River FlowRiver flow is conducted by the River Input Monitoring (RIM) Program. There are nine RIM stations in the Chesapeake watershed, measuring approximately 93% of river flow into the Bay. Estimates of nutrients and suspended material loads to Chesapeake Bay are calculated from water quality data and daily records of streamflow.
Indicator Details
River Flow
Susquehanna flow low in winter and spring; Maryland and Virginia tributaries higher than normal
Overall, total flow to Chesapeake Bay (measured at nine stations around the watershed) was average in 2009. However, the patterns of this flow were different in 2009 than on average. First, peak flow, which normally occurs in March and April each year (see figure), peaked in May and June. This shifted the amount of freshwater coming into the bay to warmer months of the year. This, combined with water temperature, can affect the amount of primary productivity (phytoplankton activity) taking place in the water column. Phytoplankton growth and die-off results in low dissolved oxygen conditions. Adding more nutrients, via freshwater flow, during May and June most likely affected the amount of low dissolved oxygen seen during the summer.
Additionally, Susquehanna River flow rates continued to be lower-than-average throughout the spring and summer months, but tributaries in Maryland and Virginia, such as the Potomac River, had higher-than-normal flow. The rain gauge station at the Baltimore-Washington International airport recorded the second highest rainfall in May on record. This is in direct contrast to the lower Susquehanna River flows affecting the mainstem. This year’s flow data reflects the influence of Maryland and Virginia tributaries on mainstem Bay processes, despite the fact that the Susquehanna River provides 50% of the freshwater flow to the mainstem.
The Susquehanna River flow rates are a preliminary indication of the amount of sediment and nutrients entering the mainstem Bay from January to September 2009 (nutrient load estimates will be made available later in the year by the USGS). A lower-than-average dissolved oxygen forecast was calculated due to these low flows from the Susquehanna River. However, higher-than-normal flows in the Patuxent, Potomac, and other tributaries showed localized effects of high runoff. Dissolved oxygen levels in these tributaries dipped below the 23 year average during May and June. This can in part be attributed to the heavy rainfall experienced in May in much of Maryland and Virginia.
For more information see:
USGS Estimated Streamflow Entering Chesapeake Bay website.