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TWo categories of floods account for most flood losses: those affecting land areas adjacent to streams or rivers (riverine flooding), and those affecting the shorelines of lakes, bays, and oceans. The main concern of this report is riverine flooding and, in particular, locations in which flash floods are likely to occur. In riverine situations, flooding results from rainfall and/or snowmelt runoff that exceeds the capacity of the main channel of the river or stream (bank full capacity). Flooding can also result from such causative events as the breach of a dam or levee, or an ice jam. The source of the threat can vary from a small creek or drainage to a large river such as the Mississippi or the Ohio. A community can be vulnerable to many sources of riverine flooding. . Both structural and nonstructural methods have been used to try to limit flood damages. The structural methods include channel enlargement and the construction of levees, reservoirs, and bypasses. While such structural measures can greatly reduce the threat of flooding and consequent losses, they may create a false sense of security and encourage development in partially protected areas. Thus, when a rare flood occurs, even greater flood losses may be sustained. This may contribute to the rising trend in flood damages shown in Figure 2. Nonstructural strategies for reducing flood losses include the regulation of flood plain use, floodproofing of buildings, temporary or permanent evacuation of threatened areas, and the development of flood forecasting and flood warning systems. The goal of a local flood warning and response system is to reduce losses by increasing the length of warning time in which a community can react to a potentially damaging event and, given the extra warning time, improve its response. The time between the causative .,. 3