PCN BASED METAL PARTITIONING IN URBAN SNOWMELT,RAINFALL/RUNOFF,AND RIVER FLOW SYSTEMS1

ABSTRACT: Drawing an analogy between the popular Soil Conservation Service curve number (SCS‐CN) method based infiltration and metal sorption processes, a new partitioning curve number (PCN) approach is suggested for partitioning of heavy metals into dissolved and particulate bound forms in urban snowmelt, rainfall/runoff, and river flow environments. The parameters, the potential maximum desorption, ψ, and the PCN analogous to the SCS‐CN parameters S and CN, respectively, are introduced. Under the condition of snowmelt, PCN (or ψ) is found to generally rely on temperature, relative humidity, pH, and chloride content; during a rainstorm, ψ is found to depend on the alkalinity and the pH of the rainwater; and in the river flow situation, PCN is found to generally depend on the temperature, pH, and chloride content. The advantage of using PCN instead of the widely used partitioning parameter, K_d, is found to lie in the PCN's efficacy to distinguish the adsorption (or sorption) behavior of metals in the above snowmelt, rainfall/runoff, and river flow situations, analogous to the hydrological behavior of watersheds.     

LOS ALAMOS FOREST FIRE IMPACT MODELING1

ABSTRACT: A controlled burn at Bandelier National Monument got out of control and burned about 43,000 acres (17,400 hectares) near Los Alamos, New Mexico, in May 2000. The wildfire caused dramatic changes in infiltration capacity and wettability of soils in many of the watersheds above Los Alamos National Laboratory (LANL) and destroyed the duff layer, dramatically reducing the interception and infiltration capacity of the formerly forested watersheds. These sudden changes in basin hydrology necessitated a rapid assessment of hydrology and hydraulics for the canyons running through LANL property to evaluate flood risk, plan emergency flood protection measures, and assess potential sediment and actinide transport. This paper presents the results of hydrologic and hydraulic modeling of Los Alamos Canyon following the wildfire. The large scale modeling effort, with over 13,000 cross sections for the hydraulic model (5,000 for Los Alamos Canyon, 8,000 for Guaje Canyon), relied heavily on a geographic information system (GIS) for model input and floodplain delineation. The HEC‐geoRAS model provided good integration between the hydraulic model (HEC‐RAS, Version 3.0.1) and the GIS (ArcView, v. 3.3). These modeling results are being used in drainage master planning efforts at LANL and in the development of sediment transport models using HEC‐6T. Sediment transport modeling results will be used to develop actinide transport models for the canyons at LANL.     

SEDIMENT DISPERSION IN SALMON SPAWNING STREAMS: THE INFLUENCE OF FLOODS AND SALMON REDD CONSTRUCTION1

ABSTRACT: Magnetically tagged particles were used to investigate the effects of sockeye salmon (Oncorhynchus nerka) and floods on the dispersion of coarse bed material in the Stuart‐Takla region, British Columbia, Canada. The dominant annual sediment transporting event in the channels is the snowmelt flood events, with lesser activity usually accomplished during summer floods. Annually in August, the channel bed material is reworked by the Early Stuart sockeye salmon spawning, as the fish excavate the streambed to deposit and bury their eggs. These nesting cavities are called redds. Results from 67 tracer recovery experiments over five years were highly variable, subject to the magnitude of floods and the returning population of salmon. Overall, the depositional pattern from nival flood events usually demonstrated a high degree of clast mobilization, long travel distances (up to 150 m), and mean depths of burial up to 18 cm. Summer flood events showed somewhat lower rates of mobilization, distances of travel, and depths of burial. Although the fish did not move the tracers very far, their effect on the bed was generally quite pervasive ‐ up to 100 percent of the clasts were mobilized, and the depth of burial was considerable (mean burial depths up to 14 cm). The amount of vertical mixing of sediment by salmon was often on the same order of magnitude as flood events. The significant vertical mixing of sediments by the fish has important implications for the mobility of sediment in the stream. Since any armoring layer formed during high flows throughout the year is subject to the bioturbation of salmon, this suggests that the transport threshold in the creeks remains relatively low. Salmon likely play an integral role in the sediment transport dynamics and annual sediment budget of the lower reaches of these creeks.     

HYDRAULIC AND ECONOMIC BENEFITS OF DOWNSPOUT DWERSION1

ABSTRACT: A downspout diversion program in an urban area is evaluated to assess the impacts on sanitary sewer flow volumes and cost effectiveness. Sanitary sewer flows and wastewater treatment cost data are compared for the five years before and 1.25 years after the downspout diversion was completed. In order to establish a cause and effect relationship between flow volumes and downspout diversion, measurements of precipitation, consumption patterns, and system loss (maintenance, fire flows, main ruptures) for the before and after time periods were obtained. The results indicate the downspout diversion contributed to a reduction of over 25 percent in the mean flow volumes within the sanitary sewer collection network during all rainfall events, with flow reductions ranging from 25 percent to 62 percent for rainfall depths between 6 mm (0.25 inches) and 25.4 mm (1.0 inches). Costs incurred for wastewater treatment were also reduced significantly, as overtime for overflow maintenance was eliminated. Downspout diversion is a viable nonstructural alternative for sthrmwater flow reduction in highly urbanized communities which may lack available space for large scale detention facilities.     

A CRITICAL APPROACH TO THE CALIBRATION OF A WATERSHED MODEL1

ABSTRACT: A complex watershed-scale water quality simulation model, the Hydrological Simulation Program-FORTRAN (HSPF) model, was calibrated for a 16 km² catchment. The simulation step size was 0.33 hours with predicted and recorded hydrologic flows compared on an annual and monthly basis during a total calibration period of four years. Unguided numerical optimization when applied alone did not yield a model parameter set with acceptable predictive capability; instead, it was necessary to apply a critical process that included sensitivity analysis, numerical optimization, and testing of derived model parameter sets to evaluate their performance for periods other than those for which they were determined. Using this critical calibration process, the model was proven to have significant predictive capability. Numerical optimization is an aid for model calibration, but it must not be used blindly.     

POTENTIAL IMPACT OF EARTHEN WASTE STORAGE STRUCTURES ON WATER RESOURCES IN IOWA1

ABSTRACT: Earthen waste storage structures (EWSS) associated with large confined (concentrated) animal feeding operations (CAFOs) were evaluated for their potential to impact water resources in Iowa. A representative sample of 34 EWSS from a digital database of 439 lagoons and basins permitted between 1987 and 1994 was analyzed. Eighteen percent (6 of 34) directly overlie alluvial aquifers that are used widely for potable water supply. Ninety‐four percent (29 of 31) were constructed below the water table based on EWSS depth data. At 65 percent of EWSS (22 of 34), 50 percent or more of the manure‐spreading area (MSA) has a water‐table depth less than 1.6 m. At 74 percent of EWSS (25 of 34), 90 percent or more of the MSA contains soil with vertical K exceeding 25.4 mm/hr. Seventy‐one percent (24 of 34) occur where 10 percent or less of the MSA is frequently flooded. No significant differences were found among leakage rates due to aquifer vulnerability class or surficial material. However, at least 50 percent of EWSS (14 of 28) leaked at rates significantly greater than 1.6 mm/d under the new construction standard. The estimated 5,000 unregulated CAFOs may have a greater potential to impact water resources in Iowa.     

NWSRFS CALIBRATION PARAMETER SELECTION AND GEOLOGIC REASONING: PACIFIC NORTHWEST CASES1

ABSTRACT: The National Weather Service River Forecast System (NWSRFS) is the new hydrologic prediction model for the National Weather Service (NWS) and provides guidance to meteorologists who issue NWS Flood Warnings to the public. The primary submodel within NWSRFS is the Sacramento Soil Moisture Accounting (SAC-SMA) model, which predicts surface runoff as a function of meteorological, geological, and soil data calibrated over a watershed. The research presented here focuses on a different approach to NWSRFS calibrations: greater utilization of geologic and soil data, in order to give the model better predictive capability. Geologic understanding can create better insights for the initial estimation and subsequent adjustment of SAC-SMA parameters. Fifteen calibrated Pacific Northwest drainages reveal a variety of hydrogeologic responses. For example, results for the Mount Rainier drainages show the complex interaction between active glaciers, impermeable volcanic surfaces, and glacial sedimentary valleys. Unweathered volcanic terrains show flashy peak flows, fast flow recessions, and low baseflow. Sedimentary terrains display subdued peak flows, slow flow recessions, and higher baseflow. Operational implementation of these calibrations at the NWS's Northwest River Forecast Center has yielded more accurate predictive results since 1995. NWS hydrologic forecasters nationwide could benefit from using drainage basin geologic characteristics in understanding and improving model calibrations and real time forecasts.     

ENERGY BALANCE OF A CORN RESIDUE-COVERED FIELD DURING SNOWMELT1

ABSTRACT: Transport of agricultural chemicals in runoff and recharge waters from snowmelt and soil thawing may represent a significant event in terms of annual contaminant loadings in temperate regions. Improved understanding of the melt dynamics of shallow snowpacks is necessary to fully assess the implications for water quality. The objective of this study was to measure the energy balance components of a corn (Zea mays L.) stubble field during the melting of its snowcover. Net radiation (Rn), soil (G), sensible (H), and latent (Q) heat fluxes were measured in a field near Ames, Iowa, during the winter of 1994–1995. Energy consumed by melting including change in energy storage of the snowpack was determined as the residual of the measured energy balance. There was continuous snowcover at the field site for 71 days (maximum depth = 222 mm) followed by an open period of 11 days before additional snowfall and a second melt period. The net radiation and snow melt/energy storage change (5) terms dominated the energy balance during both measurement intervals. Peak daily sensible and latent heat fluxes were below 100 W m^?2 on all days except the last day of the second melt period. There was good agreement between predicted and measured values of H and Q during the melting of an aged snow layer but poorer agreement during the melt of fresh snow. Both snowpacks melted rapidly and coincident changes in soil moisture storage were observed. Improved estimates of Q and H, especially for partially open surfaces, will require better characterization of the surface aerodynamic properties and spatially-representative surface temperature measurements.     

INTERPRETATION OF THE DUAL PROGRAM FOR OPTIMAL GROUNDWATER HYDRAULIC CONTROL1

ABSTRACT: Optimization formulations for hydraulic control that take the form of linear programs possess a corresponding dual linear program. The economic and physical interpretations of the dual linear program are examined for formulations in which hydraulic head in groundwater systems is constiained. In each case it is shown that the dual linear program has a physically meaningful interpretation. For a hydraulic gradient control formulation used for remedial analysis it is shown that the dual variable can be interpreted as the remedial benefit due to each gradient control constraint. The dual linear program maximizes the remedial benefit. The value of the dual variable can be used to compute such useful properties as the total remedial benefit of pumping at a specific location. For a formulation that optimizes aquifer yield while constraining drawdown the dual variable can be used to measure the total cost of drawdown capacity consumption per unit of pumping at a specific location. The dual program minimizes the cost of drawdown capacity consumption. By examining the meaning of the dual linear program an alternate statement of the problem under study is revealed. Quantities arising from the dual program add to the value of the optimization approach. Significant new information can be derived from existing linear optimization formulations with minimal additional computational effort.     

GROUND WATER MANAGEMENT OPTIMIZATION USING GENETIC ALGORITHMS AND SIMULATED ANNEALING: FORMULATION AND COMPARISON1

ABSTRACT: Genetic algorithms (GA) and simulated annealing (SA), two global search techniques, are coupled with MODFLOW, a commonly used groundwater flow simulation code, for optimal management of ground water resources under general conditions. The coupled simulation-optimization models allow for multiple management periods in which optimal pumping rates vary with time to reflect the changing flow conditions. The objective functions of the management models are of a very general nature, incorporating multiple cost terms such as the drilling cost, the installation cost, and the pumping cost. The models are first applied to two-dimensional maximum yield and minimum cost water supply problems with a single management period, and then to a multiple management period problem. The strengths and limitations of the GA and SA based models are evaluated by comparing the results with those obtained using linear programming, nonlinear programming, and differential dynamic programming. For the three example problems examined in this study, the GA and SA based models yield nearly identical or better solutions than the various programming methods. While SA tends to outperform GA in terms of the number of forward simulations needed, it uses more empirical control parameters which have significant impact on solution efficiency but are difficult to determine.