58 
not warranted at this time given ongoing collection of more appropriate shallow- 
water data. In the interim, the EPA recommends that states assess their water clarity 
criteria using the CFD methodology which uses existing published biological refer¬ 
ence curves to define the amount and pattern of allowable criteria exceedances. 
Figure V-l illustrates the biological reference curve that states should apply in the 
CFD-based water clarity criteria assessment of tidal fresh and oligohaline segments 
with shallow-water bay grass designated uses. Figure V-2 illustrates the biological 
reference curve that should be applied in the assessment of mesohaline and polyha¬ 
line segments with shallow-water bay grass designated uses. Appendix H in this 
document provides the equations for the Chesapeake Bay water clarity criteria 
biological reference curves. Preliminary results from evaluation of limited shallow- 
water monitoring data indicate that biological reference curves generated from 
mid-channel data (Figures V-l and V-2) and those generated from shallow-water 
monitoring data (see Figure VII-11 in Chapter 7) are quite similar in overall shape 
and levels of allowable exceedances. 
—i 
Oligohaline and Tidal Fresh Monthly Clarity Biological Reference Curve 
Percent of Volume 
Figure V-1. Chesapeake Bay water clarity criterion biological reference curve for application 
to tidal fresh and oligohaline shallow-water designated-use habitats. 
chapter v 
Refinements to the Shallow Water Designated-Use Assessment Procedures 
