Article written on 2015-11-22 by: Mike Renish
By Dani Long and Lee Meyers
When our Chapter applies for grant money, there’s often a question about how we can demonstrate that the conservation work we do makes a measureable difference. One way we can show that we’ve improved habitat is to take before and after measures of the steam channel. Faster water usually means cooler water, and that means a better environment for trout. Calculating width, depth and length are relatively easy measurements we can track at each project we do.
Before starting the conservation work, measure the total length of the stream segment to be improved. Make this measurement along the thalweg. Thalweg is the scientific term for that part of the stream where the main water flow occurs. In a straight cannel this would run down the middle of stream. In a stream with meander the thalweg would move back and forth following the curves in the channel. When meander happens the flowing water will create a deeper pool in the curve. In the low-gradient streams common to Wisconsin, a healthy stream will naturally have a meandering channel. When looking for a segment to restore we often look for a stream with a straight channel. In northern Wisconsin, this may be the result from past beaver dams or impacts from the logging era in the late 1800’s. In southern Wisconsin this could occur from farming activities, such as excessive cattle pasturing, or drainage of lowland areas to plant crops.
Secondly, setup transections at intervals equal (say, 10%) of the total length (every 100 feet for a 1,000 segment). At each transect, measure the total width from bank to bank and measure the depth of the stream at regular intervals (say, every foot) along this transect. Width is easily measured with a tape measure and depth with a calibrated wading stick. After all depth measurements along one transect are taken determine the average depth of each transect. When all transects are measured, average the width and depth to get a grand average width and depth for the segment. After the conservation work is finished, repeat all the measurements.
Measurements should be taken during normal stream flow (a period without rain) similar before and after work is done. After conservation work, the width and depth should significantly change. The width could decrease up to 50 percent and depth increase by 25%. The total length of the improved segment should increase and relates to how much the meander was increased. These changes will result in more and larger trout and will help maintain a cooler stream that is favorable to trout.
A cooler stream occurs because the water moving thru the improved segment should move faster as the flow is more concentrated and there are fewer shallow water “dead areas” along the edges. These “dead water” areas allow water to warm and a wider stream channel expose more surface area to the sun. Using a simple float (orange bobber works great) and a stopwatch, measure the time (feet per second) it takes the float to travel a given length. To be accurate, measure the flow at several locations along the target segment and also at intervals along the width of the channel. Average all these measurements to determine the overall speed of the stream flow.
The top of a stream flows faster than the bottom due to friction. So, the velocity has to be multiplied by a friction correction factor. For rough or rocky bottoms, multiply the velocity by 0.85. For smooth, silty, or sandy conditions, multiply the velocity by 0.9. Following conservation work, increased speed and meander will help wash away fine particles, like silt and sand, exposing coarse particulars like gravel. These coarse particles provide more food for to trout, and may even improve natural trout reproduction. The best possible result would be more trout reproduction following conservation work.
After we do conservation projects, we have quantifiable data showing that we have made the habitat better for trout. As we collect this data over time, we will be able to show the long-term effects of what we do. This can help us when we apply for more funding to do more projects.
There are many more variables that can be measured to show improvements, but these require more time and effort. Curious to know more? Check out the following:
Simonson, Timonthy, et al. 1994. Guidelines for Evaluating Fish Habitat in Wisconsin Streams. USDA Forest Service Tech. Report NC-164
Wang, Lizhu, et al. 1998. Development and Evaluation of a Habitat Rating System for Low-Gradient Wisconsin Streams. North Am. Jour. Fisheries Manage. American Fisheries Soc.
Fisher, William, et al. 2013. Freshwater Aquatic Habitat Measurements. Chapter 4, Fisheries Techniques. American Fisheries Soc.