Hiawatha Golf Course Property Master Plan Facts and Misconceptions: Groundwater Pumping and DredgingPosted on 22 July, 2019
Conditions related to groundwater are complex, so as work on the Hiawatha Golf Course Master Plan continues, it’s important to take a step back and review basic facts informing the work of the MPRB and the Hiawatha Golf Course Master Plan Community Advisory Committee
The Minneapolis Park and Recreation Board (MPRB) has spent a great deal of time studying conditions at Hiawatha Golf Course as part of an effort to create a sustainable plan for the course following catastrophic flooding in 2014.
Conditions related to groundwater are complex, so as work on the Hiawatha Golf Course Master Plan continues, it’s important to take a step back and review basic facts informing the work of the MPRB and the Hiawatha Golf Course Master Plan Community Advisory Committee.
Approximately 400 million gallons of groundwater was pumped from Hiawatha Golf Course into Lake Hiawatha in the last year
Groundwater Pumping Facts
The Minneapolis Park and Recreation Board operates six pumps at Hiawatha Golf Course. The earliest pumping happened in the early 1960s, for irrigation.
There are two large pumps that were designed to pump stormwater from the western neighborhoods through the berm and into the lake. There are two medium-size pumps and two small pumps that remove water from basins within the course that are frequently wet. The pumps may have a beneficial impact on groundwater intrusion at nearby homes by artificially lowering the high groundwater table, but that was not what the pumps were intended to do.
Groundwater ≠ Creek Water
The water being pumped is groundwater and stormwater, not water from Minnehaha Creek. Minnehaha Creek bypasses Lake Nokomis and flows directly into and out of Lake Hiawatha.
The Minnesota Department of Natural Resources (MNDNR) issues an appropriations permit that only allows for pumping 36.5 million gallons per year from the surface ponds for irrigation.
The MPRB is informed it’s actually pumping about 242 million gallons of groundwater annually, in addition to millions of gallons of stormwater per year, without a permit that allows dewatering.
The MPRB receives a dewatering permit from the MNDNR that allows slightly more than 300 million gallons of pumping annually from the golf course into Lake Hiawatha. The permit is valid through 2023. At that point the MPRB must share its plan for the property with the DNR.
Ongoing assessment of groundwater pumping finds annual pumping volume measures approximately 400 million gallons of groundwater over the last year (not including stormwater).
What Happens If We:
Much of the golf course area is below the ordinary high-water elevation of the lake (812.8’) and the natural groundwater table (about the same elevation as the lake). If pumping stops, the course would fill with groundwater until it equalized with the elevation of Lake Hiawatha.
Reduce Pumping Using Existing Pumps
The course would still fill with water, it would just fill at a slower rate until it equalizes with the elevation of Lake Hiawatha.
Reduce Pumping Using New Pumps Nearer to the Neighborhood
This is different than above. MPRB Commissioners gave direction to MPRB staff to create a master plan that follows a reduced pumping scenario. This is conceptualized in Water Management Alternative B, from the water study featured in the “Water Management Data” portion this series and linked at the end of this email.
Alternative B suggests two new pumping locations — one at the northeastern edge of the property and one at E 43rd Street and S 17th Avenue — to reduce pumping while also protecting homes from groundwater to the same degree they are protected today. Groundwater pumping can be significantly reduced by pumping from a location that is further from the lake.
Dredging Lake Hiawatha
Dredging Lake Hiawatha is frequently suggested as a solution for pumping and groundwater issues, but it would not limit groundwater pumping or lower the elevation of the lake. Dredging below the water table would only result in the dredged “hole” being filled with groundwater.
Dredging Minnehaha Creek
Eliminating structures in Minnehaha Creek that impound water from Lake Hiawatha was one of the first investigations pursued by the MPRB when searching for ways to reduce pumping. It was believed that lowering the level of Lake Hiawatha, which would require significant permitting, might offer a reasonable solution.
An investigation of the creek revealed at least 19 introduced and natural downstream obstructions in the creek’s first 2,200 feet downstream of the lake, all of which have the potential to control the elevation of water in the lake to some degree.
It’s not possible to remove all those obstructions, which include a regional sewer interceptor pipe measuring more than ten feet high and requiring an earthen cover. That structure was constructed in 1925, nine years before the course opened.
Other topics part of this informational series on the Hiawatha Golf Course Master Plan include: