River-bed erosion due to changing boundary conditions: performance of a protective measure

D Termini

doi:10.5194/piahs-364-112-2014

Abstract

Abstract. Due to the introduction of man-made sediment barriers along a river, the amount of sediment load entering the downstream river reach is different to that leaving the reach, and erosion processes occur downstream of the barrier itself. Designers are often required to take into account the scouring process and to include adequate protective measures against the local scour. This paper addresses the performance of bio-engineering protective measures against the erosion process. In particular, a green carpet, realized with real flexible vegetation, has been used as the protective measure against erosion processes downstream of a rigid bed. Analyses are based on experimental work carried out in a straight channel constructed at the laboratory of the Dipartimento di Ingegneria Civile, Ambientale, Aereospaziale, dei Materiali, Palermo University (Italy).

Highlights

Designers are often required to take into account the scouring process around structural interventions and to include adequate protective measures against the local scour
In an attempt to respond to the aforementioned question, an experimental programme has been conducted, at the Dipartimento di Ingegneria Civile, Ambientale, Aereospaziale, dei Materiali (DICAM) – Palermo
In the absence of vegetation it was observed that the scouring process develops downstream of the rigid bed

Summary

INTRODUCTION

Designers are often required to take into account the scouring process around structural interventions and to include adequate protective measures against the local scour. The experiments were conducted to examine the flow velocity field, including turbulent characteristics, within the scour hole This analysis is fundamental to correctly simulate the bed-load transport and the temporal evolution of the scour hole and to define protective measures to reduce scouring. The first run (hereafter called NV run) was conducted to analyse the evolution of a scour hole downstream of the rigidbed channel reach and to measure the flow velocity components inside the scour hole (Fig. 2(a)). During the NV run the longitudinal and vertical velocity components were measured using a two-dimensional laser anemometer, LDA2D by Dantec s.r.l.; the transverse component was measured using an ultrasonic anemometer, DOP2000 by Signal Processing s.a. The measures were performed in sections 5 cm distant from each other (starting from the initial section) along the mobile-bed channel reach. The measured data have been analysed by assuming an orthogonal reference system having origin in the initial section, at the intersection between the horizontal plane including the bed profile and the right bank (see Fig. 3)

EXPERIMENTAL RESULTS

Section 1

CONCLUSION