• Contact Us
• Site Index

• Nitrogen, phosphorus and sediment concentrations are monitored near the head of tide (river input sites) in nine of the Bay's major rivers, and at numerous locations upstream of the river input sites. The volume of water flowing past the monitoring gauges – or river flow – is also measured.
• The long-term concentration trends are adjusted to reflect the changes in flow that are largely a function of annual precipitation. Since they are independent of annual variability, the flow adjusted concentration trends allow us to evaluate the success of pollution control management programs on a watershed-wide scale.

• Since the monitoring is conducted at and above the fall line, the trends do not reflect the impact of management actions in the coastal plain areas of the watershed.
• In the mid-1980's, the USGS Chesapeake Bay River Input Monitoring (RIM) Program was established to quantify loads and long-term trends in concentrations of nutrients and suspended material entering the tidal part of the Chesapeake Bay Basin from its nine major tributaries. These nine rivers account for approximately 93% of the streamflow entering Chesapeake Bay from the nontidal part of its watershed. Results of the RIM program are being used by resource managers, policy makers, and concerned citizens to help evaluate the effectiveness of strategies aimed at reducing nutrients and sediment entering Chesapeake Bay from its tributaries.
• Water samples are collected upstream of the transition area between the tidal and non-tidal regions of the nine rivers. This transition zone historically has been referred to as the "Fall Line" for the many sets of falls and rapids that are found at this point on the rivers. Below the Fall Line in the tidal areas of these rivers, tides can transport water, nutrients, and suspended material from downstream, making it difficult to determine the cause of any observed changes. Because water-quality samples are collected above the influence of tides, any observed changes in nutrients or suspended material can be attributed to upstream causes.
• In addition to the RIM sites, water samples are collected at non-tidal monitoring sites located upstream of the RIM sites.  Flow adjusted concentration trends are shown in the featured map for 25 of those sites.

• Reducing Pollution

For more information contact: Scott Phillips at 410-238-4252

US Geological Survey