This thesis is based upon the work and experience of the author since 1956. During this period he has been engaged in the design, construction and operation of hydraulic models, first as an engineer employed by the Department of Public Works, N.S.W. and then as a Lecturer in Civil Engineering in the University of Queensland. The first chapter on the design and operation of hydraulic models is based mainly on the results of models with which the author has either been personally concerned, or with which he has been familiar in other ways. While it cavers a fairly wide range of models it is not intended to be a complete survey of the field of model investigations. Chapters 2 to 6 represent accounts of specific investigations which the author has carried out himself. Chapter 2 forms part of a larger published paper written by the author (Ref. 10 of chapter 1). It was originally published with the permission of the late Mr. W.R. Carroll, B.E., M.I.E. Aust,, Director of Public Works, N.S.W. Some small alterations have been made to the original text to make the present chapter a self contained unit, A section of chapter 2 describes a field investigation for which no model tests were required. The author justifies its inclusion by the fact that in his experience the model investigator generally ends up doing some field investigations as part of his work and that this particular investigation can be regarded as typical of these. Chapters 3 to 6 are copies of reports of investigations carried out by the author under the general direction of Dr. G.R. McKay, Reader in Civil Engineering in the University of Queensland, They have been reproduced unaltered except for a few small changes in the opening sections of Chapter 3 made to bring it into the same form as the other chapters. Acknowledgement is made to Professor J.H. Lavery, Professor of Civil Engineering in the University of Queensland for permission to use this material.