麻豆传媒

The Clyburn Brook, in the Cape Breton Highlands National Park, is an important source of freshwater. The brook overlies an unconfined aquifer that supplies potable and irrigation water for the Ingonish area. The Clyburn Brook is partially fed by baseflow and is affected by withdrawal from the aquifer. This thesis examines the physical characteristics of the lower reaches of the Clyburn Brook using seismic techniques and finite difference numerical modelling.

In the area of study, the bedrock is the Ingonish River tonalite (555 卤 Ma), which is overlain by glaciofluvial sand and gravel of Quaternary age and modern fluvial deposits. Refraction seismic data indicates a depth to bedrock of 7 to 9 m in the 'bottleneck' area of the Clyburn Brook. Reflection seismic data indicates depths to bedrock ranging from 15 to 47 m. Some of this data is used to generate lateral and trough-like profiles of the canyon.

Finite difference numerical modelling of the canyon aids in the examination of aquifer flow characteristics in different water level settings. Survey data prepared by Dr. David Hansen, topographical and seismic data assist in the construction of two models, one in plan view and the other in a cross-sectional view. The models are connected to data tables that allow water level settings to be altered with ease. The models are examined in relation to six scenarios, representing water table elevation differences of 0, 0.05, 0.5, 1.0, 2.5 and 3.0 m between the stream and the canyon walls. Based on topography, it is determined that 3 m represents the maximum water level elevation difference. Using Darcy's Law, the hydraulic head values obtained are used to determine flow rates, which are subsequently examined in relation to baseflow contribution to the stream. That is, the contribution to stream discharge from groundwater seeping into the base of the stream. This study utilizes data from previous baseflow recession work by Dr. Hansen, in which the declining rate of discharge of the stream, when fed by baseflow only, was examined.

Using discharge and baseflow recession data, two volume calculations are made: (1) a hydrograph recession-based volume calculation to determine the volume of water lost from storage for each scenario, and (2) a geometric volume calculation for the plan-view model, change in water table elevation of 2.5 m (scenario #5). The first volume is then examined, using Darcy's Law and baseflow recession formulae, to determine the hydraulic conductivity value sufficient to produce a volume comparable to the geometric volume calculation for scenario #5. A hydraulic conductivity value of 0.6 to 0.7 m/d is produced, which is much lower than the 213.3 m/d value from a previous pump test. Finally, baseflow recession analyses are compared to acceptable low flow rates for different species of fish. A figure of depth versus recession time is generated and the impact on fish habitat and water quality is assessed. It is determined that, after 90 to 96 days of recession, fish habitat preferences are negatively impacted. When flow rates decline to 1.0 to 0.1 m3/s, pumping could have a detrimental impact on the quantity of water in the brook and the quality of salmonid habitat.

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Pages: 144
Supervisor: David Hansen