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Geology topics

A. L. Ishii

Publications and source records attributed to A. L. Ishii.

5 recordsLinked to original sources
USGS1998

Operational modeling system with dynamic-wave routing

A near real-time streamflow-simulation system utilizing continuous-simulation rainfall-runoff generation with dynamic-wave routing is being developed by the U.S. Geological Survey in cooperation with the Du Page County Department of Environmental Concerns for a 24-kilometer reach of Salt Creek in Du Page County, Illinois. This system is needed in order to more effectively manage the Elmhurst Quarry Flood Control Facility, an off-line stormwater diversion reservoir located along Salt Creek. Near real time simulation capabilities will enable the testing and evaluation of potential rainfall, diversion, and return-flow scenarios on water-surface elevations along Salt Creek before implementing diversions or return-flows. The climatological inputs for the continuous-simulation rainfall-runoff model, Hydrologic Simulation Program - FORTRAN (HSPF) are obtained by Internet access and from a network of radio-telemetered precipitation gages reporting to a base-station computer. The unit area runoff time series generated from HSPF are the input for the dynamic-wave routing model. Full Equations (FEQ). The Generation and Analysis of Model Simulation Scenarios (GENSCN) interface is used as a pre- and post-processor for managing input data and displaying and managing simulation results. The GENSCN interface includes a variety of graphical and analytical tools for evaluation and quick visualization of the results of operational scenario simulations and thereby makes it possible to obtain the full benefit of the fully distributed dynamic routing results.

Conference Paper↗
USGS1989

Diffusion and consumption of methane in an unsaturated zone in north-central Illinois, U.S.A.

The distribution of CH 4 in unsaturated glacial and eolian deposits adjacent to buried low-level radioactive waste was measured, and movement of the gas from the waste source was simulated using a two-dimensional finite-difference model for gas diffusion in the unsaturated zone. Mean P CH 4 was greatest (1.56 Pa) in a pebbly-sand deposit 11.6 m below the land surface and 12 m from the waste, and generally decreased with increased horizontal distance from the waste. Mean P CH 4 was least (0.07 Pa) at depth of 1.8 m below land surface, regardless of distance from the waste. P CH 4 at the land surface averaged 0.17 Pa. Depth versus P CH 4 profiles suggest consumption of both waste-produced and atmospheric CH 4 in the upper unsaturated zone, presumably by methanotrophic microorganisms. Numerical simulations of methane movement support the consumption observation; inclusion of a term in the model for consumption of CH 4 in the upper 2 m of the unsaturated zone resulted in simulated P CH 4 within 30% of mean P CH 4 at eleven of thirteen sampling locations. A similar fit of the data was obtained for only four locations when consumption was not considered.

Illinois↗
USGS1989

A numerical solution for the diffusion equation in hydrogeologic systems

The documentation of a computer code for the numerical solution of the linear diffusion equation in one or two dimensions in Cartesian or cylindrical coordinates is presented. Applications of the program include molecular diffusion, heat conduction, and fluid flow in confined systems. The flow media may be anisotropic and heterogeneous. The model is formulated by replacing the continuous linear diffusion equation by discrete finite-difference approximations at each node in a block-centered grid. The resulting matrix equation is solved by the method of preconditioned conjugate gradients. The conjugate gradient method does not require the estimation of iteration parameters and is guaranteed convergent in the absence of rounding error. The matrixes are preconditioned to decrease the steps to convergence. The model allows the specification of any number of boundary conditions for any number of stress periods, and the output of a summary table for selected nodes showing flux and the concentration of the flux quantity for each time step. The model is written in a modular format for ease of modification. The model was verified by comparison of numerical and analytical solutions for cases of molecular diffusion, two-dimensional heat transfer, and axisymmetric radial saturated fluid flow. Application of the model to a hypothetical two-dimensional field situation of gas diffusion in the unsaturated zone is demonstrated. The input and output files are included as a check on program installation. The definition of variables, input requirements, flow chart, and program listing are included in the attachments. (USGS)

Water-Resources Investigations Report↗
USGS1987

Investigation of techniques to estimate rainfall-loss parameters for Illinois

An attempt was made by the U.S. Geological Survey to develop parameter-estimation techniques for two rainfall-loss computation methods used in the U.S. Army Corps of Engineers ' flood-hydrograph model (HEC-1). Six rainfall-loss parameters were investigated - four for the Exponential Loss-Rate method and two for the Initial and Uniform Loss-Rate method. Multiple-regression analyses using data from 616 storms at 98 gaged basins were used to attempt to develop parameter-estimation techniques for ungaged basins in Illinois. Techniques were evaluated using 102 storms at 36 uncalibrated gage basins. Estimated unit-hydrograph and rainfall-loss parameters were used to compute discharge hydrograph characteristics, which were compared with characteristics of observed discharge hydrographs. Seventy and 50% of the simulations using the Exponential Loss-Rate and the Initial and Uniform Loss-Rate methods, respectively, produced valid hydrographs. Model-sensitivity analyses to one standard error of estimate indicate that the storm-dependent rainfall-loss parameters are most significant in reproducing the sum of incremental flows and peak discharge. Time of concentrations and storage coefficient are significant in reproducing time to peak discharge and peak discharge, respectively. The small percentage of variation explained by the estimation techniques and the evaluation results using 102 storms indicates that a large degree of uncertainty exists in the computed hydrographs. (USGS)

Water-Resources Investigations Report↗