The following hydrographic data are from Maine Maritime Academy student cruise on September 25, 1992. The stations you will be working with are from the west side of the bay and are shown with colored circles here:

Homework Questions Use the figures below to answer the following questions

  1. Which property, salinity or temperature, is principally determining the density field? How did you reach that conclusion?
  2. If you were going to model the west side of Penobscot Bay as a 2-layer estuarine system, at which density level would you separate the two layers and why? Note: You will need to use both density and salinity fields to answer this.
  3. Roughly speaking, what is the average density in each of the layers you chose in the previous question?
  4. Given a rms tidal velocity, Ut, of 0.5 knot, and an average width, b, of 16 km for the Bay, and an average of 9.5 million cubic meters of freshwater per tidal cycle (12 hours) coming in to the bay from the Penobscot River (this value is a 10-year climatological average for the month of September), what is a reasonable value for the estuarine Richardson number:

    5.  

     
     
     
     
     
     
     
     

    for Penobscot Bay in September? NOTE: If you don't have your conversion sheet handy, for converting from knots (nautical miles per hour) to m/s, use the facts that 1 n.m. = 1.16 standard mile, and 1000 m = 0.6 standard mile. Show all of your work. BONUS QUESTION (0.25 pt): why are tidal velocities often given in knots rather than units like cm/s or m/s?

  5. If (one-way) entrainment into the upper layer occurs when Ri > 0.5, and two-way turbulent mixing occurs when Ri < 0.5, which do you expect to occur in this part of Penobscot Bay in September?
  6. For Penobscot Bay R/V (ratio of river input over one tidal cycle to tidal prism volume, or volume of water brought in on the flood tide) is on the order of 0.005 - 0.007. Yet the west side of the bay shows some characteristics of a highly stratified estuary rather than those of a partially mixed estuary. Why might this be? (Hint: while an estuary like the Chesapeake might 10 m deep, Penobscot Bay averages more like 60 m).
  7. BONUS QUESTION (0.5 pt): What are the mean temperature and salinity of the salt wedge coming in to Penobscot Bay? What proportion of the west bay is occupied by the wedge? What temperature and salinity would you expect to find at depth in the waters just outside the mouth of Penobscot Bay?
Here are the figures you'll need to work this problem. This type of plot is called a hydrographic section. The x-axis is distance along the transect (elapsed distance that the ship has travelled from station to station) from the head of the bay to its mouth. The y-axis is depth. The contours are of temperature, salinity and density, respectively. The color code is to the right on each section, and the black dots indicate the locations of the measurements. In reality, measurements were taken every meter, but I have plotted only every tenth measurement, for clarity. The station numbers (station number is a reference number for all the measurements taken at a given geographic location) are plotted along the top (3 4    5 ... 16       17).