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Water Table Elevations (water + table_elevation)
Selected AbstractsAnalysis of an Unconfined Aquifer Subject to Asynchronous Dual-Tide PropagationGROUND WATER, Issue 2 2008Kolja Rotzoll Most published solutions for aquifer responses to ocean tides focus on the one-sided attenuation of the signal as it propagates inland. However, island aquifers experience periodic forcing from the entire coast, which can lead to integrated effects of different tidal signals, especially on narrow high-permeability islands. In general, studies disregard a potential time lag as the tidal wave sweeps around the island. We present a one-dimensional analytical solution to the ground water flow equation subject to asynchronous and asymmetric oscillating head conditions on opposite boundaries and test it on data from an unconfined volcanic aquifer in Maui. The solution considers sediment-damping effects at the coastline. The response of Maui Aquifers indicate that water table elevations near the center of the aquifer are influenced by a combination of tides from opposite coasts. A better match between the observed ground water head and the theoretical response can be obtained with the proposed dual-tide solution than with single-sided solutions. Hydraulic diffusivity was estimated to be 2.3 × 107 m2/d. This translates into a hydraulic conductivity of 500 m/d, assuming a specific yield of 0.04 and an aquifer thickness of 1.8 km. A numerical experiment confirmed the hydraulic diffusivity value and showed that the y -intercepts of the modal attenuation and phase differences estimated by regression can approximate damping factors caused by low-permeability units at the boundary. [source] Water uptake and nutrient concentrations under a floodplain oak savanna during a non-flood period, lower Cedar River, Iowa,HYDROLOGICAL PROCESSES, Issue 21 2009Keith E. Schilling Abstract Floodplains during non-flood periods are less well documented than when flooding occurs, but non-flood periods offer opportunities to investigate vegetation controls on water and nutrient cycling. In this study, we characterized water uptake and nutrient concentration patterns from 2005 to 2007 under an oak savanna located on the floodplain of the Cedar River in Muscatine County, Iowa. The water table ranged from 0·5 to 2·5 m below ground surface and fluctuated in response to stream stage, plant water demand and rainfall inputs. Applying the White method to diurnal water table fluctuations, daily ET from groundwater averaged more than 3·5 mm/day in June and July and approximately 2 mm/day in May and August. Total annual ET averaged 404 mm for a growing season from mid-May to mid-October. Savanna groundwater concentrations of nitrate-N, ammonium-N, and phosphate-P were very low (mean <0·18, <0·14, <0·08 mg/l, respectively), whereas DOC concentrations were high (7·1 mg/l). Low concentrations of N and P were in contrast to high nutrient concentrations in the nearby Cedar River, where N and P averaged 7·5 mg/l and 0·13, respectively. In regions dominated by intensive agriculture, study results document valuable ecosystem services for native floodplain ecosystems in reducing watershed-scale nutrient losses and providing an oasis for biological complexity. Improved understanding of the environmental conditions of regionally significant habitats, including major controls on water table elevations and water quality, offers promise for better management aimed at preserving the ecology of these important habitats. Copyright © 2009 John Wiley & Sons, Ltd. [source] EFFECTS OF CONTROLLED DRAINAGE ON STORM EVENT HYDROLOGY IN A LOBLOLLY PINE PLANTATION,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2000D. M. Amatya ABSTRACT: A paired watershed approach was utilized to study the effects of three water management regimes on storm event hydrology in three experimental watersheds in a drained loblolly pine (Pinus taeda L.) plantation in eastern North Carolina. The regimes were: (1) conventional drainage, (2) controlled drainage (CD) to reduce outflows during spring fish recruitment, and (3) controlled drainage to reduce outflows and conserve water during the growing season. Data from two pit-treatment years and three years of CD treatment with raised weirs at the watershed outlet are presented. CD treatment resulted in rises in water table elevations during the summer. But the rises were small and short-lived due to increased evapotranspiration (ET) rates as compared to the spring treatment with lower ET demands. CD treatment had no effect on water tables deeper than 1.3 m. CD treatments, however, significantly (,= 0.05) reduced the stoning outflows for all events, and peak outflow rates for most of the events depending upon the outlet weir level. In some events, flows did not occur at all in watersheds with CD. When event outflows occurred, duration of the event was sharply reduced because of reduced effective ditch depth. Water table depth at the start of an event influenced the effect of CD treatment on storm event hydrology. [source] RECIRCULATING WELLS: GROUND WATER REMEDIATION AND PROTECTION OF SURFACE WATER RESOURCES,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2000Keith W. Ryan ABSTRACT: Several chlorinated solvent plumes threaten the sole-source aquifer underlying the Massachusetts Military Reservation at the western end of Cape Cod. Sensitive surface water features including ponds, cranberry bogs, and coastal wetlands are hydraulically connected to the aquifer. For one of the plumes (CS-10 the original remedy of 120 extraction and reinjection wells has the potential for significant disruption of surface water hydrology, through the localized drawdown and mounding of the water table. Recirculating wells with in-well air stripping offer a cost-effective alternative to conventional pump-and-treat technology that does not adversely affect the configuration of the water table. Pilot testing of a two well system, pumping 300 gpm, showed a capture radius of > 200 feet per well, in-well trichloroethylene (TCE) removal efficiencies of 92 to 98 percent per recirculation cycle, an average of three recirculation cycles within the capture zone, and no measurable effect on water table elevations at any point within the recirculation/treatment zone. During 120 days of operation, the mean concentration of TCE in the treatment zone was reduced by 83 percent, from 1,111 ,g/l to 184 ,g/l. Full-scale design projections indicate that 60 wells at an average spacing of 160 feet, having an aggregate recirculation 11 MGD, can contain the CS-b plume without ground water extraction or adverse hydraulic effects on surface water resources. The estimated capital costs for such a system are about $7 million, and annual operations-and-maintenance costs should be about $1.4 million, 40 percent of those associated with a pump and treat system over a 20-year period. [source] | ||||||||||