As discussed at the 5/27/98 EEGLE modeling group meeting, we have developed
a vertical segmentation scheme for the Lake Michigan 2 km hydrodynamic
model simulations.  There are 40 sigma levels (39 layers) in the segmentation.
This top 20 layers cover the upper 25% of the water column with uniform
(delta sigma = 0.0125) vertical spacing.  Between the 20th layer and the
bottom, layer thicknesses increase and decrease geometrically so that the
lowest layer thickness is also 0.0125.  Here are the levels:
 
     i   sigma
    -- ---------  
     1  0.000000
     2 -0.012500
     3 -0.025000
     4 -0.037500
     5 -0.050000
     6 -0.062500
     7 -0.075000
     8 -0.087500
     9 -0.100000
    10 -0.112500
    11 -0.125000
    12 -0.137500
    13 -0.150000
    14 -0.162500
    15 -0.175000
    16 -0.187500
    17 -0.200000
    18 -0.212500
    19 -0.225000
    20 -0.237500
    21 -0.250000
    22 -0.265407
    23 -0.284398
    24 -0.307805
    25 -0.336656
    26 -0.372217
    27 -0.416049
    28 -0.470075
    29 -0.536667
    30 -0.618745
    31 -0.700824
    32 -0.767415
    33 -0.821441
    34 -0.865273
    35 -0.900835
    36 -0.929686
    37 -0.953093
    38 -0.972083
    39 -0.987500
    40 -1.000000