Floodplains provide millions of dollars in benefits every year to people in the Chesapeake Bay and Delaware River watersheds Completed
Issue: Floodplains provide important services to people by retaining sediments, nutrients, and floodwaters, thereby improving water quality and reducing flooding impacts. Having information on how the monetary benefit that floodplains provide varies across the Chesapeake Bay and Delaware River watersheds helps resource managers describe the benefits that floodplains provide in their current state and assess tradeoffs associated with development pressures and conservation priorities.
USGS study
The USGS, in partnership with the William Penn Foundation and the Smithsonian Institute, quantified the capacity of floodplains surrounding wadable non-tidal streams and small rivers (drainage area < 3,000 km2) in the Chesapeake Bay and Delaware River watersheds to retain sediment (and associated nutrients) and flood waters and estimated the monetary value of those two services.
A monetary value was placed on floodplain sediment and nutrient retention services by integrating field data collection, geospatial analyses, modeling, and economic approaches. The service was estimated as the amount of nitrogen found in sediment that is deposited on the floodplain and eroded from streambanks. Then wastewater treatment facility costs, for the lowest treatment level, were used to provide a conservative estimate of the value of floodplain sediment and nutrient retention benefits. Sediment and nutrient retention values were aggregated to the entire study area, river basins, states, and counties.
A monetary value was placed on floodplain flood regulation for a case study within the Schuylkill River watershed located in Pennsylvania. Floodplain flood regulation services were estimated by integrating geospatial datasets, existing flood frequency estimates, and Federal Emergency Management Agency’s Hazus model. Flood regulation services were estimated by comparing the damage cost that is avoided by having the current floodplain extent compared to a scenario that removed any existing floodplain water storage for events with 0.5, 0.2, 0.1 0.04, 0.02, 0.01 annual exceedance probabilities. Avoided damages were estimated for areas surrounding 18 USGS streamgages and then average damage costs were scaled to the entire Schuylkill River watershed based on stream length.
Major findings
Results from this study indicate that floodplains provide substantial benefits by trapping sediments and nutrients, with a net annual benefit of at least 100 million USD in the Chesapeake Bay watershed and 24 million USD in the Delaware River watershed. Although streambank erosion generates a cost to society, the amount of nitrogen removed through floodplain sedimentation is a much larger benefit to society. It should be noted that other ways that floodplains retain nutrients, such as nitrate and phosphate removal from floodwaters, are not included in these benefit estimations. In the Schuylkill River watershed floodplain, flood regulation was valued at 860,000 USD annually, with an additional 7.2 million USD annually provided through floodplain sediment and nutrient retention.
Floodplain benefits and services provided to people are not evenly distributed across the study area because of variability in landscape conditions and the location of a stream within the large stream network. Floodplains with the greatest benefits were those surrounding large streams (high-order) in the Piedmont and Coastal Plain. These streams compose a small portion of the stream network, but had the highest nitrogen trapping benefits per length of stream. In contrast, headwater streams (low-order) provide the largest total nitrogen value but the lowest overall nitrogen value per length of stream.
Management implications
The floodplain ecosystem service services estimated in this study could be used to identify high-functioning floodplains for conservation or to target restoration of degraded floodplains. The local scale estimates of floodplain sediment and nutrient retention provide a resource to summarize values at many management units or spatial scales (e.g., public lands, jurisdictional boundaries, watersheds). Local scale estimates of floodplain sediment and nutrient retention can be found within the accompanying data release listed below.
Results highlight an important distinction between higher-order streams and headwater streams. While the nitrogen value is lower for headwaters than higher order streams, headwaters are a substantial source of sediment via streambank erosion, offering opportunities for stream restoration or floodplain reconnection. The Piedmont was a hotspot for streambank erosion and floodplain nutrient trapping, while Coastal Plain floodplains are a hotspot for nutrient trapping.
Publication
The results of the study have been published in the Journal of Environmental Management (with open access) at, Societal benefits of floodplains in the Chesapeake Bay and Delaware River watersheds: Sediment, nutrient, and flood regulation ecosystem services, https://doi.org/10.1016/j.jenvman.2023.118747.
Accompanying data releases
Noe, G.B., Hopkins, K.G., Metes, M.J., Ahmed, L., Claggett, P.R., Doody, T.R., Schenk, E.R., and Hupp, C.R., 2020, Predictions of floodplain and streambank geomorphic change and flux, streambed characteristics, and catchment inputs and exports of sediment and nutrients for stream reaches in the Chesapeake Bay and Delaware River watersheds: U.S. Geological Survey data release, https://doi.org/10.5066/P93OUWYZ.
Welles, J.S. and Hopkins, K.G., 2023, Depth grids for floodplain flood attenuation baseline and counterfactual scenarios in the Schuylkill River watershed, Pennsylvania: U.S. Geological Survey data release, https://doi.org/10.5066/P9YPYM5M.
For more information
The project team included Kristina Hopkins, Emily Pindilli, Gregory Noe, Peter Claggett, Jacqueline Welles, Marina Metes, and Labeeb Ahmed.
Kristina Hopkins (khopkins@usgs.gov) is the primary contact for this project and can be contacted directly to request additional briefings.
Issue: Floodplains provide important services to people by retaining sediments, nutrients, and floodwaters, thereby improving water quality and reducing flooding impacts. Having information on how the monetary benefit that floodplains provide varies across the Chesapeake Bay and Delaware River watersheds helps resource managers describe the benefits that floodplains provide in their current state and assess tradeoffs associated with development pressures and conservation priorities.
USGS study
The USGS, in partnership with the William Penn Foundation and the Smithsonian Institute, quantified the capacity of floodplains surrounding wadable non-tidal streams and small rivers (drainage area < 3,000 km2) in the Chesapeake Bay and Delaware River watersheds to retain sediment (and associated nutrients) and flood waters and estimated the monetary value of those two services.
A monetary value was placed on floodplain sediment and nutrient retention services by integrating field data collection, geospatial analyses, modeling, and economic approaches. The service was estimated as the amount of nitrogen found in sediment that is deposited on the floodplain and eroded from streambanks. Then wastewater treatment facility costs, for the lowest treatment level, were used to provide a conservative estimate of the value of floodplain sediment and nutrient retention benefits. Sediment and nutrient retention values were aggregated to the entire study area, river basins, states, and counties.
A monetary value was placed on floodplain flood regulation for a case study within the Schuylkill River watershed located in Pennsylvania. Floodplain flood regulation services were estimated by integrating geospatial datasets, existing flood frequency estimates, and Federal Emergency Management Agency’s Hazus model. Flood regulation services were estimated by comparing the damage cost that is avoided by having the current floodplain extent compared to a scenario that removed any existing floodplain water storage for events with 0.5, 0.2, 0.1 0.04, 0.02, 0.01 annual exceedance probabilities. Avoided damages were estimated for areas surrounding 18 USGS streamgages and then average damage costs were scaled to the entire Schuylkill River watershed based on stream length.
Major findings
Results from this study indicate that floodplains provide substantial benefits by trapping sediments and nutrients, with a net annual benefit of at least 100 million USD in the Chesapeake Bay watershed and 24 million USD in the Delaware River watershed. Although streambank erosion generates a cost to society, the amount of nitrogen removed through floodplain sedimentation is a much larger benefit to society. It should be noted that other ways that floodplains retain nutrients, such as nitrate and phosphate removal from floodwaters, are not included in these benefit estimations. In the Schuylkill River watershed floodplain, flood regulation was valued at 860,000 USD annually, with an additional 7.2 million USD annually provided through floodplain sediment and nutrient retention.
Floodplain benefits and services provided to people are not evenly distributed across the study area because of variability in landscape conditions and the location of a stream within the large stream network. Floodplains with the greatest benefits were those surrounding large streams (high-order) in the Piedmont and Coastal Plain. These streams compose a small portion of the stream network, but had the highest nitrogen trapping benefits per length of stream. In contrast, headwater streams (low-order) provide the largest total nitrogen value but the lowest overall nitrogen value per length of stream.
Management implications
The floodplain ecosystem service services estimated in this study could be used to identify high-functioning floodplains for conservation or to target restoration of degraded floodplains. The local scale estimates of floodplain sediment and nutrient retention provide a resource to summarize values at many management units or spatial scales (e.g., public lands, jurisdictional boundaries, watersheds). Local scale estimates of floodplain sediment and nutrient retention can be found within the accompanying data release listed below.
Results highlight an important distinction between higher-order streams and headwater streams. While the nitrogen value is lower for headwaters than higher order streams, headwaters are a substantial source of sediment via streambank erosion, offering opportunities for stream restoration or floodplain reconnection. The Piedmont was a hotspot for streambank erosion and floodplain nutrient trapping, while Coastal Plain floodplains are a hotspot for nutrient trapping.
Publication
The results of the study have been published in the Journal of Environmental Management (with open access) at, Societal benefits of floodplains in the Chesapeake Bay and Delaware River watersheds: Sediment, nutrient, and flood regulation ecosystem services, https://doi.org/10.1016/j.jenvman.2023.118747.
Accompanying data releases
Noe, G.B., Hopkins, K.G., Metes, M.J., Ahmed, L., Claggett, P.R., Doody, T.R., Schenk, E.R., and Hupp, C.R., 2020, Predictions of floodplain and streambank geomorphic change and flux, streambed characteristics, and catchment inputs and exports of sediment and nutrients for stream reaches in the Chesapeake Bay and Delaware River watersheds: U.S. Geological Survey data release, https://doi.org/10.5066/P93OUWYZ.
Welles, J.S. and Hopkins, K.G., 2023, Depth grids for floodplain flood attenuation baseline and counterfactual scenarios in the Schuylkill River watershed, Pennsylvania: U.S. Geological Survey data release, https://doi.org/10.5066/P9YPYM5M.
For more information
The project team included Kristina Hopkins, Emily Pindilli, Gregory Noe, Peter Claggett, Jacqueline Welles, Marina Metes, and Labeeb Ahmed.
Kristina Hopkins (khopkins@usgs.gov) is the primary contact for this project and can be contacted directly to request additional briefings.