Effects of debris accumulations at bridges on hydraulic conveyance

摘要

The first part of the thesis discusses the impact of floating debris, accumulated at bridge crossings, on hydraulic conditions of a stream. Initially we examine the notion of woody debris, natural and anthropogenic factors contributing to its production, transport and accumulation at bridges and other obstacles in a channel. The description of possible negative effects of these processes is followed by a detailed presentation of guidelines developed for estimating the potential for debris production, transport from contributing watershed and its delivery at bridge crossings. These guidelines take into account general characteristics of a bridge as well as its individual elements, exposed to debris accumulation. Finally, we present a method for determining the size of individual pieces of floating debris and recommendations for a field study of the site and the crossing. ududIn the second part a hydraulic model for a selected stream in Slovenia is presented. The model examines the potential of this river for debris production and transport and assesses the potential of the selected bridge crossing for accumulating debris. For this particular stream we describe the effects of debris on hydraulic conditions, namely the effect on conveyance and the extent of flooding. This has been examined partly by the application of methodology presented in the first part, and partly by the use of specific computer programmes. The thesis is concluded with an evaluation of the guidelines and their appropriacy for the application in the Slovenian context.udud