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WHAT
IS IT?
Volume
is the amount of water that flows by a set point in a given time.
It is usually measured in cubic feet per second (cfs) On average,
the South Platte River through Denver flows at _____ cfs. At
their mouths (where the rivers meet the ocean), the Mississippi
flows at 623,000 cfs, and Amazon flows at 6,335,000 cfs.
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WHY
IS IT IMPORTANT?
1. The volume
of a river affects the relative harm caused by pollutants. In
a larger river, pollutants are less concentrated, and their harmful
effects more diluted. In general: The solution to pollution is
dilution.
2. Volume affects
many other water quality factors, from Total Suspended Solids
to Alkalinity. For example, when volume increases due to snowmelt,
T.S.S. tends to increase.
3. For aquatic
life, changes in a river's volume are important, especially when
water levels are very low for long periods of time. Seasonal
lows can affect fish survival, because low waters tend to get
too warm. Also, in some rivers, when waters flow more slowly
during dry seasons, the water mixes less with the atmosphere,
which reduces the level of dissolved oxygen.
4. People use
river water for irrigation, bathing, drinking, cooking, hydroelectric
power, recreation and much more. Because farmers need water when
the flow is lowest, and households need water year round, we
store and use water to meet our needs. It can be difficult for
cities to deal with the seasonal ups and downs of water volume
in rivers. Many communities have built dams across streams and
rivers to store water, and then release it back into streams
in controlled volumes. This, however, can influence a waters
chemistry. Dams and diversions can change a river from a moving
body of water to a standing body of water. This can change the
water's chemistry and therefore effect the life forms in the
waterway.
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WHAT
INFLUENCES IT?
1. Climate,
Weather and Precipitation: Heavier winter snows mean more spring
runoff, and heavier rains wash more water into rivers.
2. Size of Watershed:
Rivers that drain larger areas usually have larger volumes.
3. Evaporation:
Streams lose water to the air because of evaporation. When the
weather is hot, the sun is strong or the air is dry, evaporation
can increase.
4. Geology and
Permeability: Depending on the texture and type of earth a river
flows over, water may seep in to the soil.
5. Water Removal
and Releases: People remove water from rivers and release water
from reservoirs for all sorts of reasons, from agriculture to
drinking water.
6. Groundwater:
Depending on geology, a percentage of the flow of a river comes
from underground water. For example, in drier seasons a majority
of the water in a stream is contributed from groundwater sources.
This is why many rivers can continue to flow even without any
contributions of precipitation.
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