All text and images courtesy of Watershed
Radio. More information can be found on their website.
Flood of 1996
In January 1996 a blizzard struck the Mid-Atlantic region,
depositing a record amount of snowfall. Within two weeks of the blizzard,
warm and extremely humid air entered the region, followed by a major
rainstorm. The combination of warm, humid air and heavy rainfall melted
the snow at an unprecedented rate. In just over one day, the combination
of two to five inches of water from snowmelt and two to five inches
of rainfall created a major flooding throughout the Mid-Atlantic region,
including the Chesapeake Bay watershed and many of the Bay's tributaries.
Sediment and nutrients flow into the Chesapeake Bay
As a result of the flooding, large amounts of nutrients and
sediment entered the Bay. Sediment, which is topsoil, sand, and minerals
washed from the land into water, is a natural part of the environment.
Too much sediment, however, clouds the water and coats the leaves
of underwater
plants, shielding the plants from the sunlight they need for growth.
In addition, the sediment also carries other pollutants with it. Phosphorus
and toxic contaminants, such as trace metals and pesticides, attach
to sediment particles and travel downstream and in to the Bay. The
flood of 1996 also brought many nutrients to the Bay. Two primary
nutrients, nitrogen
and phosphorus, occur naturally in the environment as a result of
the decomposition of plant material, deposition of atmospheric nitrogen,
and erosion of phosphorus-containing rocks. They have always been
present in the Bay, providing nourishment to plants and animals.
Similar to sediment, it is the excessive amount of nutrients that
is harmful to the Chesapeake Bay. When there are plenty of nutrients
in the water, algae grow very fast, and the abundance
of algae will cloud the water and prevent the underwater
grasses from receiving sunlight. And when the algae die, they
are decomposed by bacteria that use up the oxygen dissolved in the
water, leaving nothing for other plants and animals.
Monitoring the flow
Researchers at the U.S. Geological Survey (USGS) monitored
the amount of freshwater, nutrients, and sediment that entered the
Chesapeake Bay as a result of the flood. They found that during
the January 1996 flood, 4.9 trillion gallons of water entered the
Chesapeake Bay, almost three times as much as in an average January
month. The USGS also reported that, as a result of the flood, 5.3
million pounds of phosphorus (six times the average amount) , 63
million pounds of nitrogen (three times the average amount), and
7.5 billion pounds of sediment (17 times the average amount) entered
the Chesapeake Bay from its nine major tributaries, the majority
coming from the Susquehanna, Potomac, and James Rivers.
It could have been worse...
Fortunately for the Chesapeake Bay, the flood occurred
in the winter, a time when underwater
grasses and many living organisms were dormant in the Bay and
when farmland, rich in nutrients, was frozen, which prevented the
rain from causing excessive runoff of nutrients into the Bay. The
high amount of sediment transported to the Bay during the flood
came from streambank and river-channel erosion.
Not only in 1996
Pollution of the Bay by sediment and nutrients is not only a problem
when there is a major flood. Every day, the rivers in the Chesapeake
Bay watershed carry sediment, nutrients, and other pollutants from
all parts of the watershed down to the Chesapeake Bay. The erosion
of farmland, shorelines, and construction sites, as well as the
runoff from cities and suburbs contributes to the sediment that
gets washed into the Bay, and excess nutrients enter the Bay from
"nonpoint" sources such as airborne pollution and runoff
from city streets and fertilizer-laden farmlands, as well as from
"point" sources such as sewage-treatment plants.
To reduce the pollution of the Bay, we all need to step in and
help. Farmers can plant more vegetation buffers along streams, developers
can develop stormwater
management programs, home owners along the Bay and its tributaries
can use vegetation to reduce shoreline
erosion, people can take good care of their septic
systems, and we all need to become responsible citizens of the
watershed.
Part of this story is based on a Fact
Sheet about the January 1996 Flood, credit of the U.S. Geological
Survey.
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