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<br />15 <br /> <br />The post Piney Creek alluvium is confined to areas that were <br />periodically flooded before the advent of ,irrigation works. <br /> <br />It is therefore assumed that protohistoric, historic and Holocene <br /> <br />; <br /> <br />alluviums mapped by Swan and Whitney correspond to areas of past <br /> <br />flooding. <br /> <br />Air photo evidence suggested old ~tream channels in several <br /> <br />locations. These were ereas where creeks had for years been <br /> <br />channelized, diverted and in some case~ plowed over. Early topo- <br /> <br />'graphic maps indicated those channels that were streams at the date <br /> <br />of publica~ion (V.S, Geological Survey, 1902 and 1910), and soil <br />maps (Sweet and S1)encer, 1927; Sweet and others, 1929) ind,icated <br /> <br />those channels that contained stream alluvium. These areas that <br /> <br />air photo evidence indicated, and topographic and soil map~ con,. <br /> <br />firmed were previously stream channels, have been mapped as areas <br /> <br />of past 'flooding. <br /> <br />!. <br />I <br /> <br />Accuracy of Haps <br /> <br />The location of flood boundariAs is not precise, primarily <br /> <br />for two reasons. The first of these concerns the variable quality <br /> <br />of the criteria for mapping past floods, Air photo evidence of pas't' <br /> <br />floods is sparse, The evid,ence is often obscl'red o.robliterated by <br /> <br />agriculture or clearing of flood debris. The to'pographi,c evidence <br /> <br />can be very subtle, The quality of the eyewitness reports depends <br /> <br />on the memory of the resident. The certainty of map boundaries based <br /> <br />on surficial geology depends on the validity of the assumption that <br /> <br />'.;0 <br /> <br />these are areas that have recently flooded. Topographic and soil <br /> <br />maps were used where the air photo evidence was most vague, and only <br />