65 
To capture the temporal variability of dissolved oxygen, the new Tidal Monitoring 
Network incorporated high-frequency monitoring stations in surface and nearshore 
locations. Since then, the dissolved oxygen criteria assessment procedure has been 
modified to project the results of open-water dissolved oxygen assessments onto 
adjacent shallow-water, designated-use areas, instead of conducting a separate 
shallow-water assessment (see Chapter 4 for details). The design for collecting high- 
frequency dissolved oxygen data will likely be modified to represent dissolved 
oxygen concentrations in open-water, designated-use habitats more accurately. 
SHALLOW-WATER MONITORING DESIGN 
The intensive shallow-water monitoring program design is based on two innovative 
technologies that were extensively tested in Maryland's Magothy and Severn rivers 
as well as Tangier Sound from 1999 to 2002. The Dataflow water quality mapping 
component collects high-resolution surface data from both open tidal-tributary and 
shallow waters. The shallow-water buoy system collects high-frequency (near- 
continuous) temporal data at specific locations, resulting in a data set that better 
represents dissolved oxygen, chlorophyll a , and water clarity in time and space in 
smaller tidal tributaries, small embayments, and shallow-water habitats. In 2003, the 
Maryland Department of Natural Resources, the University of Maryland’s Chesa¬ 
peake Biological Laboratory, the Virginia Department of Environmental Quality, and 
the Virginia Institute of Marine Sciences initiated the new Chesapeake Bay Shallow- 
water Monitoring Program. The two states and their partners closely coordinate 
development of the monitoring schedules, equipment, methodologies, and quality 
assurance procedures to ensure baywide compatibility and comparability. 
The Shallow-water Monitoring Program is based on two components that collect 
spatially and temporally intensive data. Known as “Dataflow,” the spatially intensive 
component includes a sensor array and a GPS system that provide data continuously 
along a boat track in both shallow- and open-water designated-use areas. These data 
can be used to develop detailed maps of water quality conditions. The temporally 
intensive component is known as “continuous monitoring” and includes a sensor array 
at fixed locations that provides data continuously through time. These data reflect 
episodic changes in water quality or signify extremes in water quality conditions. 
The existing shallow-water monitoring design is based upon a three-year assessment 
period. Data are collected from all segments within a tidal tributary or embayment 
during the same three years. Both Dataflow sampling and continuous buoys are 
deployed for the same time period. The three-year assessment provides adequate 
time to account for variation in both weather and hydrologic conditions (see page 
151 in U.S.EPA 2003a). Assessments using fewer than three years of shallow-water 
monitoring data are discussed in the section Schedule for Assessment of Shallow- 
water Designated Use Habitats below. 
To adequately assess water quality criteria in shallow-water habitats and tidal tribu¬ 
tary open-water designated-use habitats, the EPA recommends that the states 
chapter vii 
Shallow water Monitoring and Application for Criteria Assessment 
