DRAINAGE PATTERN SIGNIFICANCE IN AIRPHOTO IDENTIFICATION OF SOILS AND BEDROCKS

THIS PAPER REPORTS THE ANALYSES OF DRAINAGE PATTERNS FOR THEIR USE IN THE IDENTIFICATION OF REGIONAL SOILS AND BEDROCKS BY MEANS OF AIRPHOTOS. THE STUDY IS ONE OF SEVERAL CONCERNING THE INTERPRETATION OF AERIAL PHOTOGRAPHS BY THE JOINT HIGHWAY RESEARCH PROJECT AT PURDUE UNIVERSITY. THE RELATIVE EASE WITH WHICH STREAM SYSTEMS CAN BE OBSERVED ON AERIAL PHOTOGRAPHS FACILITATES THE RECOGNITION OF DRAINAGE PATTERNS. IN THE NATURAL SCIENCES, IT HAS BEEN ACCEPTED FOR A LONG TIME THAT CERTAIN BASIC DRAINAGE PATTERNS SUCH AS THE DENDRITIC, TRELLIS, RADIAL, PARALLEL, ANNULAR, AND RECTANGULAR ARE ASSOCIATED WITH SPECIFIC LAND SURFACE MATERIALS. AIRPHOTO INTERPRETATION HAS REVEALED SEVERAL MODIFICATIONS OF THE BASIC DRAINAGE PATTERNS. FOR EXAMPLE, SOME OF THESE MODIFIED TYPES ARE THE RETICULAR, PHANTOM, AND LACUNATE. DRAINAGE PATTERNS, TRACED DIRECTLY FROM REPRESENTATIVE AIRPHOTOS OF VARIOUS PHYSIOGRAPHIC REGIONS THROUGHOUT THE UNITED STATES, ARE PRESENTED AS ILLUSTRATIONS OF PATTERNS WHICH DEVELOP IN THE SOILS AND BEDROCKS TYPICAL OF THE REGIONS. THESE EXAMPLES HAVE BEEN SELECTED TO SHOW NOTICEABLE DIFFERENCES IN DRAINAGE PATTERNS. FOR INSTANCE, DRAINAGE PATTERNS IN REGIONS WHERE THE ROCKS ARE BARE OR ARE COVERED ONLY WITH SHALLOW SOILS, ARE DECIDEDLY DIFFERENT THAN THOSE IN REGIONS OR DEEP GLACIAL DRIFT. LIKEWISE, DRAINAGE PATTERNS DEVELOP DIFFERENTLY IN HORIZONTAL ROCKS THAN IN TILTED ROCKS. IT IS CONCLUDED THAT SURFACE DRAINAGE PATTERNS CAN BE RELIED UPON IN THE AIRPHOTO IDENTIFICATION OF SOILS AND BEDROCKS ON A REGIONAL BASIS. /AUTHOR/