THE EFFECT OF A BEAVER COMPLEX ON THE GEOMORPHOLOGY OF A STREAM LOCATED IN THE PIEDMONT OF NORTH CAROLINA: A CASE STUDY

Geomorphic alterations driven by beaver impoundment activity is not well researched in the Piedmont region of North Carolina. Geomorphic alterations across the field site have been primarily caused by the impoundment of stream waters, which drives sediment deposition and the formation of new stream flow paths.

Field observations, sediment depths via soil probing, and 75 sediment cores were used to quantify the total sediment storage created by beaver impoundment. Aerial images taken over a 15-year period were used to track the evolution of the beaver complex. C¹⁴age dating was used to calculate sedimentation rates. Field observations focused on dam and pond dimensions, stream flow path characteristics, and changes in plant communities.

Sedimentary facies are a reflection of the stream flow conditions that existed during deposition. Five sedimentary facies were identified based on dominant textural class: 1) clay dominated, 2) silt dominated, 3) mud dominated, 4) sand dominated, and 5) gravel dominated beds. Gravel facies represent extreme high-flow or dam failure events, clay facies represent deposition during low flow and base flow conditions, and silt and mud facies represent deposition during intermediate stream flows. Sediment depths range from 0 cm in newly constructed ponds, to over 1 meter in the oldest ponds. Sedimentation rates range from 4 cmy^-1 to less than .25 cmy^-1. Variability in sedimentation rates are due to the constant shifting of sites of deposition.

Local beaver populations that were extirpated in the early 1900’s are now recovering throughout the area after their reintroduction during the 1950’s. The total length of impounded stream in the Piedmont region of North Carolina is expected to scale with population growth. Therefore, geomorphic alterations to affected watersheds will also increase. This research will help highlight how stream geomorphology could potentially be affected as a result of beaver population growth throughout the region.