''Natural Hazards Do Not Have To Become Natural Disaster.''
The
Yangtze River floods were the most disastrous ever recorded. They were caused
by torrential rain and killed more than 3.7 million people in Southern China.
So what is flooding? What are the precursors of flooding and how we can help as
citizens?
FLOODING
As water falls to the earth in the form of rain or
snow, it seeps into the ground. But if the ground is frozen or the surface is
impervious (asphalt or concrete are two contenders) or the soil is already
saturated and cannot absorb the water faster than it falls from the sky,
problems arise. Then flooding occurs. Flooding is a natural event or occurrence
where a piece of land (or area) that is usually dry land, suddenly get
submerged under water. Some floods can occur suddenly and recede quickly. Others
take days or even months to build and discharge.
Also, flood occurs when water overflows or inundates
land that's normally dry. This can happen in a multitude of ways. Most common
is when rivers or streams overflow their banks. Excessive rain, a ruptured dam
or levee, rapid ice melting in the mountains, or even an unfortunately placed
beaver dam can overwhelm a river and send it spreading over the adjacent land,
called a floodplain.
Coastal flooding occurs when a large storm or tsunami causes the sea to surge
inland.
CAUSES
OF FLOODING:a varieties of factors can increase the
likelihood of flooding. However, these factors can be classified into two:
physical and human factors.
PHYSICAL
FACTORS:
Heavy
rain: Each time there are more
rains than the drainage system can take, there can be floods. Sometimes, there
is heavy rain for a very short period that result in floods. In other times,
there may be light rain for many days and weeks it can also result in floods.
Snowmelt: In many cold regions, heavy
snow over the winter usually stays unmelted for some time. There are also
mountains that have ice on top of them. Sometimes the ice suddenly melts when
the temperature rises, resulting in massive movement of water into places that
are usually dry. This is usually called a Snowmelt
Flood
River overflow: Rivers can overflow their banks to cause flooding. This happens
when there is more water upstream than usual, and as it flows downstream to the
adjacent low-lying areas (also called a floodplain), there is a burst and water
gets into the land.
Dam Breaking: Dams are man-made blocks mounted to hold water flowing down
from a highland. The power in the water is used to turn propellers to generate
electricity. Sometimes, too much water held up in the dam can cause it to break
and overflow the area. Excess water can also be intentionally released from the
dam to prevent it from breaking and that can also cause floods.
Strong winds in coastal areas: Seawater can be carried by massive winds and hurricanes onto
dry coastal lands and cause flooding. Sometimes this is made worse if the wind
carries therain. Sometimes water from the sea resulting from a tsunami can flow
inland to cause damage.
HUMAN
FACTORS:
Urbanization:
Urbanization is the process of making an area more urban.Because
town and cities have more impermeable surface, this tends to contribute to
flooding as percolation into the ground reduces.
Deforestation:
Deforestation refers to the cutting, clearing and removing of
rain forest or related ecosystems into less bio-diverse ecosystems such as open
land, pasture, cropland or plantation. When trees and vegetation are removed
for human development, the ability of the trees and vegetation to reduce the
amount of water is intercepted and interrupted thereby increasing
run-off and ultimately flooding.
TYPES
OF FLOODING: Floods can be described according to speed (flash flood),
geography or the causes. Below are some types of flooding:
Flash floods: this kind occurs
within a very short time(2-6 hours) and sometimes within minutes and is usually
as a result of heavy rain, dam break or snow melt. Sometimes, intense rainfall
from slow moving thunderstorms can cause it. Flash floods are the most destructive
and can be fatal, as people are usually taken by surprise. There is usually no
warning, no preparation and the impact can be very swift and devastating.
Overbank flooding: What most people think of when they hear the word "flood" is
“filled to capacity because of heavy rain or melting snow, the
water within a river overflows its banks and spreads across the land around it.”
Sometimes the area covered is wide and flat; water tends to spread out and be
slow moving and may not appear to travel at all. Common in the Midwest, this
kind of flooding can take days to dissipate. In mountainous areas, where water
flows together through steep valleys, the floodwater tends to move faster and
linger for a shorter duration.
Ice jam flooding:In cold temperatures, bodies of water are often frozen. Heavy
precipitation can cause chunks of ice to push together and create a dam in what
is known as ice jam flooding. Behind the dam, water begins to pile up, spilling
over to the plains nearby. Eventually, the wall of ice breaks, and fast-moving
water rushes downstream much like a conventional flash flood, destroying
objects in its path. The water carries huge chunks of ice, which can increase
damage to surrounding structures.
Coastal flooding: This type of flooding occurs along the edges of oceans, and is driven
predominantly by storm surges and wave damage. This kind of flooding is usually
connected to hurricanes, tsunamis or
tropical storms. When low pressures occur in a storm over the ocean, they suck
the water toward the center. As long as the eye is over deep water, problems
are minimized, but as the storm moves toward land it carries a dome of water
that can exceed 25 feet (7.6 meters) in diameter. When the dome reaches the
shoreline, it can cause significant damage. At the same time, waves breaking
along the shoreline assault beaches and structures, with destructive potential.
HOW
TO PREVENT FLOODING
Humans cannot stop the rain from falling neither stop surface water from
busting its banks. These are natural events, but we can do something to prevent it
from having great impacts. Here are few ways citizens can help prevent
flooding.
I.
Planting Of Trees and vegetation: Trees, shrubs and grass helps to protect the land
from erosion by moving water. People in low-lying areas must make it a habit to
plant vegetation and shrubs. Also, planting of trees can help reduce the
impact of rainfall. The vegetation can help break the power of
flowing floodwater and reduce erosion.
II.
Reduction in the use of paving stones: Lately, the use paving stones or concrete for
walkways and open ground beatification has contributed to the reduction in
percolation of surface water to the ground. Although concrete
lasts a long time — creating durable patios, driveways, roads, and
foundations for houses — the production of concrete takes a lot of energy.
And that’s not the only problem with concrete, whenever the ground is covered
with it, rain doesn’t seep into the soil. As the rain accumulates and water
starts flowing off the concrete, it creates problems. These impervious surfaces
often divert water into streams. The rush of water may result in costly and
sometimes life-threatening floods.
III.
Education: the easiest way to combat
environmental challenges is to educate people about it. In many developing
cities like Lagos, drainage systems are chocked with litters and people have
little knowledge of the effects this can have during raining season. When it rains, waterways and culverts are
blocked by massive chunks of litters and debris, and water finds its ways into
streets and people’s homes. We need to
educate our family members, co-workers and communities on the need to clear
drains.
IV.
Detention basin:For a city like
Lagos where 65% of land is wetland, the development of communities and new
settlements will ultimately be on wetland, examples are bound in Lekki, Majidun,
part of Ojo and Badagry. Therefore it becomes imperative for land developers to incorporate
detention basin into community design. These
are small reservoirs built and connected to waterways. They provide a temporary
storage for floodwaters, this means in an event of flooding, water is drained
into the basin first, giving people more time to evacuate; it can also reduce
the magnitude of downstream flooding.
As we join the rest of the State to mark
another tree planting day, let use reflect on the recent event and make Lagos a
better place.
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