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In the Rio Grande transboundary basin, environmental flows have not been considered as an integral part of the water man- agement. This research focuses on the Big Bend, a reach located along the Rio Grande mainstem. Important natural regions of the Chihuahuan Desert are threatened due to the lack of environmental flows. In this paper is estimated the maximum volume of water available for environmental flows without affecting human and international water requirements, and without increasing the flood risk in Presidio-Ojinaga. Environmental flows are proposed based on an analysis of the prior reservoir alteration hydrology of the river. A planning model was built to simulate the water allocation system and evaluate alternative policies. A reservoir reoperation policy for Luis L. Leon reservoir is proposed to supply environmental flows without violating the system constraints. The policy that supplies the maximum water to the environment is two-thirds (66%) of the prior reservoir alteration conditions; it also improves human water supply, treaty obligations, and decreases flood risk. DOI: 10.1061/(ASCE)WR.1943-5452.0000331. © 2014 American Society of Civil Engineers. Author keywords: Environmental flows; Reservoir reoperation; Integrated water management; Adaptive management; Rio Grande.

This paper focuses on calibration and validation of a hydrologic model of the Rio Conchos Basin, a main Mexican tributary of the binational Rio Grande Basin. The Rio Conchos provides approximately 55% of the water deliveries to the United States under the 1944 water treaty signed between both countries. The hydrologic modeling has been developed using the one-dimensional, two-layer soil moisture accounting scheme embedded in the Water Evaluation and Planning (WEAP) model. A 10-year period was used to calibrate the model, which was achieved by a trial-and-error method for the adjustment of the model parameters. The results show a Nash-Sutcliffe coefficient of 0.84 at Ojinaga station (mouth of the basin) and 0.81 at La Boquilla, indicating good model performance. In general the model predicts well the monthly, annual, and maximum flows; but there are significant differences between the model values and undeveloped (naturalized) flows for low flow periods, especially at La Boquilla station. For model...

This paper presents an analysis of a newly developed draft agreement on the allocation of water and energy resources of the Syr Darya basin considering transboundary cooperation and benefits sharing. The method uses a river basin model and game theoretic concepts to assess the potential benefits to the four riparian countries, under various arrangements of cooperation, ranging from independent action to full cooperation as envisioned in the draft agreement. The analysis shows increased benefits to all countries in the basin if they follow the four-country cooperative arrangements outlined in the draft agreement. Different methods for allocating the benefits of cooperation are considered. The Shapely allocation provides each country with increased economic benefits and is stable in relation to each country’s likelihood of treaty compliance. Other methods to allocate of the gains are considered, such as proportional shares, equal shares, the Nucleolus, and Nash-Harsayni, which all result in allocations that are more likely to be violated and are less stable than the Shapley allocation. The analysis indicates the upstream country of Kyrgyzstan can be encouraged to participate in and comply with the agreement through additional compensatory payments; however, if their conditions are not right, they may be prone to noncompliance and disruption of the treaty. The concepts illustrated in this paper can be used as the basis for analyzing benefits sharing and cooperation in other transboundary basins.

The water planning and management policies of the Rio Grande basin no longer respond to the sustainable needs of water users, environment, and international commitments of this transboundary basin between Mexico and the United States. This paper describes how groundwater banking through an in lieu method is one approach leading to better water management in this basin. In lieu groundwater banking is a conjunctive water allocation policy applicable to water users supplied from surface water and groundwater sources. A basin simulation model of the Rio Grande basin, built in the water evaluation and planning system (WEAP) software, was used to evaluate the groundwater banking policy. Two scenarios are discussed: a baseline scenario without new water allocation policies implemented and a groundwater banking scenario considering the in lieu groundwater banking method implemented in the Meoqui aquifer. Results show that groundwater banking can significantly improve water management in the basin, increasing syst...

The development of relational databases from which simulation models can access data needed to describe the systems being modeled is fundamental to integrated river basin management, especially in shared, transboundary basins. Creating a geographically referenced database, a geodatabase, for the Rio Grande/Rio Bravo Basin represents the first major attempt to establish a more complete understanding of the basin as a whole, using both Mexican and United States geospatial and temporal water resources data. From the geodatabase, it is possible to obtain information about climatology, water availability, water uses, hydraulic infrastructure, and watershed properties in the basin. These data can be used in simulation models to calculate the state of basin water availability under different climatic and development scenarios and management plans in the future. This geodatabase is intended to be a tool to assist in sharing data to enhance binational cooperation between Mexico and the United States concerning water in this basin, providing accurate and reliable data necessary for analysis and resolution of water resources issues.

A multistage stochastic optimization model using linear programming was developed to provide planning tools for Lower Colorado River Authority in the operation of the Highland Lakes system, as well as a framework for examining the operation of four irrigation districts. Three primary objectives were maximized in the model: (1) Revenues from rice production, (2) recreation benefits associated with lake use, and (3) revenues from hydropower generation. The model includes stochastic inflows, weather-dependent irrigation demands, an interruptible contract decision function, a reservoir space rule to balance storage volumes between reservoirs, hydropower production, municipal and irrigation return flows, and bay and estuary inflow requirements. Model weights and coefficients were calibrated to reflect actual market prices and economic constraints, or to represent water management priorities. Stochastic optimization is used to account for meteorological uncertainty using representative inflow scenarios. Considering the uncertainty in the inflows, the model predicts optimum acreage levels, reservoir storage levels, reservoir releases, and other decisions, to maximize total expected benefits in the system.

The interdisciplinary nature of water resources problems requires the integration of technical, economic, environmental, social, and legal aspects into a coherent analytical framework. This paper presents the development of a new integrated hydrologic-agronomic-economic model in the context of a river basin in which irrigation is the dominant water use and irrigation-induced salinity presents a major environmental problem. The model’s main advantage is its ability to reflect the interrelationships between essential hydrologic, agronomic, and economic components and to explore both economic and environmental consequences of various policy choices. All model components are incorporated into a single consistent model, which is solved in its entirety by a simple but effective decomposition approach. The model is applied to a case study of water management in the Syr Darya River basin in Central Asia.

Most large nonlinear optimization models are composed of “pieces”—subsets of decision variables—and constraints whose union is the entire model. Each piece represents an additional aspect of the situation being modeled. This opens the possibility of solving the simplest piece first, adding the constraints and variables of another piece, and solving this submodel from a starting point provided by the first solution. This process is repeated until the original model is solved. This “piece-by-piece” approach provides each submodel with a good starting point, which greatly increases the probability that a good nonlinear solver will find an optimal solution. We apply it to a large multiperiod nonlinear programming (NLP) model with 13,700 variables, 10,000 equations, and a high degree of nonlinearity (54.3% of the nonzero Jacobian elements are nonconstant), arising from water resources planning and operation in a river basin. Using the GAMS modeling language and the CONOPT2 NLP solver, the piece-by-piece method...

Water saturation in the vadose zone is an important parameter for many nonaqueous phase liquid (NAPL) remediation technologies. Conventional soil boring analyses may not provide accurate average water saturation data. Previous studies have shown that a partitioning interwell tracer test (PITT) can provide an accurate estimate of average subsurface NAPL saturations. The PITT is proposed as a suitable technology for estimating average subsurface water saturations. In this research, difluoromethane was evaluated as a suitable tracer compound to partition among air, water, and NAPL phases. Method of moments analyses were used to develop equations necessary to determine water saturations from difluoromethane PITT results. One-dimensional column experiments provided air-water and air-NAPL partition coefficient data for difluoromethane. Difluoromethane is shown to be a suitable tracer for use in field PITTs to predict water saturations in the vadose zone.

This paper describes laboratory research conducted to investigate the performance of partitioning tracers for the detection of nonaqueous-phase liquids (NAPLs) in vadose zones. Once evaluated, the tracers may be used for volume estimation of NAPLs and remediation performance assessment of vadose zones. These laboratory studies used glass chromatography columns packed with: (1) Ottawa sand; and then (2) in a separate experiment, soil extracted from the Chemical Waste Landfill at Sandia National Laboratories. The columns were prepared in a manner that resulted in a three-phase system of air, water, and NAPL in the columns. Conservative and partitioning gas tracers were injected into the columns, and their elution concentrations were analyzed. The method of moments was used to estimate partition coefficients between the air and NAPL phases for each of the tracers. The partition coefficients and retardation factors, also estimated during the study, are used to select appropriate tracers for NAPL detection. This research identified several suitable perfluorocarbon tracers and demonstrated the feasibility of using partitioning tracers as a tool for NAPL detection in the vadose zone.

A screening model is developed to support the selection of alternatives for meeting future water demands and protecting sensitive ecosystems in the Edwards aquifer region of central Texas. Important attributes of the model are its basis on existing ground- and surface-water simulation models and its incorporation of uncertainty in future supplies and demands. The model is used to evaluate trade-offs involving environmental and economic risks and to identify water resources alternatives that promise to be robust (i.e., those that can be managed in a flexible manner to meet society's goals under a wide range of hydrologic scenarios). Use of the model to help determine conjunctive surface- and ground-water management policies is also demonstrated. Although limited benefits can be obtained through more coordinated operation policies, results indicate that either large investments in infrastructure or substantial reductions in projected water use will be required to meet environmental goals with a high degree ...

Water resources planners and managers are continually faced with decisions to be made under uncertainty. In planning problems such as water supply, flood control, and ground-water remediation, the trade-offs among expected cost, cost variability, and system performance and reliability must be assessed amidst inherent variability and imperfect information. Robust optimization (RO) is introduced as a framework for evaluating these trade-offs and controlling the effects of uncertainty in water resources screening models. Upon the introduction of scenarios, which represent realizations of the random parameters in the model, two types of robustness are defined: a policy is optimality-robust if it remains optimal or nearly optimal for all scenarios, and feasibility-robust if it remains feasible or nearly feasible for all scenarios. Applications to urban water transfer planning and ground-water quality management are presented, with optimality robustness related to cost variability and feasibility robustness rel...

A ground-water management model using a nonlinear programming algorithm was developed to find the minimum cost design of the combined pumping and treatment components of a pump-and-treat remediation system and includes the fixed costs of system construction and installation as well as operation and maintenance. The fixed-cost terms of the objective function are incorporated into the nonlinear programming formulation using a penalty coefficient method. Results of applying the model to an aquifer with homogeneous hydraulic conductivity show that a combined well field and treatment process model that includes fixed costs has a significant impact on the design and cost of these systems, reducing the cost by using fewer, larger-flow-rate wells. Previous pump-and-treat design formulations have resulted in systems with numerous, low-flow-rate wells due to the use of simplified cost functions that do not exhibit economies of scale or fixed costs. Two example aquifers with heterogeneous conductivity fields were al...

Multigrid methods use a series of successively coarser grids to accelerate the solution of equations arising from the numerical solution of partial differential equations. A grid-cell-based geographic information system (GIS) with a map algebra language is capable of displaying and manipulating spatial data and attributes and handling the data arrays and results arising in ground-water simulation problems. To examine the efficacy of GIS to solve ground-water flow problems, we have performed ground-water modeling directly within a GIS without going outside the system for model solution. We have applied the multigrid method to solve steady ground-water flow problems in heterogeneous aquifers. Execution times for the GIS-multigrid approach using simple iterative techniques greatly exceed those of traditional ground-water simulation models due to the creation of temporary grids for intermediate calculations during the simulation. Efficient handling of boundary conditions is another difficult problem in GIS grid-cell-based modeling.

A condensed disaggregation procedure has been employed to generate synthetic recharge sequences for the Edwards aquifer in the San Antonio region. Two stochastic processes ae used in the procedure: a multivariate annual flow generator, and an annual-to-monthly disaggregation model. The processes are multivariate, first-order autoregressive, implemented in SPIGOT, and fit to a 58-yr historical record based on U.S. Geological Survey (USGS) recharge estimates for the nine river basins of the Edwards aquifer recharge zone. Transformations of basin recharge are employed in order for the autoregressive models to reproduce the marginal distributions of recharge. Validation of the synthetic recharge generation procedure shows some discrepancies between the marginal distributions, correlations, and drought characteristics of the historical and synthetic flows.

The feasibility of using an expert geographic information system (GIS) for long‐term regional water‐resources planning is evaluated through a case study examining an existing regional water‐supply system. This system is comprised of an expert system that embodies the logical rules and expertise of water‐resources planning experts as well as a geographic information system that stores and analyzes spatially distributed data. Normal water‐demand forecasts and water‐supply data along with appropriate analysis routines are used in this new planning tool, which attempts to follow the logic of current methods and permit plans to be updated and alternatives to be analyzed more rapidly. An example application of the system is presented which analyzes the existing water supply system for the Corpus Christi, Tex., area. Given annual yields for the reservoirs, water‐demand forecasts, and institutional requirements, the expert GIS calculates potential water‐supply deficits or excesses in the region over a 50‐year pla...