Although it is well known that metabolism, feeding, and behaviour of lotic organisms is influenced by various flow characteristics, hydraulic variables usually are not accurately measured in lotic ecology studies. Using an approach we call "hydraulic stream ecology", we link organismic responses to a more comprehensive treatment of the physical environment. Since a unified analytical solution for all important hydraulic variables in running waters does not exist at the moment, we advocate a simpler view of the physical system. We demonstrate methods for estimating complex hydraulic key characteristics, like turbulence in the free flow, turbulence close to the stream bottom, and the force of flow prevailing at the bottom. Calculations of these complex key characteristics require measurement of simple hydraulic characteristics like mean velocity, water surface slope, depth, bottom roughness, kinematic viscosity, and density of the water. The hydraulic environment shows characteristic patterns within whole c...

Hydraulic Stream Ecology: Observed Patterns and Potential Applications

Field data are used to study the size distribution of bedload in paved gravel-bed streams. Similarity analysis yields the results that all grain size ranges are of approximately equal transportability when the critical condition for breaking the pavement is exceeded. This result is only approximately correct due to deviations from similarity. However, it is adequate to justify development of a method for calculating total bedload, which requires only the subpavement median grain size rather than the size distribution. A method for calculating bedload size distribution that accounts for deviation from similarity is also developed.

Closure of "Bedload and Size Distribution in Paved Gravel-Bed Streams"

Nearly 40 years of theoretical development and practical experience has been incorporated in this book, which has won numerous awards as a scientific and technical publication in China. Now updated and fully translated into English, this volume is the first attempt in the field to unify the movement of sediment and boundary conditions. Going far beyond any book of its kind, it presents a synthetic analysis and thorough coverage of many schools of thought and provides practical survey of this discipline of the science. The authors introduce a synthesis of information gleaned from more than 800 papers spanning the fields of hydraulic engineering, mathematics, physics, geology, rheology, and chemistry, giving the reader a profound understanding of the present status and direction of the industry's research efforts. The volume includes chapters dedicated to rate phenomena and topics such as hyperconcentrated flows, effect of sediment existence on water flow, large-scale hydraulic construction on sediment-laden streams, and specialized research not available outside of China.

Mechanics of Sediment Transport

Field studies of forest gravel-bed rivers in northwestern Washington and southeastern Alaska demonstrate that bed-surface grain size is responsive to hydraulic roughness caused by bank irregularities, bars, and wood debris. We evaluate textural response by comparing reach-average median grain size (D50) to that predicted from the total bank-full boundary shear stress (t0 bf ), representing a hypothetical reference condition of low hydraulic roughness. For a given t0 bf , channels with progressively greater hydraulic roughness have systematically finer bed surfaces, presumably due to reduced bed shear stress, resulting in lower channel competence and diminished bed load transport capacity, both of which promote textural fining. In channels with significant hydraulic roughness, observed values of D50 can be up to 90% smaller than those predicted from t 0 bf . We find that wood debris plays an important role at our study sites, not only providing hydraulic roughness but also influencing pool spacing, frequency of textural patches, and the amplitude and wavelength of bank and bar topography and their consequent roughness. Our observations also have biological implications. We find that textural fining due to hydraulic roughness can create usable salmonid spawning gravels in channels that otherwise would be too coarse.

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Effects of hydraulic roughness on surface textures of gravel-bed rivers

A new set of field data facilitates a detailed analysis of variations in bed material grain size within two confluent gravel-bed rivers in northeastern British Columbia, Canada A preliminary assessment of grain-size variability establishes a basis for examination of the spatial pattern of grain-size change Standard ANOVA techniques are inappropriate because individual samples have unequal variances and are not normally distributed Alternative tests for homoscedasticity and comparison of means are therefore utilized Within-site, between-sample variability is not significant The grain-size distributions that were obtained at individual sites are therefore representative of the depositional environments that were sampled In both rivers mean grain size does vary significantly between sites and there is therefore a basis for examining the data for spatial patterns such as downstream fining



Textural variations along the two rivers studied here are complex and show negligible overall fining (in over 100 km) This is the consequence of a large number of tributary inputs and non-alluvial sediment sources which are the legacy of Late Pleistocene glaciation The identification of lateral sources like these is fundamental for understanding textural changes within rivers The sedimentary link (a channel reach between significant lateral sediment inputs) provides a means of isolating fluvial maturation processes (abrasion and sorting) from contingent lateral inputs Strong fining trends are apparent in most links and classification of grain-size measurements according to their location within particular links greatly improves the statistical explanation of textural variation Identification of sedimentary links provides a means of applying models of fluvial fining processes, so isolation of link networks will aid the development of basin-scale models of textural variation © 1998 John Wiley & Sons, Ltd

Grain size along two gravel-bed rivers: statistical variation, spatial pattern and sedimentary links

Equilibrium sorting of coarse mobile bed load sediment in meander bends is considered. A theory of two-dimensional bed load transport of graded material, including the effects of gravity on lateral slopes and secondary currents, is developed. This theory is coupled with a simple treatment of flow in bends, an analytically determined bend shape, and the condition of continuity of each grain size range in transport to describe sorting. The theory indicates that the locus of coarse sediment shifts from the inside bank to the outside bank near the bend apex, as is observed.

E. D. Andrews

Papers

Sorting of Bed Load Sediment by Flow in Meander Bends