Determining Whether Willow Creek Can Support Fish
by Gavin Marston
The Corvallis fisheries class took a field trip to Willow creek on the Teller Wildlife Refuge. While we were there we took pebble counts and crosssections of the stream. As Traci Sylte states, a stream cross-section gives us the natural dimensions of the stream. (Sylte,2009) A pebble count shows the size of the substrate and its spawning potential for a fish. The fish build a redd which is formed by a fish brushing off rocks and then laying eggs in the rocks. As stated by W.J Mc’Neil 50% of the substrate has to be smaller than 102mm, more than 14% of substrate smaller than 1mm will affect the success of spawning. Bigger than 102mm will prove difficult for fish to move and smaller than 1mm could cover the fish eggs and lead to fish suffocation (Mc’niel,2004). The purpose of the trip was to identify the fish habitat and decide what Rosgen stream type Willow creek is.
For our research, we went to the Teller Wildlife Refuge on Willow Creek. To carry out a successful pebble count, you have to be able to handle the frigid cold water of the Bitterroot in the winter. To start the process you stand on one edge of the creek and put one foot out, reach down with your eyes closed, pick up a rock, and measure the medium axis in mm. You need to repeat this 99 more times while recording your measurements. The reason for reaching down with a closed eye is to eliminate the bias of picking up certain rocks, When we were doing pebble counts we had thick rubber gloves on only allowing us to pick up larger rocks which could have caused errors in the experiment. A cross-section is taken by stringing a tape measure above the water so that it is at bankfull (which is the highest a steam can be without flooding) then measuring the depth at intervals as it relates to the bankfull. My group used 6-inch increments. I found this was one of my favorite field trips even though it was cold. I enjoyed being on the body of water.
For the pebble count that we took, we found that around 97% of the pebbles were under 102mm and that there were no pebbles under 1mm meaning that this is an optimum place for a fish to spawn
Figure 1
The blue bar in (figure 1) represents how many of that size category we had and red represents the cumulative percent of the corresponding substrate cumulative percent is the percent of how many rocs there are adding up to 100%
Factors like the width to depth ratio which is bankfull divided by thalweg (deepest spot), can help us identify the Rosgen stream type; these were our findings on Willow creek The W/D ratio was 10.56. The Entrenchment which measures the stream’s access to the floodplain was 1 and, the sinuosity which is how far the streams bends out is 1.32. The slope of the stream which is rise over run was (.004).
Figure 2
Figure 3
(Figure 3) Left Bank Full 0ft Right Bank Full 24.3ft Left Waters Edge .6667ft Right Waters Edge 23.5 thalweg 2.3ft. The cross-section can show us the numbers we need to calculate W/D entrenchment which is needed to figure out our Rosgen stream type
We gained important information from our fieldwork and this info can be used to figure out more about the stream. As Dave Rosgen states " The, B stream types exist primarily on moderately steep to gently sloped terrain, with the predominant landform seen as a narrow and moderately sloping basin.”(Rosgen) Streams age throughout time, a young stream is a stream that is more steep cut while an older stream meanders and flows slower and flatter. Willow creek is an older stream because it meanders more and is not very steep cut. We figured willow creek is between a C and B steam type on the Rosgen classification chart due to the sinuosity(1.32) which falls in the B category. The slope(.004) falls in the C category and the cross-section(figure 3) falls into B category. The map (figure 2) falls into the B category stream type. With all the info we gathered, we know that Willow Creek’s habitat can support fish and is between stream type B and C.
References
“Fundamentals of Rosgen Stream Classification System”(n.d.). Retrieved January 20, 2021, from https://cfpub.epa.gov/watertrain/moduleFrame.cfm?parent_object_id=1199
USDA cross section presentation.pdf
2004 stream habitat restoration guidelines: final draft
Mc’niel (2004). Salmonid Spawning Gravel Cleaning and placement. Retrieved from https://people.wou.edu/~taylors/g407/restoration/WA_Dept_Forestory_2004_Spawning_Gravel_Maintenance_Techniques.pdf