Preface

This is intended as a useful handbook on the subject of bridge hydraulics. It includes references to articles published in 1997, just prior to its completion, so compared with similar books it is relatively up to date. It explores how to undertake the hydraulic analysis or design of a bridge, either single or multispan, with either rectangular or arched waterways. It describes how to calculate the afflux (backwater), how to improve the hydraulic performance of a bridge, and how to evaluate and combat scour. The intention is to provide a good introduction to the fundamentals for anyone not familiar with this specalised branch of engineering, with enough detailed information to appeal to those who are. This book is, in a way, the result of a mistake. Near my home town many years ago a rather old, untidy, steel truss bridge was replaced by a very elegant masonry structure. The result was that flooding upstream got worse. This raised the question: how is the size of the opening in a river bridge determined? Initial enquiries revealed that estimating the magnitude of the design flood was relatively straightforward; it was converting this into the dimensions of a bridge opening that was difficult. An expert on the subject candidly and charmingly admitted that there was much that he (and practically everyone else) did not know or understand, so if anyone cared to fill in a few gaps... Hence my research interest and the book. Another reason is that bridges are interesting: many people stand on a bridge watching the floodwater pass underneath. Hopefully some of this interest is captured in the following pages. Some engineers may question why a book on bridge hydraulics is needed when it is possible to find computer software that will do all the analysis and design for you. Such people frequently believe, because computers are capable of giving answers to 20 decimal places, that everything that comes out of them is correct and accurate. This is not true. Ignoring the fact that the input data may be inaccurate, there may be mistakes in the computer program. A sobering thought is that someone once said that if a piece of software is worth using then it must have an error in it somewhere!
Many years ago the author was invited to use the research facilities of a large, prestigious company. Part of the work involved digitising some

BRIDGE HYDRAULICS