Coulee Alignment and the Wind in Southern Alberta, Canada
Study of the distinctive pattern of alignment and geographical distribution of more than 250 coulees in the plains of southern Alberta shows that (1) the coulees in question have a mean orientation of N. 70° E., and (2) their spatial distribution is not ubiquitous but rather displays a concentration in the area from Lethbridge west to the Rocky Mountain front. Several possible hypotheses of origin of the aligned coulees are considered, including subsurface structural control, the role of regional slope, the effect of lithologic differences, and wind action. Action of postglacial wind, operating to initiate surface furrows (by wind-driven snow or rain) that were enlarged by running water, accounts for the three outstanding characteristics of the aligned coulees: (1) their preferred orientation of N. 70° E., which approximates the mean direction of the strongest chinook winds in the southern Alberta plains; (2) their geographical distribution, which coincides with that part of the region experiencing the most pronounced chinooks; and (3) their almost exclusive location on windward topographic surfaces. No other hypothesis of origin is known that can satisfactorily explain all of these observed facts.