The Effects of the Gardiner Dam on Geomorphic Processes and Morphology in the South Saskatchewan Rivery Valley: Riverhurst to Outlook
| dc.contributor.committeeMember | Acton, D.F. | |
| dc.creator | Rasid, Harunur | |
| dc.date.accessioned | 2024-01-10T20:16:38Z | |
| dc.date.available | 2024-01-10T20:16:38Z | |
| dc.date.issued | 1974-11 | |
| dc.date.submitted | November 1974 | |
| dc.description.abstract | The construction of the Gardiner Dam across the South Saskatchewan River Valley induced geomorphic changes in the valley, both downstream as well as upstream from the dam. One of the fundamental changes resulting from the creation of the new reservoir, Lake Diefenbaker, was the alteration in the hydrological regime of the South Saskatchewan River below the dam. Prior to dam construction, the South Saskatchewan River experienced peak discharges during the spring breakup and in the middle of the summer, whereas the lowest discharges were recorded during the winter. Now, with regulation of the reservoir, a fairly uniform rate of downstream discharge is maintained during the winter but in spring and summer the release is kept at a minimum so as to recover the reservoir capacity. Changes have also occurred in the volume of suspended sediment load of the river below the dam. Since the reservoir (Lake Diefenbaker) traps almost 100% of the suspended load of the inflowing South Saskatchewan River, comparatively clear water is released from the dam and this has induced channelbed degradation below the dam, of the order of 0.11 foot per year, in the 6 years (1966-1972) following the closure of the dam. A general coarsening of bed material has taken place in the river channel between the Gardiner Dam and Outlook, because relatively coarse materials no longer could be transported by the stream due to its loss of competence consequent upon decreased flow. Further, significant decrease in the width of the channel, evident by 1971, resulted from the reduction in mean annual discharge of the river downstream from the dam. Upstream from the dam, the reservoir induced fundamental changes both in the geomorphic processes as well as the morphology of the valley, drowning many typical riverine features and initiating lacustrine forms and shoreline processes in the reservoir. In the reservoir, wind-induced wave action is the principal geomorphic agent and causes cliff and shoreline erosion. In the several surveyed sections the average rate of cliff erosion in 1971-1972 was 10 ft, the highest and the lowest rates being 18 ft and 1 ft respectively. Variations in the rate of cliff erosion relates to differences in such factors as effective fetch length, duration of wind, and shore slope. The materials eroded from the shoreline are transported by direct wave movement and wave-induced longshore currents and deposited either at shallow depths along the shoreline, where they form a depositional shelf, or in deeper waters. The average annual rate of deposition along selected cross-profiles of the lake was 0.07 ft during the period 1965-1971. The exposed part of the depositional shelf above the lowest water level, which here is also called a beach, experiences rapid changes in morphology and in the distribution of surficial materials due to direct wave action. The distribution of beach materials, classed by mean grain sizes, appears to be related to the effective fetch length, magnitude of wave energy, and the beach slope. In addition to materials eroded from the shoreline and cliffs, another source for sedimentation in the reservoir is the suspended load carried by the South Saskatchewan River. The life expectancy of the reservoir, estimated on the basis of the average annual suspended load of the South Saskatchewan River (6,000 acre-feet), is about 900 years. Since most of the sediment carried by the river would be deposited in the upper zone of the reservoir, the zone near the Gardiner Dam would not receive any significant amount of river sediment for 100 years following the completion of the dam. Most of the morphologic changes occur within the limits set by high and drawdown lake levels (i.e., between 1825 ft and 1790 ft), since it is here that wave action is prominent. Thus, the beach morphology undergoes significant changes within this zone of fluctuating water levels. In addition, wave action also induces major changes immediately above the high water level as cliffs are undermined or otherwise affected. Only minor changes have occurred in the subaqueous slope and the lake bottom. The development of post-reservoir morphological features such as cliffs and beaches are controlled not only by the wave action but also by pre-reservoir morphology, slope and lithology of the valley. The processes of geomorphic change in the reservoir will be slowed down when such morphological features as beaches and cliffs attain an equilibrium with the wave energy in the lake. To illustrate this, variables affecting beach equilibrium and controlling the relative stability of the cliffs were integrated into two empirical models. From these the length of time required to attain beach equilibrium—on the basis of the logarithmic relationship that exists between the initial beach slope and the rate of change in the beach slope—has been estimated. According to this relationship, both steep beach slopes (25% to 35%) as well as moderately steep slopes (10% to 20%) would attain the equilibrium slope (approximately 5%) in a period of 30 (i5) years, following the completion of the dam. | |
| dc.identifier.uri | https://hdl.handle.net/10388/15417 | |
| dc.title | The Effects of the Gardiner Dam on Geomorphic Processes and Morphology in the South Saskatchewan Rivery Valley: Riverhurst to Outlook | |
| dc.type.genre | Thesis | |
| thesis.degree.department | Graduate Studies and Research | |
| thesis.degree.discipline | Geography | |
| thesis.degree.grantor | University of Saskatchewan | en_US |
| thesis.degree.level | Doctoral | |
| thesis.degree.name | Doctor of Philosophy (Ph.D.) |