Hydraulic Environments Research Articles

Segment-Scale Patterns and Hydraulics of Trace Metal Concentrations in Fine Grain Sediments of a Cobble and Boulder Bed Mountain Stream, Southeast Alaska

This study documents and analyzes spatial patterns of variability in 12 trace metals in sand-size and finer sediments over a 2 km segment of a boulder and cobble bed mountain stream. The analysis focuses on concentrations rather than the total metal mass budget, because it is typically variations in metal concentrations that are important for assessing potential environmental impacts. There are no consistent downstream variations in metal concentrations, which indicates that there are no significant geochemical changes or external sources of metals in the study segment. In fact, much of the spatial variability within the stream segment appears to be random, although a dimensionless shear stress model predicts the majority of locations where peak concentrations of metals contained in heavy minerals occur. The dimensionless shear stress model, however, only predicts the potential for enrichment and many sites where potential enrichment is predicted contain low concentrations of metals. Peak concentrations do not appear to be associated with metal-rich sediment waves moving through the system, but instead are probably the result of local hydraulic variability. Sampling of boulder and cobble streams should be stratified by hydraulic environments in order to capture the full range of minimum and maximum metal concentrations within the stream system.

Effects on bedload transport of experimental removal of woody debris from a forest gravel‐bed stream

AbstractExperimental removal of woody debris from a small, gravel‐bed stream in a forested area resulted in a four‐fold increase in bedload transport at bankfull discharge. This was caused by increased transportability of sediment previously stored upslope of debris buttresses or in low‐energy hydraulic environments related to debris. Bank erosion delivered additional sediment to the channel, and transport energy was increased by an inferred increase in the component of total boundary shear stress affecting grains on the bed. Increased transport following debris removal in May 1987 continued throughout the entire autumn storm season through late November 1987, indicating persistent adjustment of the stream bed and banks despite marked response to earlier flows as large as bankfull. Stream bed adjustments included development of a semi‐regular sequence of alternate bars and pools, many of which were spaced independently of former pool locations.

Dredgeability Investigations in Contrasting Geological Environments

This paper reports the results of two dredgeability investigations undertaken in Moreton Bay, Queensland. The geological and geophysical surveys conducted at Boondall and the North East Channel site were primarily directed towards determining (a) if and where shipping channels could be dredged economically; and (b) the feasibility of maintaining the channels against siltation. The contrasting geological and hydraulic environments at the two sites placed differing emphasis on survey objectives and methodology for each project.

Review of Fisheries Engineering Studies, Hydraulic Environments

Review of Fisheries Engineering Studies, Hydraulic Environments

Studies on the Hydraulic Environments in Fisheries Engineering

Studies on the Hydraulic Environments in Fisheries Engineering

Hydraulic Factors Controlling the Shape of Laminae in Laboratory Deltas

ABSTRACT The cross-bedded (internal) structure of a laboratory delta delineates successive profiles of the delta front as the latter progresses downstream. Some of the basic variables affecting the frontal profile of laboratory deltas (tabular units of cross-bedding) were studied in a series of controlled flume experiments. The variables isolated for study were: (a) stream velocity and bed shear stress, (b) the ratio of stream depth to basin depth (depth-ratio), and (c) sediment type, as expressed by relative fall velocity. The results of the investigation demonstrate that bed-load transport deposits an angular type of cross-bedding with planar foreset abutting the basin floor with an angular contact. A low velocity of flow or a bed shear stress just above the threshold for particle mov ment favors the development of a planar type of internal structure. Even at higher velocities characterized by a moderate amount of suspension transport, an angular basal contact may still persist provided the basin is relatively deep with respect to the stream (low depth-ratio). The transition stage from an angular to a tangential basal contact is characterized by the deposition of laminae that alternate from planar to incipiently tangential, that is, with the bottomset. As velocity and depth-ratio increase, the frontal profile evolves through the following stages: angularincipiently tangentialtangentialstrong y tangentiallow-angle concave. The comparative behavior of different sediment types in similar hydraulic environments can be evaluated on the basis of relative fall velocity. The latter is defined as the ratio of the median fall velocity of the sediment particles to the average velocity of streamflow. Thus a coarse-grained sediment transported by a current of given strength may yield a planar foreset with an angular basal contact, whereas a fine-grained sediment transported and deposited under comparable conditions may yield a strongly tangential contact. Wave action and small oscillations of base level may produce frontal profiles that are either convex or sigmoidal (S-shaped) in vertical section.