ASSESSMENT OF THE HISTORIC HYDROLOGY OFTHE ASSINIBOINE RIVER AND WATERSHED 1793-1870

Abstract

In the aftermath of the 1997 Red River flood, archival materials were used to reconstruct the hydrologic history of the Red River prior to 1870 as part of the Geological Survey of Canada/Manitoba Geological Survey contribution to the study of the Red River (Rannie, 1999). All historic Red River 1l00ds were documented and general runoff conditions were characterized for most water-years from 1793-94 to 1869-70. Although the report noted several large 1l00ds on the Assiniboine and described general climatic conditions as they related to the state of the Red, the Assiniboine River and watershed were given less-detailed attention. Inthis respect, the report was typical of the treatment of the Assiniboine River in other hydrologic studies. "Always the bridesmaid, never the bride", the Assiniboine has been considered mainly insofar as it contributes to the 1100d problems on the Red rather than as an important river in its own right. The two largest public expenditures in the watershed (the Shellmouth Dam and Assiniboine Diversion) were initiated as measures to assist in managing Red River floods by reducing the Assiniboine's contributions; conservation and flood control along the Assiniboine were secondary (although not unimportant) objectives. Paleoclimatic investigations in the Palliser Triangle (part of which includes the headwaters of the Qu'Appelle and Souris tributaries to the Assiniboine) have emphasized the region to the west of the Assiniboine basin and there has been little systematic study of pre-instrumental climate and How within the Assiniboine basin itself. The relative anonymity of the Assiniboine is the more surplising since it may be described as the "quintessential large Prairie river". Located between the flood-prone, subhumid, Red River valley on the east and the drought-prone, semiarid, Palliser Triangle region to the west, the Assiniboine displays characteristics of both regions. The axis of the watershed runs through the parkland ecoregion, approximately along the boundary between forests to the north and east and grasslands to the south and west. In contrast to the large rivers of the western Prairies (such as the Saskatchewan, Red Deer and Oldman) which derive much of their flow from mountain sources, the Assiniboine is dependent on the Prairies for its entire flow and, with a drainage area of 153,000 km2 at Headingley, it is the largest purely prairie-fed river in western Canada. Furthermore, the Assiniboine watershed is one of most topographically and climatologically varied of large prairie streams. This report will focus on the historical hydrology of the Assiniboine River and watershed. Its specific objectives are • to provide an overview of the hydrometeorological characteristics of the basin which are relevant to hydrologic and dendroclimatic reconstructions; • to review the literature on the pre-instrumental hydroclimate and environmental conditions in and near the watershed; and • to reconstruct the hydrologic history of the Assiniboine River prior to the beginning of gauging records, ':Jsing archival and other historical materials.