Equilibrium scour morphology downstream of rock sills under unsteady flow conditions

Stefano Pagliara,Michele Palermo

doi:10.1051/e3sconf/20184003004

Abstract

The present study aims to analyze the equilibrium scour morphology occurring downstream of rock-made sills with different shapes, under different inflow conditions. Namely, experimental tests were conducted under both steady and unsteady flow conditions. In this last case, the peak discharge was kept the same as the respective base tests performed for steady flow conditions. The scour evolution was carefully monitored, as well as the main characteristic lengths of the scour hole (e.g., maximum scour depth and axial length). The inflow discharge characteristics were varied, i.e., the maximum peak discharge was reached by adopting different hydrographs, in order to test their influence on the equilibrium morphology. Experimental results showed significant similitudes in terms of equilibrium scour morphology between steady and unsteady flow conditions when the hydrograph duration is enough long. The results of the present study can be useful for a correct design of such structure typology in usual applications.

Highlights

Experimental tests were conducted in a dedicated flume in which different rock sills were located
For the selected inflow hydrograph shape and for all the tested conditions and configurations, Qp generally occurs for 2690
It was found that substantial similitudes can be detected in terms of global equilibrium morphologies under both steady and unsteady inflow conditions when the peak discharge Qp occurs at a non-dimensional time T bigger than 3200

Summary

Introduction

Experimental tests were conducted in a dedicated flume in which different rock sills were located. For both the structures, preliminary experimental tests were conducted by keeping the discharge constant. Once reference tests had been performed, experiments were repeated by varying the inflow conditions, i.e., under unsteady flow conditions, keeping the peak discharge Qp equal to that of the corresponding reference base tests Q This methodology allowed for a direct comparison of the obtained equilibrium morphologies revealing both the similitudes and differences due to different inflow conditions. Being constant t in each test, the discharge decrement in the descending phase was set at 0.5 Q=0.5 l/s This choice well represents the usual inflow conditions characterizing natural streams. The overall precision of the main scour hole parameters was of ±1 mm

Objectives

Results

Conclusion