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)-1-8 channel depends on several factors. These include the amount and ease of transport of the material and the difference in hydraulic character- istics between the reach to be improved and the reach upstream that contains the bed material. The relationship between bed material avail- ability and channel stability is discussed in NEH, Section 3, Chapter 4, Transportation of Sediment by Water, pages 4-36 and 4-37. e The channel investigation should include an estimate of the volume of bed material available in the bed of the stream and where the deposit is located with reference to the proposed improvement. If the bottom of the deposit cannot be reached, this should be indicated in the notes. Representative samples of the bed material are to be obtained. The amount required for various gradations of material is giyen in Table 3-2, NEH, Section 8, Chapter 3. A sample of the surface armor should be obtained, if present, as well as a sample of the underlying finer accumulation. For analysis of stability, the geologist is expected to define whether discharges critical for stability should be defined as "clear water" or sediment laden flows. In most instances, the wash load will not be of sufficient concentration to classify the flows as other than "clear water". An examination of suspended load records on a regional basis will provide good clues as to the likelihood of significant concentrations. A knowl- edge of the watershed will also serve to indicate the extent of critical erosion. Reservoirs will reduce concentrations to relatively low levels. The influence of bed material on the stability of channels is discussed in NEH, Section 3, Chapter 4, pages 4-25 to 4-28. e Where bedrock is to be removed from the channel, the potential effects on stream banks and bed both upstream and downstream must be considered. Where rock is to be removed from a channel 'section, its disposal must be planned. Alternative disposal methods may include wasting in a pre- selected area, use in channel construction (riprap, filters), salvage, etc. Local highway agencies are often valuable sources of information concerning rock quality and ease of removal. Site Investigation Reports Completion of the Stratigraphic-Unit Profiles The first step in preparation of site investigation reports is to com- plete the longitudinal profile and description of stratigraphic units in the channel reach to be improved. As stated on page 3-11, this is e