OVERVIEW

Roy D. Dodson

Dodson & Associates, Inc.
Houston, Texas.

This chapter deals with the practical considerations involved in identifying the floodplain for a stream channel, and analyzing the flow characteristics of the channel system, including its floodplain. In general, any land area that is susceptible to inundation by rising or flowing flood waters from any source could be considered to be a floodplain area. This would include areas affected by coastal or lacustrine (lake) flooding. However, the emphasis of this chapter will be on riverine floodplains, which are affected by flood waters from a stream or river.

The determination of flood elevations and floodplain boundaries along stream channels has become increasingly important as more development has occurred in floodplain areas, or in areas that have been reclaimed from the floodplain.

A floodplain analysis requires a large amount of data in order to be accurate and complete. Cross sections of the stream channel and detailed geometric descriptions of bridges and other structures are required. In addition, experience is usually required to accurately assess the roughness characteristics of a channel, to properly lay out cross sections, and to adequately address many other aspects of a good flood plain analysis. Sophisticated computer programs are available to analyze the data and produce detailed computations of water surface elevations, floodplain boundaries, and other results. However, these programs can produce misleading results without a properly planned and executed analysis.

Because of the subjective judgments required for some of the input data and the uncertainty...