Regional Drainage Patterns of Indiana

This paper reports regional drainage patterns observed during the development of surface drainage maps from aerial photographs of sev­ eral counties in Indiana. This drainage mapping is a part of the current highway research program at Purdue University. The airphotos used in this work were taken during 1937-1943 in connection with the United States Department of Agriculture map program. The prints were obtained from the Agriculture Adjustment Administration along with photographs of uncontrolled mosaics known as county index sheets. Approximately 25,000 prints were required for complete stereo-coverage of the state (3 )* The development of detailed drainage maps has emphasized the fact that definite drainage patterns are repeated in soils and rocks of like textures. Only recently have highway research engineers been observing these patterns through airphoto interpretation. However, certain basic stream patterns as determined by rocks and soils of an area have long been recognized in the natural sciences of geology, physiography, and geomorphology. Horizontal exposures of bare rock in Indiana are rare occurrences, and much of the state is covered with a mantle of glacial drift; conse­ quently, the drainage systems (for the most part) have had their be­ ginnings in either residual or transported soils. In regions where the rocks are covered with shallow soils, drainage patterns are decidedly different from those in regions of deep glacial drift. Through analysis of patterns exhibited in drainage maps of several counties, a definite relationship is observed between pattern shapes and regional geologic materials. The translation of airphoto patterns into drainage and engineering soils maps is in its infancy, but its importance is being recognized by