Back to OTWB Main Page

What do we mean by structures?  That’s a good question, and an understandable source of concern for an environmental community that has been working so hard to remove barriers in streams.  One reviewer of our original concept noted that:


“I actually think this may be interesting in the location they are talking about [small headwater streams] but am a little concerned about the perception and implementation of a larger program. We have been working really hard to REMOVE blockages to fish migration, not construct them. In the headwaters of the Potomac, it may be fine since anadromous fish would have a hard time getting over Great Falls anyway, but other places may not be good.”

Since our project represents an ecologically guided attempt to restore the landscape storage of water that was once a ubiquitous component of the ecosystem created by the headwater beaver dam - why not use (and import) beavers to do the job?  Several of our project reviewers said as much, and clearly beavers would provide a more ecologically rounded service.  However, the best response to importing beavers to do the work comes from the other reviewers who said - emphatically - "you aren't planning to use beavers are you!" Or perhaps more colorfully in a recent David Heishman editorial in the Moorefield Examiner (9/10/2003) where he noted: "Beaver dams = Damn beavers. I first heard about needing more beavers several years ago when wetland preservation was front burner in Washington tree hugger circles. ...  My practical experience with flat tailed, sharp toothed, beady eyed creatures, both bureaucratic and natural led me to oppose the importation of either."

While CI agrees that beavers would "do it better",  the reality is that in the majority of areas where we might want to work the concept of importing beavers would be only slightly less palatable than importing wolves to control the deer herds. And, on a more practical level, this project seeks to quantitatively demonstrate that a series of small structures along headwater streams can provide water resource conservation that cannot be achieved in any other way, and at a water storage cost that is extremely competitive with other methods.  Ultimately, this may increase understanding of and, hopefully, tolerance for beavers but, regardless, such a demonstration will be best achieved using a system that we can control (and that most people will tolerate), which will require using man-made structures of some kind.  

On to the structures themselves.  Beaver dams come in two basic sizes.  There is the huge, valley-wide structure like the one shown below at Short Mountain in Hampshire County.  That line of shrubs to the right is the beaver dam, now well anchored with vegetation.

Beaver Pond at Short Mountain.  Click to enlargeBeaver Pond at Short Mountain.  Click to enlarge.

Then there is the bank-to-bank variety, like those below Sleepy Creek Reservoir (at least they were there before Hurricane Isabel came through).  


The bank-to-bank beaver dam provides the hydrological context for our project.  When built by beavers, they run pretty much straight across the stream, and are often started by felling a sizeable tree.  They have a tendency to 'blow-out' on the sides and, as might be apparent from the above picture at right, can exacerbate erosive forces along the banks.  As far as the beavers are concerned these are not problems.  Blowing out at the margins tends to increase the width of the stream, hence the size of the pool, and the beavers don't seem to mind doing repair work.  Its what they do after all. 

However, not being extremely industrious rodents with unlimited time on our hands, the staff of Cacapon Institute has no intention of trying to create structures  that require regular maintenance activity - like beaver dams.  We also don't want to create barriers to fish and invertebrate movement, increase erosive forces on the stream banks, or prevent the transport of sediment - something that streams are 'supposed' to do.  We simply want to raise the level of the stream so that water will seep into the banks more readily at many conditions of flow.  The structures will need to be very low maintenance and inexpensive to install.  

It turns out that this is a good time to be considering how to build such a structure, as the emerging science of natural stream restoration has developed structures that accomplish very much what we want to do.  One class of such structures is essentially a V-shaped weir, oriented so that the point of the V faces upstream, and constructed bank-to-bank, sloping down from each side toward the center.  When constructed correctly, erosive forces are focused on the center of the stream channel, not the banks.  This often creates a plunge pool - excellent fish habitat - and does not erode the stream banks if installed correctly.  

Above are two examples of cross vane structures from the Big Bear Creek, PA stream restoration project, perhaps the largest natural stream restoration project in the East so far.  The structure on the left is made from quarried sandstone, the structure on the right is made from hemlock.  Both have withstood many high water events without significant damage, including the the second largest twenty-four hour rain fall event in their recorded weather history from Hurricane Ivan in September 2004.  While Big Bear Creek is much larger than the streams CI is considering for the stream flow restoration project,  the same principles will generally apply.  Many thanks to Bill Worobec for inviting CI to tour this site, and for sharing his experiences in bringing this project to reality.


We selected a variant of the cross vane, per the Big Bear log structure above.  The following graphic shows the basic design, which has to be adapted to the unique characteristics of each structure site.  As of November 2004, 15 structures have been installed in the Site 1 meadow - which offers interesting design challenges in creating stable structures.  The stream is very tiny, meanders constantly, has deeply undercut banks just about everywhere (natural for this kind of channel), blowouts, bank calving, much multiflora rose, and often has orphaned "islands" of sedges in the middle of the stream.  Click here to see the structures that have been installed thus far.




Cacapon Institute - From the Cacapon to the Potomac to the Chesapeake Bay, we protect rivers and watersheds using science and education.

Cacapon Institute
PO Box 68
High View, WV 26808
304-856-1385 (tele)
304-856-1386 (fax)
Click here to send us an email
Frank Rodgers,  Executive Director

Website  made possible by funding from The Norcross Wildlife Foundation,  the National Fish and Wildlife Foundation, Virginia Environmental Endowment, NOAA-BWET, USEPA, The MARPAT Foundation, and our generous members.