The floods of August 1955 were an unprecedented disaster in a arge area of the northeastern United States. They rank among the most destructive in the country's his ory. Augmented by the antecedent hurricane sto m of August 11-15, the rainfall of August 17-20 accompanying hurricane Diane reached maximum val es of 17 to 19 inches in south-central Massachusett • Record-breaking floods resulted within a broad re ion extending from southeastern Pennsylvania to east rn Massachusetts. The floods were outstanding in four categories: The large geogra hie area covered by floods of such magnitude; the ex ensive damage and loss .of life ranking with the grea est recorded in this country; the degree to which prio records were exceeded; and the distribution which as such that the greatest floods occurred predominate! on the smaller streams. Property damage has been stimated to be about half a billion dollars and was most~y concentrated in the heavily industrialized valleys f New England. A death toll of 179 persons was attr"buted to the floods. Peak discharges exceeded previ usly established maxima by 2. 2 and 2. 3 times respec ively, on Blackstone River at Woonsocket, R. I. , and Q inebaug River at Putnam, Conn.; 4. 1 times on Nau atuck River near Thomaston, Conn. ; and 4. 5 times on 1 ush Kill at Shoemakers, Pa. A unit runoff of 2, 300 c 1 hie feet per second per square mile occurred from ~· 50 square miles on Powdermill Brook near Westfiel , Mass. Although the floods were generally greate t on the smaller streams, Connecticut River at Hart ord reached the third highest stage since settlement an Delaware River between Port Jervis and Trenton exce ded the previous historic flood of 1903. This adv ce report has been prepared to supply preliminary · formation needed for immediate planning. It has been r leased pending preparation of a more comprehensive r port covering a three-month period of floods within an area from Massachusetts to North Carolina. In luded herein, for the region from Massachuset s to Pennsylvania, are general descriptions of the fEods, peak discharges for the present and previous rec rd floods at gaging stations, peak discharges at m y miscellaneous sites in the areas of greatest floo ing, and detailed stage and discharge data at 51 selecte gaging stations.