07-10-2019 Workshop & Council Packet

Home Browse Search

STAFF REPORT TO:Mayor Keis and Members of City Council FROM:Chris Heineman, City Administrator Bill Dircks, Public Works Director DATE:July 10, 2019 RE:Twin Lake Update Pumping on Twin Lake has been occurring on a daily basis unless heavy rains are forecast to maintain the lake at the current permitted level of 873.5 by MnDOT and the DNR. The pump is typically turned on by staff at 7:30 a.m. and is turned off between 3:00 p.m. and 4:30 p.m. which removes all standing water in the pond area where the pump intake hose is located. This pond usually rebounds to the same level overnight, which indicates groundwater may be contributing to the resurgence of the pond. The pumping operation has been closely monitored downstream and has performed according to the predicted model at a rate of five cubic feet per second (CFS). The water levels in Owasso Basin typically rose one or two-tenths of a foot during and after pumping and dropped back down within a few hours. Gervais Lake has also bounced very little just as the model predicted. City staff met with the Watershed District, MnDOT, the DNR, Vadnais Lake Area Watershed Management Organization (VLAWMO), and Vadnais Heights on July 1. Items discussed included potential short term and long-term solutions for keeping West Vadnais water from getting to Twin Lake continued temporary pumping of Twin Lake, as well as long-term solutions for Twin Lake. One of the items that were discussed was sandbagging a depression in the West Vadnais triangle wetland embankment. This was completed that same day and made a significant difference in the flow from West Vadnais to Vadnais Lake. There were over six inches of water flowing through the 24” pipe prior to sandbagging, and shortly after sandbagging there was less than two inches in the pipe. The sandbags will be effective as long as the lake/wetland stay below the overflow elevation of approximately 884. There has been a lot of rain over the past two weeks, and it is not known if that will cause Grass Lake and West Vadnais to rise again. In order to assure that water levels will not overtop the embankment, the Ramsey-Washington Regional Watershed District is submitting an application to MnDOT for a temporary pumping permit to pump the water into the MnDOT system before it gets to the 24” pipe or Twin Lake. If the Watershed District’s application to divert water from West Vadnais Lake around Twin Lake and into the MnDOT system is approved, it should help reduce the pump capacity required to maintain or lower the lake level. In addition, the feasibility of pumping the lake level in Twin Lake lower than 873.5 becomes more reasonable from a cost and operational standpoint.