Quantitative Evaluation of Rock Weir Field Performance

Abstract

River spanning loose-rock structures are used in channels for a variety of purposes ranging from grade control to habitat complexity. Despite the use of in-channel rock weirs for a myriad of purposes, there is a lack of widely applicable guidelines for the design of the structures. Integration of field, laboratory, and numerical data sets will provide a scientific basis for predicting structure performance under various river conditions and for developing the most-effective design criteria. Investigation of surveyed structures in the field identified several important relationships between structure parameters and the degree of failure. The most notable include the relationships with throat width, open angle of the structure, profile arm angle, and distance to next upstream or downstream rock structure. In general, structures with wider throats relative to the channel width failed less frequently than those with smaller throats. Structures characterized by wider open angles and greater arm slopes tended to fail more frequently than those with narrower open angles and milder slopes. Structures placed in close sequence tended to fail less frequently than those with wide distances between structures. Additional field data continues to be collected and their inclusion in the field data set will further refine observable trends between structure parameters and degree of failure. The quantitative analysis performed in this study must be coupled with the results from the laboratory and numerical modeling components to best understand the relationships between geometric variables of the structure and structure stability.