Appropriate understanding of the hydrological processes and the associated timing and scale of the hydraulic loadings are fundamental to the design and operation of temporary and demountable flood protection solutions for any particular location. The precipitation or other source of water and the response of the catchment to this will determine the shape of the hydrograph and the characteristics of the loading on the
flood protection systems. The development of the hydraulic criteria for temporary or demountable flood defence schemes are outlined in Section 4.1. A major output from the hydraulic analyses is the available lead time. The lead time and how it affects the
design process is discussed in Section 4.2.