Answer:
Not
directly. You cannot say that because a stream rises
(doubles) from a 10-foot stage to a 20-foot stage that the
amount of water flowing also doubles. Think of a cereal
bowl with a rounded bottom. Pour one inch of milk in it.
It doesn't take much milk to make it up to the one inch
level because the bowl is least wide near the bottom. Now,
pour in milk until it is two inches deep -- it takes a lot
more milk than it did to fill the first inch because the
bowl gets wider as you go up. The same thing happens in a
stream -- the stream banks will generally be narrower at
the bottom and tend to widen as you go up the bank. So,
the amount of water flowing in a stream might double when
the stage rises from 1 to 2 feet of stage, but then it
might quadruple when it goes from 3 to 4 feet. This
graphic helps to illustrate:
To find out how much water is flowing in a stream or
river, USGS personnel have to go out and make a "discharge
measurement." USGS uses the term "discharge" to refer to
how much water is flowing, and discharge is usually
expressed in "cubic feet per second" (think of a cube of
water one foot on a side, and how many of those move past
a point in one second). To do this, we often have to go
out and stand in the creek, measure the depth and how fast
the water is moving at many places across the creek. By
doing this many, many times, and at many stream stages,
over the years we can develop a relation between stream
stage and discharge. Stream stages are not always
cooperative, so its not uncommon for someone to have to go
measure a stream at 2:00 in the morning during a storm,
sometimes in freezing conditions! Also, the stream can be
uncooperative in that it changes -- a big storm may come
along and scour out bottom material of a creek, or lodge a
big log sideways in the creek, or sometimes do both at the
same time. These kind of changes result in changes in the
relation between stage and discharge.
