Models,Assumptions, and Stakeholders: Planning for Water Supply Variability in the Colorado River Basin1

Abstract: Declining reservoir storage has raised the specter of the first water shortage on the Lower Colorado River since the completion of Glen Canyon and Hoover Dams. This focusing event spurred modeling efforts to frame alternatives for managing the reservoir system during prolonged droughts. This paper addresses the management challenges that arise when using modeling tools to manage water scarcity under variable hydroclimatology, shifting use patterns, and institutional complexity. Assumptions specified in modeling simulations are an integral feature of public processes. The policymaking and management implications of assumptions are examined by analyzing four interacting sources of physical and institutional uncertainty: inflow (runoff), depletion (water use), operating rules, and initial reservoir conditions. A review of planning documents and model reports generated during two recent processes to plan for surplus and shortage in the Colorado River demonstrates that modeling tools become useful to stakeholders by clarifying the impacts of modeling assumptions at several temporal and spatial scales. A high reservoir storage‐to‐runoff ratio elevates the importance of assumptions regarding initial reservoir conditions over the three‐year outlook used to assess the likelihood of reaching surplus and shortage triggers. An ensemble of initial condition predictions can provide more robust initial conditions estimates. This paper concludes that water managers require model outputs that encompass a full range of future potential outcomes, including best and worst cases. Further research into methods of representing and communicating about hydrologic and institutional uncertainty in model outputs will help water managers and other stakeholders to assess tradeoffs when planning for water supply variability.     

QUALITY STUDY OF GRAYWATER TREATMENT SYSTEMS1

ABSTRACT: A residential single family dwelling was retrofitted to recycle graywater for landscape irrigation and toilet flushing. The objective of this study was to determine improvements in graywater quality by evaluating five simple graywater treatment systems that were easily adapted to the household plumbing. The treatment systems consisted of (1) water hyacinths and sand filtration, (2) water hyacinths, copper ion disinfection, and sand filtration, (3) copper ion disinfection and sand filtration, (4) copper/silver ion disinfection and sand filtration, and (5) 20–μm cartridge filtration. Water quality parameters measured were fecal and total coliform indicator bacteria, nitrates, suspended solids, and turbidity. Reductions in bacterial concentration, suspended solids and turbidity were achieved by all systems tested. Treatment reduced nitrate concentrations to an average of 2.6 mg/liter. Reductions in suspended solids, and turbidity were influenced more by the quality of the graywater entering the treatment system than the efficiency of the systems themselves. The water hyacinths and sand filtration system provided the best graywater quality in terms of the concentrations of fecal indicator bacteria. The system providing the best water quality in regard to average suspended solids after treatment was the water hyacinths, copper ion, and sand filtration system, and the best average turbidity was achieved by the copper/silver ion generating unit with sand filtration. All systems were capable of significant reductions in fecal indicator bacteria, suspended solids, and turbidity; however, additional treatment or disinfection would be necessary to further reduce the level of coliform and fecal coliform bacteria to achieve regulatory standards in the State of Arizona.     

RURAL RESIDENTIAL WATER DEMAND: AN ECONOMETRIC AND SIMULATION ANALYSIS1

ABSTRACT: This study proposes that demand management through pricing policies can be used in conjunction with supply management to solve water supply problems. Economic principles are shown to apply to rural residential water use. A demand function for water was developed based on cross-sectional water use data collected in Kentucky. Price was found to be a significant determinant of the quantity of water demanded. A constant price elasticity of -0.92 was found. The demand function was used in a simulation analysis to determine reservoir capacity needed to supply water needs of a rural community. The simulation revealed that price can significantly affect required reservoir storage.     

A Retrospective Look at the Water Resource Management Policies in Nassau County,Long Island,New York1

Abstract: The residents of Nassau County Long Island, New York receive all of their potable drinking water from the Upper Glacial, Jameco/Magothy (Magothy), North Shore, and Lloyd aquifers. As the population of Nassau County grew from 1930 to 1970, the demand on the ground‐water resources also grew. However, no one was looking at the potential impact of withdrawing up to 180 mgd (7.9 m³/s) by over 50 independent water purveyors. Some coastal community wells on the north and south shores of Nassau County were being impacted by saltwater intrusion. The New York State Legislature formed a commission to look into the water resources in 1972. The commission projected extensive population growth and a corresponding increase in pumping resulting in a projected 93.5 to 123 mgd (4.1 to 5.5 m³/s) deficit by 2000. In 1986, the New York Legislature passed legislation to strengthen the well permit program and also establish a moratorium on new withdrawals from the Lloyd aquifer to protect the coastal community’s only remaining supply of drinking water. Over 30 years has passed since the New York Legislature made these population and pumping projections and it is time to take a look at the accuracy of the projections that led to the moratorium. United States Census data shows that the population of Nassau County did not increase but decreased from 1970 to 2000. Records show that pumping in Nassau County was relatively stable fluctuating between 170 and 200 mgd (7.5 to 8.8 m³/s) from 1970 to 2004, well below the projection of 242 to 321 mgd (10.6 to 14.1 m³/s). Therefore, the population and water demand never grew to projected values and the projected threat to the coastal communities has diminished. With a stable population and water demand, its time to take a fresh look at proactive ground‐water resource management in Nassau County. One example of proactive ground‐water management that is being considered in New Jersey where conditions are similar uses a ground‐water flow model to balance ground water withdrawals, an interconnection model to match supply with demand using available interconnections, and a hydraulic model to balance flow in water mains. New Jersey also conducted an interconnection study to look into how systems with excess capacity could be used to balance withdrawals in stressed aquifer areas with withdrawals in unstressed areas. Using these proactive ground‐water management tools, ground‐water extraction could be balanced across Nassau County to mitigate potential impacts from saltwater intrusion and provide most water purveyors with a redundant supply that could be used during water emergencies.     

BIODEGRADATION OF DISINFECTION BYPRODUCTS AS A POTENTIAL REMOVAL PROCESS DURING AQUIFER STORAGE RECOVERY1

ABSTRACT: The biodegradation potential of two drinking water disinfection byproducts was investigated using aquifer materials obtained from approximately 100 and 200 meters below land surface in an aerobic aquifer system undergoing aquifer storage recovery of treated surface water. No significant biodegradation of a model trihalomethane compound, chloroform, was observed in aquifer microcosms under aerobic or anaerobic conditions. In contrast, between 16 and 27 percent mineralization of a radiolabeled model haloacetic acid compound, chloroacetic acid, was observed. These results indicate that although the potential for biodegradation of chloroacetic acid exists in deep aquifer systems, chloroform entrained within these aquifers or formed in situ will tend to persist. These results have important implications for water managers planning to meet anticipated lowered permissible levels of trihalomethanes in drinking water.     

COOPERATIVE MODELING: BUILDING BRIDGES BETWEEN SCIENCE AND THE PUBLIC1

As freshwater resources become more scarce and water management becomes more contentious, new planning approaches are essential to maintain ecologic, economic, and social stability. One technique involves cooperative modeling in which scientists and stakeholders work together to develop a computer simulation model to assist in planning efforts. In the Middle Rio Grande region of New Mexico, where water management is hotly debated, a stakeholder team used a system dynamics approach to create a computer simulation model to facilitate producing a regional plan. While the model itself continues to be valuable, the process for creating the model was also valuable in helping stakeholders jointly develop understanding of and approaches to addressing complex issues. In this paper, the authors document results from post‐project interviews designed to identify strengths and weaknesses of cooperative modeling; to determine if and how the model facilitated the planning process; and to solicit advice for others considering model aided planning. Modeling team members revealed that cooperative modeling did facilitate water planning. Interviewees suggested that other groups try to reach consensus on a guiding vision or philosophy for their project and recognize that cooperative modeling is time intensive. The authors also note that using cooperative modeling as a tool to build bridges between science and the public requires consistent communication about both the process and the product.     

Modeling Megacity Drinking Water Security under a DSS Framework in a Tidal River at the North Pearl River Delta,China

A modeling study was undertaken under a decision support system (DSS) for drinking water security in the Foshan section of the Beijiang River, a typical tidal river in the North Pearl River Delta. The DSS included a database layer, application support layer, and an application layer. As an integral part of the DSS application support layer, an integrated modeling system was developed to simulate hydrodynamics. The balance of dissolved oxygen and toxicants was based on an environmental fluid dynamics code and a water quality analysis simulation program (WASP) modeling framework. Model calibration and validation was undertaken using monitoring data in normal hydrological conditions. Four scenarios for the environmental management of water, including current water temp‐spatial feature analysis, control of pollution sources, and emergency response, were designed and analyzed in the DSS. The results indicated that the tide downstream has a distinct influence on hydrodynamics and pollutant diffusion, and the DSS could be used to design effective schemes to reduce pollutant discharges and provide emergency responses for ensuring drinking water security.     

WATER RESOURCES MODELING AND OPTIMIZATION BASED ON CONSERVATION AND FLOODING POOLS1

ABSTRACT: A new and practical concept in water resources modeling and optimization is introduced. Instead of unrealistically assuming a multipurpose reservoir to be composed of a single lumped pool of water, it is treated as two different pools namely conservation and flood pools. Based on this treatment, the optimization problem is stated using the concepts of Lagrange multipliers and parameter optimization. The optimization problem consists of the material balance equation, the constraints on control and state variables and the objective function.     

Assessment of Residential Rain Barrel Water Quality and Use in Cincinnati,Ohio1

The collection, storage, and reuse of rainwater collected in rain barrels from urban rooftop areas assists municipalities in achieving stormwater management objectives and in some areas also serves as an adjunct resource for domestic water supplies. In this study, rainwater reuse and levels of select microbial indicators were monitored for six residential rain barrels located in the Shepherd Creek watershed of Cincinnati, Ohio. Water from rain barrels typically had poor microbial quality and was used for watering indoor and outdoor plants. Rain barrel water chemistry was slightly acidic, exhibited wide ranges in conductivity, turbidity, and total organic carbon (TOC) concentrations and gave no evidence of the presence of cyanobacterial microcystin toxins. Selected microbial water‐quality indicators indicated that counts of total coliform and enterococci were consistently above U.S. Environmental Protection Agency standards for secondary recreational contact water‐quality standards. Residential rain barrels can provide water appropriate for low‐contact reuses (such as plant watering), although there may be transient periods of high levels of indicator bacteria in the collected water.     

FISH AND WILDLIFE ENHANCEMENT THROUGH WATER RESOURCES DEVELOPMENT1

.Fish and wildlife enhancement through water resources development implies fish and wildlife will be enhanced or benefit directly from such development. As a matter of practicality, the opposite may be the case in that wildlife lands of prime value and stream fisheries are often lost or severely altered as a result of reservoir construction or stream channelization. Additionally, estuarine fish and wildlife can also suffer from water resources development due to reductions in volume of fresh waters reaching the estuaries and adjacent marshes. In some instances waterfowl habitat can be created by reservoir construction and with good planning waterfowl habitat and use may be enhanced. To offset losses of thousands of acres of wildlife habitat when a river system is to be totally harnessed, planners could set aside sufficiently large natural areas dedicated for use by wildlife. This, however, would be replacement rather than enhancement. Reservoir fisheries can be enhanced with good planning to include timber clearing, shoreline clearing, boat road clearing, variable level drawoff devices and tailrace escapement channels. To sum up, it is possible for some species offish and wildlife to be enhanced through water resources development but only at the expense of others, and then only through careful and integrated planning.     

Federal Decentralization and Adaptive Management of Water Resources: Reservoir Reallocation by the U.S. Army Corps of Engineers

Reservoir operations must respond to changing conditions, such as climate, water demand, regulations, and sedimentation. The U.S. Army Corps of Engineers (Corps) can reallocate reservoir storage to respond to such changes. We assembled and analyzed a database of reservoir reallocations implemented and proposed by the Corps. While only a small portion of total reservoir storage nationwide has been reallocated, there are substantial differences in reallocation frequency and magnitude across the nation: some Corps Districts and Divisions use reallocation while others do not, relying more on discretion and small‐scale adaptation of operations. This difference illustrates how water resource agencies like the Corps decentralize management decisions to allow responding to disparate conditions. Decentralized decision‐making provides a responsive approach to water management, while centralized and hierarchical decision‐making is a slower, more deliberative approach. Decentralized decision‐making may lead to the accumulation of short‐term, local decisions over time to the point that the system is managed differently than anticipated. Reallocation, which is a form of planned adaptive management, can be accommodating of multiple competing demands and different stakeholders, yet expensive and less temporally responsive. The challenge for any large water resource management agency is to balance between local‐level, responsive discretion vs. centralized, planned decision‐making.     

PLANNING LEVEL ESTIMATES OF THE VALUE OF RESERVOIRS FOR WATER SUPPLY AND FLOW AUGMENTATION IN NEW HAMPSHIRE1

: In general, the choice among reservoirs for water supply or flow augmentation is a multiobjective problem. Choices are based in part on the yield available from water supply reservoirs or, in the case of flow augmentation reservoirs, on the increase in low flows at downstream locations. Detailed estimates of these effects may be too costly for basin planning purposes. Thus this paper presents methods for rapid estimation of those quantities for New Hampshire. For water supply reservoirs, a composite empirical relation between Y95 (the draft available 95 percent of the time) and storage ratio, S*, is developed from previous studies in the region. For flow augmentation reservoirs, empirical relations between S* and degree of regulation, R*, are applied to each upstream regulating reservoir. Values of regulation arc then summed and divided by the mean flow at the downstream reach of interest. This parameter, (ΓR)*, is then related to increase in flow available 95 percent of the time by an empirical relation.     

Does More Storage Give California More Water?

Increasing reservoir storage is commonly proposed to mitigate increasing water demand and provide drought reserves, especially in semiarid regions such as California. This paper examines the value of expanding surface reservoir capacity in California using hydroeconomic modeling for historical conditions, a future warm‐dry climate, and California's recently adopted policy to end groundwater overdraft. Results show expanding surface storage capacity rarely provides sizable economic value in most of California. On average, expanding facilities north of California's Delta provides some benefit in 92% of 82 years modeled under historical conditions and in 61% of years modeled in a warm‐dry climate. South of California's Delta, expanding storage capacity provides no benefits in 14% of years modeled under historical conditions and 99% of years modeled with a warm‐dry climate. Results vary across facilities between and within regions. The limited benefit of surface storage capacity expansion to statewide water supply should be considered in planning California's water infrastructure.     

HERBICIDES AND TRANSFORMATION PRODUCTS IN SURFACE WATERS OF THE MIDWESTERN UNITED STATES1

ABSTRACT: Most herbicides applied to crops are adsorbed by plants or transformed (degraded) in the soil, but small fractions are lost from fields and either move to streams in overland runoff, near surface flow, or subsurface drains, or they infiltrate slowly to ground water. Herbicide transformation products (TPs) can be more or less mobile and more or less toxic in the environment than their source herbicides. To obtain information on the concentrations of selected herbicides and TPs in surface waters of the Midwestern United States, 151 water samples were collected from 71 streams and five reservoir outflows in 1998. These samples were analyzed for 13 herbicides and 10 herbicide TPs. Herbicide TPs were found to occur as frequently or more frequently than source herbicides and at concentrations that were often larger than their source herbicides. Most samples contained a mixture of more than 10 different herbicides or TPs. The ratios of TPs to herbicide concentrations can be used to determine the source of herbicides in streams. Results of a two‐component mixing model suggest that on average 90 percent or more of the herbicide mass in Midwestern streams during early summer runoff events originates from the runoff and 10 percent or less comes from increased ground water discharge.     

Potential Impacts of Climate Change on the Reliability of Water and Hydropower Supply from a Multipurpose Dam in South Korea

Future climate change is a source of growing concerns for the supply of energy and resources, and it may have significant impacts on industry and the economy. Major effects are likely to arise from changes to the freshwater resources system, due to the connection of energy generation to these water systems. Using future climate data downscaled by a stochastic weather generator, this study investigates the potential impacts of climate change on long‐term reservoir operations at the Chungju multipurpose dam in South Korea, specifically considering the reliability of the supply of water and hydropower. A reservoir model, Hydrologic Engineering Center‐Reservoir System Simulation (HEC‐ResSim), was used to simulate the ability of the dam to supply water and hydropower under different conditions. The hydrologic model Soil and Water Assessment Tool was used to determine the HEC‐ResSim boundary conditions, including daily dam inflow from the 6,642 km² watershed into the 2.75 Gm³ capacity reservoir. Projections of the future climate indicate that temperature and precipitation during 2070‐2099 (2080s) show an increase of +4.1°C and 19.4%, respectively, based on the baseline (1990‐2009). The results from the models suggest that, in the 2080s, the average annual water supply and hydropower production would change by +19.8 to +56.5% and by +33.9 to 92.3%, respectively. Model simulations suggest that under the new climatic conditions, the reliability of water and hydropower supply would be generally improved, as a consequence of increased dam inflow.     

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.     

消毒技术去除饮用水中病原微生物的研究进展

饮用水中存在着不同种类的病原微生物，这些病原微生物给人体健康带来危害。本文简要介绍常规消毒技术去除饮用水中病原微生物的研究现状；常规消毒剂仍然是现代饮用水处理工艺使用的主要消毒剂；近些年来，对常规消毒剂联合消毒的协同作用和联合消毒剂的概念提出了探讨，认为联合消毒荆是今后饮用水去除病原微生物的发展趋势；膜技术这种物理消毒技术，由于其高效性而得到广泛关注，膜消毒去除病原微生物也成为当今消毒技术研究的热点。     

EVAPOTRANSPIRATION AND SOIL MOISTURE DYNAMICS ON A SEMIARID PONDEROSA PINE HILLSLOPE1

ABSTRACT: Detailed measurements of soil moisture and ET in semiarid forest environments have not been widely reported in the literature. In this study, soil moisture and water balance components were measured over a four‐year period on a semiarid ponderosa pine hillslope, with evapotranspiration (ET) determined as the residual of measured precipitation, runoff, and change in soil moisture storage. ET accounts for approximately 95 percent of the water budget and has a distinctly bimodal annual pattern, with peaks occurring after spring snowmelt and during the late summer monsoon season, periods that coincide with high soil moisture. Weekly growing season ET rates determined by the hillslope water balance are found to be invariably below calculated potential rates. Normalized ET rates are linearly correlated (r²= 0.62) with soil moisture; therefore, a simple linear relation is proposed. Growing season soil moisture dynamics were modeled based on this relation. Results are in fair agreement (r²= 0.63) with the observed soil moisture data over the four growing seasons; however, for two dry summers with little surface runoff, much better results (r² > 0.90) were obtained.     

Sustainable Rainwater Catchment Systems for Micronesian Atoll Communities

Atoll island communities rely on rainwater catchment systems (RWCS) as a primary method of storing freshwater. However, stored freshwater can be depleted during times of drought, requiring importation of water to sustain community living. To maintain adequate water supply under future climatic conditions, the functioning of RWCS for atoll communities must be analyzed and optimal designs must be adopted. In this study, a quantitative analysis of stored daily water volumes is provided for atoll islands within the Federated States of Micronesia (FSM), with Nikahlap Island, Pakein Atoll, and a generic island in western FSM used as representative cases. Using a daily water balance model for the RWCS, baseline conditions are simulated for the 1997‐1999 time period, during which an intense El Niño‐induced drought occurred, and a sensitivity analysis is performed to quantify the influence of RWCS features on water system outputs, whereupon an optimal RWCS design using existing infrastructure is analyzed. Results indicate the strong influence of catchment area, system efficiency, and storage capacity on water volumes and the depletion of water during dry seasons and drought periods using current RWCS infrastructure. Adequate storage can be maintained during a major drought if unused RWCS features are employed and if minimal rationing is adopted. Study results provide water resource managers and government officials with valuable data for consideration in water security measures.     

IMPLICATIONS OF ON‐GROUND NITROGEN LOADING AND SOIL TRANSFORMATIONS ON GROUND WATER QUALITY MANAGEMENT1

ABSTRACT: This paper presents a modeling approach based on a geographic information system (GIS) to estimate the variability of on‐ground nitrogen loading and the corresponding nitrate leaching to ground water. The methodology integrates all point and nonpoint sources of nitrogen, the national land cover database, soil nitrogen transformations, and the uncertainty of key soil and land use‐related parameters to predict the nitrate mass leaching to ground water. The analysis considered 21 different land use classes with information derived from nitrogen sources such as fertilizer and dairy manure applications, dairy lagoons, septic systems, and dry and wet depositions. Simulations were performed at a temporal resolution of one month to capture seasonal trends. The model was applied to a large aquifer of 376 square miles in Washington State that serves more than 100,000 residents with drinking water. The results showed that dairy manure is the main source of nitrogen in the area followed by fertilizers. It was also seen that nitrate leaching is controlled by the recharge rate, and there can be a substantial buildup of soil nitrogen over long periods of time. Uncertainty analysis showed that denitrification rate is the most influential parameter on nitrate leaching. The results showed that combining management alternatives is a successful strategy, especially with the use of nitrification inhibitors. Also, change in the land use pattern has a noticeable impact on nitrate leaching.