The planning phase for a highway section usually involves consideration of a number of alternate highway locations, which often require construction across or along streams and floodplains. During the planning phase, evaluate the effects that location alternatives would have on stream systems. (See the for more details.) Include a preliminary hydraulic study of the various alternatives because the type and cost of drainage facilities required can determine location selection. As project development proceeds, you may find that locations selected without adequate hydraulic consideration to floodplain encroachments and extensive channel modifications are unacceptable.

Consider the environmental effects, risks, and costs of required drainage facilities in the final selection of an alternative. Analysis of alternative alignments may reveal possibilities for reducing construction costs, flood damage potential, maintenance problems, and adverse environmental impacts.

Detailed information and survey data are seldom available for an in-depth hydraulic study during the planning phase; however, it is possible to ascertain basic requirements and consequences of a particular location or alignment and the relative merits of alternatives. Topographic maps, aerial photography, stream gage data, floodplain delineation maps, and a general knowledge of the area often provide the basis for preliminary evaluations of alternatives.