2.5 Hydrologic Systems

The Department of Natural Resources? Public Waters Inventory identifies nine basins within the Lake Virginia subwatershed as under the jurisdiction of the DNR (see Figure 10).  These include five lakes and four unnamed wetlands. 

Table 3.  Public Waters in the Lake Virginia subwatershed.

DNR ID #

Name

10-9P

Lake Minnewashta

10-11P

Lake St. Joe

10-10P

Lake Tamarack

10-15P

Lake Virginia

10-208W

Unnamed

10-206W

Unnamed

10-207W

Unnamed

27-900W

Unnamed

27-132P

Rice Lake

Unnamed watercourse from Minnewashta to Virginia

Unnamed watercourse from Tamarack to Virginia

Source: Minnesota Department of Natural Resources (DNR).  See Figure 10.

The HHPLS included detailed modeling of the current and 2020 hydraulic and hydrologic conditions in the subwatershed.  That modeling includes the following results for modeled locations within the subwatershed, including lakes, wetlands, road crossings, and channels:

  • Existing Normal Water Level;
  • Existing High Water Level, peak discharge, and peak velocity for the 1.5 year, 24-hour and 100-year, 24-hour events;
  • 2020 predicted HWL, peak discharge, and peak velocity for the 100-year, 24-hour event; and the
  • Existing High Water Level for the 100-year, 10-day snowmelt event.

Those detailed results are not reproduced here, but are incorporated by reference.  The HHPLS model predicted that high water levels or peak discharges would not be significantly impacted by 2020 expected land use change, assuming that future development continues to be regulated. 

Future development may increase discharge rates in the small ditch conveying drainage from subwatershed unit LMC-5 (see Figure 2).   Two landlocked basins pose special concerns in this subwatershed.  Subwatershed units LMC-7 and LMC-8 within the City of Shorewood north of TH 7 appear to have no natural outlet.  The city has proposed constructing outlets to alleviate potential flooding issues both for existing development and future development or redevelopment.  Construction of such outlets would discharge additional stormwater volume and pollutant loading to Lake Minnewashta.

Table 4.  Modeled peak discharge from the Lake Virginia subwatershed (cfs).

Event

Existing

2020

Snowmelt

1.5 year, 24 hour

58.2

-

-

100 year, 24 hour

118.8

123.9

-

100-year, 10-day

-

-

97.3

Source:  2003 MCWD Hydrologic, Hydraulic, and Pollutant Loading Study (HHPLS)