results become a surrogate for the percentage area that these creeks represent in a 
segment. 
A STAC-convened expert panel (described in detail in Chapter 2) has reviewed the 
interpolation of spatial data. Several standardization decisions for interpolation 
methodology will need to be made to address the panel’s recommendations for 
addressing shallow-water monitoring data (STAC 2006). 
WATER CLARITY CRITERIA ASSESSMENTS USING 
SHALLOW-WATER MONITORING DATA 
The water clarity assessment uses data from the shallow-water water quality 
mapping to obtain high-resolution data in nearshore shallow waters. This section 
describes the data analysis protocols for application of high-resolution turbidity 
measurements to assess attainment of state-adopted water clarity criteria in shallow- 
water monitored tidal tributaries and embayments of the Chesapeake Bay. 
During each day of water quality mapping with the Dataflow, the operator stops at 
five to eight locations (calibration stations) to measure photosynthetic active radia¬ 
tion (PAR) so that the light attenuation coefficient (K d ) can be calculated and 
correlated with the in situ turbidity values recorded simultaneously. The protocol 
followed to derive this correlation is described below. 
The Chesapeake Bay water clarity criteria were published as the percent of light 
through water (see Table IV-1 on page 96 in U.S. EPA 2003a). Through the applica¬ 
tion of the equation: 
PLW= 100 exp(-K d Z) Equation 3 
the appropriate percent light-through-water value and the selected water clarity 
criteria application depth (Z) are inserted and the equation is solved for K d . The 
methodology developed by the Chesapeake Bay Program for assessing criteria 
attainment involves a sequence of steps that leads to a cumulative frequency diagram 
(CFD) as described in eight steps in Table II-1 in Chapter 2. As part of step 3, 
equating the in situ collected values of turbidity to estimated K d values becomes 
necessary to determine exceedance of the water clarity criterion. It is critical to 
convert in-situ turbidity to estimates of K d prior to any data interpolation in order to 
reduce the error potential. 
The relationship between turbidity and K d , therefore, needs to be quantified to deter¬ 
mine the turbidity threshold of the applicable water clarity criteria. This 
determination narrows the scope considerably from the traditional calibration curve 
in which the estimation of K d is based on measurements for a wide range of turbidity 
concentrations. In the current application, it is only necessary to accurately estimate 
K d from in situ measurements of turbidity in the neighborhood of the exceedance of 
the water clarity criteria. 
Shallow water Monitoring and Application for Criteria Assessment 
