Minimal Impact Design Standards (MIDS) represent the next generation of stormwater management in Minnesota. The emphasis today is on keeping the raindrop where it falls in order to minimize stormwater runoff and pollution and preserve natural resources. Low Impact Development (LID) is an approach to stormwater management that mimics a site’s natural hydrology as the landscape is developed and preserves and protects environmentally-sensitive site features such as riparian buffers, wetlands, steep slopes, valuable (mature) trees, floodplains, woodlands and highly permeable soils. The MIDS project offers guidelines, recommendations, and tools that will help implement LID more uniformly across Minnesota's landscape and it provides guidance to effectively implement the concepts and practices that LID promotes and encourages. MIDS contains four main elements to meet these needs:
- stormwater volume performance goals for new development, redevelopment and linear projects;
- new credit calculations that standardize the use of a range of structural stormwater techniques;
- design specifications for a variety of green infrastructure best management practices (BMP's); and
- an ordinance guidance package to help developers and communities implement MIDS.
How is MIDS used?
MIDS was specifically developed for designers, engineers, planners, contractors, elected officials, stormwater managers, landscape architects, public works staff, landscape industry, land use regulators and others involved in new development and redevelopment projects that potentially generate stormwater runoff. The concepts behind MIDS can essentially be used by all Minnesotans-we can all do our part in minimizing stormwater runoff and pollution. MIDS methodologies provide tools for individuals to quantify reductions in post-development runoff and pollutant loading from a wide variety of LID practices.
Adapting and using LID approaches offers multiple benefits including minimizing and reducing the amount of pollution reaching our lakes, rivers and streams and helps to recharge groundwater resources. MIDS establishes unified LID standards, approaches and credits so we can consistently apply these principals across Minnesota communities. MIDS helps communities measure progress toward water and natural resource protection and restoration goals. MIDS will also be used as the highest standard for meeting the stormwater practice for Minnesota Green Step Cities.
Specific examples of how the MIDS package can be used, including the MIDS calculator, include the following.
- Qualify as a Green Steps city. Green Step cities are considered to meet the highest standard for stormwater practices.
- Qualify for Blue Star Award. The Blue Star Award is a certification and award program that offers municipalities that excel in stormwater management the positive public recognition that they deserve.
- Greater involvement in voluntary initiatives, such as Complete Streets.
- Provide documentation on grant applications, such as the Clean Water Legacy grants, to show reductions in volume, TP and TSS.
- Increase likelihood of compliance with NPDES stormwater permits or other local requirements for managing stormwater. Examples include
- reporting on Total Maximum Daily Loads;
- meeting post-construction stormwater management requirements in the Municipal Stormwater General Permit; and
- meeting permanent treatment requirements in the Construction Stormwater General Permit.
Ordinance goals
A Community Assistance Package (CAP) was developed to provide ordinances and tools that help integrate LID principles, including the MIDS performance goals and calculator, into a package that can be used by local units of government. These tools can be used by communities to help them achieve MIDS performance goals for stormwater volume. The CAP includes instructions about how to use the checklists, and various training materials and approaches used during implementation in several test or pilot communities.
Calculator
The MIDS calculator is a tool designed to quantify reductions in post-development runoff and pollutant loading using a variety of LID practices. This graphic user interactive tool allows individuals to enter a project’s site conditions and determine the amount of stormwater volume retention needed and the pollution loading (sediment and phosphorus). The calculator then provides a method to enter their stormwater practices of choice and determine (calculate) the amount of stormwater volume and pollution reduction (credit) they can achieve. Currently, the calculator includes LID practices for green roofs, bioretention basins, infiltration basins, permeable pavement, infiltration trench/tree box, swales, filter strips and sand filters. Other practices will be added in the future. The calculator includes convenient links to specific design specifications for LID practices that are found within the Minnesota Stormwater Manual.
MIDS Fact Sheet: File:MIDS fact sheet.pdf
Definitions
- Impervious surface - a surface that impedes the infiltration of rainfall and results in an increased volume of surface runoff (see also the definition in the glossary of this manual).
- Land disturbance - any activity that results in a change or alteration in the existing ground cover (both vegetative and non-vegetative) and/or the existing soil topography. Land disturbing activities include, but are not limited to, development, redevelopment, demolition, construction, reconstruction, clearing, grading, filling, stockpiling, excavation and borrow pits.
- Linear project - construction or reconstruction of roads, trails, sidewalks, and rail lines that are not part of a common plan of development or sale
- New development - any development that results in the conversion of land that is currently prairie, agriculture, forest, or meadow and has less than 15 percent impervious surface. Land that was previously developed, but now razed and vacant, will not be considered new development
- Redevelopment - any development that is not considered new development (see also the definition in the glossary of this manual).
This document provides rationale for selecting the above definitions and alternative definitions: File:MIDS definitions.docx