VIMSWAVE - VIMS DIRECTIONAL WAVE DATA

 

From the fall of 1988 until the spring of 1995, the Virginia Institute of Marine Science, in cooperation with the Virginia Department of Conservation and Recreation, operated a wave station 2.5 nautical miles northeast of the Thimble Shoal Light (TSL) in Lower Chesapeake Bay to collect long-term directional wave observations. After the initial season, a second wave station was briefly placed in operation north of the Wolf Trap Light (WLT) and a third wave station was operated simultaneously with the TSL station during the winter and spring of 1993 at the eastern end of the Thimble Shoal Entrance (TSE) channel near the Chesapeake Bay mouth. Although the program was terminated in 1995 for lack of funding, these stations provide the only systematic wave observations known to exist in Chesapeake Bay. The observations are made available here in html format (Microsoft Excel).

  

 

Station Locations

 

Thimble Shoal Light (TSL): latitude 37º 2.4’N, longitude 76º 11.9’W

Thimble Shoal Entrance (TSE): latitude 36º 58.4’N, longitude 76º 2.3’W

Wolf Trap Light (WTL): latitude 37º 24.8’N, longitude 76º 11.8’W

 

Station Instrumentation

 

Waves were measured and recorded at the above stations using self-contained Sea Data Model 635-9RS directional wave gages with Paro Scientific high precision quartz pressure transducer, KVH digital compass, and Marsh-McBirney 2-axis electromagnetic flow sensor. The gages were attached to weighted tripods mounted on the bay floor and retrieved at monthly intervals for data recovery and servicing by scientists and crew of the R/V Bay Eagle commanded by Captain L. D. Ward. Scientist in charge: J.D. Boon (boon@vims.edu).

 

Wave Parameters

 

Both Sea Data wave gages were programmed to conduct burst-sampling; i.e., to power on sensors and record a burst sample of either 1024 (TSL, WTL) or 2048 (TSE) readings of pressure and current flow at 1-second intervals once every three hours. Dynamic pressure was later converted to fluctuating surface level using linear wave theory and corrected for the effects of frequency-dependent attenuation at mean sensor depth. Wave parameters determined during processing include the following international sea state definitions adopted by the International Association for Hydraulic Research:

 

·        Zero-moment wave height (Hm0) – The root mean square value of the corrected surface level (CSL) times four; considered equivalent to the significant wave height or average of the one-third highest waves in a sample wave record.

 

·        Zero-crossing wave period (Tz) – The duration of a sample wave record divided by the number of zero-up crossings of mean CSL in that record.

 

·        Spectral peak period (Tp) – The reciprocal of frequency corresponding to the highest peak in power spectral density computed for a sample wave record.

 

Other parameters recorded:

 

 

 

 

 

>20

20-16

16-12

12-8

8-6

6-4

<4

 

 

 

WAVE DATA BASE

 

Statistical summary data  - Directional wave data for the Thimble Shoal Light (TSL) wave station are organized in six files between 1988 and 1995. Two additional files contain observations for Wolf Trap Light (WTL) and the Thimble Shoal Entrance (TSE). Each file contains an array of wave parameters in columns and bursts in rows identified by date and time. Click on the files listed below to open (use Windows ‘copy’ and ‘paste’ to copy data to an Excel workbook).

 

TSL8889 TSL9091 TSL9192 TSL9293 TSL9394 TSL9495

TSE93 WTL8990

Wave records during storms – Individual waves can be viewed in simultaneous records from station TSL and TSE during three northeasters in 1993 and a brief but intense storm on September 22, 1994, that produced the largest individual wave observed at TSL (3.4 meters from crest to trough). Click on the files listed below to open (use Windows ‘copy’ and ‘paste’ to copy data to an Excel workbook).

 

TSL930211 TSE930211 TSL930226 TSE930226 TSL930313 TSE930313

TSL940922

Energy-weighted joint distribution of wave period and wave direction – The color-coded plots listed below show the periods of the most energetic waves and their direction of travel during a typical winter season. Westerly-directed Atlantic Ocean waves of 8-11 second period are characteristic of station TSE and south-southeasterly moving Chesapeake Bay waves of 4-5 second period are the norm at station WTL. Sea states at Station TSL contain a mix of these waves.

 

TSE TSL WTL

Acknowledgements – Field operations in all types of weather conditions, laboratory work maintaining instruments and tripods (including parts of one recovered in Virginia Beach) and unending data processing chores made collection of the data listed here anything but simple. Special thanks go to Bob Gammisch, Frank Farmer, Dan Hepworth, Todd Nelson, and Captain Duran Ward of the R/V Bay Eagle.