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Wetlands ProgramBrief SummaryOverview Description of the Wetlands ProgramWayne County Wetland Mitigation Bank and Wetland Preservation FundNational Association of Counties Award to Wayne County for Wetland Preservation FundLocating and Assessing WetlandsWhy Wetlands Are ImportantRouge Project Presentations on the Wetland ProgramWetland Program Technical ReportsMDEQ Wetlands Assessment Program
Wayne County Preliminary Wetland Inventory Map

Locating and Assessing Wetlands

The examples used here are from the technical report entitled A Wetland Protection Plan for the Headwaters of Johnson Creek and the Middle Rouge River - RPO-NPS-TM25.00. This study was performed with the intention of providing community planners with information and locations of valuable wetlands in their jurisdiction. In addition, it presents steps that a community planner can take to ensure the continued functioning of wetlands in their watershed. Community planners can use this information to make informed decisions that will best protect their wetland resources.


Wetland Mapping Procedure
This is the procedure that was used for mapping the Middle 1 Subwatershed of the Rouge River. The location and size were determined by merging three sources of information. One source was the National Wetland Inventory ( 1979 ) based on aerial photography obtained in 1978. The extent of hydric soils was estimated using soil survey information prepared by the Natural Resources Conservation District ( NRCS) for Washtenaw, Wayne, and Oakland counties. Hydric and wetland soil types were identified using the Hydric Soils of the State of Michigan prepared by the National Technical Committee for Hydric Soils. The third source of information was the Michigan Resource Information System (MIRIS) land use coverage previously prepared for the subwatershed. Land use classification types that are correlated with wetland plant communities were identified. This information was combined with the hydric soils and NWI information to map the wetlands of the Middle 1 Subwatershed. For purposes of this study, a wetland was mapped when two or more of these data sources overlapped. This method identified 557 wetlands in the Middle 1 Subwatershed.

The accuracy of this wetland mapping technique is dependent on the accuracy of the maps upon which it is based. Inaccuracies in aerial photo-interpretation, land use changes since the date of aerial photography, and natural changes in wetland boundaries could introduce error. While for some purposes it is crucial to understand the exact boundary of a wetland, for a regional wetland protection plan such as this it is more important to know that in fact the wetland exists, has a certain area, and may or may not be connected to a lake or stream. Perhaps more importantly, understanding functions performed by a wetland is more valuable to wetland protection than the exact boundary of the wetland.


View These Maps Online:

Hydrologic Soil Groups
Map Order Number: M-ewslhsg
View this map NOW! - EWSLHSG.PDF (2,300k)

Areas with Wetland Potential
Map Order Number: M-ewwetlu
View this map NOW! - EWWETLU.PDF (810k)

NWI, MIRIS Wetlands Maps



After identifying the valuable wetland resources in the Middle 1 Subwatershed of the Rouge River, it was necessary to assess the wetlands and determine their ability to perform specific functions. These functions included:

  • the provision of floral diversity and wildlife habitat
  • food, breeding areas, and habitat for fish and herpetiles
  • storage of flood water during wet weather events
  • the conversion and abatement of nonpoint source pollutants
  • protection of shoreline and stream bank erosion
  • aesthetic and recreational opportunity and enjoyment

Many assessment methods have fairly elaborate computational methodologies, as the evaluation of wetland functions is complex. For a project with an emphasis on regional planning, more detailed wetland assessment methods are inappropriate and labor intensive. Therefore, an evaluation procedure that quickly and easily identified wetlands important to the environmental quality of the Rouge River was developed. The method used to assess wetlands in the Middle 1 Subwatershed, called the Rapid Assessment Method ( RAM), is based on a method called the Indicator Valuation Method ( IVA). This is founded on the principle that the presence or absence of specific indicators reflect the degree to which a wetland performs a specific function. Indicators having documented scientific associations with wetland functions are used when such information is available. Hypothesized relationships are also used, if there is a strong scientific basis for the assumption. Once the wetland characteristics were established using the RAM, they were used to determine the ability of a wetland to provide the six functional benefits.

The RAM was developed in three major steps. First, functions of wetlands valued by residents and stakeholders were identified. Second, a field survey protocol designed to determine which function(s) a wetland was performing was produced. Third, wetland characteristics determined in the field were ranked according to the ability of a wetland to perform the function of interest.

As with all wetland evaluation systems, there are limitations of the RAM which should be understood. This evaluation method was not designed for impact analysis, which should be done on a long term site-specific basis. This method is not designed to be used in legal proceedings where a detailed wetland investigation is more appropriate. Finally, this method is not intended to be used as a justification for adversely impacting wetlands that do not provide a particular function or group of functions.

For the Middle 1 Subwatershed study, of the 557 wetlands identified, 199 were evaluated. There are four reasons why the number of wetlands evaluated did not reflect the number of wetlands identified:

  • Wetlands identified as being separate wetlands in the office were often found to be connected in the field, and therefore counted as one wetland.
  • Some wetlands no longer exist due to development or a change in conditions since the coverages used to identify wetlands were mapped.
  • Some areas identified by GIS methods were not actually wetlands, but detention basins, ponds, reservoirs, or lakes.
  • Many wetlands were inaccessible by public roads and therefore could not be assessed on ground. Of the wetlands which were inaccessible, the larger ones were evaluated from an airplane, while smaller wetlands were not evaluated.

A detailed copy of the Rapid Assessment Method for Evaluating Wetland Functions is available in the report. Click here to view this report.

Rapid Assessment Method Results
Wetland performance was evaluated by tabulating the number of high, medium, and low scores for each function. For example, there were six questions used to determine the quality of a wetland for floral diversity and wildlife habitat. One question asked how many vegetative communities were present. Wetlands with three or more vegetative communities received a "high" score, those with two received a "medium" score, while those with only one community received a "low" score. Answers to the other five questions were also ranked, and the number of high, medium, and low answers was tabulated. The resulting distribution of high, medium and low answers were used to represent the ability of a wetland to perform a function. Wetlands were ranked according to the number of high, medium, and low responses they had for each function. This way, the top wetlands for each function could be easily identified. A wetland was considered to perform a function if it had a greater number of high or medium scores than low scores.

Although a wetland may perform more than one function extremely well, it is unlikely that it performs most or all functions well, since some of the categories tend to be mutually exclusive. For example, a typical wetland receiving high performance scores for runoff attenuation is an emergent marsh with little open water which is not permanently inundated and has no outlet. This same wetland would receive low scores for the fishery habitat function, as wetlands good for fish are permanently inundated, have open water, and are connected to larger bodies of water such as lakes and rivers.

To view the results of this assessment, click here.

A Wetland Resource Protection Plan

The Middle 1 Subwatershed Management Study has identified that land development presents the single greatest risk to water quality in the headwaters of the Rouge River. The Middle 1 Subwatershed is unique among the subwatersheds of the Rouge River due to its relatively low levels of development. However, the rate at which this subwatershed is developing is increasing drastically. Because of this, timely identification and protection of wetlands providing ecological and economic services is more important than ever. Planning and zoning in the subwatershed should be done in the most environmentally responsible manner possible to achieve this protection.

This Management Study presents a management plan to protect the wetlands of the Middle 1 Subwatershed. This plan is intended to enhance and protect the functioning of wetlands in the watershed. This goal can be accomplished by enacting protections specific to the functions that each wetland has been determined to perform. Furthermore, this plan outlines simple steps that a community can take to protect and enhance wetland resources.

Protection measures include protecting plant diversity and wildlife habitat; protecting aquatic habitat; protecting flood water storage wetlands; protecting nonpoint source pollution abatement areas; protecting shorelines and streambanks; and finally, protecting aesthetic and recreational areas. You can find a more detailed description of the protection plan in the report. (click here)

Some of the goals of the Middle 1 Subwatershed Study that can be directly addressed through wetlands protection include:

  • Develop a storm water management plan for compliance with the Clean Water Act.
  • Develop a plan for preventing, minimizing, and reducing pollutant loading and flow variability which produce unacceptable impacts.
  • Maximize opportunity for recreational uses by inhabitants of the subwatershed.
  • Enhance and preserve a healthy and diverse ecosystem compatible with land uses within the Middle 1 Subwatershed.
  • Develop a plan to minimize the negative impacts of excessive flooding on adjacent property, including erosion.
  • Protect downstream water resources.


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Last Updated: 8/27/01

Please address all comments and suggestions about the contents of this Web page to rougeweb@co.wayne.mi.us.

The Rouge River National Wet Weather Demonstration Project is funded, in part, by the United States Environmental Protection Agency (EPA) Grants #XP995743-01, -02, -03, -04, -05, -06, -07 and C-264000-01.