The role of geomorphic variability on floodplain function: an analysis of sediment and phosphorus deposition

Excess sediment and associated phosphorus contribute to poor water quality and induce harmful algal blooms in freshwater lakes, including Lake Champlain. Floodplains can slow flood waters and create a depositional environment for sediment and nutrients, reducing downstream fluxes. The capacity of floodplains to capture sediment and nutrients is poorly understood in the Lake Champlain Basin (LCB), limiting the efficacy of remediation work to reduce phosphorus loads. This project assisted with recent work that measured deposition on well-connected floodplains. This part of the project focused on characterization of flood-deposited sediments and evaluation of the controls on measured variability in sediment deposition on selected flood events in 2019 using a classification of geomorphic controls. These classifications represent differences in depositional processes. Floodplain sediment samples from 20 sites across Vermont were analyzed for mass, total phosphorus, and particle size. Floodplain sites were classified by specific stream power. Plots within each site were classified by local geomorphic features. These analyses were used to describe how the depositional setting relates to sediment, phosphorus, and particle size measured at the study sites. We found that medium energy floodplains (class B) had higher rates of sediment and total phosphorus (TP) deposition than low energy floodplains (class C). We also identified trends in sediment and TP deposition within sites, describing patterns associated with elevation profiles, distance from channel, and floodplain feature units. Results of this work will contribute to an improved understanding of how floodplains interact with river-transported sediment and associated nutrients during floods

Exploring the role of geomorphic variability on the function of Vermont’s floodplains: an analysis of sedimentation

Excess sediment and associated phosphorus contribute to poor water quality and induce harmful algal blooms in freshwater lakes, including Lake Champlain. Floodplains alter nutrient transport by slowing flood waters and creating a depositional environment for sediment and nutrients. The capacity of floodplains to capture sediment and nutrients is poorly understood in the Lake Champlain Basin (LCB), limiting the efficacy of remediation work to reduce phosphorus loads. This project evaluated the controls on measured variability in sediment deposition on selected flood events in 2019 using a classification of floodplain surfaces. Samples from 20 sites across Vermont were analyzed for mass, total phosphorus, and particle size. Floodplain sites were classified by specific stream power and plots within each site were classified by local geomorphic features. These analyses were used to describe how the depositional setting relates to sediment, phosphorus, and particle size measured at the study sites. Results of this work will contribute to an improved understanding of how floodplains interact with sediment and associated nutrients during floods