Search

Recently, increasing nutrient (i.e., nitrogen and phosphorus) concentrations have been observed in the surface water of many countries and this nonpoint source (NPS) pollution has become an important factor in the deterioration of water quality in the upper reach of the Yangtze River Basin. In this paper, the NPS pollution loads in the upper reach of Yangtze River Basin in the year 2000 were estimated using export coefficient model and remote sensing techniques. The spatial distributions of the NPS loads within the watershed were then displayed using geographical information system. Results indicated that the total nitrogen load was 1.947 X [10.sup.6] t and the total phosphorus load was 8.364 x [10.sup.4] t. Important source areas for the nutrients were croplands in the Jinsha R. and Jialing R. watershed, as well as the Chongqing municipality. CE Database subject headings: River basins; Nonpoint pollution; Water pollution; China; Coefficients; Remote sensing; Geographic information systems.

A series of uncertainty analysis methods was applied to investigate the propagation of parameter uncertainty within a coupled model system and to evaluate the effects of uncertainty on model outputs and decision-making processes. First-order error analysis showed that among a large number of model parameters, only a few significantly affected the variation in pollutant loads at the watershed outlets and concentrations in the receiving body of water, and the variation in pollutant concentrations is greater than the variation in pollutant loads. The uncertainty analysis regarding the loads and concentrations showed different patterns, underscoring the importance of a complete uncertainty analysis and the need for an explicit quantification of the errors associated with the predicted loads. Monte Carlo simulation showed that best management practice scenarios considered as a safe scheme based on a deterministic model could actually lead to a significant risk of violating the water quality standards when model uncertainty is considered. With a modeling framework that considers uncertainty, feasible alternatives can be evaluated and ranked based on their risks of exceeding the target water quality criteria. DOI: 10.1061/(ASCE)0733-9496(2006)132:5(351) CE Database subject headings: Errors; Simulation; Watershed management; Water quality; Nonpoint pollution.

Nonpoint source pollution control requires the implementation of best management practices (BMPs) at various locations in a watershed. One important aspect of the watershed strategy is to find the optimal placement and design of BMPs so that their combined effect is most cost-effective. An innovative method is presented for optimizing the placement and configurations of BMPs at the watershed scale. Heuristic optimization techniques are coupled with a watershed model, which is the agricultural Nonpoint Source Pollution model (AnnAGNPS) in this case, and BMP simulation module to find a least cost set of solutions that meet the pollutant load reduction requirements. An impoundment module imbedded in AnnAGNPS, and modified to address the sediment accumulation and resuspension effect, is used to provide the means of evaluating the long-term performance of detention ponds. A scatter search algorithm is applied to finding the least cost solution. The optimization framework developed herein provides a tool for stormwater management practitioners to examine and analyze the treatment efficiencies of stormwater control alternatives and to determine a robust and cost-effective design of stormwater treatment systems. CE Database subject headings: Stormwater management; Optimization; Detention basins; Configuration; Best management practice; Simulation models; Nonpoint pollution; Water pollution; Watershed management.

There are significant uncertainties associated with certain aspects of the total maximum daily load (TMDL) estimation. Selection of the 'margin of safety (MOS)' term is typically made by subjectively assigning to it a small percentage (5-10%) of the TMDL load. To introduce some objectivity into the MOS estimation, the first-order error analysis (FOEA) was utilized to quantify the MOS term in the TMDL formulation. A case study, which was based on a previous study entitled 'Nitrate TMDL Development for Muddy Creek/Dry River, Virginia,' is presented in this paper. Besides computational efficiency, one of the major advantages of FOEA is its capability of determining the relative importance of the various parameters that contribute to the overall variance of the model output. Precipitation was found by far to be the most dominant source of uncertainty. Furthermore, a relationship was established to link the pollutant loads with the FOEA output concentrations. The results from testing different TMDL allocation scenarios demonstrate that with the increase of relative percentage of nonpoint sources load reduction in the total load reduction, the portion needed to be reserved for MOS increases as well. The MOS term can be related to the variability in rainfall and therefore would be different for different locations in the country. In summary, as a practical, less subjective and reliable approach to TMDL uncertainty analysis, the use of the FOEA is considered as a viable alternative to the current simple explicit and implicit methods in estimating the MOS term for TMDL calculations. CE Database subject headings: Water quality: Watershed management Models; Nutrient loads; Nonpoint pollution; Water resources management; Error analysis; Computation; Uncertainty analysis.

An analysis of the impact of total maximum daily load (TMDL) allocations on the potential leaching of nitrates to groundwater in the Muddy Creek/Dry River watershed of Virginia is presented. The Muddy Creek/Dry River watershed has experienced nitrate impairments to both surface water and groundwater. Using the Nitrate Leaching and Economic Analysis Package, this work estimates the change in the potential mass of nitrate leaching into the subsurface, given a range of feasible load allocations developed in the nitrate TMDL of this watershed. Modeling analysis suggests that TMDL allocations would reduce the leaching mass and concentrations by 8.5% on average in the Muddy Creek watershed. Furthermore, while feasible load allocations performed similarly with respect to surface water reductions, the selected TMDL allocation scenario provides only half the leaching reduction of other feasible allocation scenarios. While expanding the scope of this TMDL to also protect the subsurface water resources would have been a reasonable and prudent management approach, the expanded complexity was impossible within the short completion schedule allowed for TMDLs. DOI: 10.1061/(ASCE)0733-9496(2002)128:4(262) CE Database keywords: Nitrates; Watershed management; Leaching.

The paper presents results of field tests, conducted in Taiwan and Virginia, of the pollutant removal efficiencies of grassed swales. Swales are a low-cost storm-water best management practice (BMP) that have been reported as a cost-effective method for controlling runoff pollution from land surfaces, especially highways and agricultural lands. The Virginia experiments tested a highway median swale, while the Taiwan experiments were conducted on an agricultural test farm. Average pollutant removal efficiencies reported for the test swales vary from 14 to 99% for total suspended solids (TSS), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP). The wide range of performance results indicates the importance of such design parameters as length, longitudinal slope, and the presence of check dams. Minimum design guidelines for use of swales as a BMP are suggested.