FLOODS — BROOKS AND THIESSEN 345 



consequently a further release of snow water added to the tremendous 

 rain, making a total of 10 to 30 inches since March 9 (fig. 17), brought 

 the chief rivers to unprecedented stages. 27 The headwaters in the 

 mountains, however, were so well protected by dense coniferous 

 forests that the snow cover was not entirely removed and acted as a 

 good storage reservoir for the rain. At Pinkham Notch the depth 

 of snow cover was reduced from 48 inches on the 9th to 16.2 inches on 

 the 21st, and on Mount Washington summit from 20.5 inches to only 1 

 inch. 28 Accordingly, though great slush slides occurred, the floods in 

 the mountains were not exceptional. 



THE JOHNSTOWN FLOOD OF 1889 



The Johnstown flood of 1889, like the flood of 1936, was caused by 

 the meeting of a strong flow of tropical Atlantic air from the southeast 

 with a standing front of modified though cold polar continental air 

 near the crest of the central Appalachians. 29 Although the disaster 

 at Johnstown and vicinity, in which some 9,000 people were drowned, 

 was due chiefly to the bursting of a dam, the rainfall, averaging 6.2 

 inches over the Johnstown Valley, 30 is the outstanding occurrence of its 

 kind over the central Appalachians. 31 The maximum was 9.8 inches, 

 falling in 31 hours. Russell computes that 1.9 cubic miles of water fell 

 on the Susquehanna watershed, 1 cubic mile on the Potomac, and 0.9 

 cubic mile on the Allegheny and Monongahela watersheds. The 

 rain front swept from the Atlantic to Lake Erie in 16 hours. 32 



THE NEW ENGLAND AND NEW YORK FLOODS OF 1927, 1935, 1938 



The New England and New York floods of November 1927 were 

 caused in much the same manner as the widespread flood of 1936 and 

 the less general one of 1889. The chief flood was due to the rain of 

 November 3 to 4, when exceptional rains fell on soil thoroughly soaked 

 by the tropical storm a fortnight before. A western low and a weak 

 tropical cyclone joined forces in a deep current of tropical air, which 

 was forced northward at increasing speed by a great high centered 

 near Newfoundland. Part of the strength of this high, which at one 

 time reached 30.72 inches, was derived from a flow of cold air from 

 the Greenland region. The rainfall was due to convergence in the 



•» Cf. Uhl, W. F., Flood conditions in New England, Proc. Amer. Soc. of Civil Engineers, Mar., pp. 449- 

 483, 1937; and Grover, Nathan 0., The floods of March 1936, Part 1, New England rivers, U. S. Geological 

 Survey, Water Supply Paper 798, 466 pp., illus., 1937. 



i« For further details see Baldwin and Brooks, op. cit. 



'• Byers, H. R., Meteorological conditions during the March 1936 and other notable floods, loc. cit, p. 212. 



» Russell, T., The Johnstown flood, Monthly Weather Rev., vol. 17, pp. 117-119, 1889. 



» Hayes, M. W., Some flood-producing storms of the Atlantic Seaboard, Journ. New England Water 

 Works Assoc, vol. 51, pp. 207-208, 1937. 



» Russell, op. cit., Chart 6. 



