Approach Flow Depth Research Articles

Stability of Riprap at Bridge Piers

An experimental investigation was performed to determine the critical conditions for displacement of riprap placed on streambeds surrounding bridge piers. A functional relation between stability number, a dimensionless grouping of rock size and density to fluid velocity and density, and relative approach flow roughness, approach flow depth, riprap size, and placement depth was presented. Pier model tests conducted in a laboratory flume were used to determine the influence of each dimensionless parameter on the stability number. Analysis of the experimental results showed that the relative depth of placement and the relative rock size significantly affected the stability number for rectangular piers. A comparison of this data with similar data for round‐nosed piers and other data for unobstructed flow conditions showed that rock sizes required for stability at piers must be substantially larger than those required for unobstructed flow. In addition, rock sizes for rectangular piers must be substantially la...

Modified, Trapezoidal Venturi Channel

The flow pattern resulting from a circular cone immersed in a rectangular channel is investigated under critical flow conditions. The apparatus may be used for both permanent and mobile discharge evaluation in open channels. Owing to the low weight, the high precision of finishing, and its reasonable price when compared to the conventional structures, the modified Venturi Channel may be regarded as a useful instrument. The circular cone is particularly well suited to watercourses in which discharge spectrum is considerable, thereby resulting in moderate approaching flow depth variation. Its rating curve is investigated by accounting for streamline curvature effects. Experiments corroborate the theoretical predictions and indicate that the flow characteristics are governed by the Froude similarity law.

Stability of Rockfill in End-Dump River Closures

One method of river closure is by end-dumping loose rockfill from one or both banks progressively into the flow. Determination of stable closure material size by correlation with either mean velocity through the gap or velocity near the boundary as done in the past is not realistic. In this study the closure material stability is defined numerically by a parameter efficiency of closure material, which denotes the ratio of the volume of the material remaining in the body of the dam to the volume dumped at any stage. Analysis of all the relevant parameters indicated the Froude number of approach flow, the contraction ratio, the ratio of the closure material size to the approach flow depth and the efficiency of closure material to be the essential inter-related nondimensional variables describing stability. The functional relationship was established by the results of a laboratory study and practical design curves to directly determine the stable size of closure material, are presented.