Inner shelf sediments off Chesapeake Bay. I - General lithology and composition

The sedimentary materials and bottom topography of more than 2400 square miles of the inner continental shelf floor north off the Chesapeake Bay entrance have been surveyed for potential mineral resources. Sediments consist of two principal types: (1) fine sand and (2) medium to coarse sand. The fine sand is grey-colored, subrounded, rich in quartz and relatively 11clean 11 and well sorted. The medium-coarse sand is typically iron-stained, rich in shell and poorly sorted. The fine sand covers inner parts of the shelf floor whereas medium to coarse sand covers seaward parts. Additionally, shell-rich medium to coarse sand occurs on isolated ridges of inner parts. These preliminary geologic findings delineate several localities which contain concentrations of dark minerals, shell and gravel. i

Sediments of the James River Estuary, Virginia

The James River estuary of the Chesapeake Bay region follows the course of a former river valley drowned within the last 9,000 years by the most recent rise of sea level. The floor is shaped into a central channel bordered by submerged shoals. Observations show suspended sediment is transported mainly by alternating tidal currents and secondarily by the net nontidal estuarine circulation. Transport results in a sequence of grain size distributions reflecting the mixing of two textural end members, clay and sand. Silty clay is deposited in the river and upper estuary, whereas sand occurs near the mouth. Transitional types, clayey sand and sand-silt-clay, predominate in the middle estuary. Additionally, biogenic materials, oyster shells and fecal pellets, and small amounts of residual components eroded from older deposits are mixed into the sediments by currents, waves, and organisms. Bottom sediment types vary widely according to local relief, to varying intensity of environmental processes, and to changing rates of supply from different sources: Deposition is greatest in the middle estuary where salinity ranges from 5 to 14 parts per thousand. An elongate zone of relatively high deposition in the lower estuary corresponds to the intersection of the level of no-net-motion with the bottom. Despite substantial infilling, it is believed the estuary is maintained by the continued rise of sea level and by currents that flush part of the river-borne load through the estuary.https://scholarworks.wm.edu/vimsbooks/1015/thumbnail.jp

Surface observations, ground truth and data : NASA-USGS mission 144 : Chesapeake Bay region, Sept. 22-30, 1970

Surface observations of coastal waters and ground. truth data were obtained to aid interpretation and analyses of overflight photography and imagery. Among the broad objectives of the mission was to investigate the potential of high-altitude, multispectral photography as a tool for the improved planning necessary to cope with multidisciplinary problems within the coastal zone, specifically with regard to: 1. The inventory and evaluation of the central Atlantic coastal area natural resources; 2. The assessment of human and natural degradation of these resources; 3. The feasibility of monitoring resource allocation and management, including land use categories and the impact of urbanization on the central Atlantic coastal area. 4. The evaluation of sources and extent of water pollution. The site encompasses a major segment of the mid-Atlantic coast from Newark, New Jersey to Wilmington, North Carolina (Figure 2, inset). It; includes the southern portion of Megalopolis,. one of the world\u27s major urban-industrial complexes which is under the pressure of land use. It encompasses the silt and pollutant laden Chesapeake drainage system, the largest on the U. S, East Coast. The site includes.seaward reaches of the Delaware River system where water quality management is the chief problem. Additionally, it includes the coastal parts of North Carolina which offers a wide range of physical environments and cultural development common to the east coast. The site is an area where large spatial and temporal variations occur in tidal waters

Effect of Increasing Depth on Salinity in the James River Estuary

The effects of channel deepening on the salinity and density flow in the James River estuary, Virginia, were studied to predict changes that might affect oyster production. A hydraulic model with 1: 1,000 horizontal and l: 100 vertical scales was employed to integrate three-dimensional changes in salinity and velocity through reaches of variable bottom geometry. After natural characteristics of the tide, current, and salinity were reproduced in the model, tests were run at three levels of steady river inflow, before and after a 3-meter channel deepening. Results were combined with corollary field observations to evaluate changes in present-day ecological conditions. Deepening produced the greatest salinity change in the middle estuary where the major cut was performed. The lower water layer located mainly in the channel became saltier by about 0.5 part per thousand, whereas the upper layer over the oyster shoals became fresher by about 0.2 part per thousand. Changes in bottom water salinity were greatest at intermediate inflow and least at very low inflow. High fresh-water inflow created the greatest change in vertical salinity gradient. With greater stratification, tidal velocities were less effective in promoting vertical mixing between lower and upper estuarine water layers, and the net volume transport in each layer was reduced. Since the changes in salinity and flow pattern due to channel deepening were small, no effects inimical to the oyster fishery were predicted. Similarly the prospective changes in sedimentary regime will not offset the beneficial effects of the proposed deepening project.https://scholarworks.wm.edu/vimsbooks/1016/thumbnail.jp

Bay observations - Hydrography : Cruises of November 27, 1961, and November 20, 1962

This report presents data obtained on training cruises in the lower Chesapeake Bay. The purpose of these cruises was to study the physical and chemical characteristics of estuarine water in a section from the York River mouth to Cape Charles. In 1961 the observations were carried out aboard R/V Pathfinder; in 1962 measurements were made from the R/V Langley

Storage Efficiency of Estuaries

Estuaries or the U.S. Atlantic coast exhibit a range or storage efficiencies from complete storage to partial by-passing through the system. Efficiency, I.e. the ratio or sediment accumulation to river Input rate, ranges 0.7 in the Altamaha River, Ga. to 7.6 In the Choptank River, Md. Northern estuaries trap and store the bulk or their river input In addition to large amounts or sediment supplied from other sources. Southern estuaries accumulate major sediment loads in marshes and allow partial escape through channels to the sea. The storage efficiency or difrerent estuaries is compared with respect to key factors that can be quantified and that vary within the region, It was round that storage efficiency in northern estuaries is encouraged by low flushing velocity and high volumetric capacity relative to river inflow. The long-term rise of sea level relative to the land tends to offset sediment accumulation and maintain or increase capacity. Within the range of estuaries considered, efficiency generally increases as the flow ratio decreases. This trend suggests the estuarine circulation in partially-mixed systems is important both in trapping fluvlal sediment and in transporting sediment landward from the sea.https://scholarworks.wm.edu/vimsbooks/1188/thumbnail.jp

Consequences of sediment flux: escape or entrapment?

Estuaries exhibit a full range of flux that extends from escape of sediment into the ocean to complete entrapment and storage within the system. The trapping efficiency of U.S. East Coast estuaries is compared with respect to long-term infilling and present- day flushing velocity , volumetric capacity , and circulatory mixing. It was found that entrapment prevails in many northern estuaries as a consequence of high volumetric capacity , low flushing velocity , and the nearly closed circulation. In many estuaries, channel deepening has reversed the normal trend of long-term infilling. Although dredging enhances circulatory entrapment, large-scale ocean dumping results in escape of sediment from estuaries. Consequently, man is changing the geologic role of many U.S. East Coast estuaries from a sink for fluvial and marine sediment to a source of sediment for the ocean

Sediment characterization of South Atlantic systems

The estuarine systems selected are from the NOAA National Estuarine Inventory in the EMAP Virginian Province (Figure 1). The principal spatial unit of each system is the estuarine drainage area (EDA) defined in the NEI data atlas (U.S. NOAA, 1985). The sediment and contaminant distributions embrace the estuarine bottom area, i.e. from the head of tides to the mouth where the estuary meets the ocean, bay or sound as determined by physiographic features (U.S. NOAA, 1985). Data coverage embraces whole estuaries and farfield distributions. Chart scales are smaller than 1:80,000 andchart units larger thaqn 0.1 square kilometer

Development of the turbidity maximum in a coastal plain estuary : Final Report

A study of the turbidity maximum in the Rappahannock Estuary; Virginia was conducted to determine how high concentrations of suspended sediment accumulate to form a maximum. Time-series observations of current velocity, salinity and suspended sediment over 8 to 18 tidal cycles reveal that the maximum forms in a convergence of bottom residual currents near the transition between fresh and salty water. Sediment supplied mainly by the river is transported into the convergence by density currents and accumulates since velocity is nearly zero and settling exceeds upward mixing. The maximum forms in the middle estuary after freshet or flooding and shifts upstream with a landward shift of the salt intrusion head and diminished river inflow. At the same time, its intensity is reduced by settling out, reduced strength of the convergence and increased mixing. Prime prerequisites for development are a strong convergence and high river inflow. The maximum modulates transport through estuaries to the sea by trapping materials and deposition. High turbidity can be alleviated by increased haline mixing and reduced inflow