This page defines the reasons stormwater management is important in the state and introduces the general stormwater management principles that are used throughout the Manual website. Included is a discussion of the unique framework and stormwater management approach needed in Minnesota to address the variation in physical conditions that might affect surface water management.
The material contained in the Minnesota Stormwater Manual, and especially the background material presented on this page, can be used to educate public officials and citizens on the necessity to plan adequately for stormwater. Although the average Minnesotan is very water-savvy, there is a continual need to keep our youth and those desiring to learn better served.
Minnesota is fortunate to have many educational programs available to its citizens. Such efforts as the University of Minnesota Extension, Project NEMO, Watershed Partners, and all of the Phase II education programs developed by Municipal Separate Storm Sewer System (MS4) communities are but a few of the many available. Because this list is far too long to include in this document, the reader is referred to Minnesota Sustainable Communities Network “Next Step” to obtain a comprehensive list of education programs and contacts.
Stormwater is an all-inclusive term that refers to any of the water running off of the land’s surface after a rainfall or snowmelt event. Prior to development, stormwater is a small component of the annual water balance. However, as development increases, the paving of pervious surfaces (that is, surfaces able to soak water into the ground) with new roads, shopping centers, driveways and rooftops all adds up to mean less water soaks into the ground and more water runs off. In a forested watershed, the majority of precipitation infiltrates the soil and subsequently percolates deeper into groundwater or is evapotranspired back to the atmosphere. As urbanization occurs and the percentage of impervious surface increases, an increasing amount of precipitation runs off the landscape and eventually is discharged to receiving waters. The actual percent of water consumed by the different hydrologic processes varies depending upon location within Minnesota. Although general information exists on regional precipitation, infiltration, evapotranspiration in Minnesota, local information should be obtained from an appropriate source knowledgeable about local water data.
The Center for Watershed Protection has helped document the adverse impact that increased imperviousness (that is, water not able to soak into the ground) has on the health of receiving streams. Similar impacts occur when the watersheds surrounding lakes experience an increase in impervious cover, although in both stream and lake cases this simplistic explanation is only part of the problem. Other factors such as morphology, landscape setting, inherent soils and geology, and land use history could be equally as important.
It is important to note that the Minnesota Stormwater Manual has an urban or developing/developed area focus. This is not meant to ignore or minimize the impact that agricultural or silvicultural activities can have on our receiving waters. Rather, the Manual focuses on the transition from rural and open space to urban uses, and on the management of stormwater from the increased impervious surfaces that result. Readers are referred to the Minnesota Pollution Control Agency, the Minnesota Department of Natural Resources, or the Minnesota Department of Agriculture for further information on agricultural and silvicultural activities.
The passage of the Federal Clean Water Act (CWA) in the 1970s initiated a change in the view of pollution in the U.S. No longer was it acceptable to pollute our country’s water resources. The initial focus of implementing the provisions of the CWA was logically on point sources of pollution, or those discharges coming from the end of an industrial or municipal wastewater pipe. Progress in addressing these discharges was made rapidly, although vigilance is still required to assure continued protection.
In the 1990s the United States Environmental Protection Agency (USEPA) began to apply requirements of the CWA to stormwater runoff. Owners and operators of certain storm drainage systems are now required to comply with design, construction, and maintenance requirements set by the MPCA for the State of Minnesota. Manual users are also encouraged to check the Center for Watershed Protection for much more information on the behavior of stormwater and links to many additional sources of information.
The changes in the landscape that occur during the transition from rural and open space to urbanized land use have a profound effect on the movement of water off of the land. The problems associated with urbanization originate in the changes in landscape, the increased volume of runoff, and the quickened manner in which it moves. Urban development within a watershed has a number of direct impacts on downstream waters and waterways, including changes to stream flow behavior and stream geometry, degradation of aquatic habitat, and extreme water level fluctuation. The cumulative impact of these changes should be recognized as a stormwater management approach is assembled.
Urban development alters the hydrology (rate and volume) of watersheds and streams by disrupting the natural water cycle (Georgia Stormwater Manual, 2001). The changes in streams draining altered watersheds are very apparent as they respond to the altered hydrology during this transition. Although similar changes can occur from intensive agricultural or silvicultural activities, the Manual focuses on the impacts of changes associated with development. Notable responses include:
The changes in the rate and volume of runoff from developed watersheds directly affect the morphology, or physical shape and character, of urban streams, rivers, and often ravines and ephemeral (intermittent) drainageways. Some of the impacts due to urban development include (adapted from the Georgia Stormwater Manual, 2001):
Perhaps the most significant impact that results from the physical change to urban streams occurs in the habitat value of streams. Impacts on habitat include (adapted from the Georgia Stormwater Manual, 2001):
As impervious surfaces increase, more water flows off of urban surfaces and is delivered faster to receiving waters. The increased activity on these surfaces means that more polluting material is available, as well. Minimizing the mobilization of this material and its impact is the goal of good runoff management and the purpose of this Manual.
Diffuse sources of pollution, such as that resulting from construction, roadways, parking lots and farm fields, have been a focus for Minnesota water management because they surpass point sources in severity for many pollutants of concern. The conversion of rural and open space land to urban uses is the particular focus of this Manual.
The problems associated with the conversion of land emerge as the land surface changes from one that soaks water into the ground to one that inhibits this infiltration. What used to be a small portion of runoff from a rainfall or snowmelt event becomes a major source of runoff volume. Water that used to soak in collects and flows from these new surfaces with enough energy to erode soil that was formerly held in place with protective vegetative cover and strong roots. Streams generally depend on groundwater supplies during dry periods of the year. When infiltration is reduced or eliminated, this groundwater is no longer available to supply baseflow and support the life of the channel. For the same reason, deeper groundwater aquifer units receive less recharge.
Quantity is not the only problem resulting from changing runoff patterns. The water that washes over these new urban surfaces picks up materials laying upon those surfaces. The sediment from construction erosion, the oil, grease and metals from many automobiles, the fertilizer and pesticides from lawns, and many more new pollutants can adversely impact the receiving waters. There are several nonpoint sources of pollution, each with a distinct set of pollutants of concern.
|Pollution sources||Pollutants of concerna|
|Vehiclular traffic accounts for much of the build-up of contaminants on road surfaces and parking lots. Wear from tires, brake and clutch linings, engine oil and lubricant drippings, combustion products and corrosion, all account for build-up of sediment particles, metals, and oils and grease. Wear on road and parking surfaces also provides sediment and petroleum derivatives from asphalt. Spills from traffic accidents can occur on any street or highway.||
|Lawn and garden maintenance of all types of land uses including residential, industrial, institutional, parks, and road and utility right-of-ways accounts for additions of organic material from grass clippings, garden litter and fallen leaves. Fertilizers, herbicides and pesticides all can contribute to pollutant loads in runoff if not properly applied.||
|Air pollution fallout of suspended solids from traffic, industrial sources and wind erosion of soils builds up contaminants in soil and on urban surfaces.||
|Municipal maintenance activities including road repair and general maintenance (road surface treatment, salting, dust control, etc.).||
|Industrial and commercial activities can lead to contamination of runoff from loading and unloading areas, raw material and by-product storage, vehicle maintenance and spills.||Any raw material exposed to runoff|
|Illicit connections of sanitary services, roof/sump drains or industrial process water to storm sewers can cause contamination with organic wastes, nutrients, heavy metals and bacteria.||
|Improper disposal of household hazardous wastes can introduce waste oil and a multitude of toxic materials such as paint, solvents, auto fluids, and waste products to storm and sanitary sewers. Note that industrial and commercial hazardous materials are regulated under point source control programs.||Any household material deemed hazardous|
|Pet and wildlife feces and litter introduce organic contamination, nutrients and bacteria.||
|Construction activity can introduce heavy loads of sediment from direct runoff, construction vehicles and wind-eroded sediment. Sediment particles also: transport other pollutants that are attached to their surfaces including nutrients, trace metals and hydrocarbons; fills ditches and small streams and clogs storm sewers and pipes, causing flooding and property damage; and reduces the capacity of wetlands, reservoirs and lakes. Construction can also contribute construction debris, material spills and sanitary waste.||
|Combined sewer overflowsb (CSOs) and Sanitary Sewer Overflows (SSOs) contain a mixture of sanitary, commercial and often industrial waste, along with surface drainage.||
|Runoff from residential driveways and parking areas can contain driveway sealants, oil, salt, and car care products.||
aRepresentative list only; many additional pollutants can be associated with most of the activities listed
bCombined sewers are very limited in Minnesota, with only a few remnants still existing in the metropolitan area. However, the same concerns apply for sewage spills and accidental overflows.
The impacts of the various pollutants from nonpoint sources are felt to varying levels. It is important to recognize that the hydrologic balance of most receiving water depends on this runoff water. Simply diverting all of the flow around a water body might help reduce a pollution load, but it could also cause the water body to dry up.
The receiving water quality impacts from urban runoff vary depending upon the quality and quantity of the stormwater and the assimilative capacity, or its natural ability to absorb or accommodate certain pollutants without adverse effects, of the receiving waterbody (Conservation Toronto and Region, 2001). Depending on the chemical, biological and physical character of the waterbody, its assimilative capacity can be quite different and tolerance to pollutants may vary greatly. Some waterbodies are inherently more sensitive to types or classes of pollutants than others. For example, lakes are more sensitive to phosphorus than streams and trout streams are more sensitive to increased temperature than non-trout streams.
Potential water quality concerns resulting from stormwater include (among others):
Awareness of the potential for pollution of Minnesota’s water is an important beginning, but action must follow. A performance-based approach to action means that a management plan is put together focused on achieving or maintaining a certain goal. The methods used to achieve the goal are not entirely prescriptive. This allows the stormwater manager the flexibility to be innovative.
There are several principles consistent with integrated stormwater management and the treatment train approach that this Manual uses to promote proper runoff management. They are:
Minnesota is a large and varied state. Physical elements such as climate, occurrence of water, ecology, geology, soils and topography, and cultural features such as land use vary dramatically from one end of the state to the other. Stormwater managers in Minnesota know that conditions in the state can complicate solutions that might be simple elsewhere in the country. The extreme weather conditions (cold and hot) and physiographic variability under which we operate makes it impossible to generalize a single accepted approach for the entire state under all conditions. Flexibility in approaching problems site by site is stressed in this Manual. The following section describes some of the statewide variability that can be addressed with variable techniques in the Manual. To access additional graphics see Minnesota maps.
The climate of Minnesota is characteristic of a transition zone from the moist and temperate eastern U.S. to the dry and droughty western U.S. Minnesota’s large size also means that much variation can occur within the state in any given year. Add to that extremes in temperature, and the difficulty in trying to describe Minnesota’s climate can be appreciated. Although the temperature discussion is interesting, this Manual has been developed to address water, so other than the fact that we experience very cold winters, temperature will not be discussed.
The major factors to focus on for good statewide stormwater management are rainfall and snowfall (snowmelt). A complete picture of Minnesota stormwater runoff cannot be painted without a discussion of both. Issue Paper B in the Manual Sub-Committee series examined some questions associated with the frequency of precipitation in Minnesota. The discussion was oriented around which design events to use as a basis for unified sizing of stormwater facilities across the state.
Normal average annual Minnesota precipitation (rain plus snow) varies from less than 20 inches in the northwest to about 35 inches in the southeast. Normal average annual snowfall varies from about 40 to 64 inches and follows the same geographic distribution as overall precipitation.
Atlas 14 precipitation frequency information can be found on NOAA's precipitation frequency data server.
The real impact of the precipitation that falls in the state is felt when it runs off either as rainfall or snowmelt. Issue paper B contains a substantial amount of discussion on the proper statistical representation of “design events” based on the relationship of precipitation to runoff. The discussion was intended to set the stage for selection of the unified sizing criteria. Much of the discussion with the Manual Sub-Committee concerned the use of the US Weather Bureau’s 1961 Technical Publication 40, commonly known as “TP 40”. Even though this publication is generally considered out of date because it does not reflect recent climate changes, there is no acceptable substitute at this time (see File:Issue paper B - precipitation frequency analysis and use.pdf). Until such time as an acceptable replacement exists, graphics from TP-40 should be used in Minnesota. These include graphs showing the 1-year through 100-year, 24-hour rainfall events. This data is summarized in the following table.
Table illustrating rainfall ranges across Minnesota and the average rainfall in the Twin Cities for the 1, 2, 5, 10, 25, 50, and 100-year storm events. Data were generated using Atlas 14.
|Event frequency||Minnesota range (inches)||MSP International airport|
|2-year||2.3 - 3.1||2.83|
|10-year||3.4 - 4.6||4.24|
|25-year||4.2 - 5.8||5.37|
|50-year||4.9 - 6.8||6.37|
|100-year||5.7 - 7.9||7.50|
The determination of snowmelt volumes is more complicated that rainfall because it depends on two factors – snowfall depth and the amount of moisture (or the equivalent water moisture) in the snow. In addition, some of the melted water infiltrates the soil. The overall snowmelt volume is given by the following equation
\(S_v = (S_d S_w) - I_v\)
Statewide maps can be established estimating the snow depth at the initiation of snowmelt, the snow water equivalent at the time of snowmelt, and snowmelt infiltration based on the soil moisture content.
Details regarding Minnesota climate in general can be obtained from the Minnesota Climatology Working Group.
Of course not all of the meltwater runs off. Research indicates that some of the meltwater enters the ground as infiltration. This can be represented graphically, but graphics need local adjustment based on knowledge of ground conditions. These graphics should be considered an approximation of the amount of melt that will soak into the ground and hence be removed from the total runoff volume.
Many of the physical features that influence the behavior of stormwater are not mapped at a level of sufficient enough detail for the state. This section will generally describe the features of importance and refer the user to sources of better information.
Due to the richness and variety of Minnesota’s water resources, several classes of waters have been identified for special protections through legislation or programs designed to protect these unique resources.
Watershed-based water management began in earnest in the state in the mid-1950s and has had several additional mandates put in place since then. Watershed districts, watershed management and watershed-based planning are all common terms within the state. There are eight major watershed basins across the state. Details on local watersheds are available from local sources, the [www.dnr.state.mn.us/watersheds/map.html Minnesota Department of Natural Resources] or the Minnesota Association of Watershed District’s “Where is my Watershed?” website.
The reality associated with so many watershed units occurring in the state is that a complex planning and regulatory framework exists for water management. Many of the sub-watersheds contained within the major watershed units have watershed management organizations that typically have some level of authority through a Watershed District or Watershed Management Organization. Information on the location and operations of these organizations can be obtained from the Board of Water and Soil Resources.
Another primary watershed mapping unit for Minnesota waters is based on MPCA’s ecoregion concept. These are geographic areas reflective of similar ecological character assembled to define causative factors for water behavior. There are seven ecoregions mapped for the state:
Although not universally true, waters within each ecoregion should generally be similar in character, when all other factors (like rainfall, land use, and land cover) are similar. MPCA uses these as basic planning units for setting water quality standards and evaluating water quality variation. Keeping in mind the watershed and ecoregion within which water is being managed is an important part in structuring an effective management approach for stormwater.
The variable ecology across the state can be presented in many different ways. One example is the concept of ecoregion sections developed by the DNR. The DNR's division of ecoregions is based largely on surficial geology and geologic landforms. As with any statewide map, data should be verified with local data when used as a consideration in stormwater design.
The geologic variability across Minnesota is reflective of billions of years of igneous and sedimentary history, plus geologically “recent” glaciation which is responsible for much of Minnesota’s vast natural beauty and abundance of water related resources. In most cases, the debris left behind by the glaciers provides a thick cover between the land surface and the buried surface of the underlying bedrock. In other cases, this glacial material either by-passed a location or has been eroded away, exposing bedrock to material (and possibly pollution) that comes from the land surface. Manual users are referred to the Minnesota Geological Survey (MGS) for details on the geology of the state.
In many portions of the state, bedrock occurs at or near the surface. The “red rocks” of the southwest, igneous intrusions along the St. Croix River and North Shore, and scattered sedimentary outcrops all around the state present some challenges in stormwater management because of their proximity to the surface. Among those difficulties are a lack of soil depth for use of infiltration techniques, structural impairment to best management practice (BMP) installation and steep slopes. The stormwater management implications of shallow bedrock affect infiltration, ponding depths, and the use of underground practices. Details can be obtained from the Minnesota Geological Survey (MGS) or a reliable local source, such as the county or a local well driller.
Carbonate and possibly other forms of bedrock can erode or dissolve in a manner that opens up pathways for movement of water into and through the rock. Such karst features, if sufficiently close to the land surface or to a ground water flow pathway, can present an opportunity for surface contaminants to enter the ground water system with very little or no treatment. This has important implications with respect to geotechnical testing, infiltration, pre-treatment and ponding of runoff.
Karst regions are predominantly found in the southeastern portion of the state. Caution must be used in interpreting the geographic depiction of “Karst lands”. Local data should be used when available rather than using a generalized statewide map.
In karst settings where active karstic conditions (within 50 feet of the surface) are known to exist, additional constraints and considerations need to be evaluated prior to implementing most structural BMPs. Of particular concern in karst settings is the formation of sinkholes as a result of hydraulic head build up and/or dissolution of rock present underneath or adjacent to BMPs. Concerns also exist for ground water flow interruption, interflow and recharge particularly as it relates to stormwater facility, location, and size and the relationship of ground water to surface water. Where karst conditions exist, there are no prescriptive rules of thumb or universally accepted management approaches because of the variability intrinsic to karst terrain. An adaptation of a familiar old saying is very appropriate: the only thing predictable about the behavior of water in a karst system is its unpredictability.
In general when underlying karst is known or even suspected to be present at the site, stormwater runoff should not be concentrated and discharged into known sinkholes, but should rather be dispersed, or soaked into the ground after adequate pre-treatment, or conveyed to a collection and transmission system away from the area. In other cases, it may be impossible to remove water from an area with sinkholes or away from karst geology, so common sense clean-up of the water and discharge into the karstic area is a reasonable management approach, especially if some filtering soil is available between the land surface and the karst formation.
One of the first steps in the selection of BMPs is an assessment of the type of soils present on a site and the inherent ability of those soils to soak-up water. Soils are extremely variable throughout the state, but fortunately good information on local soil conditions is usually available. Details on surficial soils (generally to a depth of about six feet) are contained in county soil surveys, which are available from the U.S. Department of Agriculture’s Natural Resource Conservation Service (NRCS). Soil surveys for much of the state have been digitized to make electronic use practical. Note, however, that these surveys are not accurate enough to determine site specific characteristics suitable for many BMP applications, so a detailed site analysis is recommended. The primary reason for this is that soils can vary substantially with depth, and the county soil surveys depict only surficial mapped units.
Soils with low infiltration capacity are found throughout the state. On a local scale the absence of good soils that can absorb runoff (i.e., infiltrate) can be a major detriment to good stormwater management. Stormwater management limitations in areas with “tight” soils generally preclude large-scale infiltration and ground water recharge (infiltration that passes into the ground water system). These soils will typically be categorized under Hydrologic Soil Group (HSG) D and have other characteristics. The infiltration rates noted in this table are conservative estimates of long-term, sustainable infiltration rates that have been documented in Minnesota. They are based on in-situ measurement within existing infiltration practices in Minnesota, rather than national numbers or rates based on laboratory columns.
Use of HSG C or D soils for BMPs that rely on infiltration is generally not recommended unless a pre-development condition is trying to be simulated. That is, these soils can certainly be used in a system that relies only on a small amount of infiltration similar to the small amount that inherently exists on site. If a manager wants to match pre-development volume for all soils, it is apparent that D soils will continue to yield low infiltration.
Design infiltration rates, in inches per hour, for A, B, C, and D soil groups. Corresponding USDA soil classification and Unified soil Classifications are included. Note that A and B soils have two infiltration rates that are a function of soil texture.*
The values shown in this table are for uncompacted soils. This table can be used as a guide to determine if a soil is compacted. For information on alleviating compacted soils, link here. If a soil is compacted, reduce the soil infiltration rate by one level (e.g. for a compacted B(SM) use the infiltration rate for a B(MH) soil).
Link to this table
|Hydrologic soil group||Infiltration rate (inches/hour)||Infiltration rate (centimeters/hour)||Soil textures||Corresponding Unified Soil Classification|
|Although a value of 1.63 inches per hour (4.14 centimeters per hour) may be used, it is Highly recommended that you conduct field infiltration tests or amend soils.b See Guidance for amending soils with rapid or high infiltration rates and Determining soil infiltration rates.||
|GW - well-graded gravels, sandy gravels
GP - gap-graded or uniform gravels, sandy gravels
GM - silty gravels, silty sandy gravels
SP - gap-graded or poorly graded sands
|0.45||1.14||SM - silty sands, silty gravelly sands|
|0.3||0.76||loam, silt loam||MH - micaceous silts, diatomaceous silts, volcanic ash|
|0.2||0.51||Sandy clay loam||ML - silts, very fine sands, silty or clayey fine sands|
GC - clayey gravels, clayey sandy gravels
*NOTE that this table has been updated from Version 2.X of the Minnesota Stormwater Manual. The higher infiltration rate for B soils was decreased from 0.6 inches per hour to 0.45 inches per hour and a value of 0.06 is used for D soils (instead of < 0.2 in/hr).
Source: Thirty guidance manuals and many other stormwater references were reviewed to compile recommended infiltration rates. All of these sources use the following studies as the basis for their recommended infiltration rates: (1) Rawls, Brakensiek and Saxton (1982); (2) Rawls, Gimenez and Grossman (1998); (3) Bouwer and Rice (1984); and (4) Urban Hydrology for Small Watersheds (NRCS). SWWD, 2005, provides field documented data that supports the proposed infiltration rates. (view reference list)
aThis rate is consistent with the infiltration rate provided for the lower end of the Hydrologic Soil Group A soils in the Stormwater post-construction technical standards, Wisconsin Department of Natural Resources Conservation Practice Standards.
bThe infiltration rates in this table are recommended values for sizing stormwater practices based on information collected from soil borings or pits. A group of technical experts developed the table for the original Minnesota Stormwater Manual in 2005. Additional technical review resulted in an update to the table in 2011. Over the past 5 to 7 years, several government agencies revised or developed guidance for designing infiltration practices. Several states now require or strongly recommend field infiltration tests. Examples include North Carolina, New York, Georgia, and the City of Philadelphia. The states of Washington and Maine strongly recommend field testing for infiltration rates, but both states allow grain size analyses in the determination of infiltration rates. The Minnesota Stormwater Manual strongly recommends field testing for infiltration rate, but allows information from soil borings or pits to be used in determining infiltration rate. A literature review suggests the values in the design infiltration rate table are not appropriate for soils with very high infiltration rates. This includes gravels, sandy gravels, and uniformly graded sands. Infiltration rates for these geologic materials are higher than indicated in the table.
References: Clapp, R. B., and George M. Hornberger. 1978. Empirical equations for some soil hydraulic properties. Water Resources Research. 14:4:601–604; Moynihan, K., and Vasconcelos, J. 2014. SWMM Modeling of a Rural Watershed in the Lower Coastal Plains of the United States. Journal of Water Management Modeling. C372; Rawls, W.J., D. Gimenez, and R. Grossman. 1998. Use of soil texture, bulk density and slope of the water retention curve to predict saturated hydraulic conductivity Transactions of the ASAE. VOL. 41(4): 983-988; Saxton, K.E., and W. J. Rawls. 2005. Soil Water Characteristic Estimates by Texture and Organic Matter for Hydrologic Solutions. Soil Science Society of America Journal. 70:5:1569-1578.
On the opposite side of the infiltration spectrum are those soils that rapidly infiltrate water from the surface. Soils with large percentages of sand and separate from the water table transmit water very quickly and might work extremely well for infiltration practices provided precautions are taken to protect the ground water from the introduction of polluting materials. The level of treatment in sandy soils is quite variable. Although the sands can act similar to a sand filter for particulate material, soluble pollutants generally move through the soil quite rapidly and unattenuated. An example of a large-scale sandy soil condition is the Anoka Sand Plain. Similar large expanses of sandy soils exist elsewhere in Minnesota and should be recognized when planning a BMP strategy.
The elevation and topographical changes evident in Minnesota also present variable challenges to local stormwater managers. For example, the steep slopes along the North Shore and along many major river banks requires a far different approach than those practices where a deep soil cover exists on a flat plain or slowly rolling hills. Local attention is required when information on slope, topography and physiographic character is part of the stormwater management deliberation.
Most of the cultural variation in the state relates to differences in land use that have resulted as the state developed over the past 100+ years. Although the major focus of this Manual is on urbanized land uses, many urbanizing type activities, such as road building, transcend a single land use and apply throughout the state. Also in many cases urbanization occurs on land that was previously altered by agricultural, silvicultural, or pre-development activity.
The citizens of Minnesota long ago realized the potential for worsening water quality as the state grew. The solution they discovered was not to stop growth, but rather to plan for how it happens and to institute protective actions to prevent many of the negative impacts. It is virtually impossible to prevent all negative impacts, but there is a realistic expectation that efforts to minimize the impact should occur. This is the basis for the stormwater regulatory program in place in the state.
There are also many new and ever-evolving ways to manage the runoff and eliminate some of the pollution associated with it. These best management practices are proven effective measures that are readily available in both structural and non-structural ways. There are no “best” solutions that apply universally to all situations across the state. There are best solutions that can be chosen for specific applications to solve specific problems, hence the name best management practice.
The Minnesota Stormwater Manual provides insight for Minnesota stormwater managers on the nature of the stormwater problem in the state, as well as guidance on how to manage it using many available tools. We can protect our valuable receiving waters through a reasonable set of practices applied equitably across the state. This is a major objective of this Manual.