Recently, widespread valley-bottom damming for water power was identified as a primary control on valley sedimentation in the mid-Atlantic US during the late seventeenth to early twentieth century. The timing of damming coincided with that of accelerated upland erosion during post-European settlement land-use change. In this paper, we examine the impact of local drops in base level on incision into historic reservoir sediment as thousands of ageing dams breach. Analysis of lidar and field data indicates that historic milldam building led to local base-level rises of 2–5 m (typical milldam height) and reduced valley slopes by half. Subsequent base-level fall with dam breaching led to an approximate doubling in slope, a significant base-level forcing. Case studies in forested, rural as well as agricultural and urban areas demonstrate that a breached dam can lead to stream incision, bank erosion and increased loads of suspended sediment, even with no change in land use. After dam breaching, key predictors of stream bank erosion include number of years since dam breach, proximity to a dam and dam height. One implication of this work is that conceptual models linking channel condition and sediment yield exclusively with modern upland land use are incomplete for valleys impacted by milldams. With no equivalent in the Holocene or late Pleistocene sedimentary record, modern incised stream-channel forms in the mid-Atlantic region represent a transient response to both base-level forcing and major changes in land use beginning centuries ago. Similar channel forms might also exist in other locales where historic milling was prevalent.

No abstract

1. Effects of the incremental annual incorporation of new water-quality observations on trends-Graphic results for the six watersheds subject to detailed study 2. Tabular WRTDS results for period-of-record and 10-year flow-normalized trends in concentration and flux 3. Tabular WRTDS results for all stations and constituents modeled through water year 2012 [Also available on CD-ROM] 4. Effects of variability in annual sampling effort on trends-Graphic results for the eight watersheds subject to detailed study 5. Effects of variability in storm sampling effort on trends-Graphic results for the eight watersheds subject to detailed study 1. Map showing locations of major drainage basins in the Chesapeake Bay watershed and locations of CBNTN stations for which flux and (or) trend estimates were published through water year 2012 .

This review aims to synthesize the current knowledge of sediment dynamics using insights from long‐term research conducted in the watershed draining to the Chesapeake Bay, the largest estuary in the U.S., to inform management actions to restore the estuary and its watershed. The sediment dynamics of the Chesapeake are typical of many impaired watersheds and estuaries around the world, and this synthesis is intended to be relevant and transferable to other sediment‐impaired systems. The watershed's sediment sources, transport, delivery, and impacts are discussed with implications for effectively implementing best management practices (BMPs) to mitigate sediment issues. This synthesis revealed three key issues to consider when planning actions to reduce sediment loading: Scale, time, and land use. Geology and historical land use generated a template that current land use and climate, in addition to management, are acting upon to control sediment delivery. Important sediment sources in the Chesapeake include the Piedmont physiographic region, urban, and agricultural land use, and streambank erosion of headwater streams, whereas floodplain trapping is important along larger streams and rivers. Implementation of BMPs is widespread and is predicted to lead to decreased sediment loading; however, reworking of legacy sediment stored in stream valleys, with potentially long residence times in storage, can delay and complicate detection of the effects of BMPs on sediment loads. In conclusion, the improved understanding of sediment sources, storage areas, and transport lag times reviewed here can help target choices of BMP types and locations to better manage sediment problems—for both local streams and receiving waters. This article is categorized under: Science of Water > Water Quality Water and Life > Stresses and Pressures on Ecosystems Water and Life > Conservation, Management, and Awareness

For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment-visit http://www.usgs.gov or call 1-888-ASK-USGS.For an overview of USGS information products, including maps, imagery, and publications, visit http://store.usgs.gov.Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. AcknowledgmentsFunding for this study was provided by the U.S. Geological Survey (USGS) Ecosystems Mission Area as part of the Priority Ecosystem Science (PES) Program. Sincere appreciation is extended to the many landowners in all four study watersheds who provided us with access to many of the study sites. Cooperation from the U.S. Department of Agriculture, Natural Resources Conservation Service, as well as the Soil and Water Conservation Service, was instrumental for better understanding each basin and for gaining access to study sites. Additional contributions of data and information were made by the Virginia Department of Environmental Quality, Pennsylvania Department of Environmental Protection, the Maryland Department of Natural Resources, and the U.S. Environmental Protection Agency. Appreciation is extended to the Stormwater Planning Division of the Fairfax County Department of Public Works and Environmental Services for supporting elements of water-quality monitoring in Difficult Run that were incorporated into this report and for providing data on the implementation of best management practices throughout Difficult Run.We are indebted to the many USGS field technicians and hydrologists who have contributed to the collection of field samples and other technical content throughout the report. Technical reviews by Doug Burns of the USGS New York Water Science Center and Angie Crain of the USGS Indiana-Kentucky Water Science Center strengthened this report and are sincerely appreciated. AbstractDespite widespread and ongoing implementation of conservation practices throughout the Chesapeake Bay watershed, water quality continues to be degraded by excess sediment and nutrient inputs. While the Chesapeake Bay Program has developed and maintains a large-scale and long-term monitoring network to detect improvements in water quality throughout the watershed, fewer resources have been allocated for monitoring smaller watersheds, even though water-quality improvements that may result from the implementation of conservation practices are likely to be first detected at smaller watershed scales.In 2010, the U.S. Geological Survey partnered with the U.S. Environmental Protection Agency and the U.S. Department of Agriculture to initiate water-quality monitoring in four selected small watersheds that were targeted for increased implementation of con...