Boosted by Hurricane Floyd, streamflow into the Chesapeake Bay finally returned to normal levels in September, after flowing at below-average rates for more than a year.
Total streamflow into the Bay during September was about 30.6 billion gallons a day, according to the U.S. Geological Survey, about 49 percent above the long-term average of 20.5 bgd for the month. September flows into the Bay were about three times higher in September than they were in August.
Although flows from the two largest rivers entering the Bay — the Susquehanna and Potomac — rose because of Floyd, both were still below records for the month, the USGS reported.
Flows from the Susquehanna averaged 12.3 billion gallons a day in September, up from 3.6 bgd in August. Potomac flows, measured near Washington, averaged 3.7 bgd in September, up from 0.9 bgd in August.
The story was different on the Delmarva Peninsula, though, which had the heaviest rainfall from the hurricane. Rivers there were near, or broke, flow records, according to the USGS.
As a result, the USGS said impacts from increased nutrient and sediment runoff — driven from the land and into the water by heavy rains — was probably most significant in tidal Eastern Shore tributaries.
The exact impact on the Bay and its tributaries won’t be known until more monitoring information is analyzed. One of the biggest questions is Floyd’s impact on oysters. The low-flow conditions which persisted since August 1998 had created conditions ripe for the oyster-killing diseases MSX and dermo, but the fresh water from Floyd may have helped push those diseases downstream.
Besides increasing streamflow, the USGS said groundwater levels were returning to normal levels in much of the basin, although they were still below normal in much of Pennsylvania.
Floyd fulfilled what long-term weather forecasters with the National Oceanic and Atmospheric Administration had predicted months ag That the region’s persistent drought would likely continue unless it was broken by a hurricane.
NOAA forecasters say that La Nina, which was blamed for contributing to the drought, continues to persist in the Pacific, though in a weakened state.
La Nina refers to cooler-than-normal ocean waters across the Central and Eastern Equatorial Pacific. La Nina, and its climatic opposite, El Nino, affect the weather patterns across North America by changing the character of the winter jet stream, which ultimately controls weather patterns.