Simulation of Contributing Areas and Surface-Water Leakage to Potential Replacement Wells Near the Community of New Post, Sawyer County, Wisconsin, by Means of a Two-Dimensional Ground-Water-Flow Model (original) (raw)
2007
Figure 2. Diagram showing conceptual model of the hydrologic system in Sawyer County, Wis., in A, the vicinity of Grindstone Creek, and B, the vicinity of New Post, Wis. ... Figure 3. Maps showing simulated hydrologic features with analytic elements in A, the far field and B, the ...
High-capacity wells and baseflow decline in the Wolf River Basin, northeastern Wisconsin (USA)
Environmental Earth Sciences, 2016
The baseflow of the Wolf River (drainage area of 1,200 km 2) in northeastern Wisconsin has declined by over 30% during the last thirty years, whereas climatic, land cover, and soil characteristics of the basin have remained unchanged. Because groundwater basins do not always coincide with surface water basins, estimating groundwater discharge to streams using variables only pertinent to the surface water basin can be ineffective. The purpose of this study is to explain the decline in the baseflow of the Wolf River by developing a multiple regression model. To take into account variables pertaining to the groundwater basin, withdrawal rates from high capacity wells both inside the Wolf River basin and in two adjacent basins were included in the regression model. The other explanatory variables include annual precipitation and growing degree days. Groundwater discharge to the river was calculated using streamflow records with the computer program Groundwater Toolbox from the United States Geological Survey. Without the high capacity wells data, the model only explained 29.6% of the variability in the groundwater discharge. When the high capacity wells data within the Wolf River basin were included, r 2 improved to be 0.512. With the high capacity wells data in adjacent basins, r 2 improved to be 0.700. The study suggests that human activity taking place outside of the basin has had an effect on the baseflow, and should be taken into account when examining baseflow changes.
The North Platte Natural Resources District (NPNRD) has been actively collecting data and studying groundwater resources because of concerns about the future availability of the highly inter-connected surface-water and groundwater resources. This report, prepared by the U.S. Geological Survey in cooperation with the North Platte Natural Resources Dis¬trict, describes a groundwater-flow model of the North Platte River valley from Bridgeport, Nebraska, extending west to 6 miles into Wyoming. The model was built to improve the understanding of the interaction of surface-water and ground¬water resources, and as an optimization tool, the model is able to analyze the effects of water-management options on the simulated stream base flow of the North Platte River. The groundwater system and related sources and sinks of water were simulated using a newton formulation of the U.S. Geo¬logical Survey modular three-dimensional groundwater model, referred to as MODFLOW–NWT, which provided an improved ability to solve nonlinear unconfined aquifer simulations with wetting and drying of cells. Using previously published aquifer-base-altitude contours in conjunction with newer test-hole and geophysical data, a new base-of-aquifer altitude map was generated because of the strong effect of the aquifer-base topography on groundwater-flow direction and magnitude. The largest inflow to groundwater is recharge originating from water leaking from canals, which is much larger than recharge originating from infiltration of precipita¬tion. The largest component of groundwater discharge from the study area is to the North Platte River and its tributar¬ies, with smaller amounts of discharge to evapotranspiration and groundwater withdrawals for irrigation. Recharge from infiltration of precipitation was estimated with a daily soil-water-balance model. Annual recharge from canal seepage was estimated using available records from the Bureau of Reclamation and then modified with canal-seepage potentials estimated using geophysical data. Groundwater withdraw¬als were estimated using land-cover data, precipitation data, and published crop water-use data. For fields irrigated with surface water and groundwater, surface-water deliveries were subtracted from the estimated net irrigation requirement, and groundwater withdrawal was assumed to be equal to any demand unmet by surface water. The groundwater-flow model was calibrated to measured groundwater levels and stream base flows estimated using the base-flow index method. The model was calibrated through automated adjustments using statistical techniques through parameter estimation using the parameter estimation suite of software (PEST). PEST was used to adjust 273 parameters, grouped as hydraulic conductivity of the aquifer, spatial multipliers to recharge, temporal multipliers to recharge, and two specific recharge parameters. Base flow of the North Platte River at Bridgeport, Nebraska, streamgage near the eastern, downstream end of the model was one of the primary calibration targets. Simulated base flow reasonably matched estimated base flow for this streamgage during 1950–2008, with an average difference of 15 percent. Overall, 1950–2008 simulated base flow followed the trend of the estimated base flow reasonably well, in cases with generally increasing or decreasing base flow from the start of the simulation to the end. Simulated base flow also matched estimated base flow reasonably well for most of the North Platte River tributar¬ies with estimated base flow. Average simulated groundwater budgets during 1989–2008 were nearly three times larger for irrigation seasons than for non-irrigation seasons. The calibrated groundwater-flow model was used with the Groundwater-Management Process for the 2005 version of the U.S. Geological Survey modular three-dimensional groundwater model, MODFLOW–2005, to provide a tool for the NPNRD to better understand how water-management deci¬sions could affect stream base flows of the North Platte River at Bridgeport, Nebr., streamgage in a future period from 2008 to 2019 under varying climatic conditions. The simulation-optimization model was constructed to analyze the maximum increase in simulated stream base flow that could be obtained with the minimum amount of reductions in groundwater withdrawals for irrigation. A second analysis extended the first to analyze the simulated base-flow benefit of groundwater withdrawals along with application of intentional recharge, that is, water from canals being released into rangeland areas with sandy soils. With optimized groundwater withdrawals and intentional recharge, the maximum simulated stream base flow was 15–23 cubic feet per second (ft3/s) greater than with no management at all, or 10–15 ft3/s larger than with managed groundwater withdrawals only. These results indicate not only the amount that simulated stream base flow can be increased by these management options, but also the locations where the management options provide the most or least benefit to the simulated stream base flow. For the analyses in this report, simulated base flow was best optimized by reductions in groundwater withdrawals north of the North Platte River and in the western half of the area. Intentional recharge sites selected by the optimization had a complex distribution but were more likely to be closer to the North Platte River or its tributaries. Future users of the simulation-optimization model will be able to modify the input files as to type, location, and timing of constraints, decision variables of groundwater withdrawals by zone, and other variables to explore other feasible management scenarios that may yield different increases in simulated future base flow of the North Platte River.
Open-File Report, 1989
ground water. The program limits the amount of groundwater recharge to the available streamflow. It permits two or more streams to merge into one with flow in the merged stream equal to the sum of the tributary flows. The program also permits diversions from streams. Streams are divided into segments and reaches. Each reach corresponds to individual cells in the finite-difference grid used to simulate groundwater flow. A segment consists of a group of reaches connected in downstream order. Leakage is calculated for each reach on the basis of the head difference between the stream and aquifer and a conductance term. It is subtracted or added to the amount of streamflow into the reach. The stage in each reach can be computed using the Manning formula under the assumption of a rectangular stream channel. The amount of leakage in each reach (either into or out of the aquifer) is incorporated into the groundwater flow model by adding terms to the finite-difference equations. Recharge to the aquifer in a reach ceases when all the streamflow in upstream reaches has leaked into the aquifer and the stream is dry. A stream is permitted to flow again in downstream reaches if the head in the aquifer is above the elevation of the streambed. Results from the program have been compared to results from two analytical solutions. One assumes time varying areal recharge to the aquifer and discharge only to a stream and the other assumes recharge to the aquifer from a change in stream stage. Results from the program reasonably duplicated the analytical solutions. Manuscript approved for publication December 13, 1988 The groundwater flow model with the Streamflow-Routing Package has an advantage over the analytical solution in simulating the interaction between aquifer and stream because it can be used to simulate complex systems that cannot be readily solved analytically. The Streamflow-Routing Package does not include a time function for streamflow but rather streamflow entering the modeled area is assumed to be instantly available to downstream reaches during each time period. This assumption is generally reasonable because of the relatively slow rate of groundwater flow. Another assumption is that leakage between streams and aquifers is instantaneous. This assumption may not be reasonable if the streams and aquifers are separated by a thick unsaturated zone. Documentation of the Streamflow-Routing Package includes data input instructions; flow charts, narratives, and listings of the computer program for each of four modules ; and input data sets and printed results for two test problems, and one example problem.
An evaluation of analytical solutions to estimate drawdowns and stream depletions by wells
Water Resources Research, 1991
Analytical solutions for computing drawdowns and streamflow depletion rates often neglect conditions that exist in typical stream-aquifer systems. These conditions can include (I) partial penetration of the aquifer by the stream, (2) presence of a streambed clogging layer, (3) aquifer storage available to the pumping well from areas beyond the stream, and (4) hydraulic disconnection between the stream and the well. A methodology is presented for estimating extended flow lengths and other parameters used to approximate the increased head losses created by partially penetrating streams and clogging layer resistance effects. The computed stream depletion rates and drawdown distributions from several analytical solutions were compared to those obtained using a two-dimensional groundwater flow model. The stream geometry was approximated as a semicircle. Numerical simulation results indicate that, because of the use of simplifying assumptions, the analytical solutions can misrepresent aquifer drawdown distributions and overestimate stream depletion rates. Assuming that a correct simulation of the stream depletion phenomenon is provided by the numerical model, the error associated with each of the simplifying assumptions was determined. At a time of 58.5 days after pumping began, errors in computed stream depletion rates due to neglect of partial penetration were 20%, those due to neglect of clogging layer resistance were 45%, and those due to neglect of storage in areas beyond the stream were 21%. Neglecting hydraulic disconnection had only a minor effect (i.e., an error of 1% only at a time of 58.5 days after pumping began) on computed stream depletion rates and a noticeable effect on aquifer drawdown distributions. groundwater withdrawals near a stream, the water table can be lowered below the streambed elevation, thereby severing the saturated exchange between the stream and the aquifer, creating disconnection, and forming an unsaturated zone Copyright 1991 by the American Geophysical Union. Paper number 91WR00001. 0043-1397/91/91WR-00001 $05.00 below the streambed (Figure 1 c). Under these conditions, as long as the water level in the stream does not change, a further drawdown of the water table due to pumping does not significantly affect the seepage rate from the stream. Several analytical solutions are available for computing drawdowns and stream depletions caused by pumping near a stream [e.g., Theis, 1941; Glover and Balmer, 1954; Jacob, 1950; Hantush, 1965]. These solutions typically incorporate image well theory to predict the rate at which a pumping well depletes flow in a nearby stream. The solutions are based on simplifying assumptions, e.g., (1) the stream fully penetrates the aquifer, (2) the stream and the aquifer are hydraulically connected, (3) the streambed is unclogged, (4) the stream is infinitely long and straight, and (5) the aquifer underlying the stream is isotropic, semi-infinite in extent, of constant transmissivity, and that only horizontal flow (i.e., Dupuit flow) occurs in the aquifer. To account for the effects of vertical seepage from streams that only partially penetrate the full aquifer thickness and whose beds and banks are much less permeable than the aquifer, the method of additional seepage resistances [e.g., Streltsova, 1974] has often been applied [Hantush, 1965]. This technique extends the actual distance between the stream and the pumping well by an additional length, horizontal flow through which results in head losses equivalent to the additional losses created by partial penetration and clogging layer effects. Extended flow lengths based on the Hahtush [1965] solution are, however, smaller than those based on the Jacob [1950] solution. The new "effective distance" replaces the actual distance between the stream and the well as used in the Theis [1941] solution.