Floods and droughts are natural events determined by the amount
of rain that falls in a particular area at a particular time. Any
time when rainfall is much higher or lower than average, floods
and droughts become a concern.
The damage done by floods
is obvious. High waters block roads and damage property. The rapidly
moving waters wash away spawning areas and eggs, uproot aquatic
plants and temporarily cloud water with sediment from eroded soil.
However, floods can also wash away sediment, making stream bottoms
better suited for future spawning beds or create new deep pools
where fish thrive. Floodwaters also deposit fertile sediments that
nourish streamside plant communities.
While they may not seem as dramatic as floods, droughts often affect
larger areas and have greater impacts. A drought causes water tables
and water levels of streams, rivers and creeks to fall. As lake
levels drop and wetlands dry up or shrink, plants, animals and birds
can suffer from lack of habitat. The dry conditions can also increase
the danger of forest fires that can ignite and spread quickly during
Urban development increases the probability
of floods and droughts and intensifies the negative effects of these
two extremes. Roads and other paved surfaces increase runoff, making
streams, creeks and rivers rise faster and higher than they otherwise
would, increasing the likelihood of dangerous flash flooding. The
same surfaces prevent water from soaking into the ground. In times
of little rainfall, droughts are more severe because less water
has been stored in the ground.