scispace - formally typeset
Search or ask a question
Author

Robert Ettema

Bio: Robert Ettema is an academic researcher from Colorado State University. The author has contributed to research in topics: Bridge scour & Pier. The author has an hindex of 30, co-authored 224 publications receiving 3737 citations. Previous affiliations of Robert Ettema include Michigan Technological University & University of Wyoming.
Topics: Bridge scour, Pier, Flume, Abutment, Open-channel flow


Papers
More filters
Journal ArticleDOI
TL;DR: In this paper, the results of laboratory experiments on the clear-water local scour of cohesionless bed sediment at cylindrical piers are presented, where the equilibrium depth of local sink is related to the particle size distribution of the bed sediment, relative to the pier diameter, flow depth, and the mean particle size of the sediment.
Abstract: The results of laboratory experiments on the clear-water local scour of cohesionless bed sediment at cylindrical piers are presented. Based on the data, equilibrium depth of local scour is related to the particle size distribution of the bed sediment, mean particle size of the bed sediment, relative to the pier diameter, flow depth relative to both the pier diameter and the mean particle size of the bed sediment. A formula for estimating the maximum depth of local scour is also given.

385 citations

01 Feb 1980

315 citations

Journal ArticleDOI
TL;DR: In this paper, the effects of pier width on local scour depth were investigated and it was shown that scour depths do not scale linearly with pier width unless there is more-or-less complete geometric similitude of pier, flow, and loose-bed particles.
Abstract: Presented here are the results of an enquiry into the effects of pier width on local scour depth. The results show that scour depth does not scale linearly with pier width unless there is more-or-less complete geometric similitude of pier, flow, and loose-bed particles—a condition that is rare. Geometric similitude is an important prerequisite to dynamic similitude in replicating local energy gradients for flow around piers. The implications for laboratory experiments on local scour and for design estimation of scour depth are discussed.

223 citations

Journal ArticleDOI
TL;DR: In this paper, the authors show that similitude of large-scale turbulence is an important consideration influencing the equilibrium depth of local scour at vertical cylinders placed in a sand bed.
Abstract: The writers’ experiments on local scour at vertical cylinders placed in a sand bed show that similitude of large-scale turbulence is an important consideration influencing equilibrium depth of local scour. For the range of cylinder diameters used in their experiments, the writers identify a direct trend between equilibrium scour depth (normalized with cylinder diameter) and the intensity and frequency of large-scale turbulence shed from each cylinder; values of normalized scour depth increased when cylinder diameter decreased. The writers offer a scour-depth adjustment factor to account for this trend, which essentially is a scale effect incurred with experiments involving three independent length scales: cylinder diameter, bed-particle diameter, and flow depth. The consequent similitude consideration, or scale effect, has general significance for laboratory studies of local scour associated with hydraulic structures in sediment beds.

195 citations

Journal ArticleDOI
TL;DR: In this paper, large-eddy simulation (LES) and laboratory-flume visualizations were used to investigate coherent structures present in the flow field around a circular cylinder located in a scour hole.
Abstract: Large-eddy simulation (LES) and laboratory-flume visualizations were used to investigate coherent structures present in the flow field around a circular cylinder located in a scour hole. The bathymetry corresponds to equilibrium scour conditions and is fixed in LES. The flow parameters in the simulation correspond to the experimental conditions in which the approach flow is fully turbulent. Detailed consideration is given to the interaction of the horseshoe vortex (HV) system within the scour hole with the detached shear layers formed from the cylinder, and the near bed turbulence. It is found that the overall structure of the HV system varies considerably in space and time, though a large, relatively stable, primary necklace vortex is present at practically all times inside the scour hole. The simulation captures the presence of bimodal chaotic oscillations inside the HV system, as well as the sharp increase in the resolved turbulent kinetic energy levels and pressure fluctuations reported in prior experimental investigations. High levels of the mean bed shear stress are observed beneath the primary necklace vortex, especially over the region where the bimodal oscillations are strong, as well as beneath the small junction vortex at the base of the cylinder. It is also found that the detachment and advection of patches of vorticity from the downstream part of the legs of the necklace vortices can induce large instantaneous bed shear stress values. When the critical bed shear stress value for sediment entrainment on a flat surface is adjusted for bed slope effects, the LES simulation correctly predicts that the distribution of the mean bed shear stress is consistent with equilibrium scour conditions.

183 citations


Cited by
More filters
Book ChapterDOI
02 Mar 2001

984 citations

Journal ArticleDOI
TL;DR: In this article, a transport model for mixed sand/gravel sediments is presented, which uses the full size distribution of the bed surface, including sand, and incorporates a nonlinear effect of sand content on gravel transport rate not included in previous models.
Abstract: We present a transport model for mixed sand/gravel sediments. Fractional transport rates are referenced to the size distribution of the bed surface, rather than subsurface, making the model completely explicit and capable of predicting transient conditions. The model is developed using a new data set of 48 coupled observations of flow, transport, and bed surface grain size using five different sediments. The model incorporates a hiding function that resolves discrepancies observed among earlier hiding functions. The model uses the full size distribution of the bed surface, including sand, and incorporates a nonlinear effect of sand content on gravel transport rate not included in previous models. The model shares some common elements with two previous surface-based transport models, but differs in using the full surface size distribution and in that it is directly developed from a relatively comprehensive data set with unambiguous measurement of surface grain size over a range of flow, transport rate, and sediments.

803 citations

Journal ArticleDOI
TL;DR: In this article, field observations and historical evidence show that these jams can form stable structures controlling local channel hydraulics and providing refugia for riparian forest development over decades and possibly centuries.
Abstract: Field surveys document the accumulation of large woody debris (LWD) into structurally distinctive jam types in the alluvial channel of the Queets River on the Olympic Peninsula of north west Washington. Calculations, field observations and historical evidence show that these jams can form stable structures controlling local channel hydraulics and providing refugia for riparian forest development over decades and possibly centuries. Distinctive spatial patterns of LWD, pools, bars and forested islands form in association with particular jam types. The deposition of ‘key member’ logs initiates the formation of stable bar apex and meander jams that alter the local flow hydraulics and thereby the spatial characteristics of scour and deposition leading to pool and bar formation. Historical evidence and the age structure of forest patches documents the temporal development of alluvial topography associated with these jam types. Bar apex jams, for example, are associated with a crescentic pool, an upstream arcuate bar and a downstream central bar that is the focus of forest patch development. Experimental and empirical studies in hydraulic engineering accurately predict channel scour associated with jams. Individual jams can be remarkably stable, providing long-term bank protection that creates local refugia for mature forest patches within a valley floor environment characterized by rapid channel migration and frequent disturbance. Processes controlling the formation, structure and stability of naturally occurring LWD jams are fundamental to the dynamics of forested river ecosystems and provide insights into the design of both habitat restoration structures and ecosystem-based watershed management.

643 citations