The postglacial drainage of till plains and lake beds by perennial and intermittent streams in southeastern Michigan reveals local adjustments caused by human activity. The present drainage pattern reflects the construction and subsequent maintenance of the local road network. The impact of the road grid on the linear coastal drainage off the Port Huron Moraine's eastern flank was studied from Lexington Heights to Forester, Michigan. Borrow pits supplied the aggregate used to construct bridges and culverts. These facilities restrict flow and reduce transportation of sediment‐laden runoff. This results in increased but localized sedimentation. The extension, maintenance, and use of road networks has artificially increased the drainage density of the region by creating additional avenues for surface flow. Road networks also truncate natural drainage channels, forcing the coalescence of the smaller order basins, thereby increasing downcutting and runoff in channels whose natural erosional development would have been much less. Channel reaches whose upland drainage has been pirated experience decreased runoff and exhibit less erosion. Such modern changes in drainage topology pose problems to the reconstruction of historical postglacial drainage patterns, since they result in greater stream drainage density. Copyright 1979 by the American Geophysical Union.
