The City sent this week’s monitoring report for the project:
Recent Actions: Week of December 13th
Stakes have been installed the rain gardens so one can easily measure water depth.
There are 92 cells (a single rain garden can be divided into multiple cells with weirs (small raised “dams” between each cell).
Measurements on Friday, Dec. 17, 2010, 48 hours after rainfall end:
½ of the cells are draining well — dry or less than 1-inch of water
1/8 of the cells are draining a bit – 2- 4 inches of water
1/4 of the cells had 4 – 6 inches of water
1/8 of the cells had more than 6 inches of water; one of those had 11 inches of water
Saturday, Dec. 18, 2010: Vactor truck emptied cells filled with standing water
Sandbags will be replaced with more effective flow blocking asphalt plugs. To channel street runoff around the rain garden asphalt plugs that are full curb height will be placed on the inlets of most cells*, and 2-3” asphalt plugs at the most downstream outlets of a cell or series of cells. These asphalt plugs are intended to remain in place until summer, allowing the plants to establish and reduce ponding. Note that runoff will still enter rain garden cells from the sidewalks, driveways and areas where roofs downspouts have been disconnected. Project monitoring will evaluate if runoff from these sources results in standing water durations longer than our design standards; if yes, corrective action will be taken by the project team.
*The following locations will not have the curb cuts blocked:
• All cells on 30th Ave NW. Soil work and planting at this block occurred early enough in the season to allow this block to have water entering the cells this winter.
• Due to the way water is routed at a few locations along 28th NW a few of these cells will still receive runoff. ON the west side , the cell just south of 67th and the cell just south of 66th. On the east side, the cell just south of 72nd. Runoff must continue to enter these cells and then be directed back out to 28th.
For the rain garden cells not constructed to the design depth or 6” maximum ponding water, more soil will be added to those cells. However, that work cannot be conducted while the soils are saturated without negatively impacting the cells ability to drain so that work will occur after the asphalt plugs are in place. No parking signs will be reduced and those remaining will be lowered.
- Weekly meetings of the project and planning team to review the monitoring data and consider options that could improve performance
- Regular posts to blog to provide monitoring data and gather input.
Thank you for the information, City.