2.5.4 Wetlands

Approximately 12 percent of the land area within the Minnehaha Creek subwatershed is shown on the National Wetland Inventory as wetland (see Table 9). 

Table 9.  National Wetlands Inventory wetlands in the Minnehaha Creek subwatershed.

Circular 39 Type

Area (acres)

Cowardin Class

Area (acres)

Seasonal

43.8

Emergent

1,594.7

Wet Meadow

8.5

Forested

95.2

Shallow Marsh

1,546.9

Scrub Shrub

42.1

Deep Marsh

54.4

Unconsolidated Bottom

1,664.3

Open Water

1,570.7

Unconsolidated Shore

2.9

Scrub Shrub

42.1

 

 

Forested

89.9

 

 

Industrial Activity

2.3

 

 

Riverine

40.6

 

 

TOTAL

3,399.2

 

3,399.2

Source: Minnesota DNR. 

In 2001-2003 the District undertook a Functional Assessment of Wetlands (FAW) on all wetlands greater than one-quarter acre in size.  This assessment used a variant of the Minnesota Routine Assessment Method.  In contrast to Table 9 above, which shows wetland acreage and type from the National Wetlands Inventory completed in the 1980s, Table 10 below shows the acreage and type as assessed in the field.   Using the results of that analysis, individual wetlands were assigned to one of four categories – Preserve, and Manage 1, 2, or 3 (see Figure 12 and Table 11).  Wetlands that were evaluated as Exceptional or High on certain ecological or hydrologic values were assigned to the Preserve category.  The balance of evaluated wetlands were assigned to a category based on this assessment of current functions and values, with Manage 1 wetlands exhibiting higher values and Manage 2 and 3 moderate or lower values.   Refer to the Functional Assessment of Wetlands (2003) for details of methodology, classification, and management recommendations.

Table 10.  Dominant wetland type in the Minnehaha Creek subwatershed as assessed in the Functional Assessment of Wetlands. 

Circular 39 Type

Area (acres)

Seasonal

99.8

Wet Meadow

175.5

Shallow Marsh

772.6

Deep Marsh

28.8

Open Water

552.0

Scrub Shrub

432.0

Forested

418.5

Bogs

3.0

Lakes

1,347.9

Not typed

43.9

TOTAL

3,874.0

Note: Based on field assessment.  Excludes those areas determined in the field not to be wetlands, and stormwater ponds clearly excavated out of upland.   Includes some small areas that were not field assessed.

Source: MCWD 2003 Functional Assessment of Wetlands.  See Figure 11.

Table 11.  Wetland management classifications of wetlands in the Minnehaha Creek subwatershed as determined in the Functional Assessment of Wetlands.

Classification

Number

Area (acres)

% of total

Preserve

176

1,035.3

38.9%

Manage 1

157

575.6

21.6

Manage 2

128

314.7

11.8

Manage 3

371

735.5

27.6

TOTAL

 832

2,661.1

 

Note:  The FAW excluded large lakes and wetlands less than ¼ acre in size; those areas are included in the NWI, so total will not match Tables 9 or 10.

Source: MCWD 2003 Functional Assessment of Wetlands. See Figure 12.

The Minnehaha Creek subwatershed has a large number of wetlands of various sizes distributed across the landscape, including several very large wetlands and numerous wetlands through which the creek flows.  Many scored highly on vegetative diversity, fish and wildlife habitat, or aesthetics (see Figure 13).   Some of the wetlands were also evaluated for restoration potential.  Factors considered were the ease with which the wetland could be restored, the number of landowners within the historic basin, the size of the potential restoration area, the potential for establishing buffer areas or water quality ponding, and the extent and type of hydrologic alteration.  Only a few wetlands of moderate or high restoration potential are located throughout the subwatershed, and most of those are small (see Figure 14).