The following section presents the 17 watershed goals approved by the MCWD, measurable objectives, metrics and the specific goals and actions for the Lake Minnetonka subwatershed.
Promote abstraction and filtration of surface water where feasible for the purposes of improving water quality and increasing groundwater recharge throughout the watershed.
Development and the associated creation of new impervious surface increases the volume of stormwater runoff. The new runoff volume can convey more pollutants to receiving waters and may increase erosion and sediment transport, negatively affecting water quality. Development also decreases the amount of stormwater that naturally percolates into the soil to recharge groundwater, thus reducing baseflow in streams, changing hydrology in groundwater-fed wetlands, and decreasing water availability in drinking water aquifers.
Abstraction of stormwater (retained on site through infiltration, evapotranspiration, or capture and reuse) reduces the amount of runoff from the site conveying pollutants. The most common type of abstraction, infiltration, reduces runoff, which helps recharge groundwater. Filtration offers an opportunity to use soil to naturally cleanse stormwater prior to discharge. Increased infiltration and filtration in the Lake Minnetonka subwatershed is desirable for three primary reasons: 1) to recharge groundwater inputs and reduce pollutant loading into Lake Minnetonka; 2) to help prevent localized flooding in landlocked basins with no natural outlet; and 3) to protect the hydrology of the large discharge (groundwater-fed) wetlands in the subwatershed. Many of those wetlands are key resources with high ecological values that are dependant on groundwater to maintain those functions and values.
A key strategy to achieve this goal is the adoption of a volume management standard for new development and redevelopment that requires the abstraction of one inch of rainfall. Much of the subwatershed has at least moderate infiltration potential. Requiring new development and redevelopment to abstract some of the new stormwater generated would:
Desired Outcomes: Increased infiltration, reduction in pollutant loading and volumes of runoff to supplement other goals.
Metrics: Acre-feet of infiltration to meet nutrient loading reductions for water quality and volume reductions for water quantity goals.
Increase abstraction and infiltration to reduce runoff volumes carrying pollutant loads and to promote groundwater recharge.
Promote activities that maintain, support and enhance floral, faunal quantity and ecological integrity of upland and aquatic resources throughout the watershed.
The Lake Minnetonka subwatershed is dominated by Lake Minnetonka and its riparian wetlands. There are other high-value resources in the subwatershed, including other wetlands and tracts of high-value upland. Some areas within the subwatershed are located in an MCWD, local or regional conservation corridor. There is potential to connect ecological resources in the subwatershed to corridors in other subwatersheds.
Connected corridors are desirable as they provide a variety of habitats both aquatic and terrestrial as well as protected areas for passage. Within these conservation areas wherever possible the District would promote the conservation or establishment of native vegetation to increase or maintain infiltration rates; decrease or maintain runoff rates and pollutant conveyance to water resources; and minimize erosion of shorelines and streambanks. Sustaining or improving water quality and ecological integrity is necessary to meet the District goals in this plan as well as to meet state and federal nondegradation, water quality and biological integrity requirements and to prevent the need for future TMDLs.
The subwatershed includes numerous wetlands with exceptional or high fish or wildlife habitat value as well as wetlands with exceptional or high vegetative diversity. The Key Conservation Areas identified in this plan (see Figure 19) include those wetlands as well as associated upland areas of high ecological value such as maple-basswood forest. Conservation of those associated upland areas not only provides additional habitat type, but also helps preserve local runoff and infiltration rates.
The Lake Minnetonka fishery is in excellent condition and is a premier regional resource. It is actively managed and monitored by the DNR. There is no comprehensive data on aquatic vegetation communities in Lake Minnetonka, although Eurasian watermilfoil is a known nuisance in many of the bays and channels. The primary strategies for improving aquatic communities are the acquisition of new data such as vegetation surveys and management plans, and improvement of water quality. There are several wetlands in the subwatershed with exception or high vegetative diversity. These would be inspected at least annually for invasive vegetative species.
Lake Minnetonka contains a large and productive littoral zone--the shallow transition zone between dry land and the open water area of the lake. In Minnesota waters, the littoral zone extends from the shore to a depth of about 15 feet, depending on water clarity. The littoral zone is highly productive. The shallow water, abundant light, and nutrient-rich sediment provide ideal conditions for plant growth. Aquatic plants, in turn, provide food and habitat for many animals such as fish, frogs, birds, muskrats, turtles, insects, and snails. Protection the littoral zone is important for the health of the lake ecosystem as well as the overall quality although such protection may sometimes conflict with desires for navigational access. It is District policy that in such cases, the District will show preference to alternatives which first avoid and then minimize impacts to the littoral zone.
Desired Outcomes: Functional and healthy ecological corridors and waters throughout the subwatershed.
Metrics:
Maintain and improve overall ecological integrity within the subwatershed.
Maintain conditions suitable for healthy and varied fish communities within Lake Minnetonka and the other lakes.
Maintain healthy aquatic vegetation communities.
Maintain conditions suitable for a healthy and varied biologic community in Classen Creek.
Preserve, maintain and improve aesthetic, physical, chemical and biological composition of surface waters and groundwater within the District.
The HHPLS used an extensive public input process to establish water quality goals for the primary receiving waters in the District, focusing primarily on identifying target total phosphorus concentrations. This plan identifies those plus additional goals related to water quality. This plan sets forth a set of actions the District will undertake to reduce pollutant loading in the subwatershed and achieve and maintain water quality goals. The achievement of these water quality goals is not only necessary to meet state and federal water quality requirements and to prevent future TMDLs, but also to meet this plan’s ecological integrity goals.
Lake Minnetonka is a complex system of bays and channels. Modeling has been limited to individual bays, and there is an incomplete understanding of the dynamics of the lake. A whole-lake model is needed to accurately model water quality that takes into account the relationships between the bays.
Desired Outcomes: Achievement of in-lake nutrient concentration goals through achievement of nutrient loading reductions.
Metrics:
Achieve in-lake total phosphorus concentration goals as identified in this plan.
Prevent degradation of existing water quality in other Lake Minnetonka Bays and lakes in the subwatershed.
Achieve and maintain other state lake water quality standards including >1.4 m Secchi clarity and 14 ug/L chl-a for deep lakes, and >1.0 m Secchi clarity and 20 ug/L chl-a for shallow lakes.
Minimize pollutant loading contribution to Lake Minnetonka from upstream subwatersheds and Classen Creek.
Minimize the risks of threats to public health through the development of programs, plans and policies that improve the quality of surface and groundwater resources.
There are several potential threats to public health in the Lake Minnetonka subwatershed. Sewage overflows from sanitary sewer breaks or improperly functioning infrastructure could result in overflows discharged to downstream water resources. An additional potential source of pathogens is waterfowl, which are attracted to open water with easy routes from the water to vegetation on shore. The District’s role in minimizing the threats to public health in the Lake Minnetonka subwatershed is mainly to provide targeted information to landowners and LGUs.
Desired Outcomes: Minimization of threats to public health from contact with contaminated surface waters.
Metrics: Reported cases of illness transmission via surface water contact.
Minimize risks to human health and water quality from land use activities.
Maintain vegetated shorelines on the lakes where practical and effective to reduce overpopulation of the lakes with waterfowl.
Require LGUs and other agencies to manage public sanitary sewer infrastructure to minimize sewage overflows and to minimize impacts from those overflows on District water resources.
Maintain or reduce existing flows from drainage within the watershed to decrease the negative effects of stormwater runoff and bounce from existing and proposed development as well as provide low flow augmentation to surface waters.
Development and the associated creation of new impervious surface increases the volume of stormwater runoff from the landscape, changes the rates and times to peak runoff flow, and decreases the amount of stormwater that naturally percolates into the soil to recharge groundwater. The District’s long term goal in the Lake Minnetonka subwatershed is to achieve no increase in the volume of stormwater discharged from the subwatershed into the lake. Implementation strategies will include minimizing new runoff volumes from development, encouraging infiltration and groundwater recharge, and limiting new volumes in landlocked subwatersheds.
A key strategy to achieve this goal is the adoption of a volume management standard for new development and redevelopment that requires the abstraction (removal from runoff through infiltration, capture and reuse, evapotranspiration, etc.) of one inch of rainfall. Approximately 70 percent of annual runoff volume in Minnesota results from precipitation events of 1” or less (MPCA, 2000). Requiring new development and redevelopment to abstract (retain on site through infiltration, evapotranspiration, or capture and reuse) runoff from that size event would significantly reduce new volumes of runoff flowing downstream and help reduce future erosion in streams and channels; minimize new pollutant loading that would have been conveyed by that stormwater; and help maintain groundwater levels, preserving wetlands.
Limiting discharges from subwatersheds and basins that are currently landlocked is necessary to prevent further degradation of downstream water quality as well as to limit new volumes discharged downstream to channels that are already experiencing erosion. Encouraging infiltration in landlocked basins is one means of controlling runoff volumes to help prevent localized flooding.
The additional new volume could be mitigated through construction of regional infiltration basins, restoring drained wetlands, reforestation and revegetation, or other means
Table12. Modeled annual volume of runoff in the Lake Minnetonka subwatershed, and estimated reductions resulting from application of a proposed 1” abstraction rule for new development and redevelopment (acre-feet).
|
2000 modeled annual subwatershed runoff volume |
3,956 |
|
2020 modeled annual subwatershed runoff volume |
4,021 |
|
Ultimate Development modeled annual subwatershed runoff volume |
4,068 |
|
Increase between 2000 and Ultimate Development |
112 |
|
Estimated volume abstracted by 1” rule |
79 |
|
New volume to be abstracted through other means such as capital projects, wetland restorations, reforestation and revegetation, etc. |
33 |
Desired Outcomes: Management of new annual water volume discharged from the subwatershed.
Metrics: Acre-feet volume abstraction.
Reduce volume of stormwater runoff from new development and redevelopment and maintain or reduce existing water volumes discharged from the subwatershed into Lake Minnetonka.
Limit new discharges from land locked basins and subbasins to prevent new impacts to downstream lakes.
Require public stormwater conveyance and control structures in the watershed be sized and maintained properly to convey current and ultimate stormwater flows to minimize flooding and erosion potential.
Preserve the natural appearance of shoreline areas and minimize degradation of surface water quality which can result from dredging operations.
Eroding shorelines and streambanks contribute to the degradation of water quality. Native vegetation can effectively stabilize these areas, filter runoff for sediment and other pollutants, and provide habitat. Restoration of shoreline and streambanks on Lake Minnetonka Classen Creek, and the other lakes, streams, and wetlands within the subwatershed is a key strategy for meeting this plan’s goals.
The key areas identified in this plan for conservation activities include buffer zones adjacent to streams and channels. In some cases these buffer zones are riparian or flow-through wetlands, and those wetlands have been identified as key conservation areas. Where streams and channels flow through upland areas, conservation of native vegetation within these zones would also increase or maintain infiltration rates; decrease or maintain runoff rates and pollutant conveyance to water resources; and help minimize erosion. Restoration of lakeshore would have the same benefits. Sustaining or improving water quality and ecological integrity is necessary to meet District goals as well as to meet state and federal nondegradation, water quality and biological integrity requirements and to prevent the need for future TMDLs.
Desired Outcomes: Stable streambanks and shorelines to supplement other goals.
Metrics: Stream Visual Assessment Protocol (SVAP) in Classen Creek.
Promote shoreline restoration and shoreline buffer creation as methods to help meet pollutant loading reduction and ecological integrity goals.
Maintain the hydraulic capacity of and minimize obstruction to navigation without compromising wildlife habitat in watercourses and preserve water quality and navigation appearance in shoreland areas.
The District recognizes the riparian rights of property owners to have and maintain access to public waters. The District, the Lake Minnetonka Conservation District, and the Department of Natural Resources have entered into a Dredging Joint Policy Statement that serves as the basis for the District’s continuing regulation of dredging activities. Excessive growth of nuisance aquatic vegetation can also be an obstruction to navigation. The District will not participate in the removal of nuisance aquatic vegetation solely for the purpose of improving navigation, but may consider macrophyte control where excessive growth contributes to poor water quality.
Desired Outcomes: Minimization of impacts on water resources from dredging.
Metrics: Compliance with the dredging policy.
Manage dredging activities so as to preserve the natural appearance of shoreline areas; recreational, wildlife and fisheries resources of surface waters; surface water quality and ecological integrity of the riparian environment.
Improve water quality by promoting best management practices (BMPs), requiring their adoption in local plans and their implementation on development sites.
This plan and District regulations stipulate the use of Best Management Practices (BMPs) to reduce stormwater volumes and pollutant loadings, but do not prescribe which practices should be used. This allows the LGU and developers the flexibility to implement those that are most appropriate for local conditions and opportunities. A key strategy for plan implementation is providing early consultation with and technical assistance to and education of stakeholders including city staff, residents, and developers to increase knowledge and acceptance of various BMPs and to promote their adoption.
Desired Outcomes: Implementation of Best Management Practices on private and public property to supplement other goals.
Metrics: Compliance with the early consultation requirement.
Promote best management practices as methods to help meet pollutant loading and volume management goals established in this subwatershed plan.
Enhance public participation and knowledge regarding District activities and provide informational and educational material to municipalities, community groups, businesses, schools, developers, contractors and individuals.
The District conducts an active and strategic education and communication program watershed-wide to provide general information and to various stakeholder groups in accordance with its five-year strategic education and outreach plan. Targeted information will be necessary in the Lake Minnetonka subwatershed to educate these stakeholders as to the District’s specific goals for this subwatershed, the actions the District plans to take, and their role in conserving water resources in the subwatershed. The specific targeted messages in this subwatershed will emphasize shoreline management as well as stormwater volume management in landlocked basins.
Desired Outcomes: Stewardship over water resources by residents of the subwatershed to assist District activities and supplement other goals.
Metrics: Telephone survey.
Provide focused education and outreach opportunities within this subwatershed to supplement the general education and outreach program and assist in the achievement of these subwatershed goals.
Provide participation and outreach activities to increase awareness of water and other natural resources within the subwatershed.
Work cooperatively with other agencies and groups to coordinate education and outreach efforts to avoid duplication of efforts and maximize resources.
Goal 10 - Public Ditches
Maintain public ditch systems within the District as required under Statutory jurisdiction.
There are no Public Ditch goals and actions specific to the Lake Minnetonka subwatershed
Preserve, create and restore wetland resources and maximize the benefits and functionality of wetlands to the watershed.
The Functional Assessment of Wetlands (FAW) evaluated 3,049 acres of wetlands in the Lake Minnetonka subwatershed, of which 1,682 acres were in the Preserve classification (see Figure 12). There are numerous wetlands of exceptional and high quality functions and values within this subwatershed. Their conservation is integral to achieving ecological integrity goals, as well as water quality, stormwater management, and floodplain management goals.
A key strategy of this plan is regulation of wetland impacts in accordance with a management classification based on the functions and values findings of the Functional Assessment of Wetlands. Wetlands are assigned to a classification – either Preserve or Manage 1, 2, or 3 – and allowable impacts would be based on that classification. The wetlands with the highest values – those in the Preserve classification – would be allowed minimal impacts. The Manage classifications would be allowed some impacts, such as accepting new stormwater discharges, depending on classification. This strategy will conserve existing high values such as habitat, vegetative diversity, and sensitivity, while also recognizing that wetlands play an important part in managing stormwater. Wetlands provide essential storm and flood water storage.
Wetlands of exceptional or high vegetative diversity or fish or wildlife habitat value have been designated key conservation areas, as have wetlands that are riparian to streams or channels, have high restoration potential, provide key floodplain storage, or are located in important natural resources conservation areas such as wildlife corridors.
Except for those in the Preserve classification, which will be managed to an even higher standard, these conservation wetlands will be managed as if they were Manage 1 classification wetlands, with limitations on the amount of new runoff that can be directed to them, and a requirement to pretreat any new discharges to them.
An important part of achieving the goal of no net loss of wetland size, quality, and type will be tracking wetland impacts to assist in identifying future restoration or wetland creation needs.
Equally important to the regulation of wetlands is the restoration of degraded wetlands within the subwatershed. Figure 14 identifies wetlands based on restoration potential. Restoring wetlands increases specific functions and values of the resource within the watershed ranging from management of flows to water quality improvement to enhancement of the overall ecosystem, particularly within identified corridors.
Desired Outcomes: Maintain existing quantity and quality of wetlands throughout subwatershed; improve wetland and surface water quality within Key Conservation Areas.
Metrics:
Maintain existing acreage of wetlands in the subwatershed and achieve no net loss in their size, quality, type, and biological diversity.
Increase the quantity, quality, and biological diversity of Lake Minnetonka subwatershed wetlands through the restoration of impacted wetlands.
Protect and maintain existing groundwater flow, promote groundwater recharge and improve groundwater quality and aquifer protection.
Maintenance of groundwater recharge is important in the Lake Minnetonka subwatershed to maintain hydrology to the groundwater-fed discharge or combination wetlands as well as to recharge aquifers that supply public and private water wells. Development, with the associated creation of new impervious surface, increases the volume of stormwater runoff and reduces the amount of stormwater that naturally percolates into the soil to recharge groundwater.
Increased infiltration in the Lake Minnetonka subwatershed is desirable for three primary reasons: 1) to recharge groundwater inputs and reduce pollutant loading into the lake; 2) to help prevent localized flooding in landlocked basins with no natural outlet; and 3) to protect the hydrology of discharge (groundwater-fed) wetlands in the subwatershed. Some of those wetlands are key resources with high ecological values that are dependant on groundwater to maintain those functions and values. Much of the subwatershed has moderate to high infiltration potential. Requiring new development and redevelopment to infiltrate some of the new stormwater generated would reduce new volumes downstream and help reduce future erosion in streams and channels; minimize new pollutant loading that would have been conveyed by that stormwater; and help maintain groundwater levels, preserving wetlands.
Some parts of the subwatershed are areas of aquifer sensitivity or are or may be designated in the future as drinking water wellhead protection areas, where care should be taken when infiltrating stormwater. Proper design of infiltration practices is necessary to avoid groundwater contamination.
Groundwater management in the Lake Minnetonka subwatershed will focus on increasing the amount of infiltration in the subwatershed, and minimizing opportunity for groundwater contamination from land use practices.
Desired Outcomes: Maintain function of existing groundwater flow, assist in the protection of drinking water supply, no degradation in surficial groundwater quantity or quality.
Metrics:
Protect and maintain groundwater recharge and groundwater quality.
Reduce the severity and frequency of flooding and high water by preserving and increasing the existing water storage capacity below 100-year flood elevations on all waterbodies within MCWD.
The primary strategy in the management of stormwater and prevention of flooding in the Lake Minnetonka subwatershed is the preservation of the stormwater storage. Key areas identified in this plan for conservation include wetlands that provide floodplain storage and areas that provide channel and stream floodplain and riparian zones.
Desired Outcomes: No net loss of floodplain storage.
Metrics: Acres net floodplain fill.
Preserve the existing water storage capacity below the 100-year event elevation.
Utilize District hydrologic and hydraulic data to identify potential public infrastructure high water impacts.
Control temporary sources of sediment resulting from land disturbance and identify, minimize and correct the effects of sedimentation from erosion-prone and sediment source areas.
Lake Minnetonka is the primary recreational water resource in this subwatershed, although other lakes and wetlands provide aesthetic enjoyment, wildlife viewing, and other recreational values. District and local efforts to improve ecological integrity and conserve corridors will enhance those aesthetic and recreational values across the subwatershed. There are numerous public and private beaches, lake accesses and fishing piers. The Luce Line Trail, Southwest LRT, and future Three Rivers Trail cross the subwatershed. The District’s primary strategies in promoting and supporting recreational use of the lakes is improving water quality and managing aquatic vegetation.
Desired Outcomes: Manage surfaces waters to achieve water quality goals so designated use is maintained and unimpaired.
Metrics:
Support recreational use of Lake Minnetonka and other lakes in the subwatershed by achieving the District’s summer mean total phosphorus goals and other water quality goals through the implementation of the programs and projects identified in this plan to reduce phosphorus loads and improve lake water quality.
Support the fisheries through the implementation of the programs and projects identified in this plan to maintain ecological integrity and promote shoreline restoration.
Erosion within the subwatershed can result in sediment being transported to lakes, wetlands, and streams, where it can degrade water quality and habitat. Sediment accumulating in channels, culverts, and other facilities can reduce their ability to convey stormwater, while erosion can undermine their stability. Shoreline erosion on Lake Minnetonka is of special concern.
The key areas identified in this plan for conservation activities include buffer zones adjacent to streams and channels. In some cases these buffer zones are riparian or flow-through wetlands, and those wetlands have been identified as key conservation areas. Where streams and channels flow through upland areas, conservation of native vegetation within these zones would also increase or maintain infiltration rates; decrease or maintain runoff rates and pollutant conveyance to water resources; and help minimize erosion. Restoration of lakeshore would have the same benefits. Identifying, addressing, and preventing erosion is necessary to meet District goals as well as to meet state and federal nondegradation, water quality and biological integrity requirements and to prevent the need for future TMDLs.
Requiring new development and redevelopment to infiltrate some of the new stormwater generated would reduce post-development volumes downstream and help reduce future erosion in streams and channels; minimize new pollutant loading that would have been conveyed by that stormwater; and help maintain groundwater levels, preserving wetlands. Limiting discharges from subwatersheds and basins that are currently landlocked is necessary to prevent further degradation of downstream water quality as well as to limit new volumes discharged to channels that are already experiencing erosion.
Strategies in the Lake Minnetonka subwatershed will focus on promoting shoreline restoration with native vegetation and identifying erosion problems on an ongoing basis and working with LGUs to correct them.
Desired Outcomes: Reduction in pollutant loading of temporary and permanent nature from erosion to supplement other goals.
Metrics:
Identify and address erosion problems in the subwatershed.
Control temporary sources of sediment resulting from land disturbance and identify, minimize and correct the effects of sedimentation from erosion-prone and sediment source areas.
Erosion within the subwatershed can result in sediment being transported to lakes, wetlands, and streams, where it can degrade water quality and habitat. Sediment accumulating in channels, culverts, and other facilities can reduce their ability to convey stormwater, while erosion can undermine their stability. Shoreline erosion on Lake Minnetonka is of special concern.
The key areas identified in this plan for conservation activities include buffer zones adjacent to streams and channels. In some cases these buffer zones are riparian or flow-through wetlands, and those wetlands have been identified as key conservation areas. Where streams and channels flow through upland areas, conservation of native vegetation within these zones would also increase or maintain infiltration rates; decrease or maintain runoff rates and pollutant conveyance to water resources; and help minimize erosion. Restoration of lakeshore would have the same benefits. Identifying, addressing, and preventing erosion is necessary to meet District goals as well as to meet state and federal nondegradation, water quality and biological integrity requirements and to prevent the need for future TMDLs.
Requiring new development and redevelopment to infiltrate some of the new stormwater generated would reduce post-development volumes downstream and help reduce future erosion in streams and channels; minimize new pollutant loading that would have been conveyed by that stormwater; and help maintain groundwater levels, preserving wetlands. Limiting discharges from subwatersheds and basins that are currently landlocked is necessary to prevent further degradation of downstream water quality as well as to limit new volumes discharged to channels that are already experiencing erosion.
Strategies in the Lake Minnetonka subwatershed will focus on promoting shoreline restoration with native vegetation and identifying erosion problems on an ongoing basis and working with LGUs to correct them.
Desired Outcomes: Reduction in pollutant loading of temporary and permanent nature from erosion to supplement other goals.
Metrics:
Identify and address erosion problems in the subwatershed.
Promote effective planning to minimize the impact of development and land use change on water resources as well as achieve watershed District Goals.
The District’s regulatory program is the means by which many of the goals enumerated here would be accomplished. As development and redevelopment occurs, property owners and developers are required to treat and control stormwater, limit impacts to wetlands, and meet other standards. Additional regulation may be necessary in the Lake Minnetonka subwatershed to implement the actions in this plan.
Desired Outcomes: Utilize regulatory program to cost-effectively manage land use to achieve other goals.
Metrics:
In consultation with LGUs through an appropriate rulemaking process, amend existing or adopt new rules to implement the actions identified here within two years of adoption of this plan.
Solicit input from the general public with the intent that policies, projects and programs will address local community values and goals as well as protect historic and cultural values regarding water resources; strive to manage expectations; base decisions on an educated public; foster an educated and informed public within the watershed.
The District has good working relationships with the LGUs within the watershed, and maintains a Citizens Advisory Committee to obtain regular public input on issues of concern to the District and its citizens. As the District implements the actions identified in this plan, including the education and communication actions described above, it will be important to obtain direct input from water resource users. The Lake Minnetonka Conservation District is a resource.
Desired Outcomes: Engage the public to encourage involvement in District activities and stewardship of area resources.
Metrics: Number of opportunities for public involvement.
Work cooperatively with interest groups and property owners.
