50 
EPA recommends that the states assess shallow-water bay grass designated-use 
attainment based on the acres of mapped SAV (see Chapter 8). 
ASSESSMENT BASED ON THE SINGLE BEST YEAR OF SAV 
Baywide and segment-specific SAV restoration goals were defined for the Chesa¬ 
peake Bay by evaluating the historical (1930s- 1970s) and more recent (1980s-2000) 
SAV distributions (U.S. EPA 2003b). Historical aerial photographs, available for 
selected years in the 1930s, 1950s, and 1960s, were converted to digital maps. Then 
acreages of SAV for all photographed shallow-water areas in Chesapeake Bay, its 
tidal tributaries and embayments were quantified. To set restoration goals for the 
Bay, the single best year of SAV coverage was defined as the restoration goal for 
each segment. The combined individual restoration acreages yielded a baywide goal 
of 185,000 acres. (See pages 105-122 in U.S. EPA 2003b for detailed documenta¬ 
tion on the entire goal-setting process.) 
This baywide restoration goal was established “to reflect the historical abundance, 
measured as acreage and density from the 1930’s to present” as committed to in the 
Chesapeake 2000 agreement (Chesapeake Executive Council 2000) and essentially 
represents the “existing use” as defined by the Clean Water Act. The single-best-year 
approach was necessary because a common basis was needed to define the area of 
SAV that should be present. The historical photography was not consistent through 
time for all areas of the Bay and SAV acreages varied through time. Since at least 
some coverage was available for most of the Bay, the single best year offered the best 
option for setting goals (in selected cases with little or incomplete historical data, a 
composite of multiple years of historical data was used to define the “single best 
year”) (U.S. EPA 2003b). 
Because the segment-based SAV restoration goals were established based on the prin¬ 
ciple of a “single best year,” the assessment of attaining that goal within an individual 
Chesapeake Bay Program segment’s shallow-water bay grass designated-use habitat is 
defined in a similar manner. Attainment of the SAV restoration goal is reached when 
the single best year of SAV acreage during the applicable preceding three-year assess¬ 
ment period equals or exceeds the established goal (defined as “SAV restoration acres” 
in the states’ water quality standards regulations) for that segment. 
In nine segments, SAV restoration goals were not published in 2003 because no SAV 
was mapped in the available historical photography or through the baywide aerial 
survey (U.S. EPA 2003b). At the same time, existing information does not support 
delineation of these entire segments as SAV no-grow zones following the detailed 
decision rules documented by the U.S. EPA (2003b). The EPA recommends the 
jurisdictions maintain the shallow-water designated use in the nine segments that 
didn’t have an SAV restoration goal published in 2003 but were previously deter¬ 
mined not to be an SAV no-grow zone (Table V-l). 
chapter v 
Refinements to the Shallow Watei Designated Use Assessment Procedures 
