Field and Laboratory Investigation of Submerged Vanes

Field Work:

This study is a continuation of work begun in 2000 to determine the effectiveness of submerged vanes for controlling bluff erosion in a steep gradient and varied bed material stream.  North Fish Creek, located in northwest Wisconsin, near Ashland, is a tributary to Lake Superior.  It is a productive spawning habitat for many fish species and is an important recreational fishery.  Over the course of the last century, the stream has undergone significant down-cutting and erosion due to land-use changes and logging that occurred in the late 1800’s and early 1900’s.  This process has resulted in a dramatic increase in sediment loading to the river and subsequently to Chequamegon Bay and Lake Superior.  The increased sediment load negatively impacts the spawning and development of the various fish populations as well as the water quality of Lake Superior.  The sediment load has been estimated at 15,000 tons per year with greater than 65% coming from 17 large over-steep bluffs that have developed at bends as the river has down-cut (Fitzpatrick; 1998).

Submerged vanes were proposed for the bluff sites as they are suitable for manual installation at these isolated locations (not accessible to heavy machinery), and the bluff slopes are too steep for vegetation.  Additionally, vanes are visually, environmentally, and physically less intrusive than traditional stabilization techniques (Whitman; 2002). The vanes are arranged in a series of arrays through the bend along the bluff toe with heights set at 1/3 of the bankfull flow depth (the design flow for the vanes) and at an angle into the flow.  The vanes re-direct the high velocities away from the bluff toe by imposing a torque on the flow opposite to the secondary circulation in the bend.  Additionally, the vortex (shed from the top of the vane) causes scour away from the bluff toe, which in turn moves the channel thalweg to a more desirable location.  Eventually, the vanes will alter the cross section of the channel and allow the bluffs to slough to a stable position, thereby minimizing the amount of bluff.

Submerged vanes were first installed at two sites, one in 2000 and the other in 2001; their effects on the channel at the sites have been monitored since then.  In the summer of 2004, a third site was selected for vane installation and study.  The site, however, contained many interesting features that presented additional challenges to the installation and eventually changed the approach to a solution.  In the new approach, an old channel along the existing point bar was deepened and widened so that it is the preferred flow path for the water.  Submerged vanes were installed in the upstream portion of the bend, leading to the bluff.  The vanes were placed along the point bar side of the channel and angled into that bank to help cut back the point bar and align the upstream portion with the new channel.  A 3.2 mega-pixel, self-contained, time-lapse camera setup was developed and installed to monitor the site.

North Fish Creek experienced two large flood events in the summer and fall of 2005 that damaged much of what has been accomplished to that point.  The third site fared the best of the three sites because of the newly opened channel that carried the bulk of the flood waters.  Prior to the floods, the vanes were effective in stabilizing the first site (2000).  The second site (2001) was also beginning to stabilize, though at a slower rate.  Significant amounts of work by hand were done at all three sites to increase the effectiveness of the vanes.  Through this work and by examining the dynamics of flood flows in the system, new design considerations were revealed that will continue to help refine the process of bluff stabilization with submerged vanes.

Publications:

Storrar, C.S. (2006). Field and Laboratory Investigation of Submerged Vanes on Channel Morphology: Independent Study Report for Master of Science Degree.  Civil and Environmental Engineering Dept., University of Wisconsin at Madison,  Wis., 145p.

Fitzpatrick, F.A., Peppler, M.C., Schwar, H.E., Hoopes, J.A., and Diebel, M.W. (2004). Monitoring channel morphology and bluff erosion at two installations of flow-deflecting vanes, North Fish Creek, Wisconsin, 2000–03: U.S. Geological Survey Scientific Investigations Report 2004–5272, 34p.

Whitman (Schwar), H.E. (2002). Demonstration of the Effects of Submerged Vanes on Bluff Erosion and Channel Characteristics at North fish Creek, Wisconsin: Independent Study Report for Master of Science Degree.  Civil and Environmental Engineering Dept., University of Wisconsin at Madison,  Wis., 198p.

Hrzic, M.A. (2000). Initiating a River Channel Meander with Submerged Vanes And Simulating the Flow Field in a Straight, River Channel with and without a Single, Submerged Vane using Fluent 5 (CFD Software):  Independent Study Report for Master of Science Degree.  Civil and Environmental Engineering Dept., University of Wisconsin at Madison,  Wis., 40p.

Boomstra, N.E. (1998). Streambank Protection Using Vanes: M.S. Thesis. Civil and Environmental Engineering Dept., University of Wisconsin at Madison, Wis.

Poggi, D. (2000). Laboratory Submerged Vane Study. Independent Study Report for Master of Science Degree.  Civil and Environmental Engineering Dept., University of Wisconsin at Madison,  Wis.

Vaine, A. (1999). Numerical Study of Submerged Vanes: M.S. Thesis:  Civil and Environmental Engineering Dept., University of Wisconsin at Madison,  Wis.

On aspect of the lab work was to determine the effects on channel morphology of flat plate, submerged vanes.  To accomplish this goal four objectives were formulated: (1) develop a set of equations to predict the channel morphology in steady, uniform flow in a uniform sand channel, with independent variables of flowrate and sediment feedrate and with bedload (lower regime, Froude number < 1) transport conditions; (2) test the predictions in a flume; (3) add vanes in various patterns and measure their effects on stable channel morphology; and (4) compare these results with available predictive relations.

A small, mobile bed flume is used to test the channel geometry equations.  To quantify the changes in the bed morphology, a non-contact, laser, surface profiler was borrowed from the National Soil and Erosion Research Laboratory.  This allows for detailed measurement of the flume bed that are then compared to predictive equations.  In addition, with the precision available in the profiler, the effects of submerged vanes can be quantified in a model setting.