Prediction and Modeling of Flood Hydrology and Hydraulics

The basic principles underlying the most commonly used physically-based models of the rainfall-runoff transformation process are reviewed. A thorough knowledge of these principles is a pre-requisite for flood hazard studies and, thus, this chapter reviews several physically-based methods to determine flood discharges, flow depths, and other flood characteristics. The chapter starts with a thorough review of linear system theory applied to the solution of hydrologic flood routing problems in a spatially aggregated manner -Unit Hydrograph approaches. The chapter then proceeds to a review of distributed flood routing approaches, in particular the kinematic wave and dynamic wave approaches. The chapter concludes with a brief discussion about distributed watershed models, including single event models in which flow characteristics are estimated only during the flood, and continuous event models in which flow characteristics are determined continuously during wet periods and dry periods. INTRODUCTION Flood prediction and modeling refer to the processes of transformation of rainfall into a flood hydrograph and to the translation of that hydrograph throughout a watershed or any other hydrologic system. Flood prediction and modeling generally involve approximate descriptions of the rainfall-runoff transformation processes. These descriptions are based on either empirical, or physically-based, or combined conceptualphysically-based descriptions of the physical processes involved. Although, in general, the conceptualizations may neglect or simplify some of the underlying hydrologic transport processes, the resulting models are quite useful in practice because they are simple and provide adequate estimates of flood hydrographs. In modeling single floods, the effects of evapotranspiration, as well as the interaction between the aquifer and the streams, are ignored. Evapotranspiration may be ignored because its magnitude during the time period in which the flood develops is negligible when compared to other fluxes such as infiltration. Likewise, the effect of the stream-aquifer interaction is generally ignored because the response time of the subsurface soil system is much longer than the response time of the surface or direct runoff process. In addition, effects of other hydrologic processes such as interception and depression storage are also neglected. Event-based modeling generally involves the following aspects: 1Ramírez, J. A., 2000: Prediction and Modeling of Flood Hydrology and Hydraulics. Chapter 11 of Inland Flood Hazards: Human, Riparian and Aquatic Communities Eds. Ellen Wohl; Cambridge University Press.