U.S. Army Corp of Engineers Waterways Experiment Station

This is a study of the interactions of solitary waves climbing up a circular island. A series of large-scale laboratory experiments with waves of different incident height-to-depth ratios and different crest lengths is described. Detailed two-dimensional run-up height measurements and time histories of surface elevations around the island are presented. A numerical model based on the two-dimensional shallow-water wave equations including runup calculations was developed. Numerical model predictions agreed very well with the laboratory data and the model was used to study wave trapping and the effect of slope. Under certain conditions, enhanced runup and wave trapping on the lee side of the island were observed, suggesting a possible explanation for the devastation reported by field surveys in Babi Island off Flores, Indonesia, and in Okushiri Island, Japan.

CE‐QUAL‐ICM is a three‐dimensional, time‐variable, eutrophication model. CE‐QUAL‐ICM incorporates 22 state variables that include physical properties; multiple forms of algae, carbon, nitrogen, phosphorus, and silica; and dissolved oxygen. The model is part of a larger package that includes a three‐dimensional hydrodynamic model and a benthic‐sediment diagenesis model. Application to Chesapeake Bay over a three‐year period, 1984–86, indicates the model successfully simulates water‐column and sediment processes that affect water quality. Phenomena simulated include formation of the spring algal bloom subsequent to the annual peak in nutrient runoff, onset and breakup of summer anoxia, and coupling of organic particle deposition with sediment‐water nutrient and oxygen fluxes. The study demonstrates that complex eutrophication problems can be addressed with coupled three‐dimensional hydrodynamic and water‐quality models.

Microbial community composition associated with benzene oxidation under in situ Fe(III)-reducing conditions in a petroleum-contaminated aquifer located in Bemidji, Minn., was investigated. Community structure associated with benzene degradation was compared to sediment communities that did not anaerobically oxidize benzene which were obtained from two adjacent Fe(III)-reducing sites and from methanogenic and uncontaminated zones. Denaturing gradient gel electrophoresis of 16S rDNA sequences amplified with bacterial or Geobacteraceae-specific primers indicated significant differences in the composition of the microbial communities at the different sites. Most notable was a selective enrichment of microorganisms in the Geobacter cluster seen in the benzene-degrading sediments. This finding was in accordance with phospholipid fatty acid analysis and most-probable-number-PCR enumeration, which indicated that members of the family Geobacteraceae were more numerous in these sediments. A benzene-oxidizing Fe(III)-reducing enrichment culture was established from benzene-degrading sediments and contained an organism closely related to the uncultivated Geobacter spp. This genus contains the only known organisms that can oxidize aromatic compounds with the reduction of Fe(III). Sequences closely related to the Fe(III) reducer Geothrix fermentans and the aerobe Variovorax paradoxus were also amplified from the benzene-degrading enrichment and were present in the benzene-degrading sediments. However, neither G. fermentans nor V. paradoxus is known to oxidize aromatic compounds with the reduction of Fe(III), and there was no apparent enrichment of these organisms in the benzene-degrading sediments. These results suggest that Geobacter spp. play an important role in the anaerobic oxidation of benzene in the Bemidji aquifer and that molecular community analysis may be a powerful tool for predicting a site's capacity for anaerobic benzene degradation.

Several models that can be used to optimally size water distribution pipes were applied to a hypothetical system. The results are summarized in this paper. The models produced solutions with costs that were within 10% of one another, although the solutions were quite different. While the models were helpful in sizing pipes, some manual calculations and a good deal of engineering judgment were required to apply them.

Since the pioneering work of Seed and Lee (32), the potential for liquefaction of saturated sands under seismic loading conditions has been carefully considered by many investigators. Typical of these investigations is the laboratory determination of cyclic strength of sands by means of cyclic triaxial tests (3,14,19,20,2 1, 31,35,37,38, 41, 42), cyclic simple shear tests (8,10,28,34), cyclic torsional shear tests (6, 11, 12, 13,44,45), and shaking table tests (5,7,9,30,33,36,40,43).

When the Lattice Boltzmann Method (LBM) is used for simulating continuum fluid flow, the discrete mass distribution must satisfy imposed constraints for density and momentum along the boundaries of the lattice. These constraints uniquely determine the three-dimensional (3-D) mass distribution for boundary nodes only when the number of external (inward-pointing) lattice links does not exceed four. We propose supplementary rules for computing the boundary distribution where the number of external links does exceed four, which is the case for all except simple rectangular lattices. Results obtained with 3-D body-centered-cubic lattices are presented for Poiseuille flow, porous-plate Couette flow, pipe flow, and rectangular duct flow. The accuracy of the two-dimensional (2-D) Poiseuille and Couette flows persists even when the mean free path between collisions is large, but that of the 3-D duct flow deteriorates markedly when the mean free path exceeds the lattice spacing. Accuracy in general decreases with Knudsen number and Mach number, and the product of these two quantities is a useful index for the applicability of LBM to 3-D low-Reynolds-number flow.

Physical processes constituting fine, cohesive sediment transport in estuarial waters are described. These processes, which include settling and deposition, consolidation, erosion and transport in suspension, are typically interlinked by the cyclic nature of the tide dominated environment. Complexities in process characterization arise as a consequence of the dual dependence of sediment aggregate properties on the physico‐chemical properties of the sediment‐water mixture as well as the turbulent flow field. Present day knowledge of the processes enables reliable predictions of rates of sedimentation and erosion in navigable channels, waterways and harbors through numerical modeling. Further research is required for improving procedures for measuring settling velocities, identification of depth at which a definable bed is encountered, and the behavior of near‐bed high density suspensions.

Abstract Microgravimetric and gravity gradient surveying techniques are applicable to the detection and delineation of shallow subsurface cavities and tunnels. Two case histories of the use of these techniques to site investigations in karst regions are presented. In the first case history, the delineation of a shallow ( approximately 10 m deep), air-filled cavity system by a microgravimetric survey is demonstrated. Also, application of familiar ring and center point techniques produces derivative maps which demonstrate (1) the use of second derivative techniques to produce a 'residual' gravity map, and (2) the ability of first derivative techniques to resolve closely spaced or complex subsurface features. In the second case history, a deeper ( approximately 30 m deep), water-filled cavity system is adequately detected by a microgravity survey. Results of an interval (tower) vertical gradient survey along a profile line are presented in the second case history; this vertical gradient survey successfully detected shallow (<6 m) anomalous features such as limestone pinnacles and clay pockets, but the data are too 'noisy' to permit detection of the vertical gradient anomaly caused by the cavity system. Interval horizontal gradients were determined along the same profile line at the second site, and a vertical gradient profile is determined from the horizontal gradient profile by a Hilbert transform technique. The measured horizontal gradient profile and the computed vertical gradient profile compare quite well with corresponding profiles calculated for a two-dimensional model of the cavity system.

The lattice Boltzmann method (LBM) is used to simulate viscous fluid flow through a column of glass beads. The results suggest that the normalized velocity distribution is sensitive to the spatial resolution but not the details of the packing. With increasing spatial resolution, simulation results converge to a velocity distribution with a sharp peak near zero. A simple argument is presented to explain this result. Changes in the shape of the distribution as a function of flow rate are determined for low Reynolds numbers, and the large-velocity tail of the distribution is shown to depend on the packing geometry. The effect of a finite Reynolds number on the apparent permeability is demonstrated and discussed in relation to previous results in the literature. Comparison with velocity distributions from NMR (nuclear magnetic resonance) spectroscopy finds qualitative agreement after adjusting for diffusion effects in the NMR distributions.

In calibrating a water distribution system model, the model user usually adjusts pipe roughness (e.g., Hazen‐Williams C factor) or water use so that pressures and flows predicted by the model agree with values observed in the field. This paper presents formulas to assist the user in deciding whether to adjust C or water use and by how much. The key to using the formulas is to observe pressures in the system for at least two significantly different use rates. Such data are often collected during fire flow tests. A model is considered calibrated to the extent that it can predict the behavior of the water distribution system over a wide range of operating conditions and water use.

Seismic design procedures are proposed for geosynthetic-reinforced soil structures. The procedures are based on a pseudo-static limit equilibrium analysis, which considers horizontal acceleration and incorporates a permanent displacement limit. Internal and external stability analyses are conducted to determine the required strength and length of geosynthetic, considering different modes of failure. Parametric studies illustrate the effects of seismic acceleration on the design of reinforced soil structures having different slope angles and soil properties. For vertical slopes at small seismic acceleration, tieback/compound failure dictates the required geosynthetic length. The length required to resist direct sliding increases rapidly as the seismic acceleration increases. This length may become impractical at moderate design accelerations. For such cases, an alternative approach based on a tolerable displacement against direct sliding is proposed for design. The proposed procedures are compared with the performance of several geosynthetic-reinforced soil structures during recent major earthquakes. A detailed design example is included to illustrate usage of proposed procedures.

A simulation and verification study assessing the performance of 10 censored data reconstitution methods was conducted to develop guidance for statistical comparisons among very small samples (n < 10) with below detection limit observations in dredged sediment testing. Censored data methods were evaluated for preservation of power and nominal type I error rate in subsequent statistical comparisons. Method performance was influenced by amount of censoring, data transformation, population distribution, and variance characteristics. For nearly all situations examined, substitution of a constant such as one-half the detection limit equaled or outperformed more complicated methods. Regression order statistics and maximum likelihood techniques previously recommended for estimating population parameters from censored environmental samples generally performed poorly in very small-sample statistical hypothesis testing with more than minimal censoring, due to their inability to accurately infer distributional properties and their consequent low power or high type I error rates.

A description has been given of the general features of the cap model as used to represent geological materials. In addition, the theoretical basis for the model has been indicated and a particular example of the model has been presented. The model is intended to represent the behavior of a wide range of geological materials in problems for which the nonlinear hysteretic nature of such materials is significant. Although the primary area of application of the model in the past has been in the numerical computation of ground shock effects in layered sites due to explosive sources, the model should be applicable to other fields of interest such as earthquakes and various types of penetration into soils and rocks.

An algorithm for modifying biological rates as a function of temperature has been developed using the basic form of the logistic equation. Versions of this basic algorithm are then used to modify growth, respiration, and mortality rates as a function of four characteristic temperatures.

Experimental data are presented that demonstrate the existence of a family of gravitational water waves that propagate practically without change of form on the surface of shallow water of uniform depth. The surface patterns of these waves are genuinely two-dimensional and fully periodic, i.e. they are periodic in two spatial directions and in time. The amplitudes of these waves need not be small; their form persists even up to breaking. The waves are easy to generate experimentally, and they are observed to propagate in a stable manner, even when perturbed significantly. The measured waves are described with reasonable accuracy by a family of exact solutions of the Kadomtsev-Petviashvili equation (KP solutions of genus 2) over the entire parameter range of the experiments, including waves well outside the putative range of validity of the KP equation. These genus-2 solutions of the KP equation may be viewed as two-dimensional generalizations of cnoidal waves.

A practical measure for water‐distribution system reliability, based on hydraulic availability is presented and incorporated in an optimal design procedure for component sizing. The measure combines hydraulic and mechanical availability in a form that defines the proportion of the time that the system will satisfactorily fulfill its function. However, rather than a simple discrete failure relationship with absolute failure if pressure heads fall below a prescribed minimum the hydraulic availability is modeled with continuous increasing acceptability as higher pressures occur. Availability is considered in a nonlinear optimization model that is. reduced in complexity by linking the optimizer with a network solver to implicitly solve the hydraulic constraints. The results of the model application show an increasing marginal cost for higher levels of availability, and the optimal designs tend to follow the engineering rules of thumb for system design.

The transformation of monochromatic and directionally‐spread irregular waves passing over a submerged elliptical mound was studied in a controlled laboratory experiment. A directional spectral wave generator was used to generate waves with equal peak frequencies and spectral energy, along with monochromatic waves of equivalent significant height and period. Spectra with both narrow and broad frequency and directional spreads were generated. Results indicate that monochromatic waves provide a poor approximation of irregular wave conditions if there is directional spread or high wave steepness.

Recommended methods for the statistical analysis of extreme waves are presented. Proper data selection is stressed. Data from different seasons and/or of different type or origin should be analysed separately. Use of the peaks over threshold method is recommended. It is advised that a three parameter Weibull distribution is fitted to the observed storm peak data giving due consideration to data censoring.

Concise equations for the tangential, radial, and axial velocities as well as the water‐surface profile of air‐core vortices at hydraulic intakes have been derived. The equations were developed by modifying the equation for tangential velocity originally proposed by Rosenhead in 1930. Laboratory experiments were conducted on strong air‐core vortices near a water intake. The results indicate the equations agree with experimental measurements and are applicable to vortex motion in general. The equations for radial and axial vortex velocities contain an eddy‐viscosity term, which should be proportional to vortex circulation. Dimensionless parameters describing the circulation and intake Froude numbers and the intake submergence are also used in the analysis. Using these equations, the depth and three velocity components of an air‐core vortex at certain hydraulic intakes can be predicted. This information may be helpful to the practicing engineer in determining the submergence required to avoid air‐entraining vortices at intakes.

The published literature was reviewed to investigate (A.) the functional importance of aquatic plants to fish, (B.) how aquatic plant and fish populations are measured in vegetated habitats, (C.) the spatial scale at which previous investigators have quantified fish-plant interactions, and (D.) how proximate fish behaviors influence population structure at a macrolevel. Based on results of comparative studies, the typical conclusion bas been that intermediate levels of plants promote high species richness and are optimal for growth and survival of fishes. Predictable responses by fishes to aquatic plants were noted: vegetated habitats supported higher fish densities than unvegetated areas; aquatic plants led to reduced risk of predation; and structurally oriented fish exploited aquatic plant beds. Pelagic species and benthic omnivores often declined in abundance with increased plant cover, and phytophilic fishes showed rapid population increases during plant growing seasons. When plants occupied an entire water body, fish growth became stunted due to depletion of food resources. These interactions have been assessed largely at a macroscale where aquatic plants are generally mapped from aerial photography or surface measurements and fish data are averaged as standing crop, density, catch-effort, or percent abundance relative to plant coverage. Because direct observation of fish in dense plant beds is difficult, few attempts have been made to define and quantify structural complexity of plants at a scale perceived by fishes. Aquatic plant attributes potentially important to growth and survival of fishes are provided, and these authors suggest that microscale assessment of fish behaviors can be linked to macroscale fishery management strategies through analysis of aerial distribution of aquatic plants.