Quantification of hydraulic effects from transverse instream structures in channel bends.

摘要

Meandering river channels possess hydraulic and geomorphic characteristics that occasionally place anthropogenic interests at risk. Loss of valuable land holdings and infrastructure due to outer-bank channel encroachment from erosion processes and complications for channel-bend navigation have prompted development of techniques for reconfiguration of instream hydraulics. Transverse instream structures are one type of technique and have been implemented in channel bends to reduce outer-bank erosivity and improve navigability. Instream structures use less material and have ecological and habitat benefits over traditional revetment type bank protection. Structures are typically constructed in series, extend from the outer-bank into the channel center, and are designed with various crest heights and slopes. Current design recommendations for the structures in natural channels provide generalized ranges of geometric parameters only; no specific information pertaining to hydraulic reconfiguration is provided. Understanding specific hydraulic response to alteration of geometric structure parameters is requisite for educated structure design.;Focusing on two types of transverse instream structures, the spur-dike and vane, a mathematical design tool was developed for the quantification and prediction of induced hydraulic response. A series of dimensionless groupings were formulated using parameters obtainable from field data of natural channels and grouped using dimensional analysis. Each dimensionless grouping had an identifiable hydraulic influence on induced hydraulics. A conglomerate mathematical expression was established as the framework for induced instream structure quantification.;The mathematical model was tailored to produce twenty-four hydraulic relationships through regression analysis utilizing a robust physical model dataset collected within rigid-bed, trapezoidal channel bends. Average and maximum velocity and boundary shear-stress data were segmented into outer-bank, centerline, and inner-bank regions and then normalized by bend-averaged baseline conditions. Velocity equations were developed for an all-structure dataset, a spur-dike dataset, and a vane dataset. Boundary shear-stress equations were developed for spur-dike structures only. Regression equations quantified laboratory hydraulics to a high level of accuracy. Equation response to independent parameter alteration coincided with continuity principles and physical hydraulic expectations. Methods performed well in application to extraneous natural channel data from the literature.;Developed methodologies from this research presented a fundamental addition to the current design procedures for the installation of structures in migrating channel bends. Quantification of the reduction of outer-bank erosive potential and increase at the shifted conveyance zone within natural channels was made possible using readily measured field data and the proposed methodology. Equations allow for previously unattainable investigation of configuration geometry combinations to meet installation objectives using simple mathematical formulas. Configuration geometry optimization to meet hydraulic design criteria using the proposed methods may hold substantial economic benefit over traditional design protocols.