Real-time monitoring of currents and water level at second narrows to improve port efficiency in Vancouver harbour

A real-time monitoring system for currents and water levels was installed at Second Narrows in the Port of Vancouver in March 2001. Second Narrows restricts the movement of marine traffic into the upper harbour because of its strong tidal streams, limited depth and the presence of both a vehicular bridge and a rail bridge. The Port of Vancouver undertook a joint project with the Canadian Hydrographic Service (CHS), CN Rail and terminal operators in the upper harbour to replace the present system of predicted water levels and currents with an on-site measurement system at the rail bridge. Water levels and currents are measured at the Narrows; bridge and draft clearances are calculated and the results telemetered to the Port management and traffic control centre for real-time display. Current data are provided by an Acoustic Scintillation Flow Meter (ASFM), manufactured by ASL Environmental Sciences Inc. of Sidney, BC. Water level data are provided by an Aquatrak sensor manufactured by Bartex of Annapolis, MD. Currents are measured at two depths, and water level at one point under the bridge, every 5 minutes. The display shows a 24-hour history of currents at both levels, and the measured water level (the full data history is also stored). The current data show significant departures from the predicted tidal flows as, to a lesser extent, do the water level data. The system has operated in a trial mode for the past two years to assess its operational reliability. During this period two significant outages occurred. Modifications to the installation and to maintenance procedures to prevent their recurrence are described, and future plans for the operational use of the system are discussed.