Analytical Versus Numerical Estimates Of Water Level Declines Caused By Pumping And A Case Study Of The Iao Aquifer Maui Hawaii
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Analytical Versus Numerical Estimates Of Water Level Declines Caused By Pumping And A Case Study Of The Iao Aquifer Maui Hawaii
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Author : Delwyn S. Oki
language : en
Publisher:
Release Date : 2001
Analytical Versus Numerical Estimates Of Water Level Declines Caused By Pumping And A Case Study Of The Iao Aquifer Maui Hawaii written by Delwyn S. Oki and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2001 with Water table categories.
Report on adopting the Robust Analytical Model (RAM) for establishing sustainable-yield values for the Iao Aquifer which lies on the northeastern flank of the West Maui Volcano on the Island of Maui. The report describes comparisons between model-calculated water levels from RAM and those from numerical ground-water flows models based on the case study of the Iao Aquifer.
Water Resources Investigations Report
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Author :
language : en
Publisher:
Release Date : 2000
Water Resources Investigations Report written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2000 with Hydrology categories.
Monthly Catalog Of United States Government Publications
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Author :
language : en
Publisher:
Release Date : 2001
Monthly Catalog Of United States Government Publications written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2001 with Government publications categories.
New Publications Of The U S Geological Survey
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Author :
language : en
Publisher:
Release Date : 2001-07
New Publications Of The U S Geological Survey written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2001-07 with Geology categories.
New Publications Of The U S Geological Survey
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Author : Geological Survey (U.S.)
language : en
Publisher:
Release Date : 2001-07
New Publications Of The U S Geological Survey written by Geological Survey (U.S.) and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2001-07 with Geology categories.
New Publications Of The Geological Survey
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Author : Geological Survey (U.S.)
language : en
Publisher:
Release Date : 2001
New Publications Of The Geological Survey written by Geological Survey (U.S.) and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2001 with Geology categories.
Vadose Zone Response To Pumping In Unconfined Aquifers
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Author : Melissa Irene Bunn
language : en
Publisher:
Release Date : 2011
Vadose Zone Response To Pumping In Unconfined Aquifers written by Melissa Irene Bunn and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
The interaction between drainage from the variably saturated zone above the water table, and the response of an unconfined aquifer to pumping has been the source of debate for many decades. While various field tests (Nwankwor et al., 1992 and Moench et al., 2001) have supported the concept that variably saturated flow processes delay drainage above a falling water table, Neuman (1972, 1974, 1975), has asserted that the impact is minimal, delay in response of the water table is due to elastic storage effects, and instantaneous yield above the water table is a reasonable assumption in unconfined aquifer analysis. This assumption results in exceedingly low estimates of specific yield in comparison to other analysis techniques (Neuman, 1987). A 7-day pumping test by Bevan et al. (2005) in the unconfined aquifer at Canadian Forces Base Borden has highlighted the complexity in drainage from above the water table during pumping, as the tension saturated zone was found to increase in thickness as a function of both proximity to the pumping well, and elapsed pumping time. This extended thickness persisted for the 7-day pumping duration. Analytical analysis of the test by Endres et al. (2007) resulted in significant underestimates of specific yield in comparison to laboratory values for most solutions. Narasimham (2007) suggested that the use of numerical simulators which include variably saturated flow may provide the most accurate representation of the test results. An attempt to replicate test results using a numerical simulation of variably saturated flow by Moench (2008) could not provide a complete physical mechanism for the extension observed by Bevan et al. (2005). This study provides a detailed investigation on the effect of heterogeneity, hysteresis, and entrapped air on drainage during unconfined pumping tests using numerical simulations, field experiments, and laboratory observations. The results of the Bevan et al. (2005) pumping test are used as a standard for comparison. Three variably-saturated groundwater flow numerical codes were evaluated for their ability to replicate the variations in soil moisture content observed during pumping by Bevan et al. (2005). Results of the numerical simulations were also analyzed for their similarity to the peak and subsequent decrease in vertical gradients observed during pumping in the Borden aquifer. While the models generated vertical gradients through the capillary fringe during pumping, these gradients dissipated significantly before 1000 min. of pumping. No gradients in the saturated zone generated by the numerical model would be capable of shifting the pressure head sufficiently to cause an apparent capillary fringe extension following the first few hours of pumping. Significant gradients were persistent throughout the test at locations where saturation was less than 85%. Accounting for the formation of vertical gradients, no simulation was able to replicate the soil moisture distributions observed by Bevan et al. (2005). Based on these results, heterogeneity, hysteresis, and entrapped air were proposed as processes with the potential to significantly affect drainage from above the water table during pumping, as their investigation may provide the physical mechanism for the observed capillary fringe extension. Compaction of the aquifer material was dismissed as a potential mechanism based on the results of a proctor test. The effect of heterogeneity on drainage from the Borden aquifer during pumping was investigated numerically using geostatistical methods. A log-normal saturated hydraulic conductivity distribution was used to represent the Borden aquifer. Brooks and Corey parameters were used to describe the pressure-saturation-relative conductivity relationships. The air-entry pressure parameter was scaled to the saturated conductivity using the scaling relationship for Borden sand proposed by Keuper and Frind (1991). The Brooks and Corey lambda parameter was kept constant. A Monte Carlo analysis was performed on the results. While several realizations of the hydraulic conductivity distribution resulted in the formation of perched water during drainage, the ensemble capillary fringe thickness was unchanged from the thickness generated using a homogeneous conceptual aquifer model. No single realization produced a capillary fringe extension in which the magnitude was a function of elapsed pumping time, or distance from the pumping well. Approximation of the effect of air-entry barriers on drainage did not increase the estimated capillary fringe thickness. The presence and location of finer grained layers appeared to have a much greater impact on the thickness of the capillary fringe than the drawdown induced by pumping. Ensemble results for the hydraulic head drawdown provided improved matches to the field observations in comparison to the homogeneous numerical model during intermediate and late times in the pumping test. A mild degree of heterogeneity appears to have sufficient effect on drainage from above the water table during pumping to impact hydraulic drawdown. The effect would be magnified with the greater degree of heterogeneity that is more typical of natural aquifer systems. A 24-hour pumping test was conducted at CFB Borden to gain a better understanding of the nature of drainage during a pumping test. Due to the wet site conditions prior to the test, the moisture profile during pumping was significantly influenced by hysteresis. The hydraulic head drawdown generated during the test was insufficient to generate any drainage due to the lowering of the top of the saturated zone, and the formation of perched lenses could not occur. Hysteresis in the moisture profile was a controlling factor in this result. Although there was no significant drainage initiated due to the lowering of the top of the saturated zone, an inflection point was still apparent in the time-drawdown curve for the four monitoring wells observed. Vertical gradients measured throughout the saturated zone, including the capillary fringe, remained low throughout the duration of pumping, and no significant increase was apparent in the transition from saturated to tension-saturated conditions. Hysteresis has the potential to increase the delay in drainage as the water table falls during pumping. A laboratory tank apparatus was used to determine the effect of entrapped air, grain size distribution, and horizontal gradient on drainage in a primarily horizontal flow regime. The tank was packed on three separate occasions, once with a coarse well sorted silica sand, and twice with sand from the Borden aquifer. For each packing, the tank was drained twice, using two different horizontal gradient magnitudes. Results show that horizontal gradient magnitude has no impact on soil moisture distributions during drainage. Air-entry pressure was elevated in comparison to gravity drainage derived pressure head - saturation curves. This elevation was not transient, nor dependant on gradient or grain size distribution. The increase in air-entry pressure does not appear to be due to insufficient equilibration time between water level drops or flow redistribution around the TDR Rods. Results of this study support a conceptual model of unconfined aquifer response in which drainage from above the water table is a complex and time dependant process. Individually, heterogeneity and hysteresis have been shown to cause a time delay between the lowering of the water table and the subsequent drainage of the tension saturated zone during intermediate to late pumping times. The magnitude and duration of this delay varies by process and is a function of the degree of heterogeneity, moisture conditions in the aquifer prior to pumping, and the drawdown rate of the water table. While no individual process tested could produce the capillary fringe extension observed by Bevan et al. (2005), the investigation of each has led to an improved conceptual understanding of the response to pumping in unconfined aquifers. Due to the complex interaction of these processes it is unlikely that pumping test results, even those which include moisture content observations, could be used to accurately predict unsaturated flow parameters. Storage parameter (i.e. specific yield) estimates made using analytical solutions may not be appropriate unless delayed drainage from above the water table is properly accounted for.
Numerical Simulation Of Groundwater Flow In The Columbia Plateau Regional Aquifer System Idaho Oregon And Washington
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Author : David Matthew Ely
language : en
Publisher:
Release Date : 2015
Numerical Simulation Of Groundwater Flow In The Columbia Plateau Regional Aquifer System Idaho Oregon And Washington written by David Matthew Ely and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with Groundwater flow categories.
A three-dimensional numerical model of groundwater flow was constructed for the Columbia Plateau Regional Aquifer System (CPRAS), Idaho, Oregon, and Washington, to evaluate and test the conceptual model of the system and to evaluate groundwater availability. The model described in this report can be used as a tool by water-resource managers and other stakeholders to quantitatively evaluate proposed alternative management strategies and assess the long-term availability of groundwater. The numerical simulation of groundwater flow in the CPRAS was completed with support from the Groundwater Resources Program of the U.S. Geological Survey Office of Groundwater. The model was constructed using the U.S. Geological Survey modular three-dimensional finite-difference groundwater-flow model, MODFLOW-NWT. The model uses 3-kilometer (9,842.5 feet) grid cells that subdivide the model domain by 126 rows and 131 columns. Vertically, the model domain was subdivided into six geologic model units. From youngest to oldest, the units are the Overburden, the Saddle Mountains Basalt, the Mabton Interbed, the Wanapum Basalt, the Vantage Interbed, and the Grande Ronde Basalt. Natural recharge was estimated using gridded historical estimates of annual precipitation for the period 1895-2007. Pre-development recharge was estimated to be the average natural recharge for this period. Irrigation recharge and irrigation pumping were estimated using a remote-sensing based soil-water balance model for the period 1985-2007. Pre-1985 irrigation recharge and pumping were estimated using previously published compilation maps and the history of large-scale irrigation projects. Pumping estimates for municipal, industrial, rural, residential, and all other uses were estimated using reported values and census data. Pumping was assumed to be negligible prior to 1920. Two models were constructed to simulate groundwater flow in the CPRAS: a steady-state predevelopment model representing conditions before large-scale pumping and irrigation altered the system, and a transient model representing the period 1900-2007. Automated parameter-estimation techniques (steady-state predevelopment model) and traditional trial-and-error (transient model) methods were used for calibration. To calibrate the steady-state and transient models, 10,525 and 46,460 water level measurements, respectively, and 50 base-flow estimates were used. The steady-state model simulated the shape, slope, and trends of a potentiometric surface that was generally consistent with mapped water levels. For the transient model, the mean and median difference between simulated and measured hydraulic heads is -10 and 4 ft, respectively, with a standard deviation of 164 ft over a 5,648 ft range of measured heads. The residuals for the simulation period show that 52 percent of the simulated heads exceeded measured heads with a median residual value of 43 ft, and 48 percent were less than measured heads with a median residual value of -76 ft. The CPRAS model was constructed to derive components of the groundwater budget and help understand the interactions of stresses, such as recharge, groundwater pumping, and commingling wells on the groundwater and surface-water system. Through these applications, the model can be used to identify trends in groundwater storage and use, and quantify groundwater availability. The annual groundwater budgets showed several patterns of change over the simulation period. Groundwater pumping was negligible until the 1950s and began to increase significantly during the 1970s and 1980s. Recharge was highly variable due to the interannual variability of precipitation, but began to increase in the late 1940s due to the increase in surface-water irrigation projects. Groundwater contributions to streamflow (base flow) followed recharge closely. However, in areas of significant groundwater-level decline, base flow is reduced. Groundwater pumping had the greatest effect on water levels, followed by irrigation enhanced recharge. Commingling was a larger factor in structurally complex upland areas where hydraulic-head gradients are naturally high. Groundwater pumping has increased substantially over the past 40-50 years; this increase resulted in declining water levels at depth and decreased base flows over much of the study area. The effects of pumping are mitigated somewhat by the increase of surface-water irrigation, especially in the shallow Overburden unit, and commingling wells in some areas. During dry to average years, groundwater pumping causes a net loss of groundwater in storage and current condition (2000-2007) groundwater pumping exceeds recharge in all but the wettest of years.
The Effects On Groundwater Resources From Irrigation Supply Changes In The Odessa Subarea Of The Columbia Plateau Aquifer
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Author : Nyamaa Mendsaikhan
language : en
Publisher:
Release Date : 2022
The Effects On Groundwater Resources From Irrigation Supply Changes In The Odessa Subarea Of The Columbia Plateau Aquifer written by Nyamaa Mendsaikhan and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2022 with Groundwater categories.
Global population growth is driving the need for crop production expansion to meet increasing food supply demands. To support this crop production, both surface and groundwater are used for irrigation. However, reliance on groundwater has been significantly increasing in recent decades due to changes in demand as well as surface water availability and/or reliability. As a consequence, groundwater declines have been observed worldwide where irrigation is the leading cause. In this study, spatial and temporal changes in hydraulic head are evaluated in response to the Odessa Groundwater Replacement Program (OGWRP). The Odessa Subarea is a region in the Columbia Plateau Regional Aquifer System (CPRAS) of the Pacific Northwest that has been experiencing severe groundwater declines due to irrigation pumping since the 1960s. The OGWRP will replace groundwater rights with surface water rights in an attempt to stabilize the water levels in the deep basalts from which the majority of irrigation water is pumped. Numerical flow models assist in estimates of groundwater availability in a study area and the evaluation of water level trends. Using an existing CPRAS model developed by the U.S. Geological Survey (USGS), the composite hydraulic heads resulting from systematic pumping changes in wells found within the Odessa Subarea were simulated. This work tested the hypothesis that aquifer recovery is feasible in response to OGWRP implementation. The study results showed that irrigation supply changes in Odessa impact beyond its boundary. The Grande Ronde Basalt, which supplies most of irrigation water demands in Odessa, has the greatest potential to recover of up to 49.8% by 2050 to predevelopment state if groundwater pumping stopped in 2008. Moreover, the study found two main limitations of the model related to uncertainties in commingling flow and recharge mechanisms in the deep aquifers. Without improved knowledge of recharge pathways and controls and timescales of the intra-borehole flows that are induced in uncased wells, it is difficult to quantify the overall model performance. To reduce model uncertainty the calibration of commingling wells is suggested.
Simulation Of Groundwater Flow And The Interaction Of Groundwater And Surface Water In The Willamette Basin And Central Willamette Subbasin Oregon
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Author : Nora B. Herrera
language : en
Publisher:
Release Date : 2014
Simulation Of Groundwater Flow And The Interaction Of Groundwater And Surface Water In The Willamette Basin And Central Willamette Subbasin Oregon written by Nora B. Herrera and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014 with Groundwater flow categories.
"Full appropriation of tributary streamflow during summer, a growing population, and agricultural needs are increasing the demand for groundwater in the Willamette Basin. Greater groundwater use could diminish streamflow and create seasonal and long-term declines in groundwater levels. The U.S. Geological Survey (USGS) and the Oregon Water Resources Department (OWRD) cooperated in a study to develop a conceptual and quantitative understanding of the groundwater-flow system of the Willamette Basin with an emphasis on the Central Willamette subbasin. This final report from the cooperative study describes numerical models of the regional and local groundwater-flow systems and evaluates the effects of pumping on groundwater and surface-water resources. The models described in this report can be used to evaluate spatial and temporal effects of pumping on groundwater, base flow, and stream capture. The regional model covers about 6,700 square miles of the 12,000-square mile Willamette and Sandy River drainage basins in northwestern Oregon--referred to as the Willamette Basin in this report. The Willamette Basin is a topographic and structural trough that lies between the Coast Range and the Cascade Range and is divided into five sedimentary subbasins underlain and separated by basalts of the Columbia River Basalt Group (Columbia River basalt) that crop out as local uplands. From north to south, these five subbasins are the Portland subbasin, the Tualatin subbasin, the Central Willamette subbasin, the Stayton subbasin, and the Southern Willamette subbasin. Recharge in the Willamette Basin is primarily from precipitation in the uplands of the Cascade Range, Coast Range, and western Cascades areas. Groundwater moves downward and laterally through sedimentary or basalt units until it discharges locally to wells, evapotranspiration, or streams. Mean annual groundwater withdrawal for water years 1995 and 1996 was about 400 cubic feet per second; irrigation withdrawals accounted for about 80 percent of that total. The upper 180 feet of productive aquifers in the Central Willamette and Southern Willamette subbasins produced about 70 percent of the total pumped volume. In this study, the USGS constructed a three-dimensional numerical finite-difference groundwater-flow model of the Willamette Basin representing the six hydrogeologic units, defined in previous investigations, as six model layers. From youngest to oldest, and [generally] uppermost to lowermost they are the: upper sedimentary unit, Willamette silt unit, middle sedimentary unit, lower sedimentary unit, Columbia River basalt unit, and basement confining unit. The high Cascade unit is not included in the groundwater-flow model because it is not present within the model boundaries. Geographic boundaries are simulated as no-flow (no water flowing in or out of the model), except where the Columbia River is simulated as a constant hydraulic head boundary. Streams are designated as head-dependent-flux boundaries, in which the flux depends on the elevation of the stream surface. Groundwater recharge from precipitation was estimated using the Precipitation-Runoff Modeling System (PRMS), a watershed model that accounts for evapotranspiration from the unsaturated zone. Evapotranspiration from the saturated zone was not considered an important component of groundwater discharge. Well pumping was simulated as specified flux and included public supply, irrigation, and industrial pumping. Hydraulic conductivity values were estimated from previous studies through aquifer slug and permeameter tests, specific capacity data, core analysis, and modeling. Upper, middle and lower sedimentary unit horizontal hydraulic conductivity values were differentiated between the Portland subbasin and the Tualatin, Central Willamette, and Southern Willamette subbasins based on preliminary model results."--Summary.