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<br />3-12 <br /> <br />Complexity in the geomorphology of the site has a strong bearing on all <br />phases of the investigation. Contrasting levels of complexity may <br />include on the one hand a geomorphology as simple as one having a single <br />stratigraphic unit uninterrupted by discontinuities, or maybe thin beds <br />of sand or gravel that lack continuity and can be treated as one highly <br />variable unit, to another that consists of a number of overlapping units <br />frequently broken by discontinuities or disappearances from one reach to <br />the next. In all ins tances, including those with the mos t complex array <br />of stratigraphic units, an understanding is needed of the sedimentation. <br />processes and geologic history facilitates correlation and delineation <br />of units, locations of discontinuities, etc. <br /> <br />e <br /> <br />The presence of dispersive clay soils along proposed channel alignment <br />will have an effect on the intensity of investigation. <br /> <br />Dispersive clay soils often occur in lenses, spots and discontinuous <br />strata. In order to tentatively identify dispersion problems, it will <br />be necessary to check each stratigraphic unit at each test hole site for <br />dispersive clays by means of the field "crumb" test performed on material <br />at natural moisture. If field tests indicate pOSSible dispersion <br />problems, sufficient holes and samples should be established to delineate <br />the problem areas or depths. <br /> <br />Location of Sites for Sampling and ~ogging <br /> <br />The location of pit or drill hole sites is based on the tentative delinea- e <br />tion of stratigraphic units. There is a two-fold purpose in selection of <br />these sites. One purpose is to obtain representative samples, the other <br />is to "prove out" the tentatively identified stratigraphic units shown on <br />the profile. If the logs at one test site fail to correlate with those <br />at the site next upstream or downstream, then another site should be <br />chosen between them, at least for the purpose of correcting the profile <br />if not for additional sampling. <br /> <br />For long reaches where continuity of stratigraphic units has been estab- <br />lished, it is best to sample widely from anyone stratigraphic unit rather <br />than concentrate in a small part of the total reach. This will improve <br />the possibilities for discerning variations within the unit. <br /> <br />The usual location for test hole sites is on top of the bank near to but <br />not necessarily immediately adjacent to the stream. The preliminary <br />geomorphic determinations should indicate whether sites on both sides of <br />the channel must be investigated. <br /> <br />e <br />