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<br />3-10 <br /> <br />based on their appearance and lithology. Decisions on sampling sites, <br />units to be sampled, and types of samples to be obtained must await <br />their approximate delineation through the reach to be improved. Soil <br />surveys along ,a proposed channel alignment can be useful in organizing <br />the investigation and identifying stratigraphic units. It should be <br />borne in mind that soil survey information is limited to a depth of <br />about 5 feet and is frequently not reflective of stratigrahpic units <br />at greater depth. <br /> <br />The inspection of the alluvial soil profile may be achieved by one or <br />a combination of several means. Exposures along the banks of streams <br />offer a frequently available means of study. This has the advantage <br />of enabling observation of in-place characteristics as well as relating <br />these characteristics to erosion from stream flow or bank stability from <br />seepage forces. Bank stability may be due to protection by vegetation, <br />or an irregular alignment which increases the roughness and thereby <br />reduces the velocity or other reasons. <br /> <br />From the standpoint of bank stability from seepage forces, the existing <br />channel could have sufficient vegetation, a protecting coating of fine <br />sediment, or a ground-water level which has adapted to the channel depth <br />over time. New excavation could cause problems which do not presently <br />exist. Information gained from inspection of stream banks and bottom <br />must be supplemented by borings or test pits when exposures along the <br />banks do not provide sufficient information on the in-place character- <br />istics of the deposits. <br /> <br />Exposed banks are often disturbed, desiccated or cracked and exhibit a <br />different set of properties than the protected materials along the <br />proposed cut and gradelines. <br /> <br />The place of observation along the channel is identified on the profile. <br />Observation points in addition to those along the channel alignment will <br />usually be required in order to interpret the stratigraphy and continuity <br />of the valley deposits. The tentative upper and lower surfaces of strati- <br />graphic units are determined and recorded on the profile. Each unit is <br />to be numbered and geomorphically classified. For example, unit I is a <br />recent sediment deposit overlying unit 2, a buried soil profile. Field <br />notes and logs should describe the appearance and condition, including <br />color, grain size, texture, structure, moisture, etc. of each unit in <br />accordance with ASTM D-2488. Geomorphic terms are to be used in cor- <br />relating between observation points. Identification as a stratigraphic <br />unit is required in addition to the specific characteristics that can <br />be described. <br /> <br />e <br /> <br />e <br /> <br />e <br />