guide the design of the outlet.

The presentation is anticipated to take 10 minutes.

Staff met with Wes Saunders-Pearce, DNR North Metro Area Hydrologist, on October 25 and discussed the plans.  He liked the plans and that the City is moving towards providing a permanent outlet structure for Wetland 114P.  He asked for some additional information to be provided with the plans.  The DNR normal water level for the wetland was recorded using the NGVD29 datum.  The current elevation datum is NAVD88.  Staff contacted a surveyor that has done work for the City and asked what the correction factor is to convert from NGVD29 to NAVD88.  The NAVD88 is 0.34 ft higher than NGVD 29.  THe DNR provided a normal water level of 858.1.  Staff is proposing using this elevation based on NAVD88 which will result in the water level of the wetland being 0.34 ft higher than when the DNR recorded the elevation.  

The DNR also asked for the hydrology model for the wetland and drainage basin.  The 2-year elevation is 856.8 ft, 0.5 ft above the normal elevation. The 10-year elevation is 859.8 ft, 0.8  ft above normal elevation. The 100-year elevation is 859.6 ft, 1.5 ft above normal elevation.  The rims of the existing sanitary manholes in the project area will be set at 860.6 ft, 1 foot above the 100-year elevation.

We also discussed timing for the DNR permit that is required to modify the outlet elevation.  The DNR Permit can take up to 60 days from submittal of the application to receipt of the permit. Raising the sanitary sewer manholes is planned for late January/early February to take advantage of frozen conditions to allow access to the structures.  Mr. Saunders-Pearce recommended submitting the application soon to allow time for processing.  He indicated the application can be updated during the review process.   
 

Staff recommends bringing the project to the December 13, 2022 City Council meeting for authorization to advertise the project to receive quotes for the work.

Motion to recommend the City Council authorize advertising for quotes for this project.