Discharge is the amount of water flowing down a stream.
It is expressed as the volume of water flowing past a
point per unit time, usually in cubic meters per second
(m3/sec). The largest river in the world is the Amazon,
with a discharge of 150,000 m3/sec. In contrast, the
Mississippi River, the largest in North America, has a
discharge of about 17,500 m3/sec, approximately one
ninth that of the Amazon.
A stream’s discharge can change dramatically from
month to month or even during a single day. For example,
the Selway River, a mountain stream in Idaho, has a
discharge of 100 to 130 m3/sec during early summer,
when mountain snow is melting rapidly. During the dry
season in late summer, the discharge drops to about 10
to 15 m3/sec (Fig. 14–2). A desert stream may dry up
completely during summer but become the site of a flash
flood during a sudden thunderstorm.
Stream velocity increases when discharge increases.
Thus, a stream flows faster during flood, even though its
gradient is unchanged. The velocity of a stream also generally
increases in a downstream direction because tributaries
add to the discharge.
Discharge is the amount of water flowing down a stream.It is expressed as the volume of water flowing past apoint per unit time, usually in cubic meters per second(m3/sec). The largest river in the world is the Amazon,with a discharge of 150,000 m3/sec. In contrast, theMississippi River, the largest in North America, has adischarge of about 17,500 m3/sec, approximately oneninth that of the Amazon.A stream’s discharge can change dramatically frommonth to month or even during a single day. For example,the Selway River, a mountain stream in Idaho, has adischarge of 100 to 130 m3/sec during early summer,when mountain snow is melting rapidly. During the dryseason in late summer, the discharge drops to about 10to 15 m3/sec (Fig. 14–2). A desert stream may dry upcompletely during summer but become the site of a flashflood during a sudden thunderstorm.Stream velocity increases when discharge increases.Thus, a stream flows faster during flood, even though itsgradient is unchanged. The velocity of a stream also generallyincreases in a downstream direction because tributariesadd to the discharge.
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