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

The Compleat Wetlander: What’s wrong with this stream? Part I

The Final Compensatory Mitigation Regulations published in 2008  formalized requirements for avoiding, minimizing and mitigating alteration of streams.  Previously dredging and filling of streams was often mitigated with wetland restoration.  But while the rule required loss of stream functions to be avoided or replaced, stream restoration science and practices lagged far behind the science of wetland restoration and this has created significant challenges in carrying out the Section 404 program.  To date, many of the practices to implement stream mitigation have focused on stabilizing streams banks and improving riparian habitat.  But is this restoration and is it the correct goal for mitigation?  What about water quality that may be affected by stream alteration? Furthermore, what kind of stream should be restored when a stream is altered?  Should it be a stream that flows year round (perennial)?  What about those that are fed by groundwater part of the year (intermittent) or those fed only by rainstorms, snowmelt and other surface runoff (ephemeral)?  Finally, how can we recognize a successfully restored stream?

The answers to these questions are further complicated by the extensive alterations that have happened to streams since European settlement.  Streams and rivers are affected by what happens on the land they drain.  In the United States nearly all of these lands have been cut for timber, cleared for farming, mined or grazed or developed for houses and businesses.  Sometimes three of four of these activities have occurred or reoccurred on the same piece of land over the past 200 years.  In addition 100 million acres of wetlands have been drained further changing streams. Nationwide Stream in Daniel Boone National Forestfarmers routinely altered the location of streams in their fields moving them from the middle of a valley to the toe of the nearest hillside to provide more room for crops.  As a result, even a stream that looks ‘natural’ may not bear any resemblance to what the stream was like prior to these changes.   For example the stream pictured on the left is located in Daniel Boone National Forest in Kentucky.  To most people, including myself, it is beautiful.  Trees and lush vegetation line the bank.  The clear water flows over rocks and gravel lying on flat Plant and tree roots separated from groundwaterbedrock.  The stream follows the toe of a steep hillside.  On the other side of the stream is a gently sloping field that forms the narrow valley floor.

But appearances are deceiving.  This stream, like the Headcut on feeder streammajority of rivers and streams in this country has been moved — this one to the side of the valley floor — and straightened.  Erosion from forestry and farming and mining has piled three to six feet of sediment on the valley floor.  As a result the stream is separated from its historic floodplain and has eroded down to the bedrock.  The trees are separated from groundwater as well.  Headcuts (little waterfalls) can be found on smaller streams that run into this one indicating that erosion is ongoing. Headcuts can move up rivers and streams for decades or even hundreds of years after rivers and stream are altered.   The stream is in fact acting as a very effective drainage ditch.  It drains the valley aquifer.  It is unfriendly to macroinvertbrates and amphibians which are washed away whenever there is a major rain event because there is no woody debris or adjacent wetlands to create quiet water to take refuge in.  The drainage of the aquifer also means that the stream dries out for part of the year. Stabilizing the banks will not address any of these issues.

Because wetland restoration science has preceded stream restoration science, many of the approaches used to successfully restore wetlands to mitigate losses are being adapted to address stream restoration. For example reference condition – using a healthy wetland that is similar to the one being altered to set restoration goals-–has been used extensively to establish standards for successfully restoring or creating a wetland.  But what is the standard to restore to if there are no streams in good condition? Remember, the scale of stream alteration in this country is difficult to comprehend because it is so pervasive.   This is a question that merits serious and thoughtful scientific investigation.

There is already applied research ongoing and the benefits of a more comprehensive approach to stream restoration are impressive.   We’ll examine some possible solutions to this issue in an upcoming Compleat Wetlander “What’s Wrong with This Stream Part II”.

This entry was posted in Uncategorized. Bookmark the permalink.

Leave a Reply

Your email address will not be published. Required fields are marked *