| Popis: |
At the shallow heads of canyons and seavalleys (shoaler than about 250 m), currentmeter records have shown high frequency of up- and downvalley alternation, but in the seavalley off the Fraser Delta at an axial depth as shallow as 85 m, the alternation is clearly in phase with the tides. The explanation is thought to be related to the larger range of the tides than we have found elsewhere. At 85 m in Fraser Seavalley, the currents run up the valley with the rising tide and down the valley with the ebbing tide. The fastest currents are found during the diurnal ebb tides of the spring tide period. The record at 220 m axial depth shows essentially an inverse relation to the tides so that the current is flowing upvalley during ebbs and down during floods. This contrast is interpreted as perhaps due to internal waves of tidal period moving down the valley axis. |
