SPRING ICE-JAM FLOODING OF THE PEACE-ATHABASCA DELTA - EVIDENCE OF A CLIMATIC OSCILLATION

A historic record of spring ice-jam floods of the Peace-Athabasca Delt a was analyzed for the years 1826-1995, The temporal pattern of floodi ng is non-random. The likelihood of a flood following a flood, or a no n-flood following a non-flood, is greater than expected by chance. Pro bability analysis of flood occurrence reveals that the period 1860-188 0 was a time of unusually few floods, and the period 1915-1950 was a t ime of unusually frequent floods. The long-term flood frequency is 1 f lood in 6.25 years. Changes in flood frequency over the record reveal a pattern of oscillation described by a sine-based model that is corre lated with the long-term (Gleissberg) cycle of solar activity. Monte C arlo simulation was used to test a Bennett Dam Model and a Cyclic Mode l. The Bennett Dam Model is unlikely to have generated the observed fl ood history (p = 0.04). The observed flood history shows a better fit to the Cyclic Model (p = 0.65), No correlations between floods and ENS O cold or warm events was detected. The most recent wet period began a bout 1900 and ended in the early 1960's prior to completion of the W. A. C. Bennett Dam in British Columbia. As independent corroboration of climatically-driven changes in flood frequency we present three addit ional lines of evidence. The pattern of annual muskrat returns (95 yea r record) reveals both 10 year cycles and long-term patterns that agre e well with the observed flood cycle. The annual area burned in Wood B uffalo National Park is inversely related to flood occurrence. Incised channels and dendritic drainage patterns in the bed of Lake Mamawi pr ovide probable evidence of a previous dry period in the delta. Climati c change or oscillation likely underlies the drying trend observed in recent decades in the Peace-Athabasca Delta.