New study shows importance of streambank erosion and floodplain deposition on sediment, phosphorus, and nitrogen sources and transport in the Chesapeake watershed
Issue: As Chesapeake Bay Program partners work to reduce pollution, knowing sources of sediment, phosphorus, and nitrogen transported to the Bay is critical for effective and efficient management. Streams and their associated floodplains have an important influence on the transport of nutrients and sediment through the Chesapeake watershed and into tidal waters. The USGS is conducting investigations to better quantity the erosion and deposition of nutrients and sediment as they are transported through the watershed.
USGS Study
To be able to predict rates of stream bank erosion and floodplain deposition across the watershed, the USGS developed new widespread measurements and models. New measurements included long-term rates of stream geomorphic change, sediment characteristics, and the dimensions of stream valleys at 53 sites throughout the Chesapeake watershed (and 15 in the Delaware River watershed) (Figure 1).
The measurements were used to calculate the amount of sediment and attached nutrients being trapped through floodplain accretion and lost through erosion of streambanks. The USGS then created statistical models to extrapolate these rates to all nontidal streams to better understand the importance of stream geomorphic change to sediment and nutrient transport through the watershed to the Bay.
Major Findings
- Measured long-term rates of streambank erosion and floodplain deposition were highly spatially variable across landscapes and varied in different physiographic regions of the watersheds (Figure 2).
- Geomorphic change and resulting loads of sediment and nutrients, for both streambank and floodplain, were most influenced by and increased with upstream urban and agricultural land use and the drainage area of the upstream watershed.
- The land use, and natural hydrologic, soils, and geology of watersheds generate the conditions in the Chesapeake that lead to hotspots of stream geomorphic change. In addition to greater rates of streambank erosion and floodplain deposition downstream of intensive land use in the urban and agricultural Piedmont and agricultural Valley and Ridge physiographic provinces, high rates of floodplain trapping occur in the Coastal Plain (Figure 3).
- Headwater streams were net erosional with more streambank erosion than floodplain deposition, whereas downstream reaches were on average net depositional with more floodplain deposition than streambank erosion. The transition between erosive vs. depositional stream-floodplains is thought to be roughly 3 km2 drainage area.
- Over the entire Chesapeake watershed, regional cumulative sediment loads from streambank erosion (−5.1 Tg yr−1) are nearly balanced by floodplain deposition (+5.3 Tg yr−1). Although both streambank erosion and floodplain deposition each individually generate very large changes in sediment load, when considered together they indicate that other sediment sources outside of perennial streams (like soil erosion in uplands and erosion of gullies and ephemeral streams) also must contribute to downstream sediment loads.
- Geomorphic changes in stream valleys had substantial influence on watershed sediment, phosphorus, carbon, and nitrogen budgets in comparison to existing predictions of upland erosion and delivery to streams and of downstream sediment loading (Figure 4).
- Predictions of the amount of streambank erosion and floodplain deposition (and associated nitrogen, phosphorus, and carbon load) for every stream in the watershed are available.
- The unprecedented scale of these novel findings provides important insights into the balance of erosion and deposition in streams within disturbed landscapes and the importance of geomorphic change to stream water quality and carbon sequestration.
Management Applications
These findings can be useful for prioritizing where and how to improve water quality – for example, where to restore streams to reduce streambank erosion, or where to restore or conserve floodplains to remove pollutants, to have the biggest impacts on sediment, phosphorus, and nitrogen loads.
The findings of this study will be used to improve the next-generation watershed model of the Chesapeake Bay to more accurately reflect where and how much stream erosion and deposition influences pollutant sources and transport.
For more information
Article information
Noe, G., K. Hopkins, P. Claggett, E. Schenk, M. Metes, L. Ahmed, T. Doody, and C. Hupp. 2022. Erosional and depositional streams: Measuring and modeling geomorphic change and watershed material budgets. Environmental Research Letters 17: 064015, doi.org/10.1088/1748-9326/ac6e47
https://iopscience.iop.org/article/10.1088/1748-9326/ac6e47
Open Access: free to download
Field and lab measurements of streambank erosion, floodplain deposition, and sediment physico-chemistry
Noe, G.B., Hupp, C.R., Schenk, E.R., Doody, T.R., and Hopkins, K.G., 2020, Physico-chemical characteristics and sediment and nutrient fluxes of floodplains, streambanks, and streambeds in the Chesapeake Bay and Delaware River watersheds: U.S. Geological Survey data release, https://doi.org/10.5066/P9QLJYPX.
Model predictions of streambank erosion and floodplain deposition
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.
Associated FACET output of stream, streambank, and floodplain dimensions (FACET is automated software to estimate the size and shape of streams and floodplains)
Hopkins, K.G., Ahmed, L., Metes, M.J., Claggett, P.R., Lamont, S., and Noe, G.B, 2020, Geomorphometry for Streams and Floodplains in the Chesapeake and Delaware Watersheds: U.S. Geological Survey data release, https://doi.org/10.5066/P9RQJPT1.
Issue: As Chesapeake Bay Program partners work to reduce pollution, knowing sources of sediment, phosphorus, and nitrogen transported to the Bay is critical for effective and efficient management. Streams and their associated floodplains have an important influence on the transport of nutrients and sediment through the Chesapeake watershed and into tidal waters. The USGS is conducting investigations to better quantity the erosion and deposition of nutrients and sediment as they are transported through the watershed.
USGS Study
To be able to predict rates of stream bank erosion and floodplain deposition across the watershed, the USGS developed new widespread measurements and models. New measurements included long-term rates of stream geomorphic change, sediment characteristics, and the dimensions of stream valleys at 53 sites throughout the Chesapeake watershed (and 15 in the Delaware River watershed) (Figure 1).
The measurements were used to calculate the amount of sediment and attached nutrients being trapped through floodplain accretion and lost through erosion of streambanks. The USGS then created statistical models to extrapolate these rates to all nontidal streams to better understand the importance of stream geomorphic change to sediment and nutrient transport through the watershed to the Bay.
Major Findings
- Measured long-term rates of streambank erosion and floodplain deposition were highly spatially variable across landscapes and varied in different physiographic regions of the watersheds (Figure 2).
- Geomorphic change and resulting loads of sediment and nutrients, for both streambank and floodplain, were most influenced by and increased with upstream urban and agricultural land use and the drainage area of the upstream watershed.
- The land use, and natural hydrologic, soils, and geology of watersheds generate the conditions in the Chesapeake that lead to hotspots of stream geomorphic change. In addition to greater rates of streambank erosion and floodplain deposition downstream of intensive land use in the urban and agricultural Piedmont and agricultural Valley and Ridge physiographic provinces, high rates of floodplain trapping occur in the Coastal Plain (Figure 3).
- Headwater streams were net erosional with more streambank erosion than floodplain deposition, whereas downstream reaches were on average net depositional with more floodplain deposition than streambank erosion. The transition between erosive vs. depositional stream-floodplains is thought to be roughly 3 km2 drainage area.
- Over the entire Chesapeake watershed, regional cumulative sediment loads from streambank erosion (−5.1 Tg yr−1) are nearly balanced by floodplain deposition (+5.3 Tg yr−1). Although both streambank erosion and floodplain deposition each individually generate very large changes in sediment load, when considered together they indicate that other sediment sources outside of perennial streams (like soil erosion in uplands and erosion of gullies and ephemeral streams) also must contribute to downstream sediment loads.
- Geomorphic changes in stream valleys had substantial influence on watershed sediment, phosphorus, carbon, and nitrogen budgets in comparison to existing predictions of upland erosion and delivery to streams and of downstream sediment loading (Figure 4).
- Predictions of the amount of streambank erosion and floodplain deposition (and associated nitrogen, phosphorus, and carbon load) for every stream in the watershed are available.
- The unprecedented scale of these novel findings provides important insights into the balance of erosion and deposition in streams within disturbed landscapes and the importance of geomorphic change to stream water quality and carbon sequestration.
Management Applications
These findings can be useful for prioritizing where and how to improve water quality – for example, where to restore streams to reduce streambank erosion, or where to restore or conserve floodplains to remove pollutants, to have the biggest impacts on sediment, phosphorus, and nitrogen loads.
The findings of this study will be used to improve the next-generation watershed model of the Chesapeake Bay to more accurately reflect where and how much stream erosion and deposition influences pollutant sources and transport.
For more information
Article information
Noe, G., K. Hopkins, P. Claggett, E. Schenk, M. Metes, L. Ahmed, T. Doody, and C. Hupp. 2022. Erosional and depositional streams: Measuring and modeling geomorphic change and watershed material budgets. Environmental Research Letters 17: 064015, doi.org/10.1088/1748-9326/ac6e47
https://iopscience.iop.org/article/10.1088/1748-9326/ac6e47
Open Access: free to download
Field and lab measurements of streambank erosion, floodplain deposition, and sediment physico-chemistry
Noe, G.B., Hupp, C.R., Schenk, E.R., Doody, T.R., and Hopkins, K.G., 2020, Physico-chemical characteristics and sediment and nutrient fluxes of floodplains, streambanks, and streambeds in the Chesapeake Bay and Delaware River watersheds: U.S. Geological Survey data release, https://doi.org/10.5066/P9QLJYPX.
Model predictions of streambank erosion and floodplain deposition
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.
Associated FACET output of stream, streambank, and floodplain dimensions (FACET is automated software to estimate the size and shape of streams and floodplains)
Hopkins, K.G., Ahmed, L., Metes, M.J., Claggett, P.R., Lamont, S., and Noe, G.B, 2020, Geomorphometry for Streams and Floodplains in the Chesapeake and Delaware Watersheds: U.S. Geological Survey data release, https://doi.org/10.5066/P9RQJPT1.