Nearshore-Offshore Transport in the Great Lakes: Nearshore Physical Oceanography Measurements

C. R. Murthy, K. Miners, F. Chiocchio, J. Bull (CCIW)

Co-Principal Investigators: M.J. McCormick, D.J. Schwab, G. Miller, J. Saylor, and B.J. Eadie

Expected Project Duration: To coincide with EEGLE (2 field years '98-'99, '99-'00, followed by 2 years for analyses and modelling)

Summary:

It is our hypothesis that the episodic current reversals in the nearshore zone of Great Lakes are one of the major mechanisms for nearshore-offshore transport of water masses and sediments and biologically important materials (BIM).

Our experimental program is designed to test this hypothesis through the analysis of carefully planned field measurements in collaboration with Saylor et al., and Eadie et al., measurements and the application of numerical models developed by Schwab and Beletsky, and Bedford as outlined in the EEGLE program description. The specific mooring sites and the measurements proposed here are designed to extend the measurements collected by the above researchers into the high risk nearshore region in order to meet the following specific objectives:
  1. To identify and quantify the physical transport processes in shallow water during episodic current reversals responsible for nearshore-offshore transport of BIM's during winter/spring and summer conditions.
  2. To determine the climatology of coastal energetics of the episodic nearshore current reversals during winter/spring and summer conditions.
  3. To establish the dominant temporal and spatial scales of episodic events from nearshore current measurements (moored nearshore current meter array, shore based meteorological stations and nearshore transmission measurement stations).
  4. To undertake a comparative study of coastal ocean processes from this program and past programs undertaken in the Great Lakes.
  5. To establish and provide a data base of all our measurements and make them easily accessible to other program participants.
The measurement set that will be collected by the NOAA/COP EEGLE program: (1) Physical Oceanography Observations: Saylor, Miller, McCormick for the two field years (1998-2000) will be extended shoreward from the 20 m contour to the 12 m contour by establishing 5 current meter moorings inshore of stations V1,V4, A1, A4 and V9 (see EEGLE program description). These moorings will each consist of a SACM current meter deployed in a bottom mounted configuration with a measurement depth of 1 m off of the bottom. These instruments will provide records of water currents and temperature at 15 minute intervals coincident with the VACM and ADCP measurements that will be deployed by the NOAA researchers above. Although these moorings are considered high-risk in terms of damage or loss should a major storm or ice-scouring event occur during the deployments, the definition of the inshore flows is considered essential to identify and quantify the physical transport processes during the episodic current reversals responsible for nearshore-offshore transport of sediments. NWRI will assume the risk associated with deploying these devices in a highly energetic zone. In addition to the above moorings, a 1200Khz ADCP will be moored at site A2, alongside NOAA's 300Khz ADCP to collect bottom temperature with water current and backscatter data at 1 meter intervals throughout the water column. The water current and temperature information from this device will assist in the quantification of the physical transport processes while backscatter data for two frequencies from the same site will enable researchers Bedford & McDonald to estimate the vertical particle concentration profile.

In order to ensure that the local meteorological forcing is sufficiently delineated over the spatial scales involved in the study area, meteorological stations will be set out at two shore-based locations, one near St. Joseph and the other at a site near the Michigan-Indiana border. Each site will record wind speed (WS), wind direction (WD), air temperature (AT) and solar radiation (SR) on a Campbell 21x logger system as 15 minute averages.

In addition to the above instruments NWRI will establish 2 recording transmissometer systems as part of the GLERL sediment traps (Eadie et al) each consisting of a SEATECH 25cm transmissometers and a Brancker analogue recorder. Recordings will be made every 15 minutes consistent with the rest of the physical instrumentation deployed for this study. These systems will determine episodic events of high sediment loading at the sediment trap locations.

Project Rationale:

The EEGLE program is the most intensive scientific program on the Great Lakes since the Canadian initiated IFYGL program on Lake Ontario in 1972/73. In our opinion, Canadian participation is crucial to maximizing the potential scientific benefits of this research program.

Our Canadian colleagues are highly experienced with making successful nearshore current measurements. They have recognized a potentially major weakness in the EEGLE observation strategy and have proposed a viable option for correction while assuming all of the considerable risks associated with nearshore measurements. In addition, the results of the research efforts proposed here directly addresses coastal concerns common to both of our countries and all of the Great Lakes and if fully successful will generate tangible products to aid resource management.

Project Linkages:

EEGLE