TWIN LAKES IMPROVEMENTS City of Burnsville Stormwater Management Project

The City of Burnsville contains several lakes and ponds which provide recreational opportunities, water quality benefits, flood control, and serve as a great attraction for our City. Several of these water bodies are connected via a major storm sewer line that runs from the South end of the City to the Minnesota River. As you may have noticed, No-Wake zones have been enforced at lakes, such as Crystal Lake, to prevent degradation of the shoreline. In addition, the Twin Lakes (North and South, part of the same chain of critical water bodies as Crystal Lake) have been known to be prone to flooding. The City initiated a study that focused on alternative approaches to reducing flooding in and around the Twin Lakes as well as reducing the high-water and No-Wake periods of Crystal Lake.

Project Goals:

  • Better understanding of drainage infrastructure and lake dynamics.
  • Feasibility of reducing high-water periods in Crystal Lake.
  • Development of alternative approaches to reducing flooding levels and duration of flooding in Twin Lakes, taking into account the future conditions with the planned development of the Reserve at Twin Lakes townhome complex.


  1. Crystal Lake Outlet Modifications
  2. New South Twin Lake Outlet
  3. Regional Pond Expansion


1. Crystal Lake Outlet Modifications

Crystal Lake has one outlet which controls the discharge of Crystal Lake to the downstream storm water system. In order to reduce the drawdown time of Crystal Lake, it is proposed that the existing outlet structure be removed and a new outlet structure be installed. The proposed new outlet structure will increase the drainage rate out of Crystal Lake which is estimated to help Crystal Lake drawdown roughly 37% faster allowing for shorter high water and No-Wake periods.


2. New South Twin Lake Outlet

In order to reduce the high water level and duration of flooding of South Twin Lake and North Twin Lake during significant rainfall events, it is proposed that a new outlet structure be installed at South Twin Lake. The existing outlet will remain in place as it provides a critical connection to North Twin Lake. The new outlet structure will be similar in design to the outlet structure that currently exists on the west side of North Twin Lake. This outlet structure is estimated to lower the high water levels of both North and South Twin Lake during flood events. The new outlet structure will also reduce the duration of flooding by up to 29%. A second outlet is critical because in the event debris builds ups, North Twin Lake can rely on this outlet without reduction in capacity.



3. Regional Pond Expansion

The regional pond, just north of North Twin Lake is proposed to be expanded to create additional live storage to reduce flooding within Twin Lakes. This expansion is proposed to reduce high water levels and the duration of flooding within Twin Lakes. In addition, a townhome development is being proposed for the area directly west and north of the regional pond. This expansion will also help to ensure that there will be no negative impacts to the Twin Lakes system as a result of the townhome development. Costs for this portion of the project will be shared with the PUD developer.


Q: Is South Twin Lake planned to be dredged with this project?

A: No, dredging the lake is not part of this project. The MN DNR regulates all dredging activities in public waters which includes South Twin Lake. The DNR does generally allow maintenance dredging near outfalls that bring in stormwater but they do not typically allow dredging of a whole water body or large sections of a water body to make it deeper.

Q: What is the diameter of the outlet pipe from North Twin Lake to Earley Lake?

A: The storm sewer pipe leaving the outlet control structure at North Twin Lake is a 36-inch reinforced concrete pipe. As the pipe system heads west, the pipe size gradually increases with a 78-inch pipe discharging into Earley Lake.

Q: How steep is the side slope going to be for the regional pond expansion

A: The slope of the embankment will be a 3:1 slope or three feet horizontal to everyone foot vertical.

Q: What type of landscaping is proposed on the new slope of the regional pond?

A: Native prairie along with transplanted trees are being proposed.

Q: What is the difference between the existing Crystal Lake outlet and the proposed Crystal Lake outlet?

A: The proposed outlet structure will increase the opening area which allows Crystal Lake to drawdown faster, reducing the duration of elevated water levels within the lake.

Q: What will be the impact of the new housing construction north of the pond?

A: The new housing construction is using the existing regional pond which was sized to handle the development. By expanding it with this project we are able to lower the high water levels and reduce the duration of drawdown for both North and South Twin Lakes. In addition, expanding the regional pond will provide increased water quality benefit for downstream receiving waters.