Association of State Wetland Managers - Protecting the Nation's Wetlands.

The Compleat Wetlander: Identifying Wetlands That Store Floodwater

The past couple years have been a roller coaster ride for the people who live along the Mississippi. Flood was followed by drought was followed by flood.  While drought still persists in the western half of the United States, the main stem Mississippi states are no longer too dry.  In April the problem was too much water.

The literature about wetland values routinely identifies flood storage as one of the benefits of wetlands on the landscape.  Wetlands also provide other benefits for wildlife, water quality, sediment retention, recreation, etc.  Some wetlands are good for specific kinds of wildlife.  For example, prairie potholes are essential to migratory waterfowl. Others retain sediment or filter water.  It follows that some wetlands are better suited to store floodwaters.   However, in the past tools did not exist to identify which lost wetlands should be restored specifically to provide flood storage or nutrient retention or other specific benefits.  On the Mississippi and its tributaries, wetlands restoration in the right places could reduce flood heights.  Plus these same wetlands might also store water and minimize the impact of sustained droughts, reduce nutrients reaching the gulf and support wildlife populations.

Last week’s Salameander blog provided one example of a project that identified the wetlands that would retain sediment in a watershed

So how about identifying the wetlands that are best for floods storage?

There are maps for that!  Unfortunately they have not been created for the Mississippi Watershed. But they could.

Up through the end of the last century, national wetland policy was focused primarily on reducing the loss of wetland acreage.   But in the 1990’s interest grew in understanding how specific wetlands functioned and dozens of methods for evaluating wetland functions were created.  One of the methods was developed by Ralph Tiner at the U.S. Fish and Wildlife Service. It is called NWI+.  It integrated the National Wetland Inventory (NWI) wetland maps which use the Cowardin classification system (a vegetative description) with a hydrogeomorphic approach (a shape and water flow description). This integrated approach assigned one or more of 11 functions to individual wetlands.  They are:

  • surface water detention (for nontidal wetlands only),
  • coastal storm surge detention,
  • streamflow maintenance,
  • nutrient transformation,
  • retention of sediment and other particulates,
  • carbon sequestration,
  • bank and shoreline stabilization,
  • fish and aquatic invertebrate habitat,
  • waterfowl and waterbird habitat,
  • habitat for other wildlife, and
  • unique, uncommon, or highly diverse plant communities

In addition NWI+ identifies and assigns these functions, including flood storage, to wetlands that have been lost and could be restored. It divides restorable wetlands into two categories: those wetlands that would be good candidates for restoration and those that would be poor candidates.

While the Mississippi states do not have NWI+ maps, there are states that do including Massachusetts, Connecticut, Delaware and Maine.  It is possible to examine these maps on the NWI+ wetland mapper.  There is also other information about NWI+ here.

NWI+ is by no means the only method out there. Other sophisticated methods are being designed and deployed.  For example WetCat (Wetland Condition Assessment Tool) is scheduled to be launched this summer in Virginia.  Oregon State University has collaborated with partners in the Midwest to create another planning tool to create networks of small wetlands to prevent spring flooding and mitigate drought.

But while the need for flood storage is increasingly recognized and discussed as a goal of public policy, on the ground wetland losses continue.

The tools are there.  It is possible to create maps of existing and lost wetlands and determine which are most useful for flood retention as well as other functions that meet regional priorities and goals. Restoring and protecting wetlands is not the whole answer to addressing floods. But it’s an important part of a long term solution. Public policy and funding and programs need to catch up.

Restoring Wetlands to help Prevent Future Flooding

In Midwest, Drought Gives Way to Flood

Historic Flooding Unfolding Along Mississippi, Ohio Rivers

Estimating Potential Reduction Flood Benefits of Restored Wetlands

Flood Reduction through Wetland Restoration: The Upper Mississippi River Basin as a Case History

Reducing Flood Damage Study

Mississippi Floods Can Be Restrained With Natural Defenses

Floodwater Storage Function Overview and Statistical Summary

Illinois River Flooding

Unit 6: Additional Regulatory Measures

An evaluation of wetland assessment techniques and their applications to decision making

This entry was posted in drought, flooding, mapping, Mississippi, NIW, NWI+, restoration, wetlands and tagged , , . Bookmark the permalink.

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