Comparison of Aquifer Sustainability Under Groundwater Administrations in Oklahoma and Texas1

Mittelstet, Aaron R., Michael D. Smolen, Garey A. Fox, and Damian C. Adams, 2011. Comparison of Aquifer Sustainability Under Groundwater Administrations in Oklahoma and Texas. Journal of the American Water Resources Association (JAWRA) 1‐8. DOI: 10.1111/j.1752‐1688.2011.00524.x Abstract: We compared two approaches to administration of groundwater law on a hydrologic model of the North Canadian River, an alluvial aquifer in northwestern Oklahoma. Oklahoma limits pumping rates to retain 50% aquifer saturated thickness after 20 years of groundwater use. The Texas Panhandle Groundwater Conservation District’s (GCD) rules limit pumping to a rate that consumes no more than 50% of saturated thickness in 50 years, with reevaluation and readjustment of permits every 5 years. Using a hydrologic model (MODFLOW), we simulated river‐groundwater interaction and aquifer dynamics under increasing levels of “development” (i.e., increasing groundwater withdrawals). Oklahoma’s approach initially would limit groundwater extraction more than the GCD approach, but the GCD approach would be more protective in the long run. Under Oklahoma rules more than half of aquifer storage would be depleted when development reaches 65%. Reevaluation of permits under the Texas Panhandle GCD approach would severely limit pumping as the 50% level is approached. Both Oklahoma and Texas Panhandle GCD approaches would deplete alluvial base flow at approximately 10% development. Results suggest periodic review of permits could protect aquifer storage and river base flow. Modeling total aquifer storage is more sensitive to recharge rate and aquifer hydraulic conductivity than to specific yield, while river leakage is most sensitive to aquifer hydraulic conductivity followed by specific yield.     

Evaluating Hydrologically Connected Surface Water and Groundwater Using a Groundwater Model

Determination of the nature and extent of the connection between groundwater and surface water is of paramount importance to managing water supplies. The development of analyses that detail the surface water‐groundwater system may lead to more effective utilization of available water. A tool was developed to help determine the effects of groundwater and surface water interactions. The software tool includes two graphic user interfaces to allow full compatibility with numerical MODFLOW groundwater models. This case study shows the tool, in conjunction with MODFLOW groundwater models and carefully designed scenarios, can successfully calculate the rates of stream‐groundwater interactions, thereby providing the basis for designating management areas with the most significant hydrologic impact. This tool can be applied in other regions with similar settings and needs for integrated water management.     

A provider-based water planning and management model--WaterSim 4.0--for the Phoenix Metropolitan Area

Uncertainty in future water supplies for the Phoenix Metropolitan Area (Phoenix) are exacerbated by the near certainty of increased, future water demands; water demand may increase eightfold or more by 2030 for some communities. We developed a provider-based water management and planning model for Phoenix termed WaterSim 4.0. The model combines a FORTRAN library with Microsoft C# to simulate the spatial and temporal dynamics of current and projected future water supply and demand as influenced by population demographics, climatic uncertainty, and groundwater availability. This paper describes model development and rationale. Water providers receive surface water, groundwater, or both depending on their portfolio. Runoff from two riverine systems supplies surface water to Phoenix while three alluvial layers that underlie the area provide groundwater. Water demand was estimated using two approaches. One approach used residential density, population projections, water duties, and acreage. A second approach used per capita water consumption and separate population growth estimates. Simulated estimates of initial groundwater for each provider were obtained as outputs from the Arizona Department of Water Resources (ADWR) Salt River Valley groundwater flow model (GFM). We compared simulated estimates of water storage with empirical estimates for modeled reservoirs as a test of model performance. In simulations we modified runoff by 80%-110% of the historical estimates, in 5% intervals, to examine provider-specific responses to altered surface water availability for 33 large water providers over a 25-year period (2010-2035). Two metrics were used to differentiate their response: (1) we examined groundwater reliance (GWR; that proportion of a providers' portfolio dependent upon groundwater) from the runoff sensitivity analysis, and (2) we used 100% of the historical runoff simulations to examine the cumulative groundwater withdrawals for each provider. Four groups of water providers were identified, and discussed. Water portfolios most reliant on Colorado River water may be most sensitive to potential reductions in surface water supplies. Groundwater depletions were greatest for communities who were either 100% dependent upon groundwater (urban periphery), or nearly so, coupled with high water demand projections. On-going model development includes linking WaterSim 4.0 to the GFM in order to more precisely model provider-specific estimates of groundwater, and provider-based policy options that will enable "what-if" scenarios to examine policy trade-offs and long-term sustainability of water portfolios.     

ESTIMATING WATER BUDGET IN A REGIONAL AQUIFER USING HSPF‐MODFLOW INTEGRATED MODEL1

ABSTRACT: Integrated water resources management is important, especially in watersheds where substantial interactions exist between the ground and surface water sources. This management warrants the need for reliable estimates of both an overall basin water budget and hydrologic fluctuations between ground water and surface water sources. The objectives of this study were to estimate the total water budget and to simulate the effects of the management of water in the Big Lost River Basin in Idaho. The study used the FIPR Hydrological Model (FHM), a hydrological model developed by the University of South Florida for the Florida Institute of Phosphate Research (FIPR). The FHM is an integrated model that simulates the full water budget of the surface and ground water systems. It has two public domain components: Hydrological Simulation Program ‐ FORTRAN (HSPF) and Modular Three‐Dimensional Finite‐Difference Ground Water Flow Model (MODFLOW). This study quantified the hydrologic fluxes between ground water and surface water and determined a comprehensive and accurate water budget for the Big Lost River. The study showed an annual amount of 10.44 m3/sec leaves the basin and never to return to the system. The study is useful in developing and calculating the annual water budget in the Big Lost River, and this process should be applicable to estimating water budgets in other basins.     

MODELING THE IMPACT OF SUBSURFACE NUTRIENT FLUX ON WATER QUALITY IN THE LOWER TRUCKEE RWER,NEVADA1

ABSTRACT: The impacts of regional groundwater quality and local agricultural activities on in-stream water quality in the Lower Truckee River, Nevada, were assessed through a detailed program of monitoring and computer simulation. An agricultural diversion and return-flow were monitored in great detail to determine mass loading rates of nutrients from agriculture in the area. Once characterized, the cumulative impacts of agricultural diversions and return-flows were evaluated using the Water Quality Assessment Program (WASP) to model nitrogen, phosphorus, periphyton, and dissolved oxygen. Monitoring showed that a significant proportion of the water diverted for agricultural purposes returned to the river as surface point return-flow (estimated at 13.9 percent $ 0.1 percent), and as groundwater diffuse return-flow (estimated at 27 percent $ 6 percent). Modeling efforts demonstrated the significant effect of assumed regional groundwater quality (nitrate) upon predicted periphyton growth and associated diel fluctuations of dissolved oxygen.     

SWATMOD‐Prep: Graphical User Interface for Preparing Coupled SWAT‐MODFLOW Simulations

This article presents SWATMOD‐Prep, a graphical user interface that couples a SWAT watershed model with a MODFLOW groundwater flow model. The interface is based on a recently published SWAT‐MODFLOW code that couples the models via mapping schemes. The spatial layout of SWATMOD‐Prep guides the user through the process of importing shape files (sub‐basins, hydrologic response units [HRUs], river network) from an existing SWAT model, creating a grid, performing necessary geo‐processing operations to link the models, writing out SWAT‐MODFLOW files, and running the simulation. The option of creating a new single‐layer MODFLOW model for near‐surface alluvial aquifers is available, with the user prompted to provide groundwater surface elevation (through a digital elevation model), aquifer thickness, and necessary aquifer parameter values. The option of simulating nitrate transport in the aquifer also is available, using the reactive transport model RT3D. The interface is in the public domain. It is programmed in Python, with various software packages used for geo‐processing operations (e.g., selection, intersection of rasters) and inputting/outputting data, and is written for Windows. The use of SWATMOD‐Prep is demonstrated for the Little River Experimental Watershed, Georgia. SWATMOD‐Prep and SWAT‐MODFLOW executables are available with an accompanying user's manual at: http://swat.tamu.edu/software/swat-modflow/ . The user's manual also accompanies this article as Supporting Information.     

SIMULATION OF INTEGRATED SURFACE WATER AND GROUND WATER SYSTEMS - MODEL FORMULATION1

ABSTRACT: The unique characteristics of the hydrogeologic system of south Florida (flat topography, sandy soils, high water table, and highly developed canal system) cause significant interactions between ground water and surface water systems. Interaction processes involve infiltration, evapotranspiration (ET), runoff, and exchange of flow (seepage) between streams and aquifers. These interaction processes cannot be accurately simulated by either a surface water model or a ground water model alone because surface water models generally oversimplify ground water movement and ground water models generally oversimplify surface water movement. Estimates of the many components of flow between surface water and ground water (such as recharge and ET) made by the two types of models are often inconsistent. The inconsistencies are the result of differences in the calibration components and the model structures, and can affect the confidence level of the model application. In order to improve model results, a framework for developing a model which integrates a surface water model and a ground water model is presented. Dade County, Florida, is used as an example in developing the concepts of the integrated model. The conceptual model is based on the need to evaluate water supply management options involving the conjunctive use of surface water and groundwater, as well as the evaluation of the impacts of proposed wellfields. The mathematical structure of the integrated model is based on the South Florida Water Management Model (SFWMM) (MacVicar et al., 1984) and A Modular Three-Dimensional Finite-Difference Groundwater Flow Model (MODFLOW) (McDonald and Harbaugh, 1988).     

Historical Groundwater Trends in Northern New England and Relations with Streamflow and Climatic Variables

Water‐level trends spanning 20, 30, 40, and 50 years were tested using month‐end groundwater levels in 26, 12, 10, and 3 wells in northern New England (Maine, New Hampshire, and Vermont), respectively. Groundwater levels for 77 wells were used in interannual correlations with meteorological and hydrologic variables related to groundwater. Trends in the contemporary groundwater record (20 and 30 years) indicate increases (rises) or no substantial change in groundwater levels in all months for most wells throughout northern New England. The highest percentage of increasing 20‐year trends was in February through March, May through August, and October through November. Forty‐year trend results were mixed, whereas 50‐year trends indicated increasing groundwater levels. Whereas most monthly groundwater levels correlate strongly with the previous month's level, monthly levels also correlate strongly with monthly streamflows in the same month; correlations of levels with monthly precipitation are less frequent and weaker than those with streamflow. Groundwater levels in May through August correlate strongly with annual (water year) streamflow. Correlations of groundwater levels with streamflow data and the relative richness of 50‐ to 100‐year historical streamflow data suggest useful proxies for quantifying historical groundwater levels in light of the relatively short and fragmented groundwater data records presently available.     

Transboundary Groundwater Policy: Developing Approaches in the Western and Southwestern United States1

Hathaway, Deborah L., 2011. Transboundary Groundwater Policy: Developing Approaches in the Western and Southwestern United States. Journal of the American Water Resources Association (JAWRA) 47(1):103‐113. DOI: 10.1111/j.1752‐1688.2010.00494.x Abstract: The western and southwestern United States include dozens of groundwater basins that cross political boundaries. Common among these shared groundwater basins is an overlay of differing legal structures and water development priorities, typically, with insufficient water supply for competing human uses, and often, a degraded ecosystem. Resolution of conflicts over ambiguously regulated groundwater has clarified transboundary groundwater policy in some interstate basins, while transboundary groundwater policy in international basins is less evolved. This paper identifies and contrasts approaches to transboundary groundwater policy, drawing from recent conflicts and cooperative efforts, including those associated with the interstate compacts on the Arkansas and Pecos Rivers; the Hueco and Lower Rio Grande Basins shared by New Mexico, Texas, and Mexico; and the Mexicali Basin in California and Mexico. Some efforts seek to fit groundwater policy into existing surface water allocation procedures; some strive for a better fit – incorporating scientific understanding of key differences between groundwater and surface water into policy frameworks. In some cases, neither policy nor precedent exists. The collective experience of these and other cases sets the stage for improved management of transboundary groundwater; as such, challenges and successes of these approaches, and those contemplated in several hypothetical model agreements, are examined.     

EVAPOTRANSPIRATION CONCEPTUALIZATION IN THE HSPF‐MODFLOW INTEGRATED MODELS1

In 1988, the Florida Institute of Phosphate Research (FIPR) funded project to develop an advanced hydrologic model for shallow water table systems. The FIPR hydrologic model (FHM) was developed to provide an improved predictive capability of the interactions of surface water and ground water using its component models, HSPF and MODFLOW. The Integrated Surface and Ground Water (ISGW) model was developed from an early version of FHM and the two models were developed relatively independently in the late 1990s. Hydrologic processes including precipitation, interception, evapotranspiration, runoff, recharge, streamflow, and base flow are explicitly accounted for in both models. Considerable review of FHM and ISGW and their applications occurred through a series of projects. One model evolved, known as the Integrated Hydrological Model IHM. This model more appropriately describes hydrologic processes, including evapotranspiration fluxes within small distributed land‐based discretization. There is a significant departure of many IHM algorithms from FHM and ISGW, especially for soil water and evapotranspiration (ET). In this paper, the ET concepts in FHM, ISGW, and IHM will be presented. The paper also identifies the advantages and data costs of the improved methods. In FHM and IHM, ground water ET algorithms of the MODFLOW ET package replace those of HSPF (ISGW used a different model for ground water ET). However, IHM builds on an improved understanding and characterization of ET partitioning between surface storages, vadose zone storage, and saturated ground water storage. The IHM considers evaporative flux from surface sources, proximity of the water table to land surface, relative moisture condition of the unsaturated zone, thickness of the capillary zone, thickness of the root zone, and relative plant cover density. The improvements provide a smooth transition to satisfy ET demand between the vadose zone and deeper saturated ground water. While the IHM approach provides a more sound representation of the actual soil profile than FHM, and has shown promise at reproducing soil moisture and water table fluctuations as well as field measured ET rates, more rigorous testing is necessary to understand the robustness and/or limitations of this methodology.     

CONTROLLING NONPOINT EXTERNALITIES WITH INPUT RESTRICTIONS IN AN IRRIGATED RIVER BASIN1

ABSTRACT: Irrigated agriculture is a major nonpoint source of surface water quality degradation. Nonpoint source discharges can be controlled by either output taxes or restrictions, or input taxes or restrictions. The economic theory of externality control with taxes or restrictions on input use is developed. The effectiveness of alternative input control policies in improving surface water quality is demonstrated with a mathematical model of the agriculture and water quality in Washington State's Yakima River Basin. Water quality parameters considered were river nitrogen concentration, water temperature, and cropland soil losses. Producer and social abatement costs were the most important measures of policy effectiveness.     

Wind‐Powered Desalination: An Estimate of Saline Groundwater in the United States1

James Androwski, Abraham Springer, Thomas Acker, and Mark Manone, 2011. Wind‐Powered Desalination: An Estimate of Saline Groundwater in the United States. Journal of the American Water Resources Association (JAWRA) 47(1):93‐102. DOI: 10.1111/j.1752‐1688.2010.00493.x Abstract: Increasing scarcity of freshwater resources in many regions of the world is leading water resource managers to consider desalination as a potential alternative to traditional freshwater supplies. Desalination technologies are energy intensive and expensive to implement making desalination using renewable energy resources a potentially attractive option. Unfortunately, saline groundwater resources are not well characterized for many regions hindering consideration of such technologies. In this assessment, we estimate the saline groundwater resources of the principal aquifers of the United States using a geographic information system and correlate these resources to wind resources potentially sufficient to supply the energy demand of desalination equipment. We estimate that 3.1 × 10¹⁴ m³ saline groundwater, total volume, are contained in 28 of the country’s principal aquifers known to contain saline groundwater. Of this volume, 1.4 × 10¹⁴ m³ saline groundwater are co‐located with wind resources sufficient for electrical generation to desalinate groundwater.     

Assessment of Groundwater Depletion and Implications for Management in the Denver Basin Aquifer System

The Denver Basin Aquifer System (DBAS) is a critical groundwater resource along the Colorado Front Range. Groundwater depletion has been documented over the past few decades due to the increased water use among users, presenting long‐term sustainability challenges. A spatiotemporal geostatistical analysis is used to estimate potentiometric surfaces and evaluate groundwater storage changes between 1990 and 2016 in each of the four DBAS aquifers. Several key depletion patterns and spatial water‐level changes emerge in this work. Hydraulic head changes are the largest in the west‐central side of the DBAS and have decreased in some areas by up to 180 m since 1990, while areas to the northwest show increases in hydraulic head by over 30.5 m. The Denver and Arapahoe aquifers show the largest groundwater storage losses, with the highest rates occurring in the 2000s. The results highlight uncertainty in the volumetric predictions under various storage coefficient calculations and emphasize the importance of representative aquifer characterization. The observed groundwater storage depletions are due to a combination of factors, which include population growth increasing the demand for water, variable precipitation, and drought influencing recharge, and increased groundwater pumping. The methods applied in this study are transferable to other groundwater systems and provide a framework that can help assess groundwater depletion and inform management decisions at other locations.     

Assessment of Water Availability and Scarcity Based on Hydrologic Components in an Irrigated Agricultural Watershed Using SWAT

This study assesses the water availability and the water scarcity based on the hydrologic behavior under different weather conditions and crop coverages in an irrigated agricultural area of Rincon Valley in New Mexico using the SWAT (Soil and Water Assessment Tool) model. Two spatial crop coverages included normal (2008) and dry (2011) years with 14 different crop sets for each year. The SWAT was applied to generate the five essential indicators (surface flow, evapotranspiration, soil water, groundwater recharge, and irrigation water) to evaluate the integrated water availability based on hydrologic response units (HRUs) along with the Arrey Canal to supply irrigation water in the crop areas. The water availability index scores (0–1 range with 1 being the most available and 0 the least available) of alfalfa, corn, cotton, and pecans were 0.21, 0.56, 0.91, and 0.20, respectively, in the normal year and 0.16, 0.78, 0.88, and 0.24, respectively, in the dry year. In the dry year, water scarcity values were high in mostly alfalfa areas, whereas cotton areas have mostly no stress with good water availability. The major water users of crops, ranked in order, were alfalfa, pecans, cotton, and corn. During the dry year, water availability showed to be balanced in terms of water supply and demand by controlling crop patterns from reducing alfalfa acreage by 12% and increasing cotton acreage by 13%.     

WATER RIGHTS,ALLOCATION, AND CONFLICTS IN THE TONGUE RIVER BASIN,SOUTHEASTERN MONTANA1

ABSTRACT: Southeastern Montana's Tongue River basin is experienceing rapid development of its extensive coal deposits which is significantly impacting the basin's hydrologic systems. Energy development projects may require more water than is available and threatens to dewater the river, degrade water quality, and endanger aquatic econosystems. The Montana Water Use Act promised to end the uncertainty which has existed in Montana water law. However, serious difficulties have been encountered in implementing the law and Tongue River water rights remain in a state of uncertainty. The Tongue River's water was allocated in 1978 but the division of the river's water is meaningless due to Indian lawsuits and lack of an agreement between Montana and Wyoming concerning the Yellowstone River Compact. Thus water which is hydrologically available may not be legally available.     

OPTIMIZATION MODELING OF A NEW FACILITY FOR THE CALIFORNIA STATE WATER PROJECT1

ABSTRACT: A non-linear optimization model is applied to the California State Water Project (SWP) and portions of the Central Valley Project (CVP). The model accounts for the major hydrologic, regulatory, and operational features of both projects. The model maximizes long-term SWP yields over a 70-year period, using a quarterly time step. The potential for increased yield associated with a proposed facility improvement is evaluated with the model. The proposed facility is an extension of the Folsom-South Canal, which would allow water to be conveyed from the American River below Folsom Reservoir into New Melones Reservoir on the Stanislaus River or into the California Aqueduct. Model results indicate that extension of the Folsom-South Canal has the potential to increase SWP yields by 13 percent.     

Drought Resilience of the California Central Valley Surface‐Ground‐Water‐Conveyance System1

Abstract: A series of drought simulations were performed for the California Central Valley using computer applications developed by the California Department of Water Resources and historical datasets representing a range of droughts from mild to severe for time periods lasting up to 60 years. Land use, agricultural cropping patterns, and water demand were held fixed at the 2003 level and water supply was decreased by amounts ranging between 25 and 50%, representing light to severe drought types. Impacts were examined for four hydrologic subbasins, the Sacramento Basin, the San Joaquin Basin, the Tulare Basin, and the Eastside Drainage. Results suggest the greatest impacts are in the San Joaquin and Tulare Basins, regions that are heavily irrigated and are presently overdrafted in most years. Regional surface water diversions decrease by as much as 70%. Stream‐to‐aquifer flows and aquifer storage declines were proportional to drought severity. Most significant was the decline in ground water head for the severe drought cases, where results suggest that under these scenarios the water table is unlikely to recover within the 30‐year model‐simulated future. However, the overall response to such droughts is not as severe as anticipated and the Sacramento Basin may act as ground‐water insurance to sustain California during extended dry periods.     

TREE-RING RECONSTRUCTION OF UPPER GILA RWER DISCHARGE1

ABSTRACT: Effective planning for use of water resources requires accurate information on hydrologic variability induced by climatic fluctuations. Tree-ring analysis is one method of extending our knowledge of hydrologic variability beyond the relatively short period covered by gaged streamflow records. In this paper, a network of recently developed tree-ring chronologies is used to reconstruct annual river discharge in the upper Gila River drainage in southeastern Arizona and southwestern Arizona since A.D. 1663. The need for data on hydrologic variability for this semi-arid basin is accentuated because water supply is inadequate to meet current demand. A reconstruction based on multiple linear regression (R²=0.66) indicates that 20th century is unusual for clustering of high-discharge years (early 1900s), severity of multiyear drought (1950s), and amplification of low-frequency discharge variations. Periods of low discharge recur at irregular intervals averaging about 20 years. Comparison with other tree-ring reconstructions shows that these low-flow periods are synchronous from the Gila Basin to the southern part of the Upper Colorado River Basin.     

Water Supply Planning Considering Uncertainties in Future Water Demand and Climate: A Case Study in an Illinois Watershed

Ensuring an adequate, reliable, clean, and affordable water supply for citizens and industries requires informed, long-range water supply planning, which is critically important for water security. A balance between water supply and demand must be considered for a long-term plan. However, water demand projections are often highly uncertain. Climate change could impact the hydrologic processes, and consequently, threaten water supply. Thus, understanding the uncertainties in future water demand and climate is critical for developing a sound water supply plan. In Illinois, regional water supply planning attempts to explore the impacts of future water demand and climate on water supply using scenario analyses and hydrologic modeling. This study is aimed at developing a water supply planning framework that considers both future water demand and climate change impacts. This framework is based on the Soil and Water Assessment Tool to simulate the watershed hydrology and conduct scenario analyses that consider the uncertainties in both future water demand and climate as well as their impacts on water supply. The framework was applied to water supply planning efforts in the Kankakee River watershed. The Kankakee River watershed model was calibrated and validated to observed streamflow records at four long-term United States Geological Survey streamflow gages. Because of the many model parameters involved, the calibration process was automated and was followed by a manual refinement, resulting in good model performance. Long-range water demand projections were prepared by the Illinois State Water Survey. Six future water demand scenarios were established based on a suite of assumptions. Climate scenarios were obtained from the Coupled Model Intercomparison Projection Phase 5 datasets. Three representative concentration pathways (RCPs), RCP2.6, RCP4.5, and RCP8.5, are used in the study. The scenario simulation results demonstrated that climate change appears to have a greater impact on water availability in the study area than water demand. The framework developed in this study can also be used to explore the impacts of uncertainties of water demand and climate on water supply and can be extended to other regions and watersheds.