Ground-water/Stream Flow Model of the Monocacy River Basin, Maryland and Pennsylvania Phase I: Steady-State Model (original) (raw)
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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.
Calibrated models as management tools for stream-aquifer systems: the case of central Kansas, USA
1993
We address the problem of declining streamflows in interconnected stream-aquifer systems and explore possible management options to address the problem for two areas of central Kansas: the Arkansas River valley from Kinsley to Great Bend and the lower Rattlesnake Creek Quivira National Wildlife Refuge area. The approach we followed implements, calibrates, and partially validates for the study areas a stream-aquifer numerical model combined with a parameter estimation package and sensitivity analysis. Hydrologic budgets for both predevelopment and developed conditions indicate significant differences in the hydrologic components of the study areas resulting from development. The predevelopment water budgets give an estimate of natural groundwater recharge, whereas the budgets for developed conditions give an estimate of induced recharge, indicating that major groundwater development changes the recharge-discharge regime of the model areas with time. Such stream-aquifer models serve to link proposed actions to hydrologic effects, as is clearly demonstrated by the effects of various management alternatives on the streamflows of the Arkansas River and Rattlesnake Creek. Thus we show that a possible means of restoring specified streamflows in the area is to implement protective stream corridors with restricted groundwater extraction. Statement of the problem Many regions of western and central Kansas have experienced significant groundwater and streamflow declines, especially during the last two decades (Sophocleous, 1981; Sophocleous and McAllister, 1987, 1990). Our region of interest (Fig. 1), which is located within the boundaries of the Big Bend Groundwater Management District No. 5 (GMD5), shows streamflow and groundwater declines with time (Figs. 2(a) and 2(c)), whereas precipitation patterns and amounts show no corresponding changes (Fig. 2(a)), implying no
2015
Groundwater modeling has been used since the 1970's as a way to analyze complex groundwater systems and to provide scientific evidence for management and policy determinations. The fundamental objective of this research was to develop a digital groundwater-flow model of the Rush Springs aquifer to assist in these determinations. The Rush Springs aquifer covers approximately 10,360 km 2 in westcentral Oklahoma and is the state's second most developed aquifer. This model will be used by government agencies to inform management decisions as well as gain insight about the aquifer's response to different scenarios such as policy determinations, changes in climate, or groundwater use. A steady-state simulation was first generated from the model. Hydraulic conductivity and recharge parameters were adjusted during calibration of the model to the 1956 head observations. The relationship between observed and simulated heads had a R 2 value of 0.97 and a mean residual of-11 m. A transient model was constructed for 1956 to 2013 with monthly time steps. Specific yield, recharge, and specific storage were adjusted for this simulation. The average residuals for the analyzed years ranged from-8 to-13 m. The second objective of this research was to utilize these models to analyze how groundwater use affects stream baseflow throughout the aquifer. Three different groundwater use scenarios from 2013-2023 were generated to compare how various management practices affect baseflow conditions including current groundwater use rates, assigning a 6093 m 3 /ha pumping rate out of every well in the model, as well as allowing for maximum irrigation use in the aquifer. Groundwater discharge to streams decreased for all three while recharge to the aquifer from the streams stayed relatively the same at approximately 1.5 m 3 /s. Recharge was also found to be a contributing factor in baseflow. Like the groundwater use scenarios, stream leakage out of the aquifer was larger than flow into the aquifer for all of these recharge scenarios. Unlike the groundwater use scenarios, stream leakage from the streams to the aquifer changed during the simulation period. This indicates that recharge has a greater effect on losing streams within this groundwater system than groundwater use. v
Scientific Investigations Report, 2005
The base flow in parts of Chevelon and Clear Creeks and of the Little Colorado River near Blue Spring in northeastern Arizona is sustained by discharge from the C aquifer, and in some reaches supports threatened and endangered fish species. C aquifer water is proposed as a replacement supply to relieve pumping from the N aquifer-the current source of water for a coal slurry pipeline used to transport coal mined from Black Mesa to Laughlin, Nevada. Locations of the proposed withdrawals are in the area of Leupp, Arizona, about 25 miles from a perennial reach of lower Clear Creek. A simulation tool was needed to determine possible effects of the proposed withdrawals from the C aquifer, particularly the effects of depletion of streamflow in Clear Creek, Chevelon Creek, and the Little Colorado River in the area of Blue Spring. A numerical groundwater change model was developed for this purpose. The model uses the U.S. Geological Survey finite-difference model code MODFLOW-2000 and data sets representing key features of the C aquifer to simulate change in the system that would result from withdrawing water at proposed locations. Aquifer thickness was estimated from a hydrogeologic framework model, and values of aquifer properties such as hydraulic conductivity and specific yield were estimated from aquifer-test data. Two scenarios with differing withdrawal rates were run for a 101-year period that included 51 years of withdrawals followed by 50 years of no withdrawals. About 6 percent of the ultimate volume of depletion occurs in the 101-year period for either scenario. The maximum streamflow depletion rate for all reaches in the scenario with the greatest withdrawal rates was computed to be about 0.6 cubic foot per second. The depletion rate was highest in lower Clear Creek, the reach that is closest to the well field. A model that simulates historical conditions was used to help select the most reasonable parameter sets for a Monte Carlo analysis of computed stream depletions.
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.
MODFLOW is a ground-water flow model that can be used to assess ground-water resource problems and to make management decisions on the development of ground-water supplies at a variety of scales. It also has the ability to assess the effects of ground-water withdrawals on surface water using several options that simulate ground-water interactions with streams and lakes. The surface processes in MODFLOW do not include surface-water and energy budgets for partitioning precipitation into evapotranspiration, runoff, interflow, and unsaturated flow beneath the soil zone. Typically, runoff, infiltration, and unsaturated flow reaching the water table (assumed ground-water recharge) are estimated externally to MODFLOW. MODFLOW was coupled to the U.S. Geological Survey (USGS) Precipitation-Runoff Modeling System (PRMS) to improve how recharge is estimated for ground-water modeling studies and to provide a complete accounting of the water budget in a watershed or basin. This coupled model is called GSFLOW. Additional code was added to GSFLOW to facilitate the coupling of the two models. The connection in MODFLOW is through a new Unsaturated Zone Flow (UZF1) Package that is designed to route flow from the soil zone used in PRMS to the water table.
The use of groundwater models is prevalent in the field of environmental science. Models have been applied to investigate a wide variety of hydrogeologic conditions. More recently, groundwater models are being applied to predict the transport of contaminants for risk evaluation.