Hydraulics Of Bridge Waterways

Introduction

There was a time, now past, when backwater caused by the presence of bridges during flood periods was considered a necessary nuisanceCfirst, because the public clamored for bridges to replace ferries and fords; and second, because there was no accurate means of determining the
amount of backwater a bridge would produce after it was in place. With the spread of urbanization; with indefinite, unenforceable restrictions on the construction of housing and business establishments on flood plains of rivers and streams throughout the country; with new highway bridges being constructed at an ever-increasing rate; and with property values increasing at an unprecedented rate in the past two decades, it is now imperative that the backwater produced by new bridges be kept within very knowledgeable and reasonable limits. This places demands on the hydraulic engineer, who has not been consulted too often in the past, to promote and develop a more scientific approach to the bridge waterway problem. Progress in structural design has kept pace with the times. Structural engineers are well aware of the economies which can be attained in the proper type, selection and design of a bridge of a given overall length and height. The role of the hydraulic engineer in establishing what the length and vertical clearance should be and where the bridge should be placed is less well understood due principally to the lack of hydrological and hydraulic information on the waterways. In fact, until recently, bridge lengths and clearances have been proportioned principally on rough calculations, individual judgment, and intuition. This may still be true in some cases. Today, traffic volumes have become so great on primary roads that bridge failures or bridges out of service for any length of time can cause severe economic loss and inconvenience; even closing one lane of an arterial highway for repairs creates pandemonium.