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The erosion caused by jets issued from hydraulic structures progressively develops a confined scour-hole on the riverbed. A realistic scour assessment must consider both the influence of the air entrained when the jet plunges into the pool and the flow patterns induced by bottom geometry. This experimental study systematically analyzes the combined influence of jet aeration and pool confinement on the dynamic pressures affecting the water-rock interface and inside 3D fissures around a block. The results show that confinement reduces mean pressures and pressure fluctuations when the pool is relatively deep, but almost no influence is found when the pool is shallow, while air entrainment has an opposite effect. Three mechanisms are identified, two of them depend on the pool depth. Furthermore, when a block is mobile, pressures are attenuated inside the surrounding joints. The consequent block vibrations and the presence of air reduce pressure waves celerity inside the fissures. Key words: air entrainment, plunging jets, flow pattern, rock scour, plunge pool, high-velocity jets, lateral jet confinement. L'erosion causee par des jets issus de structures hydrauliques developpe progressivement une fosse confinee sur le lit. Une evaluation realiste de l'affouillement considere l'influence de l'air entraine quand le jet plonge, ainsi que des flux induits par la geometrie du fond. Cette etude experimentale analyse systematiquement l'influence combinee de l'aeration et du confinement de la fosse sur les pressions dynamiques affectant l'interface eau-roche et les fissures 3D autour d'un bloc. Les resultats montrent que le confinement reduit les pressions moyennes et ses fluctuations si le bassin est relativement profond, mais l'influence est negligeable quand le bassin est peu profond, tandis que l'aeration a un effet inverse. Trois mecanismes sont identifies, deux d'entre eux dependent de la profondeur du bassin. Quand un bloc est mobile, les pressions sont attenuees a l'interieur des fissures. Les vibrations du bloc, comme la presence d'air, reduisent la celerite des ondes de pression dans les fissures. Mots-cles: entrainement d'air, jets plongeants, caracteristiques d'ecoulement, affouillement, fosse d'erosion, jets a haute vitesse, confinement laterale du jet., Introduction High-velocity jets issued from high-head hydraulic structures, such as dams, have the potential to generate erosion when impacting rocky riverbeds, where a confined scour hole progressively develops (Schleiss 2002). [...]

Sedimentation in the main pool of a deep (maximum depth: 50 m), 227 [km.sup.2] hydropower reservoir was modeled using a three-dimensional numerical model of hydrodynamics and sedimentation for different wind, inflow, and outflow conditions. Short-term velocity measurements made in the reservoir were used to validate some aspects of the hydrodynamic model. The effects of thermal stratification on sedimentation patterns were investigated, since the reservoir is periodically strongly stratified. Stratification alters velocity profiles and thus affects sedimentation in the reservoir. Sedimentation of reservoirs is often modeled considering only the deposition of sediments delivered by tributaries. However, the sediments eroding from the shorelines can contribute significantly to sedimentation if the shorelines of the reservoir erode at sufficiently high rates or if sediment delivery via tributary inflow is small. Thus, shoreline erosion rates for a reservoir were quantified based on measured fetch, parameterized beach profile shape, and measured wind vectors, and the eroded sediments treated as a source within the sedimentation modeling scheme. The methodology for the prediction of shoreline erosion was calibrated and validated using digital aerial photos of the reservoir taken in different years and indicated approximately 1 m/year of shoreline retreat for several locations. This study revealed likely zones of sediment deposition in a thermally stratified reservoir and presented a methodology for integration of shoreline erosion into sedimentation studies that can be used in any reservoir. DOI: 10.1061/(ASCE)0733-9429(2007)133:3(255) CE Database subject headings: Sedimentation; Deposition; EFDC; Shoreline erosion; Reservoir; Stratification.

This paper describes the experimental methods developed to understand the self-healing or progressive erosion of core cracks in earth dams. Concentrated leaks through two types of core cracks are simulated experimentally in flow cells of different configurations. Results of experimental investigations indicate that the current empirical filter criterion for base soils with fines content more than 85%, which stipulates that ([D.sub.15F]/[d.sub.85B]) should be less than 9, is conservative. However, analysis of experimental results suggests that the ([D.sub.15F]/[d.sub.85B]) ratios can not indicate the rate of self-healing or progressive erosion. It also leads to a conclusion that mechanistic understanding, rather than another improved empirical criterion, may be needed for quantitative prediction of self-healing or progressive erosion. In this study, we identified two groups of quantitative parameters influencing the mechanism of self-healing: (1) characteristics of base soils and filters, and (2) hydraulic, geometric, and physicochemical conditions. Experimental methods are presented to evaluate these parameters for which no standardized methods are reported in the current literature. CE Database subject headings: Dams, earth; Dam safety; Soil structure; Pipes; Erosion; Cracking.

This paper describes a mechanistic model developed to understand the self-healing mechanism of two types of cracks in impervious cores of earth dams; Type A core cracks which extend from the interior of the core to the downstream filter, and Type B core cracks which extend from the upstream face of the core to the downstream filter. The base soil-crack-filter system is idealized using a four-element one-dimensional continuum to consider various processes in the core and the filter. The model is numerically implemented to predict self-healing in the idealized domain. The model predictions are validated using results from experimental investigations. A parametric study conducted with the model indicates two conditions essential to foster self-healing: a nominal erosion of the base soil, and a seepage velocity in the filter that is less than its critical seepage velocity. This study suggests that the mechanism leading to different rates of self-healing is the interplay of several parameters, viz, characteristics of base soils and filters, geometrical features of cracks, hydraulic conditions, etc. Application of the one-dimensional mechanistic model to a three-dimensional field-scale scenario is demonstrated. CE Database subject headings: Dams, earth; Dam safety; Pipes; Erosion; Cracking.

Local clear-water and live-bed scour tests were performed for a range of water depths and flow velocities with two different uniform cohesionless sediment diameters (0.27 and 0.84 mm) and a circular pile with a diameter of 0.15 m. The tests were performed in a tilting flume (1.5 m wide, 1.2 m deep, and 45 m long) located in the Hydraulics Laboratory at the University of Auckland in Auckland, New Zealand. These tests extend local scour data obtained in controlled experiments to velocity ratio (V/[V.sub.c]) values as high as 6. This is near the velocity where the peak live-bed scour occurs for the sediment and flow conditions. Scour depth predictions are made with four different local scour equations for the conditions of the tests and the results compared with the measured values. DOI: 10.1061/(ASCE)0733-9429(2006) 132:7(635) CE Database subject headings: Scour; Experimentation; Piers; Piles; Bridge foundation; Erosion; Bedforms.

Methods for interpreting data from in situ flume measurements of cohesive sediment dynamics are evaluated and a technique for estimating various erosion parameters using in situ measurements is proposed. There is currently a lack of uniformity in analysis techniques for cohesive erosion data collected in flumes and with in situ instruments and the proposed technique resolves some of these inconsistencies. The data set used in this study was derived from field experiments conducted with a straight benthic in situ flume in different aquatic environments in New Zealand. The experiments with stepwise increases in flow velocity revealed that peaks in the erosion rate at the beginning of each velocity step are most likely associated with heterogeneous bed structure, as transient hydrodynamic effects due to the experimental procedure were found to be insignificant. The field data showed an exponential decay of the erosion rate with time that is indicative of depth-limited erosion. These data are used to illustrate methods for the parameterization of the proposed semiempirical erosion equation, taking into account the time dependency of the erosion process. DOI: 10.1061/(ASCE)0733-9429(2006)132:6(581) CE Database subject headings: Cohesive sediment; Shear stress; In situ tests; Erosion; Flumes; Data analysis; Measurement.

The research department Energetic Materials within TNO Defence, Security and Safety is involved in the development and (safety and insensitive munitions) testing of conventional (nitro cellulose based) and thermoplastic elastomer (TPE) based gun propellants. Recently our testing capabilities have been extended with vented vessel tests in order to investigate whether or not newly developed (low vulnerability (LOVA)) gun propellants or propellant formulations perform better in erosion tests. At the moment we have two vented vessel tests available, making it possible to determine the extent of erosion from a relatively low loading density to one comparable to a large caliber gun (maximum allowable pressures from 20 to 400 MPa). Test pieces of various materials have been used and a number of LOVA and conventional gun propellants have been tested. From the results of these experiments the wear and wear rate have been determined. The erosion dependency on propellant properties like impetus, flame temperature, and combustion gas composition has been determined. Furthermore, an internal ballistics code has been adapted to model the pressure and temperature development in a vented vessel. The results are compared with the experimental results. This model will be described in short and the results presented. [DOI: 10.1115/1.2172956]

This paper presents the results of an experimental study of the scour created by a siphon flow through a vertical tube of diameter d of 9.7 to 20.4 mm in a cohesionless sand bed of approximately uniform size D of 0.58 mm. The position of the inlet of the siphon tube ranged from -101.6 to 6.4 mm relative to the surface of the sand bed and the velocity of flow through the tube [U.sub.0] varied from 0.34 to 6.41 m/s. Data from this and previous studies are used to show the radial extent of the scour hole and the maximum depth of scour depend primarily on the densimetric Froude number [F.sub.0], where [F.suv.0] = [U.sub.0] / [square root of (g([DELTA[rho]/[rho])D, g is the gravitational acceleration. [DELTA][rho]is the difference in density between the sediment and fluid, and [rho] is the density of the fluid. A theoretical analysis of the problem is used to further assess the data and it is found that viscous effects are also important to consider. The profile of the scour hole at equilibrium, for all tube positions, is found to be similar when the scour depth is measured relative to the tube inlet. DOI: 10.1061/(ASCE)0733-950X(2005)131:3(115) CE Database subject headings: Siphons; Abatement and removal; Suction; Dredging; Cohesionless sediment; Sand; Scour; Erosion.

Laboratory experiments have been performed to investigate the recession of soft cliffs due to oblique wave actions. The experiments were conducted in a wave tank with irregular waves. A test cliff was constructed of wet sand and (in one test) a sand/clay mixture, which was found to be appropriate for simulating the principal failure mode of soft cliffs fronted by erodeable beaches. The recession process is characterized by the following sequence: toe erosion--cliff failure--erosion of debris--toe erosion. The recession of the cliff top was measured from still photographs taken by an overhead camera. The longshore and cross-shore extents of individual failures and the time interval between two successive failures are obtained. CE Database subject headings: Cliffs; Erosion; Failure modes.

A simple procedure is proposed to assess the vulnerability of bridge piers in rivers, taking into account the phenomena governing fluvial dynamics during flood events. The procedure requires an estimation of the maximum scour depth of the soil surrounding both the pier and the foundation as well as an analysis of the bearing capacity of the pier-foundation-soil geotechnical system. The scour depth is determined in terms of the physical and mechanical properties of the streambed soil, the shape of the pier foundation and the destabilizing effects induced by hydrodynamic forces. The coupling of both the hydraulic and geotechnical analyses enables to identify the most significant factors characterizing scour depth and affecting pier vulnerability. Two levels (low, medium) of allowable vulnerability, bounded by an extreme condition of high vulnerability, are defined and analytically determined in function of the maximum scour depth and the foundation depth. Specific diagrams corresponding to each category of foreseen actions allow a quick evaluation of the vulnerability of a bridge pier. CE Database subject headings: Stream erosion; Bridge maintenance; Algorithms; Bearing capacity; Shallow foundation; Scour; Bridges, piers.

The subaqueous portion of a levee bank in the Sacramento-San Joaquin River Delta of central California was instrumented to quantify the impact of boat-generated waves. Typical erosion rates associated with recreational craft are too small for direct measurement of bank retreat on a per-boat-passage basis; therefore, two independent analytical methods of estimating linear erosion were developed based on colocated suspended sediment concentration and velocity time series. The algorithms were tested using data measured during a field experiment in which a 7.5 m boat was driven past the site over a range of speeds to generate waves of varying size. A cross-shore array of electromagnetic current meters and optical back-scatterance sensors measured the character of boat-generated waves and the resultant sediment suspension. In near-bank, shallow-water (d DOI: 10.1061/(ASCE)0733-950X(2002) 128:4(152) CE Database keywords: Sediment suspension; Levees; Erosion; Ship motion; California; Measurement.

This paper presents the dendrochronological markers used to date the erosive activity of ice and waves on the shores of two large lakes in Northern Quebec. Damages to trees are dated by detailed analysis of anomalous tree rings in response to the shore geomorphic activity associated with extreme water levels over the last 2 centuries. Spring floods are dated using ice scars on trees and shrubs. Lake ice breakup occurs 4-6 weeks after snowmelt. Marks on trees made by ice displaced by the wind indicate the flood levels. Once ice breakup is complete, waves erode forest edges. Tree tilting, dated by counting rings in compression wood, mark high lake levels at the beginning of summer. At submerged sites that are not subject to waves and ice, stress related to prolonged submersion results in narrow tree rings. Trees located in the immersion zone show narrow rings compared to wider rings in unsubmerged trees. However, tree response is not immediate; they can primarily respond to sequences of several consecutive years of stress, reducing the resolution of dating to 2-3 years. Rings of submerged trees are denser than average. These high water level markers, as well as population recruitment showed by the age structure of shoreline trees and shrubs, which establish during intercalary years of low water levels, were used to date the extreme levels of two large lakes at the interface between the upper boreal and subarctic regions in northeastern Canada. During the past 200 years, the annual extreme levels have been increasing, becoming even more pronounced in the 1930s, and may be due to a century-long increase in snow precipitation. The summers seem to be drier. The 1930s, 1950s, and 1970s were marked by a high frequency of high water levels. Intercalary periods of low water levels allowed regeneration of shoreline forests and recovery of trees damaged during these events. It appears that episodes similar to the recent period of low waters experienced in the American northeast since 1982 may have occurred in the past during the 1920s, 1940s, and 1960s.

To obtain in situ measurements of sediment erodibility in defined bottom shear stress environments, a portable, straight flume was built, tested, and deployed in the field for six experiments at three locations in Quincy Bay of Boston Harbor, Mass. The flume had a 1.0-m-long inlet section, which included a boundary-layer trip and a roughened, plexiglass bottom; this design prevented erosion of the sediment bed in the boundary-layer-development region. Downstream of the inlet section was a 1.2-m-long sediment test section, which had a laboratory-verified, uniform bottom stress. In the absence of algal mats, our flume experiments on sites exhibiting a range of bed properties indicated quite uniform erodibility, with a critical shear stress tau(sub c) of 0.10 +/- 0.04 Pa and an erosion rate constant M of 3.2 +/- 0.2 X 10(super -3) kg m(super -2) s(super -1) Pa(super -1) (R(super -2) = 0.92, N = 17, where N is the total number of erosion rate measurements made in the absence of algal mats). The measured rates were consistent with those of many other in situ studies. We observed markedly reduced erodibility in early October 1995 when the sediment was covered by a benthic diatom mat, and measured erosion rates were lessened by 50-80%. The possibility of depth-dependent sediment erodibility in near surface (top 3 mm) was investigated by calculating a set of depth-dependent erosion parameters. The parameters obtained suggested that both the critical shear stress and the erosion rate constant were depth-sensitive (both doubling by 1 mm into the sediment).

The disturbance of bed sediments by the wash of ship's propellers, and the resulting structural and environmental impact, is an increasing problem. Consequently, there is a need for an accurate method of scour prediction. The scouring action of the wash generated by a number of propellers in the confines of quay structures was investigated in the laboratory. Empirical equations have been developed for the prediction of the maximum depth of scour, for any given exposure period, for both flee expanding jets and those in close proximity to harbor structures.

Experiments have been done in order to determine the effects of particle size and bulk density on the erosion of quartz particles. Average particle sizes ranged from 5 to 1,350 p,m, while bulk densities ranged from approximately 1.65 to 1.95 g/[cm.sup.3]. For the larger particles, the sediments behaved in a noncohesive manner, i.e., they consolidated rapidly and the surface eroded particle by particle. For the smaller particles, the sediments behaved in a cohesive manner, i.e., they consolidated relatively slowly and the surface eroded in chunks. Erosion rates were a very strong decreasing function of density for the finer particles and were essentially independent of density for the larger particles. For a particular bulk density and shear stress and as the particle size increased, the erosion rate increased rapidly for the smaller particles, reached a maximum, and then decreased rapidly for the larger particles. Critical stresses for erosion were strongly dependent on particle size and, for the smaller particles, were also strongly dependent on bulk density.

Erosion tests were run on soft cohesive sediment beds freshly deposited from a concentrated slurry, in a large rotating annular flume. A total of seven tests were carried out with the bed age varying between 1.8 and 18.9 days. A surface type erosion was observed for the applied shear stress range (0.1 to 1 Pa). Following the increase in the water flow, the erosion rate increases quickly to a peak value and then drops off to about zero. The eroded depth was less than 8 mm for all beds, but the resistance to erosion at a given depth and for a given bed structure increased with increasing bed age. This phenomenon was attributed to thixotropy. The erosional strength of a given sediment layer is found to be one order of magnitude lower than its undrained and drained mechanical shear strengths measured with innovative testing methods. Hypotheses are given to explain that difference. However, at constant density and soil-water chemistry, the erosional and mechanical strengths seem to be affected by the same factors, i.e., bed age, structure, and temperature.

This paper presents the results of a laboratory study on the erosion of noncohesive sediment beds made of three different mixtures by deeply submerged plane turbulent wall jets. The sediment mixtures had median sizes of 6.75, 1.32, and 1.62 mm, and geometric standard deviations of 1.32, 2.02, and 3.13. The main objectives were to study the effect of sediment gradation on the asymptotic scour size and determine an effective size for the sediment mixtures for predicting erosion. The experimental observations and analysis presented in this study established that the sediment nonuniformity has a significant effect on the size of the scour hole produced by the jet. The effective size of the sediment mixture for obtaining a good correlation for the depth of scour was found to be [d.sub.95] rather than [d.sub.50] for defining the densimetric particle Froude number, [F.sub.o]. The average reduction due to armoring in the maximum scour depth and dune height was found to be [approximately]60%, and it was found to be 50% for the scour hole length and the distance of the dune.

A relatively original point of view is introduced in order to classify sedimentation phenomena according to the spatial scale. Three categories are identified: large-, medium-, and short-scale models. The distinction is made in terms of the relationships between the hydrodynamic adaptation length, the sedimentologic adaptation length, and the study scale. This allows determination of the right type of mathematical modeling for each particular case. The main features of the models involved and of the associated numerical methods are briefly described. Case studies for the different types of models are presented for illustration.

Analytical solutions provide a simple and economical means of quickly estimating qualitative and quantitative responses of the shoreline to a wide range of environmental and engineering conditions. This paper presents analytical solutions for shoreline evolution in the vicinity of coastal structures, including detached breakwaters, seawalls, and jetties with and without wave diffraction. The solution for a detached breakwater illustrates the growth of a salient with time behind the breakwater and the associated initial shoreline retreat at locations across from the breakwater tips. A simple solution describing flanking of a seawall is obtained by using two different solution areas where the longshore sand transport rate and breaking-wave angle vary. A similar technique is used to model diffraction downdrift of a groin or jetty by allowing the wave angle to vary with the distance alongshore according to a specified function or by employing a large number of solution areas. Cases are also presented for the accumulation updrift a groin and the shoreline response in a groin compartment with a breaking wave angle that varies sinusoidally in time. A solution for a single groin illustrates the impact of bypassing on the updrift accumulation.

An experimental program has been conducted to examine the feasibility of using seawater solar ponds in mariculture operations along the Texas gulf coast to protect fish crops from the potentially lethal, cold temperatures experienced in outdoor ponds. Seawater solar ponds in the form of floating thermal refuge areas are proposed as a method for reducing the loss of heat from small sections of a pond. Gradient zone erosion under various ambient and operating conditions is examined. Comparisons with previous laboratory studies show a much lower entrainment rate in the natural environment. For conditions which are typical of those encountered in mariculture pond operation, the entrainment rate was found to depend only weakly on the Richardson number. For these conditions, a simple (linear) correlation of entrainment rate with wind speed was developed.

The ability to predict the stability of eroding riverbanks is a prerequisite for modeling alluvial channel width adjustments and a requirement for predicting bank-erosion rates and sediment yield associated with bank erosion. However, there are a number of limitations of existing bank-stability analyses that limit their physical basis and predictive ability. Some of these limitations are addressed through the development of a new bank-stability analysis. The new approach is applicable to steep, cohesive, nonlayered riverbanks that fail along planar failure surfaces. Pore-water and hydrostatic confining pressure terms are included in the analysis. The failure plane is not constrained to pass through the toe of the bank. The predictive abilities of four bank-stability analyses (Lohnes and Handy 1968; Huang 1983; Osman and Thorne 1988; and the present analysis) were assessed using field data. The new analysis is the most successful of the tested analyses in terms of predicting the stability of riverbanks with respect to mass failure.

Mine soils developed from mine spoils commonly have a wide range of particle size. The slopes of old spoil piles usually are marked by gullies due to years of uncontrolled erosion. These characteristics raise questions about applicability of available theories and models for estimating runoff and erosion. An investigation was made to determine whether available erosion models can work for mine soils and can account for gully erosion. The investigation at an abandoned surface mine consisted of measurement of soil and sediment properties, measurement of runoff and erosion, observations of armor by rock fragments on gully floor, and calculations with available theories of sediment transport and slope stability. The results at this site suggest that (1) predictions with the ANSWERS model have about the same accuracy as those made for agricultural lands; (2) armor provided by rock fragments are temporary as they are periodically removed by debris flows; (3) detachment by rainfall impact is the primary cause of erosion on short steep slopes; and (4) a simplified method can be used for estimating erosion on such slopes.

Retention of pools to allow navigation has produced a characteristic, anomalous topography on a number of rivers (e.g., Ohio, Illinois, Kanawha). A gently sloping subaqueous bench at and just below minimum pool stage has been observed at hundreds of sites on these rivers. Bench formation is the result of bank failure and erosion processes including seepage-induced erosion, localized failure of undermined layers, reworking of failed soils by waves, and erosion by current forces. Benches are prevalent along alluvial banks composed of layered soils. The shallow-water zones over these benches are ecologically significant. Design and construction of bank protection measures must address the mechanisms that produce these benches.

In this work, a study has been conducted to predict blade erosion and surface deterioration of the free power turbine of an automotive gas turbine engine. The blade material erosion model is based on three-dimensional particle trajectory simulations in the three-dimensional turbine flow field. The particle rebound characteristics after surface impacts were determined from experimental measurements of restitution ratios for blade material samples in a particulate flow tunnel. The trajectories provide the spatial distribution of the particle impact parameters over the blade surfaces. A semi-empirical erosion model, derived from erosion tests of material samples at different particulate flow conditions, is used in the prediction of blade surface erosion based on the trajectory impact data. The results are presented for the three-dimensional particle trajectories through the turbine blade passages, the particle impact locations, blade surface erosion pattern, and the associated erosion parameters. These parameters include impact velocity, impact angle, and impact frequency. The data can be used for life prediction and performance deterioration of the automotive engine under investigation.

Seepage erosion - in particular, slope failures (bank slumps, mass wasting) - is prevalent on most sandbars downstream from the Glen Canyon Dam, Ariz. The public is concerned about the loss of the extant biomass and recreational facilities on these sandbars. It is alleged that the operation of the Glen Canyon Dam is responsible for the erosion of the sandbars. In this contribution, a simple, approximate analysis is developed to determine the extent of slope failures due to seepage of bank stored water from transient dam flow. The analysis is intended to assist environmentalists, dam operators, planners, and others to predict zones in which riparian habitat and recreation use will be negatively impacted by fluctuating flows. The affected area of a sandbar was found to be dependent on the range of flows; the rate of rise of river stage; the duration of the peak discharge; and the permeability, friction angle, and cohesion of the soil. Comparison of the predictions of the analysis with field data show good agreement.

Sand and gravel mining from a river bed results in irregular pits on the river bed. The migration of the pits might potentially threaten the safety of downstream bridge piers and other in-stream hydraulic structures. Models were developed to simulate the movement of pits for predicting the effect of migrating pits on in-stream structures. In view of random characteristics inherently residing in hydraulic and hydrologic processes, it is essential for an engineer to assess the overall uncertainty features of a hydraulic model output subjected to its stochastic input parameters. As an illustration, this paper analyzes the uncertainties of a pit migration model recently proposed by Lee et al. (1990) using three methods including the first-order variance estimation method, point estimation technique, and Latin hypercubic sampling. Comparisons of merits and limitations of these methods are also made.

Two modes of headcut migration are generally recognized: (1) Rotating headcuts that tend to flatten as they migrate; and (2) stepped headcuts that tend to retain nearly vertical faces. A mathematical description of the sediment detachment potential immediately upstream and downstream of the headcut is used to delineate these modes of migration. The delineating parameter is the ratio of the time required to erode the headcut face from above to the time required to undermine the headcut face from below. This erosional time-scale ratio is a dimensionless function of flow, sediment, and geometry parameters. For the limiting case of homogeneous cohesive soils, the time-scale ratio is a simple function of a Froude number and the aspect ratio of drop height to normal flow depth. This relationship is calibrated using original laboratory experiments of headcut migration in initially vertical headcuts and verified by independent field experiments of headcuts propagating in four different homogeneous cohesive soils.

Field surveys and experiments in a tilting flume on hyperconcentrated sand-water mixture (SWM) flows were conducted. At slopes slightly smaller than the equilibrium slope, a rapid development of sand bars propagating upstream was observed. These bars consist of an almost horizontal terrace with subcritical flow, a steep lee-side slope with supercritical flow, and a hydraulic jump between subsequent bars. The erosion processes on the bar are limited by the high sand concentrations and flow velocities on the steep slopes. As a result, the erosion rate is more moderate than predicted by the pickup functions used in classical sediment-transport theory. A simple one-dimensional model is presented to study the behavior of triangular schematized bars. From an analysis of the equations it is concluded that an increase in erosion rate requires an increase in bed slope to maintain equilibrium flow conditions. Finally, simulations with the model are compared with observations in the field and in the tilting flume. The agreement appears to be reasonable.

Vertical effective stress on the sand bed and momentary liquefaction resulted in the settling of concrete armor blocks off the coast of Japan. The occurence and depth of this momentary liquefaction induced by periodic waves is studied using the boundary layer approximation solution for pore-water pressure. It was found that as the shear modulus of solid skeleton to the effective bulk modulus of pore-water increases, the permeability coefficient, density of porewater, wave period and water depth decrease with liquefaction depth increase.

A process-based erosion model is used to study parameterization problems of sediment entrainment equations in overland flow areas. One of the equations for entrainment by flow is developed based on a theory of excess stream power, while the other two relate to excess hydraulic shear. The investigation is conducted in two steps. The first step examines parameter optimization for simulated data sets where the parameter values are known. In the second step, parameter optimization for the most robust equation is examined using experimental data from rainfall simulator plots. Results demonstrate that although the model is capable of estimating total sediment yields with relatively small errors in parameter estimates, the converse is true when the optimization is performed for sediment concentrations. Although sediment yields calculated from simulated sediment concentrations match well with observed data, the parameter estimates generally underestimate sediment concentrations on the rising limb of the sediment graphs, and they overestimate them on the falling limb. This difficulty might be related to structural problems in the model, and unique solutions for parameter estimates cannot be obtained.

Various critical aspects of flow-driven particle impact erosion (PIE) are discussed. Undesirable PIE must be eradicated through the maximization of resistance to wear and the alteration of critical parameters of erosive particle-fluid suspensions. There solutions must be tackled stochastically, using the Lagrangian solution of the particle motion. Lastly, the significance of the different components of PIE must be determined.