Big Harris Stream Restoration
Cleveland County, NC
The Biological and Agricultural Engineering Department of the North Carolina State University, in consultation with Stantec, has implemented a research-based monitoring program at the Big Harris stream restoration project in Cleveland County, North Carolina. As part of their pre-restoration assessment, Stantec had estimated the volume of sediment eroded annually from streambanks throughout the project. This was achieved by estimating the Bank Erosion Hazard Index (BEHI) and Near Bank Stress (NBS) for all streambanks in the project. The BEHI is an index (Very Low, Low, Moderate, High, Very High, Extreme) that represents the degree of erodibility of a streambank. The NBS (Low, Moderate, High, Very High, Extreme) represents the magnitude of shear stress that will act on a streambank. Previous research in Wyoming, Colorado, and northwest North Carolina has assigned an annual erosion rate to each unique combination of BEHI and NBS (Rosgen, 2001).
NCSU collected data from the Big Harris watershed in April 2009 to support the ongoing research regarding the relation between BEHI/NBS combinations and erosion rate. This information will allow Stantec to refine the estimates of soil eroded from streambanks over the entire project area and improve erosion estimates for future projects in the region. After project implementation, EEP and Stantec will be able to quantify project benefits with regards to streambank erosion.
Methods
This monitoring study includes surveys and documentation of the erosive potential of streambanks in the vicinity of the restoration project. Eight actively eroding streambanks were identified on streams within the Big Harris watershed. All streambanks are located in areas that will not undergo restoration or enhancement activities under the currently planned mitigation program. This will allow for future data collection from these undisturbed areas.
At each of the eight eroding streambanks, the following tasks were conducted:
Task 1: Site Setup and Documentation
- Installation of permanent cross-section pins
- Establishment of a station for bank profile measurements (either through installation of a toe pin or notation of a station on the cross-section)
- Photodocumentation
- Site notation on a map
Task 2: Cross-section and Bank Surveys
- Survey of the cross-section through the subject streambank, using a sight level and measuring tape pulled taut between the cross-section pins
- Measurement of the profile of the subject streambank
- Measurement of the water surface slope of the stream feature at the subject streambank
- Measurement of the overall reach water surface slope
Task 3: BEHI/NBS assessment
- Detailed documentation of the BEHI of the subject streambank
- Documentation of the NBS at the subject streambank
- In order to calculate streambank erosion rates, the cross-section and bank profile surveys must be replicated at least annually over the next several years. During the surveys, the field crews should confirm the 2009 observations of BEHI and NBS.
