This technical paper presents a general overview of the Corps of Engineers' past involvements, present practices, and the future roles in dealing with alluvial fan flooding problems. The Corps' approach to alluvial fan flooding studies and the analytical methods they use to assess potential flood hazards are summarized. Selected case studies are presented. Six important issues that need to be considered as part of an effective alluvial fan management approach are presented. An extensive list of references is also included. (fr).

Alluvial fans are gently sloping, fan-shaped landforms common at the base of mountain ranges in arid and semiarid regions such as the American West. Floods on alluvial fans, although characterized by relatively shallow depths, strike with little if any warning, can travel at extremely high velocities, and can carry a tremendous amount of sediment and debris. Such flooding presents unique problems to federal and state planners in terms of quantifying flood hazards, predicting the magnitude at which those hazards can be expected at a particular location, and devising reliable mitigation strategies. Alluvial Fan Flooding attempts to improve our capability to determine whether areas are subject to alluvial fan flooding and provides a practical perspective on how to make such a determination. The book presents criteria for determining whether an area is subject to flooding and provides examples of applying the definition and criteria to real situations in Arizona, California, New Mexico, Utah, and elsewhere. The volume also contains recommendations for the Federal Emergency Management Agency, which is primarily responsible for floodplain mapping, and for state and local decisionmakers involved in flood hazard reduction.

Last year the Hydrologic Engineering Center (HEC) and the Waterways Experiment Station incorporated the results from more than ten years of research and development into a new version of computer program HEC-6: 'Scour and Deposition in Rivers and Reservoirs' (HEC, 1977). Because of the extensive modifications made to HEC-6, an entirely new User's Manual was also prepared. HEC released a Beta Test Version of the program in the fall of 1989, for field testing. Public release of the new version of HEC-6 is scheduled for September 1990. This paper describes the present status of the program as of April 1990, the expanded capabilities, and the improved documentation to be included in the forthcoming release of computer program HEC-6. Keywords: Computer programs; User manuals; Sediment transport modeling; Deposition; One-dimensional mobile boundary model; Rivers; Reservoirs. (CP).

A two-dimensional horizontal finite element numerical model (RMA-2) was applied to a 15 mile (24 km) river channel-floodplain reach in West Germany. Previous applications of such models have been restricted to much smaller scales. The results indicate that finite element schemes may successfully estimate river stage in large scale floodplain applications. Computed stage hydrographs compared well with observed data using loss coefficients within expected ranges. Two-dimensional flow models have been applied to certain classes of river channel problems. Applications have included detailed analyses of flow patterns near structures such as bridges and floodplains. In all these problems the scale of interest has been small, e.g. reaches of river a few river widths long. Many estuary studies have been done that were of large scale; some of these utilized a hybrid (numerical plus physical) modeling technique. In a review of the application of finite element methods to river channels, Samuels reported that the river channel was resolved separately from the floodplain in only two studies. Missing in previous work is attention to large scale floodplain modeling. The work reported in this paper focuses on the feasibility and accuracy of applying a two-dimensional flow model to a large floodplain. Traditional floodplain studies have used semi-empirical flow routing with steady, one-dimensional computation of water surface elevations to define inundated areas. Keywords: Army Corps of Engines. (kr).

The Corps' Hydrologic Engineering Center (HEC) has developed a generalized simulation model capable of analyzing complex river-reservoir systems. The development of the model, 'HEC-5, Simulation of Flood Control and Conservation Systems' (Eichert, 1974, 1975) has been paced by the changing mission of the Corps as well as the evolution of computer systems. HEC-5 development and management, including code development, testing, documentation, training and field application experience, is discussed. (fr).