Journal of Water Resources Planning and Management

This paper addresses the diffuse [non-point source (NPS)] contamination problem by integrating the environmental impact analysis in production practices with the economics of spatial management methods. It employs a combination of geostatistical simulation and unsaturated zone transport modeling to evaluate the effect of spatial variability of soil-related parameters on NPS ground water contamination. Five management scenarios of spatially variable nutrient application are developed and evaluated on the basis of their impact on production agriculture and possible environmental pollution. The scenarios are evaluated considering the spatial variability of residual soil nitrate, yield, and hydraulic conductivity in the field. The process is applied to three realistic cases, differing in the extent of spatial variability, ranging from low to high variability. The modeling results indicate that the identified framework holds promise for evaluating spatial management practices in terms of production as well as protection of the environment. For example, results indicate that variable application of nutrient, based on spatially variable parameters, not only reduced the overapplication but also reduced the overall ground water contamination potential. However, the results suggest that the spatial management system may not necessarily result in a decrease in contamination loading for some fields, particularly those which exhibit a low variability of selected parameters. Furthermore, results indicate the presence of a break-even point between the benefits of spatial management technology and the efforts used in implementing this technology for various degrees of spatial variability. Beyond this point, the excess efforts appear to result in relatively small marginal benefits.

A methodology for finding the optimal layout of a detection system in a municipal water network is formulated and demonstrated. The detection system considered consists of a set of monitoring stations aimed at detecting a random external input of water pollution. The level of service provided to the consumers is defined by the maximum volume of consumed polluted water prior to detection. The methodology involves the establishment of an auxiliary network that represents all possible flow directions for a typical demand cycle, an “all shortest paths” algorithm to identify domains of pollution, and a “set covering” algorithm to optimally allocate the monitoring stations. The algorithm outcome is a minimal set of monitoring stations that satisfies a given level of service. The methodology is demonstrated on a small illustrative case and on a midsize water network.

Delineating the wellhead protection area (WPA) is a vital component in the development of a comprehensive wellhead protection program. WHPA is a series of computer programs developed for the U.S. Environmental Protection Agency to delineate WPAs. In the state of Tennessee, the WPA is delineated using a two-dimensional particle tracking code (GPTRAC) in a leaky-confined aquifer, or a modified containment front tracking code (RESSQC) in an unconfined aquifer. Both WHPA delineation methods require constant values for all model parameters. To overcome the difficulty of estimating values for each input parameter and to provide some measure of the uncertainty in the size and shape of wellhead protection zones, the Environmental Protection Agency WHPA models are integrated into a parallelized Monte Carlo (MC) simulation. The MC-WHPA model is used to compute a discrete two-dimensional cumulative distribution function for a WPA. MC-WHPA uses a parallel virtual machine computing environment developed over a network of computers. The MC-WHPA model is used to delineate the wellhead protection and management zones for two wellfields in western Tennessee.

A hyperbolic model for the simulation of flood wave propagation on initially dry land is presented. The convective inertia terms are neglected in the momentum equations. This assumption allows the use of a finite element scheme with linear shape functions for the free surface elevations and constant unit discharges inside each element. An appropriate use of the explicit and implicit approximation of the spatial derivatives is able to avoid the introduction of internal boundaries in the case of vertical discontinuities of the terrain elevation. This is obtained without losing the desirable features of the system matrix or limiting the maximum Courant number. The efficiency and the reliability of the proposed method are investigated for a flood in the south of Sicily, Italy, where a detailed description of the ground morphology has been proved to be essential for obtaining a good match between measured and computed maximum water depths.

A two-stage methodology for assessment of reliability of water distribution networks recognizing uncertainties in nodal demands, pipe capacity, reservoir/tank levels, and availability of system components is proposed. In the first stage, the probability distribution functions for nodal heads are derived from a linearized hydraulic model on the basis of known probability distribution functions of the nodal demands, pipe roughnesses, and reservoir/tank levels. The effects of nonlinearity in the network hydraulic model are accounted for in this step by partitioning the nodal demands into a number of categories or intervals. The probability of supply failure calculated in this first stage assumes that the system state or configuration is fixed, e.g., certain pipes and pumps are specified as being out of operation; that the pipe capacity varies randomly; and that demands vary around a specified level. The second step involves combining this probability with the probabilities of different system configurations and demand levels to generate the overall reliability measured for the whole system or a particular area of the system.

A land use management plan is currently under consideration in the Turtle Lake area of North Dakota that would help preserve wetlands and allow land development for irrigation. The plan is unique because it includes a wetland component, recognizing the potential benefits to society from preserving wetland acreage. The contingent valuation method is used to estimate wetland benefits from the plan. The wetland benefits from the proposed plan are estimated to range from $832,000 to $2,100,000 annually. Agricultural benefits from the plan are estimated to be about $1,570,000 annually. The response rate to the mail survey used for this analysis was low. Therefore, survey techniques that increase response rates, such as in-person or telephone surveys, are recommended for future wetland valuation studies. Including a wetland component in the Turtle Lake plan substantially increases benefits while adding a relatively small amount to project costs.