Geology topics

Research about Mid-Atlantic region

Source-linked reports with geographic coverage including Mid-Atlantic region.

2 recordsLinked to original sources

USGS2011

Anthropocene streams and base-level controls from historic dams in the unglaciated mid-Atlantic region, USA

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.

Delaware, Maryland, Newe Jersey, New York, Pennsyl↗

USGS1984

Calculations of seabird population recovery from potential oilspills in the mid-Atlantic region of the United States

Calculations were made of herring gull and common tern population recovery from potential oilspill damage in the U.S. mid-Atlantic Outer Continental Shelf (OCS) oil leasing area. Population recovery was examined using a density-dependent age-specific life history table for each species. Both a deterministic and a stochastic approach were used in the calculations. In the deterministic approach, it was assumed that an oilspill contact to a seabird colony had occurred. Using the density-dependent model, population recovery was calculated for several different mortality scenarios. Assuming that all age classes suffer 95% mortality from an oilspill contact, a worst case scenario, it was estimated that the herring gull and common tern populations could recover to their pre-spill levels in approximately 45 years and more than 100 years, respectively. In the stochastic approach, the probabilities of oilspill contacts to these seabird colonies were calculated using an oilspill trajectory analysis model. Oilspill contacts to these colonies were simulated during the expected 30 year active life of the lease area. For each lease lifetime, the number of oilspill contacts to a seabird colony was sampled from a Poisson distribution and assigned randomly on a seasonal basis. This analysis indicated that the oilspill risks from the development of proposed lease tracts in the mid-Atlantic region pose minimal risk (3–5%) of severe population reduction for both herring gulls and common terns. If the oilspill risks from tanker transportation of crude oil imports are included along with the proposed lease tracts, then the risks of severe population reduction are increased to approximately 10% for herring gulls and 18% for common terns.

Mid-Atlantic region↗