Stabilization of Angular-Shaped Riprap under Overtopping Flows
Riprap is mostly used to prevent erosion by flows down the steep slopes in river engineering. A total of 53 stability tests performed on angular riprap with a median stone size ranging from 15 to 278 mm and slope ranging from 1 to 40% are used in this study. The existing equations for the prediction of medium size of angular stones are checked for their accuracy using the available data. Predictions of median size using these equations are not satisfactory and results show deviation by more than ±20% from the observed values. A multivariable power regression analysis is performed to propose a new equation relating the median size with unit discharge, bed slope, riprap thickness and coefficient of uniformity. The proposed relationship satisfactorily predicts the median angular stone size with ±20% error. Further, the required size of the rounded stone is more than the angular stone for the same unit discharge and the ratio increases with unit discharge and also with embankment slope of the riprap. Keywords—Angularity, Gradation, Riprap, Stabilization
Roughness of Loose Rock Riprap on Steep Slopes
A discussion of a paper with the aforementioned title by C.E. Rice, K.C. Kadavy, and K.M. Robinson, published in this journal (Volume 124, Number 2, February 1998), is presented. The discusser cites a 1981 paper that might be used for further analysis of the computation of the friction coefficient in conduits with a large roughness.
Free Surface, Velocity Gradient Flow Past Hemisphere
The drag on a hemisphere in a finite-flow field with free surface effects is evaluated by successively studying six flow fields, which allows the study of one new variable at a time. These flow fields are: the semi-infinite uniform and nonuniform flow fields, the finite uniform and nonuniform flow fields without free surface effects, and the finite uniform and nonuniform flow fields with free surface effects. Three regimes of flow are defined for the hemisphere which are: (1) A regime of pronounced free surface effects, (2) a regime of moderate free surface effects, and (3) a regime of negligible free surface effects. The effect of these variables and range of conditions under which they are effective is considered.