47 
chapter \f 
Refinements to the 
Shallow-Water Designated-Use 
Assessment Procedures 
BACKGROUND 
Submerged aquatic vegetation (SAV) is a critically important component of the 
Chesapeake Bay ecosystem. These underwater plants provide habitat used by many 
fish and shellfish species and provide food for migratory waterfowl, while also 
improving water quality by generating oxygen, stabilizing sediment, and taking up 
nutrients. Historically, the Chesapeake Bay was once known for its extensive SAV 
beds. During the 1960s, however, much of the SAV disappeared. Poor water clarity, 
caused by excessive algal growth and high levels of suspended sediment (Dennison 
et al. 1993), was the primary factor in the decline of these beds. Both of these water 
quality impairments result from human activities in the Chesapeake watershed that 
cause excessive nutrient and sediment loadings to the Bay. 
In 2003, after consultation with the watershed jurisdictions, the EPA published water 
clarity criteria, SAV restoration goals, and shallow-water Bay grass designated-use 
delineations for the Chesapeake Bay as well as its tidal tributaries and embayments 
(U.S. EPA 2003a, 2003b). When applied as state water quality standards regulations, 
these standards define the water clarity needed in delineated shallow-water habitats 
to support SAV restoration to agreed-upon acreages. 
The water clarity criteria and SAV restoration goals were designed to define attain¬ 
ment of the shallow-water Bay grass designated use in three ways (U.S. EPA 2003a, 
2004a). First, once the targeted acreage of SAV in a given segment is reached, that 
segment is considered in attainment of the shallow-water Bay grass designated use. 
Measurement of SAV goal restoration attainment is based on annual aerial surveys 
in which the beds are photographed and mapped, acreages quantified, and the single 
best year of acreage determined. Second, if sufficient shallow-water area with the 
water clarity necessary to achieve restoration of the targeted SAV acres exists, then 
the segment is considered in attainment. These “water clarity acres” are measured by 
routinely mapping water clarity using data from the Chesapeake Bay Shallow-water 
Monitoring Program (see Chapter 7 for details). Third, if the water-clarity criteria 
were attained throughout the shallow-water designated use reaching to a specific 
chapter v • Refinements to the Shallow-Water Designated-Use Assessment Procedures 
