Hydraulics & Waterways
397995 - Design High Water Levels for Tidally-affected River Crossings
Thursday, June 7
10:30 AM - 12:00 PM
Location: Regency Room
The Upper Cook Inlet of Alaska is known for its wide range of tidal elevations, shifting mudflats, glacially-fed rivers, and the Turnagain Arm bore tide. The Alaska Department of Transportation & Public Facilities (DOT&PF) is currently in the design phase of the Seward Highway MP 75-90 Project which includes replacement of 8 bridges along the Turnagain Arm of Upper Cook Inlet. These bridges cross glacially-fed rivers near their mouths whose stages are tidally-affected. The bridge designs must account for water levels due to the 1% chance of exceedance discharge but also for extreme tide levels. Scour at the bridges will be most impacted by high discharges coupled with low tidal tailwaters. The NOAA tide station at the Port of Anchorage provides an excellent record of both predicted and measured tidal elevations but conditions further up Turnagain Arm are affected by winds, atmospheric pressure, Coriolis forces, river discharge, and geometry of the Arm itself, with tidal amplification as distance up Turnagain Arm increases. This presentation describes the results of a tidal measurement program at the 8 bridge locations, correlations to the NOAA Anchorage tide station, techniques to determine the design water levels and scour at the bridges, and methods to facilitate construction scheduling.