21 
CLARIFICATION OF WATER CLARITY 
ASSESSMENT PROCEDURES 
U.S. EPA 2007, on pages 54-55, stated “Calculation of water clarity acres should be 
based on spatially intensive shallow-water monitoring turbidity data converted to K d , 
interpolated as described in Chapter 2 and then compared to the corresponding K d 
threshold assigned to each interpolator grid cell”. A 2007 review of the published 
language, however, found this did not correctly capture the approach to obtaining the 
K d attainment assessment when using water clarity acres. An analysis (Appendix C) 
conducted by the Chesapeake Bay Program partners shows the two methods did not 
produce dramatically different results for the selected example cruise tracks, but the 
analysis did suggest that: 
1. The originally published guidance method was simpler to conduct than this 
revised method which requires GIS-related software; 
2. The revised method predicts with slightly less error; and 
3. The revised method allows detection of spatial patterns in the individual 
parameters including better depiction of areas of uncertainty due to, for 
example, interpolation across land. 
The following revisions, which have been made by the Criteria Assessment Protocol 
Work Group under the U.S. EPA Chesapeake Bay Monitoring and Analysis Subcom¬ 
mittee, are clarifications of the published methods used by the jurisdictions for 
calculating water clarity acres. 
STATISTICAL MODEL REVISION 
The original publication of the statistical model suggested a multiplicative model of 
turbidity, chlorophyll and salinity was appropriate for converting turbidity to K d . The 
regional regressions are, however, additive multiple regression equations. The gener¬ 
alized form of such a model has been provided in Table IV-1 with an expression that 
captures the region specific coefficients, exponents involved in the root for turbidity 
and recognition of region-specific constants in accordance with what the jurisdic¬ 
tions are using to fulfill their assessments. 
Shallow-water habitat area acreage goals have been previously defined for water 
clarity acres as 2.5x each SAV acre needed to meet the SAV restoration goal acreage 
(p. 54, U.S. EPA 2007). Segment-specific SAV restoration goal acreages were previ¬ 
ously published in U.S. EPA 2003a, 2004 and 2007. 
CONVERTING TURBIDITY TO K d FOR CALCULATION OF 
WATER CLARITY ACRES 
On pages 54-55, U.S. EPA (2007) recommended “Calculation of water clarity acres 
should be based on spatially intensive shallow-water monitoring turbidity data 
converted to K d ”. To address the issue of converting turbidity measures into K d 
values, multiple regression equations were derived for determining light attenuation 
chapter iv 
Refinements to Procedures for Assessing Chesapeake Bay Water Clarity and SAV Criteria 
