Quantifying Floodplain Ecological Processes and Ecosystem Services in the Delaware River Watershed

Science Center Objects

Floodplain and wetland areas provide critical ecosystem services to local and downstream communities by retaining sediments, nutrients, and floodwaters. The loss of floodplain functionality due to land use conversion and degradation reduces the provisioning of these services. Assessing, quantifying, and valuing floodplain ecosystem services provide a framework to estimate how floodplain systems influence human well-being and provide information to decision makers on tradeoffs associated with development pressures and conservation priorities.

Floodplain inundated with water

Floodplain inundated with water (Public domain.)

Research Questions:

  • What ecosystem services and associated socio-economic values are provided by floodplains in the Delaware River watershed?
  • How do the ecosystem functions of sediment/nutrient retention and flood attenuation vary spatially within floodplains in the Delaware River watershed?
  • Where are opportunities to target conservation of high functioning floodplains and restoration of incised streams with eroding banks to optimize ecosystem services in the Delaware River watershed?

Project Approach:

This project integrates lidar mapping, field data collection, and modeling to quantify the ecosystem service of sediment and nutrient retention that floodplains provide in the Delaware River watershed. Ecosystem services are then valued using a replacement cost approach for nutrient and sediment retention and damage cost avoided for flood attenuation.

Mapping Floodplain Features:

Floodplain geomorphic features will be extracted from bare-earth Digital Elevation Models (DEM) with resolutions of 3-m spanning the non-tidal portion of the Delaware River watershed. Floodplain features will be extracted using a new tool called the Floodplain and Channel Evaluation Toolkit (FACET) developed in partnership with the NOAA National Water Center. FACET is a standalone Python tool that uses open source modules to map the floodplain extent and compute stream channel and floodplain geomorphic metrics such as channel width, streambank height, active floodplain width, and stream slope from DEMs. 

Digital elevation models are used to map the stream banks and the extend of the floodplain during flood events

Digital elevation models are used to map the stream banks and the extent of the floodplain during flood events 
(Public domain.)

Field Data Collection Using Dendrogeomorphology:

Images of exposed tree root ball and tree ring cross sections.

Scientists can estimate stream bank erosion rates using exposed tree roots by taking a cross section of the root (Public domain.)

A total of 15 field sites were selected to include 9 study sites in the Appalachian Plateau and 6 sites spread equally among Coastal Plain, Piedmont, and Valley & Ridge physiographic provinces. Field data collection employed dendrogeomorphic techniques to estimate rates of stream bank erosion and floodplain sediment deposition at each site.

Stream bank erosion rates were determined using root “cookies” to estimate time of root exposure from anatomical changes. Floodplain deposition was quantified at each site by estimating the average depth of sediment burial above the tree root collar divided by the age of the tree determined from annual tree rings taken from a tree core.

Samples of sediment were collected from banks and floodplains and returned to the laboratory for physico-chemical analysis, including nutrient content.  Channel, bank, and floodplain topography was surveyed at two cross-sections in each site.  Finally, pebble counts measured stream bed particle size along the reach at each site.

Modelling:

The mapping and field datasets will be combined to develop predictive models to estimate sediment and associated nitrogen, phosphorus, and carbon trapping and export for each stream reach within the non-tidal portion of Delaware River watershed. The effort will generate predictions of the magnitude and uncertainty of floodplain deposition and bank erosion for each stream reach in the study area.

Field Sampling Sites within the Delaware River Basin

Field Sampling Sites within the Delaware River Basin (Public domain.)