Document Type

Thesis

Date of Degree Completion

Summer 2024

Degree Name

Master of Science (MS)

Department

Cultural and Environmental Resource Management

Committee Chair

Karl Lillquist

Second Committee Member

Megan Walsh

Third Committee Member

Clay Arango

Abstract

Waterways are valuable resources for communities and habitats, but are subject to degradation in the form of incision. This is a type of streambed erosion where streams narrow and deepen. Sediment control dams were placed on East Foster Creek in Douglas County, WA to control incision following the 2020 Pearl Hill fire. This study examined sediment capture in the ponds behind these dams, which included beaver dam analogues (BDAs), one rock dams (ORDs), and post-assisted log structures (PALS). Sediment capture may be influenced by several factors, including dam type, height, width, distance between dams, vegetation, land use, topography, soil type, and study area. The goal of this was to provide information that can be used for future dam installation decisions.

Sediment capture was measured from transects placed in ponds that created quadrats. Sediment volume was determined as 1) total sediment volume per measured pond and 2) mean sediment volume per quadrat. Based on the results, all dams captured sediment, but amount varied by factor. The results suggested dam type had no significant influence on sediment capture, but dam placement impacted sediment capture efficacy. A positive correlation was observed between distance from nearest upstream dam and total sediment volume per measured pond. Additionally, vegetation density was found to have declined since the fire. Furthermore, sediment capture increased downstream of a bridge in the upper study area. Distance from WA Highway 17 was negatively correlated with sediment capture. However, mean channel bank slope angle positively correlated with sediment capture. Pond size was positively correlated with total sediment volume per measured pond. Of the soil textures present, dams placed on finer soils had the most sediment volume capture. Finally, the lower and upper study areas had significant differences in mean sediment volume per quadrat. These findings suggest that resource managers can improve sediment capture and incision reduction by placing dams in areas with erosive sediments and steep slopes similar to those in this study.

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