Evaluating floodplain potential for sediment and phosphorus deposition: Development of a framework to assist in Lake Champlain Basin planning

Diehl, R. (2021). Evaluating floodplain potential for sediment and phosphorus deposition: Development of a framework to assist in Lake Champlain Basin planning (Technical Report No. 100). Grand Isle, VT: Lake Champlain Basin Program

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• Dataset 2

The study described in this report was motivated by a need to provide a baseline understanding of the functioning of floodplains in the Lake Champlain Basin. Because floodplains can store and transform sediment and nutrients derived from the upstream watershed, many stakeholders in the Lake Champlain Basin are interested in restoring, protecting, or enhancing these natural features to optimize their role in water quality improvements. There is a lack of data, however, on the distribution of floodplains and the rate at which river-derived sediment and associated nutrients are deposited.

In this project, we collected and analyzed data that describe the status and function of floodplains along Lake Champlain Basin rivers to assist in watershed planning for improved water quality. First, we created an inventory of floodplains and identified their degree of hydrologic connectivity, through the development of a low-complexity floodplain mapping model. Flood-derived sediment and phosphorus deposition rates collected from a floodplain monitoring network provided a measure of the capacity of floodplains to capture sediment and phosphorus. Statistical models were developed to describe the functional relationship between deposition rates and the physical attributes of the upstream watershed, and more locally along the river channel and floodplain. We then used these statistical models to establish a framework for evaluating where to prioritize floodplain management efforts and the efficacy of such investments in meeting load reduction targets. Our efforts focused on those streams in Vermont whose upstream drainage area was 10 mi2 or greater, and on a range of watershed settings where it was likely that floodplains can act as sediment sinks. The resulting management framework may be applied throughout the Basin, given the availability of high resolution geo-spatial datasets.