Vince Tidwell

The food-energy-water nexus: Transforming science for society

Emerging interdisciplinary science efforts are providing new understanding of the interdependence of food, energy, and water (FEW) systems. These science advances, in turn, provide critical information for coordinated management to improve the affordability, reliability, and environmental sustainability of FEW systems. Here we describe the current state of the FEW nexus and approaches to managing resource conflicts through reducing demand and increasing supplies, storage, and transport. Despite significant advances within the past decade, there are still many challenges for the scientific community. Key challenges are the need for interdisciplinary science related to the FEW nexus; ground-based monitoring and modeling at local-to-regional scales; incorporating human and institutional behavior in models; partnerships among universities, industry, and government to develop policy relevant data; and systems modeling to evaluate trade-offs associated with FEW decisions.

A Compartmental-Spatial System Dynamics Approach to Ground Water Modeling

High-resolution, spatially distributed ground water flow models can prove unsuitable for the rapid, interactive analysis that is increasingly demanded to support a participatory decision environment. To address this shortcoming, we extend the idea of multiple cell (Bear 1979) and compartmental (Campana and Simpson 1984) ground water models developed within the context of spatial system dynamics (Ahmad and Simonovic 2004) for rapid scenario analysis. We term this approach compartmental-spatial system dynamics (CSSD). The goal is to balance spatial aggregation necessary to achieve a real-time integrative and interactive decision environment while maintaining sufficient model complexity to yield a meaningful representation of the regional ground water system. As a test case, a 51-compartment CSSD model was built and calibrated from a 100,0001 cell MODFLOW (McDonald and Harbaugh 1988) model of the Albuquerque Basin in central New Mexico (McAda and Barroll 2002). Seventy-seven percent of historical drawdowns predicted by the MODFLOW model were within 1 m of the corresponding CSSD estimates, and in 80% of the historical model run years the CSSD model estimates of river leakage, reservoir leakage, ground water flow to agricultural drains, and riparian evapotranspiration were within 30% of the corresponding estimates from McAda and Barroll (2002), with improved model agreement during the scenario period. Comparisons of model results demonstrate both advantages and limitations of the CCSD model approach.

Evaluating Reservoir Operations and Other Remediation Strategies to meet Temperature TMDL's in the Willamette Basin, Oregon

Water managers in the Willamette River Basin face a number of difficult and closely interrelated challenges associated with the Endangered Species Act (ESA), the Clean Water Act (CWA), and other associated concerns. For example, under the CWA, the Oregon Department of Environmental Quality (ODEQ) has recently released a total Maximum Daily Load (TMDL) for temperature in the Willamette Basin. Some of the major factors impacting temperature in the Willamette include operation of the multiple reservoirs, permitted industrial and municipal discharges, land-use types, and irrigation practices. Possible mitigation strategies include changes in land-use to increase shading along streams, installations to cool or store point-source discharges, changes in how and when water is released from the reservoirs, installation of multiport withdrawal structures on the reservoirs, and remediation of riparian and hyporheic zones. Each of these strategies comes with ecological, economic, and/or social costs and/or benefits that must be weighed and understood before meaningful dialogue about how to best manage the basin can occur. To address this problem a collaborative team from Sandia National Laboratories, the Institute for Water Resources, David Evans and Associates, and the Portland District of the Corps of Engineers have been working with stakeholders in the basin to design and collaboratively develop an integrated systems model of the basin to examine the linkages between the various strategies and their tradeoffs. The model domain includes the main stem of the Willamette, 7 major tributaries, and 12 USACE operated reservoirs. It is built as a series of system dynamics lumped parameter models, and provides real-time feedback and scenario testing capabilities. Outputs from the model include changes in temperature at key monitoring points and costs per kcal of energy saved due to different remediation strategies, relative changes in nutrient loading and CO2 emissions due to riparian shade planting, impacts on recreational opportunities and the economic impacts of those changes, and salmonid habitat suitability as it relates to temperature. This presentation will describe the technical collaborative processes in which the model was developed and how it will be used to inform reservoir operation and other policy decisions in the basin.

Examining the Effects of Variability in Short Time Scale Demands on Solute Transport

Variations in water use at short time scales, seconds to minutes, produce variation in transport of solutes through a water supply network. However, the degree to which short term variations in demand influence the solute concentrations at different locations in the network is poorly understood. Here we examine the effect of variability in demand on advective transport of a conservative solute (e.g. chloride) through a water supply network by defining the demand at each node in the model as a stochastic process. The stochastic demands are generated using a Poisson rectangular pulse (PRP) model for the case of a dead-end water line serving 20 homes represented as a single node. The simple dead-end network model is used to examine the variation in Reynolds number, the proportion of time that there is no flow (i.e., stagnant conditions, in the pipe) and the travel time defined as the time for cumulative demand to equal the volume of water in 1000 feet of pipe. Changes in these performance measures are examined as the fine scale demand functions are aggregated over larger and larger time scales. Results are compared to previously developed analytical expressions for the first and second moments of these three performance measures. A new approach to predict the reduction in variance of the performance measures based on perturbation theory is presented and compared to the results of the numerical simulations. The distribution of travel time is relatively consistent across time scales until the time step approaches that of the travel time. However, the proportion of stagnant flow periods decreases rapidly as the simulation time step increases. Both sets of analytical expressions are capable of providing adequate, first-order predictions of the simulation results.

Potential Drought Impacts on Electricity Generation in Texas

Many power plants in the Electric Reliability Council of Texas (ERCOT) region require a large amount of water for system cooling. To improve the understanding of potential risks of electricity generation curtailment due to drought, an assessment of water availability and its potential impacts on generation during drought was performed. For this impact analysis, we identified three drought scenarios based on historical drought records and projected climate data from the Geophysical Fluid Dynamics Laboratory global climate model, for greenhouse gas emission scenario A2 defined by the Intergovernmental Panel on Climate Change. The three drought scenarios are (1) 2011 drought conditions (the worst drought in history), with the current level of water use; (2) a single-year drought (2022) projected for the period of 2020–2030, with the assumed projected water use level for 2030; and (3) a multiple-year drought constructed with climate data for 1950–1957 and water demand projected for 2030. The projected drought scenario in 2022 and the historical droughts in 2011 and 1950–1957 represent two different precipitation patterns in the Texas-Gulf river basin.The hydrologic model constructed for the Texas-Gulf river basin covers most of the ERCOT region. The model incorporates climate and water use data that correspond to three drought scenarios, respectively, to estimate evapotranspiration, water yield from watersheds, stream flow and water storage in reservoirs. Using criteria based on observed (< 50% storage) and predicted (< 55% storage) reservoir data, we identified 15 low-storage reservoirs in 2011, 10 in 2022, and 20 in 1956 (the last year of the multiple-year drought). The power plants that are supported by these reservoirs would be potentially at risk of being derated for thermoelectric cooling because of a lack of water supply. These power plants are located mainly in watersheds near and between Houston and Austin, as well as surrounding Dallas.Copyright