Evaluating the Long-Term Morphological Response of a Headwater Stream to Three Restoration Techniques

The stream restoration industry has been growing since the addition and modification of Section 404 to the Clean Water Act. Many projects follow the guidelines of Natural Channel Design and use in-stream structures to stabilize stream channels. Post-project monitoring rarely exceeds 3-5 years, and the lack of guidance, funding, and pre-restoration data prevents meaningful post-project assessment of the design techniques. The Virginia Tech Stream Research, Education, and Management (StREAM) Lab is a research facility where a stream restoration project was completed along 1.3 km of Stroubles Creek in 2010. The study site provides a unique opportunity to compare the use of three restoration treatments with different intensities of restoration actions. Following exclusion of cattle from all three sites, the first treatment reach was left to naturally revegetate (Treatment 1) and along Treatment 2 the streambanks were re-graded to a 3:1 slope and replanted. An additional inset floodplain was constructed within the active channel of Treatment 3. Pre-restoration data, including topographic surveys and erosion pin measurements, provided a baseline for quantification of morphological response 11 years post-restoration. This project utilized as-built survey data from 2010 and a follow-up survey in 2021. The spatial data were analyzed to quantify important stream metrics: cross-sectional area, width, maximum depth, hydraulic depth, and width-to-depth ratio. Overall, the percent change per year of each metric decreased substantially following the restoration, indicating an increase in stability. While Treatment 3 continues to show minor erosion on average (+3.3% in area, +3.2% in width, and +11.2% in maximum depth), Treatments 1 (excluding cross section 5) and 2 decreased on average in area (-3.4% and -18.6%) and hydraulic depth (-13.3% and -10.8%). Treatment 1 eroded by an average of 11.7% in width compared to a decrease of -13.4% in Treatment 2 and an increase in 3.2% in Treatment 3. Comparisons of each treatment to Virginia Mitigation Banking Standards indicated Treatment 1 met the fewest number of criteria, followed by Treatment 2 and then Treatment 3, indicating that hard structures are not necessary to meet mitigation bank standards, even in urban watersheds. In an urban, incised channel with cattle impacts, re-grading the streambanks, actively planting woody riparian vegetation, and incorporating an inset floodplain will accelerate the establishment of channel stability, as compared to the more passive approach of simply removing cattle access to the channel.