Conceptualization and analysis of ground-water flow system in the Coastal Plain of Virginia and adjacent parts of Maryland and North Carolina

John F. Harsh; Randell J. Laczniak

doi:10.3133/pp1404f

Home/Archive/USGS

USGS · pp1404F

Conceptualization and analysis of ground-water flow system in the Coastal Plain of Virginia and adjacent parts of Maryland and North Carolina

John F. Harsh·Randell J. Laczniak

View original source ↗Read source document ↗Export metadata ↓

Abstract

This report presents the results of a study of the ground-water flow system in the Coastal Plain of Virginia and adjacent parts of Maryland and North Carolina. The ground-water flow system consists of water-table aquifer and an underlying sequence of confined aquifers and intervening confining units composed of unconsolidated sand and clay .Water levels have declined steadily, and cones of depression have expanded and coalesced around major ground-water withdrawal centers. A digital flow model was developed to enhance knowledge of the behavior of the ground-water flow system in response to its development. Transmissivity and vertical leakance maps were developed for each aquifer and confining unit. The model was calibrated to simulate ground-water flow within the system under both prepumping and pumping conditions. Simulated prepumping potentiometric-surface maps indicate that regional movement of ground water was from the Fall Line toward coastal areas and that local movement of ground water was from interfluves toward major river valleys. Maps of simulated prepumping flow across confining units show that most recharge occurred in narrow bands approximately parallel to the Fall Line and under interfluves and that discharge was toward major river valleys and coastal water. Simulated prepumping rates of recharge into the confined aquifer system from the water-table aquifer varied up to 3 .2 inches per year (in/yr), and rates of discharge out of the confined system varied up to 2.8 in/yr. Ten pumping periods covering 90 years (yr) of withdrawal simulated the history of ground-water development. Simulated potentiometric-surface maps for 1980 show lowered water levels and the development of coalescing cones of depression around the cities of Franklin, Suffolk, and Williamsburg and the town of West Point, all in Virginia. The largest simulated decline in water level, about 210 feet (ft) ,was near Franklin. Water budgets indicate that over the period of simulation (1891-1980) (1) pumpage from the model area increased by about 105 million gallons per day (Mgal/d), (2) lateral boundary outflow increased by about 5 Mgal/d, (3) ground-water flow to streams and coastal water decreased by about 107.5 Mgal/d, (4) lateral boundary inflow increased by about0.7 Mgal/d, and (5) water released from aquifer storage increased by about 1 .6 Mgal/d. The difference between total inflow and total outflow is the numerical truncation error of the digital simulation. Analysis of water budgets for individual confined aquifers shows that the major source of water supplied to wells was vertical leakage induced through confining units by pumping. Simulated rates of recharge into the confined aquifer system at the end of the final pumping period (1980) varied up to 3.8in/yr,and simulated rates of discharge out of the confined system varied up to 2.2in/yr. Results of simulations show an increase of about 110Mgal/d into the confined system from the unconfined system over the period of simulation. This increase in flow into the confined system affected local discharge of ground water to streams and regional discharge to coastal water. Withdrawal of groundwater from the confined aquifers also induced brackish water from Chesapeake Bay into the confined system. Results of sensitivity analyses indicate that simulated water levels are more sensitive to decreases in aquifer transmissivity and confining unit vertical hydraulic conductivity than to increases in these properties. Lowering the storage coefficient of an aquifer had minimal effect on simulated water levels, whereas increasing the storage coefficient had a much more significant effect. The effect of confining unit storage is shown to be insignificant if it is assumed that the water released from confining unit storage is attributable to the compressibility of water only.

Explore related subjects

Professional Paper Report

Source-reported bounding extent: 35.96911507577482° to 39.757879992021756° latitude; -79.365234375° to -74.696044921875° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

John F. Harsh, Randell J. Laczniak. 1990. Conceptualization and analysis of ground-water flow system in the Coastal Plain of Virginia and adjacent parts of Maryland and North Carolina. https://doi.org/10.3133/pp1404f

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

Resurvey of the Marble Canyon and Bridge Canyon dam sites in Grand Canyon National Park—Changes in sediment storage and evidence supporting the occurrence of bedrock incision through the mid-20th century

The Bureau of Reclamation developed an extensive plan for a network of dams, water tunnels, and hydropower plants in and around Grand Canyon, Arizona, in the 1940s through 1960s. The two largest of these planned dams were the Marble Canyon and Bridge Canyon Dams on the Colorado River. Though these dams were ultimately never built, Reclamation conducted extensive topographic, bathymetric, and subsurface exploration work at the sites proposed for these dams in the 1940s and 1950s. Resurveys of these dam sites were conducted between 1998 and 2021 to determine the changes in sediment storage at these dam sites caused by the upstream construction and operation of Glen Canyon Dam and by the recession of Lake Mead, the reservoir impounded by Hoover Dam. The resurveys of the Marble Canyon dam sites indicate that the post-1950s changes in sediment storage at these dam sites are broadly consistent with flux-based estimates of voluminous sand erosion from Marble Canyon since the 1963 closure of Glen Canyon Dam. These resurveys also suggest that the pre-dam longitudinal variation in sediment thickness over bedrock played a key role in determining the locations of the sand erosion induced by Glen Canyon Dam; more sand eroded from locations where more sand was present in the 1950s. The resurvey of the Bridge Canyon dam sites indicates that the Colorado River’s incision of the Lake Mead delta is regulated both by bed-sediment grain size and downstream hydraulic controls. Finally, analyses of bed-sediment thickness and sedimentological data at the dam sites, and observations of bed scour and gravel transport, suggest that sufficient bedrock was exposed to allow bedrock incision during commonly recurring pre-dam snowmelt floods that entrained small boulders into transport.

Arizona↗

USGS2026

The eruptive behavior of distributed volcanism forming low shield edifices—A case study of Sentinel-Arlington volcanic field, U.S.A.

Distributed volcanic fields are present in various tectonic settings worldwide, and their characteristics reflect differing influences from magmatic and tectonic processes. In the southwestern United States alone, there are 37 Quaternary distributed volcanic fields. After the primary period of extensional tectonics in the southern Basin and Range 15–5 million years ago, the Sentinel-Arlington volcanic field developed in southwestern Arizona between 4 and 1 million years ago. The Sentinel-Arlington volcanic field consists primarily of low relief shield volcanoes, a type of distributed volcanism with poorly understood temporal evolution. The Sentinel-Arlington volcanic field is less than 200 kilometers (km) from the Colorado Plateau, Gulf of California, and southern San Andreas Fault system. This work identifies and examines controls on the emplacement of the Sentinel-Arlington volcanic field by documenting shallow and surficial structures as well as eruption characteristics and style through time. The Sentinel-Arlington volcanic field consists of 21 volcanoes with a total of 33 vents over an area of about 770 square kilometers (km 2 ). The prominence of low relief shield volcanoes may be explained by ascent of basaltic magmas through thin Basin and Range crust, without much crustal contamination, and low viscosities common to mafic compositions. Typical eruption characteristics involve the construction of low relief shield volcanoes followed by Strombolian fissure eruptions at the summits or near-summit medial areas that produce scoria lapilli, which may weld to form agglomerate. The total lifetime erupted volume of about 4.3 cubic kilometers (km 3 ) represents an average eruptive flux of approximately 2x10 -3 km 3 per thousand years (k.y.). This erupted volume is low relative to Neogene basaltic intraplate distributed volcanic fields worldwide, which typically range from 10 -3 to 1 km 3 k.y. -1 . Sentinel-Arlington volcanic field eruptions were likely triggered by intermittent rejuvenation of transient magmatic zones that exist in thinned crust. Instantaneous flux from point sources feeding the lava flows is estimated to be on the order of 10 -1 to 10 cubic meters per second.

Arizona↗

USGS2026

Capitalization of positional (Lower/Middle/Upper) and temporal (Early/Middle/Late) adjectives in the names of formal chronostratigraphic and geochronologic units of the Phanerozoic

Many authors are understandably confused about the capitalization of the words “lower,” “middle,” “upper,” “early,” and “late.” Where these words are used simply as descriptive adjectives, they should be in lowercase; where they form the first word of a formal chronostratigraphic or geochronologic unit name, they should be in uppercase.

Professional Paper↗