Closure dams are constructed for a variety of very different purposes; such as thecreation of a separate tidal basin for power generation or as sea defence structuresto increase safety. Compared to closure works, few other engineering works havesuch an extensive impact on the environment in all aspects. For instance, the mainpurpose of the construction of the Afsluitdijk closure dam in the Netherlands wasto provide protection against high storm surge levels and to facilitate land reclamation.Additional advantages were fresh water conservation and a road connectionbetween the provinces of Holland and Friesland. The purpose of a closuredam may be one or more of such objectives, but these are automaticallyaccompanied by other side effects, some of which may be negative. A thoroughstudy of these impacts is part of the design process. This book focuses on the technical aspects of the construction of a closure dam ina variety of circumstances. Every closure operation is a struggle against nature.Every action taken to obstruct the water flow will immediately be counteracted bynature itself. The knowledge gained from experience, whether successful or not,is supplemented by the results of advanced research and experiment. Nevertheless,the changes in conditions during the progression of the closure are sometimes difficult to predict. Allowing for flexibility in operations that areincorporated in the design provides an important tool.