Journal of Water Resources Planning and Management

Alternative water management scenarios for a portion of the mainstem Klamath River from Keno, Oregon, to Seiad Valley, California, were evaluated using computer models of water quantity (MODSIM) and quality (HEC-5Q). These models were used to explore the potential for changing system operations to improve summer/fall water quality conditions to benefit declining anadromous fish populations such as steelhead, coho, and fall chinook salmon. By comparing and contrasting several model simulation results, some operational strategies that could improve water quality were determined. Most of the alternatives evaluated decreased water temperature less than 2°C. For some alternatives, dissolved oxygen could be changed as much as 5 mg/L, but was often reduced, rather than increased (or improved). Resource managers need to be made aware that implementation of any strategy to enhance water quality conditions in the Klamath River could produce desirable beneficial results that are both spatially and temporally limited. In addition, undesirable water quality conditions, i.e., higher water temperature or lower dissolved oxygen concentration at other upstream or downstream locations, may also result.

The MODSIM river basin network flow model is extended to directly incorporate constraints on concentrations of conservative water quality constituents. The extended model MODSIMQ is linked with the U.S. Environmental Protection Agency's QUAL2E streamflow water quality model and a model for estimating quality of irrigation return flows. An iterative procedure based on the Frank-Wolfe nonlinear programming algorithm links MODSIMQ and the water quality models to assure convergence to solutions satisfying water right priorities, while attempting to maintain minimum water quality requirements. Irrigation return flows, canal seepage, reservoir seepage, deep percolation, and river depletion due to groundwater pumping are modeled using stream depletion factors from the U.S. Geological Survey. Application of MODSIMQ to the lower Arkansas River basin in Colorado successfully models the complex legal and administrative issues under Colorado water law and the Arkansas River Compact, including the many water exchange mechanisms governing use of off-stream reservoirs in the basin. Model calibration exercises conducted for the case study area confirm that MODSIMQ reasonably reproduces both historical flows and salinity levels for the calibration period. Results from various management scenarios indicate that appropriate conjunctive use of surface and groundwater can simultaneously satisfy water demands for users while enhancing control of salinization.

Watersheds and river basins, referred to as hydrologic units (HUs) are independent of territorial boundaries, and therefore compel the partners representing all the nations or other administrative units within an HU to adopt a holistic approach to resource management. A basic requirement for the holistic approach is a comprehensive hydrologic unit database (HUD) developed under a common framework of classification with a uniform nomenclature and codification system. Currently, the classification of HUs differs from one country to another, as a result of which, the HU boundaries drawn by different HU partners fail to match with each other at the territorial boundaries, causing inconsistency in the HUD. Conventions for uniform classification and codification of HUs are suggested to develop a comprehensive HUD and a framework of concepts and strategies for different levels of HUs. The suggested conventions will help in the development of a global hydrologic unit database and assignment of unique global hydrologic unit codes to each HU identified on the globe. The proposed code will work as a tool to develop a Web site for a global resource information system.

This work explores the sensitivity of optimal remedial design policies and their associated costs to the residual constraint violation, which is the sum of any small violations in constraints that may occur over all points of interest. To evaluate the sensitivity, a genetic algorithm is used to solve two different groundwater remediation design problems: pump-and-treat using granular activated carbon and enhanced in situ bioremediation. The sensitivity to the residual violation is tested given a range of water quality goals and for static and dynamic cases. The range of residual constraint violations tested was small, so that in all cases greater than 98% of the remediation goal was reached. Nevertheless, it was found that the cost sensitivity to these small constraint relaxations was of the same magnitude as the cost sensitivity to changes in the ultimate water quality goal. The greatest sensitivity was seen for the lowest water quality goals. This work indicates that a remediation designer using optimization tools should consider the trade-offs in cost and performance that will occur depending upon one's approach to constraint enforcement.

Groundwater contaminated with non-aqueous-phase liquids (NAPLs) poses human health risks and evaluation of these risks requires estimated groundwater NAPL concentrations. Site NAPL concentrations are typically evaluated using the U.S. Environmental Protection Agency's tiered risk-based corrective action (RBCA) system. Tier 1 uses conservative assumptions and little site-specific data, while tier 2 requires more detailed site-specific data. This paper presents an engineering approach that can be used to predict maximum groundwater NAPL concentrations resulting from NAPL spills. This screening tool was developed by deriving an analytical solution for a partial differential equation describing NAPL transport through the unsaturated zone. Model processes include dissolution, advection, dispersion, sorption, volatilization, and first-order degradation. Results are obtained using two nondimensional parameters and engineering plots for a wide range of conditions. A brief study is provided to demonstrate the application of the model. Because the engineering plots are easy to use and facilitate sensitivity analyses, the model is recommended for screening and RBCA tier 2 analyses.

There is a potential for overinvestment of resources into flow reduction when two cities jointly own a wastewater treatment plant. One city can shift more of the plant's total fixed cost onto the other city if it reduces its share of the wastewater flow into the sanitary system. Each city has an incentive to reduce its flow of groundwater infiltration and storm runoff into its sanitary system as long as the additional repair cost of doing so is less than the reduction in its total variable (treatment) cost plus the reduction in its fixed cost payment.

The development of a probabilistic modeling framework to conduct a priori simulations (forecasts) of the concentration of total ammonia (T-NH₃) and status with respect to toxicity standards and criteria is documented for ammonia-polluted Onondaga Lake, Syracuse, N.Y. This framework utilizes a previously tested mass balance nitrogen model, long-term (27 year) simulations, and the Monte Carlo technique. Variability is accommodated, based on long-term records, for several parameters and forcing conditions, including (1) tributary runoff, (2) in-lake vertical mixing, (3) in-lake rate of nitrification, (4) T-NH₃ concentration in the effluent of a wastewater-treatment plant, (5) lake pH, and (6) lake temperature. The probabilistic framework performed well in simulating the broad variations in T-NH₃ concentrations observed in the lake over a 6-year period (1989–1994). The major sources of the observed interannual variability in the lake's T-NH₃ pool are demonstrated to be natural variations in runoff and the irregular occurrence of “nitrification events” during fall mixing. Predictions are presented in the form of frequency distributions of T-NH₃ concentrations and violations/exceedances of the standard/criterion, consistent with the format of U.S. Environmental Protection Agency toxicity criteria. Application of the probabilistic model is recommended for the total maximum daily load analysis that will establish the T-NH₃ limit for the wastewater-treatment plant effluent.