Amity Creek

Listed: 2004

Impairment(s):  Turbidity

Current Status:  TMDL study has not yet begun

More Information:  http://www.pca.state.mn.us/water/tmdl/tmdl-303dlist.html

Projects:

 

1. Amity Creek Bank Stabilization

 

A reconnaissance of the stream revealed several failing banks.  The two banks chosen to stabilize were among the worst and accessible.  Funding for this project was provided by the Weber Stream Restoration Initiative and the Great Lakes Basin Program.

What and Why:

The project is addressing two banks that are approximately 10-20 feet high that are un-vegetated and composed of clay soils.  The banks are near an old abandoned farm field on City of Duluth property behind Hawk Ridge where the East and West Branches of Amity Creek come together.  In the process of its natural meander pattern the creek has intersected the valley wall.  The valley wall is composed of clay and eroding into the stream.   The cause of the erosion is two fold.  One cause is by the stream intersecting the  and eroding the bottom of the slope therefore causing the banks to be very steep.  This combined with surface and groundwater has made the banks unstable and results in periodic large inputs of clay into Amity Creek from these banks.  This input of clay soils results in stream turbidity (water is red colored versus clear) and can impact the fisheries and aesthetics of the creek.  The banks historically were also weakened by the removal of large conifers and other trees that counteracted the forces of the river.  Currently small aspen are growing near the banks which do not have the root mass compared to large white pine or spruce that may have been present prior to the old farm being established. 

How:

The project will reduce the input of clay sediments into the river and in the process create fisheries habitat through the creation of pools and additional woody debris.  This is accomplished through the use of stream vanes, a bankfull bench, root wads, riparian plantings, and excavation of the banks to a more stable angle.  The stream vanes will be constructed of rock and placed in the stream in such a manner and angle as to direct the high (bankfull and above) flows away from the eroding bank.  This will also create a depositional flat above the vanes further helping to stabilize the banks.  The bankfull bench will be created at the bottom of the unstable slope and will also help in spreading out of the high flows before they are able to affect the toe of the slope.  The root wads placed into the stream banks will further enforce the banks and allow for fisheries habitat through the placement of the woody debris.  Finally, the banks will be excavated, seeded, and planted such as to create a more stable bank angle.  In the future long lived conifer trees will be planted on the slope. 

 Alternatives:

1. Do nothing:

This alternative would result in further bank slumping and sediment delivery to the creek.  Therefore this alternative was not selected.

2. Rip Rap banks:

This alternative was not selected due to the limited habitat improvements gained from such a solution.  While effective at bank stabilization in banks in question, rip rap if improperly applied can have negative effects downstream. 

3. Move channel away from the banks:

This alternative was considered during preliminary design.  In discussions with DNR Fisheries and others it was decided that not enough information was known regarding the geomorphic stability of the stream.  Therefore this alternative was not selected.

Reason for selecting chosen alternatives

The reason for selection of the bankfull bench with root wads and logs along with stream vanes are the following:

This option will allow the stream thalweg to be redirected away from the banks and therefore taking the main erosive force away from the banks.  The bankfull bench will allow for bank protection while providing habitat with the root wads and large woody debris.  The stream vanes along with redirection of the thalweg will allow for the formation of a pool area downstream of the j-hook portion of the vane.  This will create additional pool habitat for the trout species present in the stream.

Results

The project was completed in the summer of 2009.  The project area had a good start on vegetation before snow cover.  The site also experienced a couple significant rain events that elevated flows.  The elevated flows did not reveal any problems.  The project site will be assessed several times a year for the next few years and it is likely that several minor adjustments will need to be made.  After vegetation is established, and the site has experienced spring snowmelts, it should require little to no maintenance.