2.0 Land and Water Resources Inventory

2.1 Location

The Minnehaha Creek subwatershed encompasses all the MCWD downstream of the Grays Bay dam, and is commonly referred to as the “lower watershed”  The cities of Plymouth, Wayzata, Minnetonka, St. Louis Park, Hopkins, Edina, Minneapolis, and Richfield have land within this subwatershed (see Figure 1).  The Minnehaha Creek subwatershed is 30,290 acres in size (47.3 square miles).

2.2 Physical Environment

2.2.1 Topography and Drainage

The lower portion of this subwatershed generally east of the city of Hopkins is located within the Mississippi Valley Outwash region, which is typified by gently rolling terraces and bottom lands punctuated by small lakes formed from melted blocks of glacial ice.  The upper portion of this subwatershed is located within the Emmons-Faribault moraine region, an area characterized by gently rolling to steep hilly landscapes with numerous lakes formed in deep irregular depressions called “kettles.”

The 2003 MCWD Hydrologic, Hydraulic, and Pollutant Loading Study (HHPLS) subdivided the Minnehaha Creek subwatershed into 184 subwatershed units, designated MC-1 through MC-184 (see Figure 2).   Minnehaha Creek is formed at the outlet of Grays Bay and flows 22 miles to the Mississippi River.  The Chain of Lakes in the City of Minneapolis (Brownie, Cedar, Isles, Calhoun, Harriet) drain parts of Minneapolis and St. Louis Park and discharge to Minnehaha Creek.  Lake Hiawatha is located in-line to Minnehaha Creek and is heavily influenced by it.

2.2.2 Geology and Soils

The depth to bedrock within the subwatershed varies from 100-200 feet in the upper subwatershed to 0-100 feet in the lower subwatershed near the Mississippi River.  In the upper subwatershed, quaternary deposits – the surficial material overlaying the bedrock - are generally high relief New Ulm loamy till, with pockets of peat and muck and glacial outwash along the Minnehaha Creek corridor.    In the lower subwatershed, glacial outwash overlays the bedrock with pockets of peat and muck.  Glacial drift deposits up to 300 feet thick lie in the buried bedrock valley under the area near Lakes Calhoun and Harriet.  At Minnehaha Falls and the Mississippi River the glacial drift has eroded away, exposing bedrock.

Soils within the watershed are predominantly urban disturbed soils that have not been classified.  The HHPLS assumed that Urban Disturbed soils were primarily classified as Natural Resources Conservation Service Hydrologic Soil Group B soils. Where the soils have been classified, they are mainly Group B (loamy soils with moderate infiltration potential) and D (clayey soils with very low infiltration potential) (see Figure 3).  The Group D soils are found in low-lying areas and are generally hydric, or showing indications of inundation (see Figure 4) or are in areas of mucky soils.  There are also scattered areas of Group A soils, sandy loam soils with high to moderate infiltration potential.  

2.2.3 Unique Features and Scenic Areas

The subwatershed contains numerous regional recreational facilities.  The National Park Service oversees the Mississippi National River and Recreational Area, which includes the Mississippi River gorge area within the subwatershed, including Minnehaha Falls.  The Falls area includes a number of structures constructed by the Works Progress Administration (WPA), including retaining walls along the creek.  The Minneapolis Park and Recreation Board (MPRB) operates a popular park and trail system around the Chain of Lakes and along Minnehaha Creek east of Lake Harriet.  The North and South branches of the Three Rivers Park District’s Southwest LRT Regional Trail connects the Chain of Lakes with the western subwatershed.    

Camp Coldwater Spring, a site with significance to Native American communities and the location of the first white settlement in Minnesota, is located in the extreme southeast part of the subwatershed.  The Minnesota Historic Features database notes over 1300 historic features in this subwatershed, most residences or commercial buildings.  Three Historic Districts are listed on the National Register of Historic Places: the Minnehaha District in the vicinity of Minnehaha Falls; the Nokomis Knolls District, a residential district at the southwest corner of Lake Nokomis; and the Country Club District in Edina, an area of over 500 historic residences, commercial buildings, and other properties, including the Minnehaha Grange.  More detail regarding Camp Coldwater Spring and other locations significant to the watershed’s early history can be found in the Water Resources Management Plan.  

2.3 Biological Environment

2.3.1 Vegetation

Land cover as classified by the Minnesota Land Cover Classification System (MLCCS) is shown on Figure 5.  Urban areas with moderate to high densities of impervious surface characterize the subwatershed, which is entirely developed.  There are some sizable areas of wetland and forest/woodland in the city of Minnetonka and in some locations along the creek corridor.  An extensive but narrow park system surrounds the Minneapolis lakes and Minnehaha Creek and along the Mississippi River.

2.3.2 Biologic Integrity

Landscape

Development in this subwatershed has left few large areas of undisturbed or minimally disturbed forest and wetland in the subwatershed.   Three areas, including the Grays Bay outlet wetland complex; Diamond Lake; and part of the creek corridor in the Mississippi River gorge have been designated Regionally Significant Ecological Areas by the DNR (see Figure 6).   The Minnesota County Biological Survey (MCBS) did not identify any areas of biodiversity significance in the subwatershed.   The creek corridor and the Chain of Lakes in the lower subwatershed are part of a DNR-designated Metro Conservation Corridor. 

The Minnesota Natural Heritage Information System lists several rare species in this subwatershed, as shown in Table 1.

Table 1.  Rare species in the Minnehaha Creek subwatershed.

Species

Status

Acadian flycatcher

State concern

Biennial gaura

Being evaluated

Blanding’s turtle

State threatened

Lake sturgeon

State concern

Prairie vole

State concern

Pugnose shiner

State concern

Rock clubmoss

State threatened

Valerian

State threatened

Source:  Minnesota DNR.

Lakes

The MPRB has prepared vegetation surveys for some of the Chain of Lakes, and has conducted phytoplankton and zooplankton surveys of those lakes.  A vegetation survey compiled by the MPRB for Diamond Lake in 2004 indicated the presence of curly leaf pond weed on that lake.  Most of the city lakes have been colonized by Eurasian watermilfoil.

The MPRB periodically harvests milfoil on Harriet, Calhoun, Lake of the Isles, Cedar, and Nokomis to support swimming and boating.  Such harvesting was completed in 2004 on Harriet, Calhoun, Isles, and Cedar.   In addition, the MPRB is working together with the University of Minnesota to explore the use of a native weevil to naturally control nuisance milfoil growth. Lakes treated include Calhoun, Hiawatha, Harriet, and Isles.

Fishery.  Because of their status as regional resources, the Minnesota DNR conducts regular fish surveys of the Chain of Lakes.  Other lakes are surveyed less frequently.  Powderhorn Lake is managed by the DNR as part of its Fishing in the Neighborhood program and is stocked regularly with black crappie and bluegill and most recently with channel catfish.

Table 2.  DNR fish survey data.

Lake 

Survey Year

Fishery – fish stocked

Dominant Fish

Brownie

1993

Pan

Bluegill, black crappie

Cedar

2003

Sport

Bluegill, black crappie, northern pike, yellow perch, pumpkinseed sunfish, largemouth bass, muskellunge, walleye

Isles

2003

Sport – muskellunge

Bluegill, black crappie, largemouth bass, northern pike, yellow perch

Calhoun

2003

Sport – walleye and muskellunge

Bluegill, black crappie, northern pike, yellow perch, pumpkinseed sunfish

Harriet

2003

Sport – walleye and muskellunge

Bluegill, black crappie, yellow perch, pumpkinseed sunfish

Nokomis

2001

Sport – walleye and muskellunge

Yellow perch, black crappie, bluegill

Hiawatha

2001

Pan

Black bullhead, black crappie, bluegill, yellow perch

Diamond

1993

 

Black bullhead, carp, bluegill, green sunfish

Powderhorn

2003

Pan – black crappie and bluegill

Black crappie, bluegill, black bullhead

Source:  Minnesota DNR.

Streams

Minnehaha Creek has been listed on the State of Minnesota’s 303(d) list of Impaired Waters for its impaired biotic community.  A fish survey was conducted at nine locations on Minnehaha Creek in 2003.  Most of the fish species between I-494 and Minnehaha Falls were lake species with few adults, indicating a lack of suitable habitat for riverine species.  Lack of adults indicates that there is little refuge for overwintering and low flow periods.  Below the falls the creek is connected to the Mississippi River and there is better habitat for riverine species.

Macroinvertebrate sampling on Minnehaha Creek was conducted as a part of the 2004 MCWD Minnehaha Creek Stream Assessment.  Twenty-six sites were sampled; only about half yielded more than the 100 organisms typically needed to assure a statistically valid score.  An F-IBI score – an Index of Biotic Integrity identified to the organism’s family level – was calculated for thirteen reaches.  Macroinvertebrate family diversity was very low, primarily due to habitat limitations and the influence of the various impoundments and wetlands through which the creek flows.

Aquatic habitat in Minnehaha Creek is generally poor.  Stream substrates are homogenous and dominated by small gravels and sand, and gravel or cobble riffles are infrequent and widely spaced.  Large woody debris is virtually absent, limiting direct use by macroinvertebrates and fish and reducing the number of accumulation points for leaf and other debris.  Stream flows from Grays Bay dam discharge range from sustained high volumes and velocities to minimal or intermittent flows, creating undesirable conditions. 

The low diversity of macroinvertebrates reflects the lack of diversity in habitat.  Lack of riparian vegetation, erosion, sediment deposition, removal of large woody debris, sustained high flows, extreme flood peaks, lowered base flows, and to a lesser extent water quality combine to limit species diversity.  See Section 2.5.2 below for additional discussion.

Wetlands

A high density of wetlands are present in the subwatershed.  A number of wetlands were identified in the 2003 MCWD Functional Assessment of Wetlands (FAW) as having exceptional to high aesthetic values (see Figure 13).  Wetlands riparian to and in-line with Minnehaha Creek as well as several wetlands adjacent to lakes were noted as having high fish habitat potential.  Only a few of the larger wetlands were assessed as having high wildlife habitat potential, primarily because wetland size is an important factor.  Only a scattering of wetlands were identified as having exceptional to high vegetative diversity, unsurprising given the urbanized nature of the subwatershed and the likelihood of wetland disturbance and hydrologic impacts.

2.4 Human Environment

2.4.1 Present Land Use

The predominant land use in the subwatershed is single family residential, followed by park and open space (see Figure 7 and Table 3).  Most of the vacant land is large wetland or woodland tracts.  The subwatershed is fully developed at typical urban and suburban densities and land uses.

Table 3.  Percent of Minnehaha Creek subwatershed by 2000 land use.

Land Use 2000

Acres

% of Subwatershed

Single - Family Residential

   16,680.3

55.0%

Parks and Open Space

     3,877.9

12.8%

Water

     1,674.0

5.5%

Vacant or Undetermined

     1,660.8

5.5%

Institutional

     1,469.5

4.8%

Commercial

     1,443.7

4.8%

Roads and Highways

     1,422.8

4.7%

Multi - Family Residential

     1,133.0

3.7%

Industrial

       939.3

3.1%

Agricultural

            -  

0.0%

 

30,301.3

 


Source: Metropolitan Council.   See Figure 7.

2.4.2 2020 and 2030 Land Use Planning

Because so much of the subwatershed is already developed, future land use in the subwatershed is not expected to change dramatically by 2020 or 2030 (see Figure 8 and Figure 9), although there will be redevelopment.   Redevelopment and infill development will provide opportunities to retrofit with stormwater quantity and quality measures in areas that currently have no measures or inadequate measures.

2.4.3 Aquatic Recreation

There are numerous boat accesses and beaches on the lakes in the subwatershed.  There are seventeen canoe landings on Minnehaha Creek (see Figure 6).  Most of these have parking available, and several have picnic areas and restrooms.

2.5 Hydrologic Systems

The Department of Natural Resources’ Public Waters Inventory identifies 86 basins and three watercourses within the Minnehaha Creek subwatershed as under the jurisdiction of the DNR (see Figure 10).  These include the Chain of Lakes; other named lakes, ponds, and marshes; and numerous unnamed basins, listed in Table 4.

Table 4.  Public Waters in the Minnehaha Creek subwatershed.

Name and DNR ID#

Name and DNR ID#

Name and DNR ID#

Name and DNR ID#

Bass (27-15 P)

Mother (27-23 P)

Unnamed (27-717 W)

Unnamed (27-755 W)

Brownie (27-38 P)

Nokomis (27-19 P)

Unnamed (27-718 P)

Unnamed (27-756 P)

Calhoun (27-31 P)

Norby's Pond (27-685 W)

Unnamed (27-719 P)

Unnamed (27-757 W)

Cargill Pond (27-754 W)

Pamela Pond (27-675 P)

Unnamed (27-720 W)

Unnamed (27-758 W)

Cedar (27-39 P)

Sanctuary Marsh (27-665 P)

Unnamed (27-721 P)

Unnamed (27-759 W)

Cemetery (27-17 P)

Taft (27-683 P)

Unnamed (27-722 W)

Unnamed (27-762 W)

Diamond (27-22 P)

Twin (27-656 P)

Unnamed (27-723 W)

Unnamed (27-763 W)

Duck (27-25 P)

U.S. Lock & Dam #1 (27-3 P)

Unnamed (27-724 W)

Unnamed (27-771 W)

Edina Mill Pond (27-41 P)

Unnamed (27-1087 W)

Unnamed (27-725 W)

Unnamed (27-772 W)

Grays Bay Outlet (27-761 W)

Unnamed (27-657 P)

Unnamed (27-726 W)

Unnamed (27-773 W)

Hannan (27-52 P)

Unnamed (27-658 W)

Unnamed (27-728 W)

Unnamed (27-774 W)

Harriet (27-16 P)

Unnamed (27-659 W)

Unnamed (27-736 W)

Unnamed (27-779 W)

Harvey (27-670 W)

Unnamed (27-660 P)

Unnamed (27-737 W)

Unnamed (27-780 W)

Hiawatha (27-18 P)

Unnamed (27-661 W)

Unnamed (27-739 W)

Unnamed (27-83 W)

Lake of the Isles (27-40 P)

Unnamed (27-662 W)

Unnamed (27-740 W)

Unnamed (Cedar Manor) (27-713 W)

Lamplighter Park (27-710 P)

Unnamed (27-663 W)

Unnamed (27-741 W)

Unnamed (Cobblecrest) (27-53 P)

Legion (27-24 P)

Unnamed (27-666 W)

Unnamed (27-748 W)

Unnamed (Westling Pond) (27-714 W)

Meadowbrook (27-54 P)

Unnamed (27-667 W)

Unnamed (27-749 W)

Victoria (27-51 P)

Melody (27-669 W)

Unnamed (27-682 W)

Unnamed (27-750 W)

Windsor (27-82 P)

Milner Pond (27-684 W)

Unnamed (27-712 W)

Unnamed (27-751 W)

Wolfe Park (27-664 P)

Minnehaha Marsh (27-84 P)

Unnamed (27-715 W)

Unnamed (27-752 W)

Minnehaha Creek

Minnetonka (27-133 P)

Unnamed (27-716 W)

Unnamed (27-753 W)

Unnamed from Brownie to Calhoun

 

 

 

Unnamed from Harriet to Minnehaha Creek

Source: Minnesota 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 (lakes, ponds, channels, and crossings) within the subwatershed (see Table 5):

  • 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 land use changes would not significantly impact high water levels in the subwatershed.   However, it was noted that overtopping of the creek banks can occur.   Numerous land locked subwatershed units or small basins occur in the subwatershed, and management of discharge from those landlocked basins as well as from land use change is important to minimizing or preventing further streambank erosion

Table 5.  Modeled peak discharge from the Minnehaha Creek subwatershed (cfs).

Event

Existing

2020

Snowmelt

1.5 year, 24 hour

219.7

-

-

100 year, 24 hour

676.2

677.9

-

100-year, 10-day

-

-

618.5

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

The HHPLS scour analysis identified nearly 120 locations along the creek as having high erosion potential based on soils and modeled velocity.  The Stream Assessment included a geomorphologic analysis of creek stability as well as a detailed survey of the creek for sites actually experiencing erosion and streambank failure (see Section 2.5.2 below).  

2.5.1 Lakes

The Minnehaha Creek subwatershed includes the Chain of Lakes in Minneapolis and several other smaller lakes.  Powderhorn Lake in Minneapolis does not drain to the creek, but rather is pumped to the Mississippi River. 

Table 6.  Physical characteristics of lakes in the Minnehaha Creek subwatershed.

Lake 

Surface Area

Maximum Depth

Watershed to Lake Area Ratio

DNR Classification

Brownie

12

20

20:1

Natural Environment

Cedar

170

51

11:1

Recreational Development

Isles

103

31

7:1

Recreational Development

Calhoun

408

90

7:1

Recreational Development

Harriet

353

82

3:1

Recreational Development

Nokomis

204

33

4:1

Natural Environment

Hiawatha

54

30

2145:1

Natural Environment

Diamond

54

6

16:1

General Development

Powderhorn

11

20

26:1

Natural Environment

Source: Minnesota DNR.

Several of the lakes in this subwatershed are listed on the State of Minnesota’s 303(d) list of Impaired Waters.  Six lakes are listed for excess nutrients, and the MCWD is preparing a Total Maximum Daily Load (TMDL) analysis for four of those lakes.  Two lakes are proposed for de-listing – Brownie and Lake of the Isles.   The TMDL will establish phosphorus load reductions and include an implementation plan that incorporates specific strategies to reduce phosphorus loading.  Six lakes are listed for fish consumption impairment by mercury.  The MPCA is preparing a region-wide TMDL for that contaminant.

Table 7.  Selected water quality goals and current conditions of lakes in the Minnehaha Creek subwatershed.

Lake 

1997 TP Goal (μg/L)

HHPLS TP Goal (μg/L)

1997-2004 Average TP (μg/L)

Water Quality Impairments

2004

TP (μg/L)

Chl-a (μg/L)

Secchi (m)

TSI

Brownie 

50

35

38

Nutrients

Mercury

45

19

1.5

58

Cedar

50

25

22

Mercury

25

7

3.7

47

Isles

50

40

40

Nutrients

Mercury

50

28

1.8

58

Calhoun

30

25

24

Mercury

15

3

5.2

40

Harriet

30

20

23

Mercury

15

3

5.2

43

Nokomis 

50

50

59

Nutrients

Mercury

PCBs

80

28

1.0

64

Hiawatha

50

50*

68

Nutrients

68

17

1.3

60

Diamond

-

90

 

Nutrients

178

38

0.8

69

Powderhorn

90

120*

 

Nutrients

118

37

0.7

68

*Hiawatha’s interim goal in the draft TMDL is 61 and Powderhorn’s is 90.

Source:  MCWD. 

The MCWD and partners including the MPRB, City of St. Louis Park, City of Minneapolis, and Hennepin County have undertaken numerous projects in this subwatershed to improve water quality in the lakes.  These include:

Table 8.  Previous projects to improve water quality in Minnehaha Creek subwatershed lakes.

LakeYearProjectPurpose
Brownie
  • None specific

Cedar
  • 1995-96
  • 1996-97
  • 1998
  • Twin Lakes Park Pond & Dredging
  • Cedar Meadows
  • Cedar Alum Treatment
  • Fish Screen
  • Increases storage capacity of Twin Lakes and treats water entering Twin Lake
  • Treats water entering Cedar Lake
  • Treats phosphorus in lake
  • Prevents rough fish migration from Cedar Lake to Cedar Meadows
Isles
  • 2004-present
  • MPRB Isles Renovation Plan
  • Shoreline stabilization, native plant restoration, wetland enhancement and restoration

Calhoun
  • 1999
  • Lake Calhoun Ponds
  • Three cell wet detention system to treat stormwater prior to entering Lake Calhoun
  • Alum treatment
Harriet
  • 1994-present
  • MPRB/Minneapolis BMPs
  • Increased street sweeping, additional grit chambers (1994-96), constructed wetlands (1998), and littoral alum treatment (2001)
Nokomis
  • 2001
  • Lake Nokomis Improvements
  • Three ponds to treat runoff, additional grit chambers, an inflatable weir at the outlet, rough fish removal
Hiawatha 
  • None specific
 
Diamond
  • 2000
  • 60th Street & 1st Avenue Pond
  • Alleviates flooding and treats stormwater discharging to Diamond Lake
Powderhorn
  • 2001-present
  • MPRB/City Restoration Plan
  • Five continuous deflective separation grit chambers (2001), native plantings (2002), alum treatment (2003)

2.5.2 Streams

Minnehaha Creek is the primary stream within the subwatershed.  It is formed at the outlet of Grays Bay in Minnetonka and flows 22 miles to the Mississippi River.  One lake, Lake Hiawatha, is in-line to the creek and heavily influenced by it.

As the outlet for Lake Minnetonka and the upper watershed, Minnehaha Creek must discharge large volumes of water during spring snowmelt runoff, summer and fall.  During a typical year, 4-6 inches of runoff from the 122 square mile watershed tributary to the outlet are discharged to Minnehaha Creek.  The typical average flow in the creek from this discharge is 60 to 90 cfs.

An operating plan was established for the Grays Bay dam headwaters control structure when it was put into service in 1980.  The plan was intended to emulate the historical discharge hydrograph produced by previous controls and the natural outlet of Lake Minnetonka. 

In drier periods Lake Minnetonka typically does not discharge water.  Development in the lower watershed has changed subwatershed hydrologyWetlands and depression storage that naturally extend the period of flow have been largely eliminated in the lower watershed.  A large volume of surface runoff is produced by the impervious area but it is discharged over a short period of time, leaving the creek dry at times.  It is also likely that development has decreased groundwater discharge to the creek so the base flow to the creek from that source has been diminished.

Stream Assessment

Minnehaha Creek was studied in-depth in 2003-4 as part of the District’s Minnehaha Creek Stream Assessment, which included a physical inventory, erosion survey, fluvial geomorphic assessment to determine channel stability, and a biological assessment.

Flow in the creek is controlled by numerous structures, including major weirs at the Grays Bay Dam outlet, the Browndale Dam, West 54th Street, and Hiawatha Avenue. There are more than 100 bridge crossings, many of which provide grade stabilization.  Some of those crossings provide a grade control substantial enough to create an impoundment of hydraulically stagnant water upstream.

There are 178 identified storm sewer outfalls larger than eight inches in diameter along the length of the creek.  Most of those outfalls are located downstream of the Browndale Dam in Edina and Minneapolis.  Many are experiencing local bank erosion and scour.  Eleven exposed utility crossings were identified along the creek, eight of which are in the city of Minneapolis. 

Approximately 15 percent of the streambank is armored by concrete or masonry retaining walls, riprap, or other protection such as gabion baskets.  These are generally for the purpose of controlling erosion and meandering to prevent loss of property, stabilizing steep banks, or protecting structures such as bridges and storm sewer outfalls.  Many of these stream walls were presumably constructed by the Works Progress Administration (WPA) during or following the Great Depression.

The Stream Assessment identified 35 sites of significant erosion or bank failure - typically more than one to two feet in height - and lesser erosion damage and bank failures along much of the creek.  Most of the significant failures were downstream of the Browndale Dam in the city of Minneapolis.  Other significant features cataloged in the Stream Assessment include 26 sites with deltas and sandbars; 20 sites with small amounts of miscellaneous debris, 16 private docks, and numerous miscellaneous features such as islands, side channels, stairs, wetlands, inlet channels, and rock piles. 

A fluvial geomorphic assessment was completed as part of the Stream Assessment to evaluate channel stability.  In general the assessment determined that although erosion and incision has occurred in the creek, it now has a relatively stable channel profile because numerous bridge crossings and other structures will prevent further incising.  However, the channel width is not stable in several locations and was observed to be expanding.  Eighteen of the 30 reaches were assessed as stable, eight as stable with a tendency to aggrade or degrade, and six are aggrading (accumulating sediment).  Aggradation is likely the result of the numerous vertical controls such as bridges that create impoundments.

Water Quality

Minnehaha Creek is included in the District’s Annual Hydrologic Data monitoring program.  Water quality and flow in the creek is monitored at eight locations.  Phosphorus and TSS concentrations in Minnehaha Creek are comparable to the North Central Hardwood Forest ecoregion mean, which is generally a result of the good quality of water discharged into the creek from Lake Minnetonka.   In general nutrient and sediment loads increase upstream to downstream, although the impoundments at the major grade controls impact those concentrations.  While the flow-weighted average chloride concentrations in the creek were lower than the state chronic standards of 230 ug/L, several individual grab samples did exceed that standard, although none exceeded the acute standard of 830 ug/L.

Grab samples from seven sites were tested for the presence of e. coli bacteria.   While the acute standard was not violated in 2004 in the creek, the 30 day geometric mean standard was violated at five sites on the lower creek for the months of September and October 2004.  In 2005 the District expanded the creek monitoring to additional sites and adjusted sampling frequency to assist in identifying the source or sources of e. coli.  In addition, samples are being analyzed for traces of caffeine, which may indicate that human waste is one of the sources of e. coli.  Results are pending.   Dissolved oxygen was measured at eight locations and generally maintained levels greater than the 5 mg/L State of Minnesota standard for class 2B waters.   Measurements did dip below the 5 mg/L standard periodically, depending on flow in the creek and on location relative to large riparian wetland complexes.

Biologic Integrity

Minnehaha Creek is listed on the State of Minnesota’s 303(d) list of Impaired Waters for impaired biotic integrity.   The most limiting factor for the ecology of Minnehaha Creek is its variability of flow, which as noted above ranges from intensive periods of high volume and velocity flow to periods of low or no flow.  During those latter periods much of the channel runs dry, leaving few pools or backwaters to serve as refuge for fish and macroinvertebrates.   The creek also has a lack of physical complexity.  The channel is mostly of relatively constant dimensions, has very small amounts of woody debris, and little variation in depth and slope.  These factors severely limit opportunities for aquatic life to sustain viable populations.  Section 2.3.2 above discusses stream biologic integrity more fully.

Creek Visioning

The District in 2005 undertook a joint partnership with the United States Army Corps of Engineers to develop a large-scale, long-term Vision for Minnehaha Creek to serve as guidance for organizations that share Creek corridor management responsibilities.  A Citizen Advisory Committee of community representatives and a Technical Advisory Committee of agency representatives through a lengthy community input process developed a common vision and management recommendations. 

The 2005 MCWD Minnehaha Creek Visioning Partnership Final Report presents the results of that process and summarizes the Partnership’s recommendations for future Creek management. Erosion control and support of aquatic life were overall the highest ranked priorities for improvement.   However, when considered reach by reach, support and maintenance of recreation were the highest priority for the reaches upstream of the Browndale dam, followed by improvement of aquatic life and erosion control.  Erosion control and streambank stabilization was the highest priority for the reach downstream of the Browndale dam.   The Partnership recommended the District consider bioengineered stabilization techniques over hard armoring where possible, and that habitat improvement be focused on the management of riparian vegetation and retention of large woody debris rather than on in-stream habitat management.  The Partnership also recommended that water quality be improved through the reduction of peak stormwater flows; pretreatment of discharges; application of BMPs and good housekeeping practices in the subwatershed; and repair of existing erosion.

An important part of the visioning process was the discussion of several streamflow management scenarios developed by the Corps to model what would happen with changes to the operation of the Grays Bay dam.  The dam is managed to discharge water from Lake Minnetonka into the Creek only when the DNR-established runout elevation of the lake is exceeded.  During dry periods lake level falls and there is minimal discharge; flow in the creek falls to minimal flow-related aquatic habitat conditions and canoeing is not possible.   The Corps developed a number of scenarios that would provide targeted releases for recreation or habitat purposes, and then modeled the resulting impact on water level in Lake Minnetonka; the percent of time creek flow fell within optimal conditions for aquatic habitat and recreation; the percent of time potentially erosive flows could be expected; and resulting estimated water quality.  Each scenario attempted to balance these often competing interests; in the end the Partnership recommended that further study be completed to find a way to optimize and balance year round minimum flows and moderated extreme flows with recreational and lake uses.

2.5.3 Ditches

Three public drainage ditches established under Minnesota Statutes Chapter 103E are located within this subwatershed (see Figure 10).  The purpose of the ditches was likely to drain wetlands to provide additional land for agriculture and development.  These ditches have been converted to stormsewer and no longer provide that function today.

County Ditch #14

This ditch in St. Louis Park and Minneapolis was established prior to 1908 and originally connected a wetland northwest of Bass Lake to Bass Lake.  It then outletted Bass Lake to the east and flowed to the southwest corner Lake Calhoun.  It has largely been converted to storm sewer, but a portion of the ditch through the Minnekahda Golf Course remains an open channel along a similar alignment to the original.  The area previously served by the ditch is now served by stormsewer, and the ditch no longer serves its original purpose.

County Ditch #17

County Ditch #17 was established in 1908 and was intended to drain a large wetland complex in St. Louis Park, Minneapolis, and Edina.  The alignment extends from what is now the intersection of Morningside and Browndale to the outlet at Lake Calhoun around

37th Street.  It has been entirely converted to storm sewer that does not follow the exact path of the ditch but generally receives drainage form the same area.  These storm sewers were intercepted and diverted into the stormwater ponds constructed by the MCWD as part of the Southwest Lake Calhoun Ponds project.  The area previously served by the ditch is now served by storm sewer, and the ditch no longer serves its original purpose.

County Ditch #29

This ditch in St. Louis Park begins at about Minnetonka Boulevard and Highway 100 and runs east to its terminus near the railroad tracks.  The ditch has been completely converted to storm sewer which is for the most part located in the alignment of the former ditch.  The area previously served by the ditch is now served by storm sewer, and the ditch no longer serves its original purpose.

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).

2.5.5 Floodplain

Floodplain is shown on Figure 15.  In 2005 the District completed an evaluation of flood elevations on Minnehaha Creek, and four upper watershed streams: Gleason Creek, Long Lake Creek, Painter Creek, and Six Mile Creek.  Figure 15 shows the elevations of floodplains modeled by the District and other floodplains in the subwatershed.  

2.5.6 Groundwater

There are a number of springs and seeps in the Mississippi River gorge area, including Camp Coldwater Spring, the largest limestone bedrock spring in the Metro area.    Hydrologic analysis and monitoring completed by the District in 2000/2001 indicating potential construction impacts to the springflow led to a requirement that the Minnesota Department of Transportation modify its design for a new interchange at TH 55 and TH 62.  The District is continuing to monitor the spring to evaluate long-term trends.

Minnehaha Creek flow monitoring indicates that some reaches of the creek may be gaining baseflow from groundwater while other reaches may be losing baseflow, likely from a combination of natural geologic conditions and the artificial creek elevation modifications at the weirs and dams.  The District is expanding its monitoring program to better understand the extent of these areas of infiltration (gain) and exfiltration (loss).

The HHPLS identified the infiltration potential of the upland areas within the subwatershed as high to medium with some areas of variability where the soils are organic in nature (see Figure 16).   Most of the lower subwatershed is classified by the Hennepin County Geologic Atlas as being of high to very high aquifer sensitivity, reflecting the glacial outwash deposits that underlay the soils and the shallow depth to bedrock.  The upper subwatershed, an area of loamy till, is classified as being generally of low to moderate sensitivity to pollution except along the Creek and in the large Grays Bay wetland complex (see Figure 17). 

Large areas of the upper subwatershed have been designated by the Minnesota Department of Health (MDH) as Wellhead Protection Areas, including three in St. Louis Park, four in Minnetonka, and eight in Edina.   The Drinking Water Sensitivity Management Areas (DWSMA) for St. Louis Park wells have been designated by the MDH to be of high risk and vulnerability to contamination of the drinking water supply while the DWSMAs for the other wellhead Protection areas are generally of low vulnerability.  Figure 18 shows the DWSMAs and associated Wellhead Protection Areas.

The County Well Index has records of approximately 975 wells in the subwatershed, mostly shallow (less than 300 feet deep) domestic water supply wells but about 30 wells deeper than 500 feet, mostly municipal supply wells.