Streambank Erosion Associated with Grazing Activities in Kentucky

Streambank Erosion Associated with Grazing Activities in Kentucky

Summary

Monthly surveys, performed at fifty permanent cross sections within grazed pastures receiving three levels of best management practices (BMPs), were conducted to determine the degree of stream bank erosion associated with cattle activity at the University of Kentucky’s Animal Research Center (Figures 1-2). Photographic documentation and GPS surveys were also conducted to monitor changes to the stream banks. A multiple linear regression statistical model is being developed to determine the effects of different grazing and BMPs on stream bank erosion.

Objectives/Performance Targets

The goal of this project is the provide the agricultural community with a better understanding of the impacts of cattle grazing on stream bank erosion, thus enhancing current cattle production methods on small farms in Kentucky and possibly the eastern United States. Important to note is that this project is a subset of a larger research endeavor into the grazing impacts of cattle and BMPs on the water quality of a Kentucky stream whose objectives are to 1) determine whether the provision of cultural forms of BMPs such as an alternate water source, an alternate shade source, and/or the placement of supplemental feeding areas alter cattle behavior, 2) determine if the above BMPs collectively improve water quality, 3) determine if the inclusion of a fenced riparian zone with the BMP package significantly improves water quality over the BMP package alone, and 4) educate the agricultural community, especially livestock producers, about management systems that minimize the adverse environmental effects of grazing while maintaining production levels. This particular project, in combination with the larger research endeavor of which it is a part, address two main goals of the Sustainable Agriculture Research and Education (SARE) program by providing an assessment and evaluation of animal production practices to strengthen the agricultural competitiveness of Kentucky’s cattle producers while seeking to conserve soil, water and stream habitats.

Accomplishments/Milestones

Fifty permanent cross sections were established along the streambanks using guidelines set forth by Harrelson et al. (1994). Cross sections were erected at both random locations and near areas anticipated as frequent travel paths for cattle. Each cross section was established perpendicular to stream flow. Cross-sectional surveys were conducted monthly from April 2002 until November 2003 resulting in a total of 18 collection periods. Conventional leveling techniques, as outlined in Harrelson et al. (1994), were employed, and elevation measurements were taken at 0.3 m intervals. Data from all of the cross-sectional surveys were used in the analysis except for those collected during January 2003 (when the soil was frozen).

Computation of cross-sectional area changes with subsequent surveys was an involved process. Each recorded elevation within a cross section was subtracted from an upper plane (i.e. constant elevation) that was greater than all of the measured elevations for that cross section to reduce the magnitude of the computed cross-sectional areas. This step was performed for all 50 cross sections and for all 17 periods. The cross sectional areas (AT,j,k) for each cross section and for each sample period were computed using
(1)
where x is the lateral station along the cross section and y is the elevation at the corresponding lateral station. Lateral station is represented by the subscript i, sample period is represented by the subscript j, and cross section location is represented by the subscript k. At each individual cross section, increased values of AT,j,k from one cross-sectional survey period to the next indicate soil loss or erosion while decreased values of AT,j,k from one cross-sectional survey period to the next indicate soil gain or aggradation.
(2)
Cross-sectional areas computed for each individual cross section at each sampling period were then normalized using two different procedures. In the first procedure, all of the cross-sectional areas for each individual cross section and each period were normalized in relation to the original, respective cross-sectional surveys as seen in equation two, where Anorm,j,k is the normalized cross sectional area for each cross section at each sampling period and the subscript o represents the original cross sectional area (i.e. April 2002). For the second procedure, as outlined in equation three, the cross-sectional areas were normalized in relation to the previous cross-sectional survey.
(3)
Values of Anorm,j,k greater than one indicate that the normalized area for a cross-sectional survey increased in relation to the original cross-sectional survey (i.e. erosion). Similarly, aggradation was seen when values of Anorm,j,k were less than the original cross-sectional survey. A result of no change indicated equal values of Anorm,j,k and AT,o,k.
(4)
Finally, the fraction of change (Fj,k) between cross-sectional areas as compared to the original cross sectional survey was determined for each cross section and each period by equation four.
As with equation two, values of Fj,k greater than one indicate erosion, less than one indicate aggradation, and values equal to one indicate no change. Graphs of the cross sections at various points throughout the year are available at http://www.bae.uky.edu/WQ406.

A total of 30 permanent photo stations were installed in May 2002. The photo stations allow for the photographic documentation of changes at the research site. Each photo station was established such that the maximum amount of the pasture plots, and especially the streams, could be monitored. Digital images are taken at each photo station once per month, and all digital photographs are taken using the same camera and settings for purposes of uniformity (Figures 3). Collection of the images coincided with the surveying of the cross sections.

Sixteen cattle were collared in May, August and November of 2002 for a period of 28 days (Figure 4). The 28-day period was selected because this is the interval that the cattle are captured for weighing. Periodically weighing the cattle provides handlers not only with the opportunity to determine the animal’s average daily weight gain, but it also allows up-close examination of the cattle for any potential health related issues. Data was collected at 5-minute intervals allowing for a 15 day data collection period, thus the collars remained on the cattle for a portion of time even when they were not actively collecting data. Information collected from the collars provided an understanding of the level and location of cattle activity along the riparian areas.

Cattle were weighed monthly (Table 1). Data was not collected in December 2002 because the scale malfunctioned.

A newsletter detailing the aspects of the project was created in March 2002. The newsletter is available for viewing at http://www.bae.uky.edu/WQ406. Copies of the newsletter were provided to the appropriate extension personnel within the Biosystems and Agricultural Engineering Department for distribution (Appendix A). Plans are underway to update the newsletter once statistical analysis of the data is completed.

Four separate tours were conducted at the University of Kentucky’s Animal Research Center that included aspects of this project. The tours included visits by 1) Dr. Nancy Cox, Associate Dean of Research in the College of Agriculture at the University of Kentucky, 2) Dr. Wendy Baldwin, Vice-President for Research at the University of Kentucky, 3) Dr. Colien Hefferan, Administrator of Cooperative State Research, Education, and Extension Service (CSREES), United States Department of Agriculture and Dawn Riley, Director of Legislative and Intergovernmental Affairs Research, Education, and Economics, United States Department of Agriculture, and 4) Dr. Joseph Jen, Under Secretary for Research, Education, and Economics, United States Department of Agriculture and Dawn Riley.

Efforts are underway to develop a multiple linear regression statistical model based on the results from the cross section surveys. The current newsletter will be updated during Year 3 to relate the results of the project to the agricultural community through field days and the Internet. Results will also be published in a peer-reviewed journal.

Impacts and Contributions/Outcomes

This project provides information regarding the impacts of cattle grazing on stream bank erosion on two central Kentucky streams. Results from this project will assist in understanding the effectiveness of different best management strategies for conserving stream habitats located in grazed pastures.

Collaborators: