WAVE, CURRENT, AND DOCK MOTION MEASUREMENTS-SITKA, AK 


Wave energy entering New Thomsen Harbor in Sitka, AK 
was causing motion to harbor structures. Current, wave, 
and dock displacement measurements were requested 
both inside and outside of the harbor. The Alaska District 
Corps of Engineers required a wave/current gauge 
deployed immediately outside the harbor and a wave 
gauge deployed inside the harbor. The gauges needed to 
be capable of measuring wave periods between 4 and 24 
seconds. In addition, an accelerometer was needed to 
measure the displacement of the dock during the extreme 
dock movement events. The measurements were to be 
collected for a minimum of 6 months. 

SCOPE AND APPROACH 

For the dockside motion sensor system, EHI installed a 
modified TriAxys buoy payload connected to shore power 
with a battery backup. Motion data were collected at 4 Hz 
sampling rate each half hour. The data was both logged 
internally and transmitted via VHF to a receiving station 
located in the Harbor Master building at the dock facility. 
After the collection of each 30 minute burst, the data was 
sent electronically from the Harbormaster’s computer to the 
EHI Seattle office and Anchorage Corps of Engineers 
office. Based on background information supplied by the 
Corps, the in-harbor wave gauge was deployed 105 feet 

Dock motion sensor installation with 
pipe guardrail for protection from dock 
carts and snow shovels. 


from the dock motion sensor. The out-harbor wave/current 
gauge was deployed 1005 feet from the center of 
breakwater opening. 

RESULTS 

The instrumentation performed well however, no significant 
winter storms occurred during the measurement period. 
Wave measurements were extremely small both at the 
dock site and the in-harbor site. An interesting feature 
seen in the data record was the gradual decrease in water 
temperature near mid March. Comparisons with air 
temperature records from the Sitka Airport showed new 
extreme low records set for this time period. Minimum 
water temperature lagged minimum air temperature by two 
days. . 

Client Reference 

Ms. Deidre Ginter 
Pacific Ocean Alaska District 
US Army Corps of Engineers 

(907) 753-2805 
deidre.m.ginter@poa02.usace.army.mil 
Project Timeframe 

September 2005 – June 2006