CGRG Bibliography of Canadian Geomorphology
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Author : Brooks, G.R.; St. George, S.; M ichael Lewis, C.F.; Medioli, B.E.; Nielsen, E.; Simpson, S.; and Thorleifson, L.H,
Date : 2003.
Title : Geoscientific Insights Into Red River Flood Hazards In Manitoba. The Final Report of the Red River Flood Project
Publication : Geological Survey of Canada, Open File Repor
Issue : 4473.
Page(s) : 35 p.
Abstract
The Red River Flood Project contributes relevant geoscience information on the Red River flood hazard problem. The research provides a century to millennium time-scale context for the modern flood problem. The results enhance understanding of the frequency-magnitude of extreme Red River floods and geological processes that may be affecting the long-term trend of flooding. The 1826 flood is interpreted to be the largest Red River flood since at least AD 1648, based on tree-ring flood signatures within bur oak trees. The historical pattern of high magnitude Red River flooding implies that the frequency magnitude relationship changes over time and that flood flows are not independent and randomly distributed. Better estimates of flood frequency-magnitude could be provided by techniques that account for non-stationarity and non-randomness in the discharge records. Historical and tree ring evidence indicates that the peak flows of the Red and Assiniboine rivers coincided in 1826 and 1852. Accounting for this synchronism is critical in modeling the 1826 flood accurately. Peak flow at Winnipeg during the 1826 flood coincided with extremely strong, persistent winds from the south. Wind set-up should be considered by any future hydraulic studies of the 1826 flood. The rate of valley enlargement through lateral channel migration and incision is not significantly altering the discharge capacity of the shallow valley occupied by the river over time-scales of up to several centuries. The flood hazard on the adjacent clay plain is not being appreciably affected by changes to the valley cross-sectional area. Differential uplift has caused the Red River to lose gradient gradually over time. Hydraulic modeling for past scenarios of gradient implies that broad, shallow floods are intrinsic to the basic setting of the Red River valley and are not the product of ‘recent’ landscape changes. The minor rise in mean depth occurring from the continued loss of gradient over the next few centuries will not significantly alter the flood hazard. Hydroclimatic reconstructions indicate that climate in southern Manitoba has been relatively stable over the last two hundred years, but was more variable prior to 1800. Climatic case studies in regional drought planning that are based exclusively on 20th century instrumental records may under-estimate worst-case scenarios. Natural fluctuations in hydraulic head from climatic variability within the Upper Carbonate Aquifer near Winnipeg have been much smaller than the effects of groundwater withdrawals during the 20th century. Groundwater usage from this aquifer is the most important consideration for management purposes.
Bibliography of Canadian Geomorphology