INTRODUCTION
Flooding is a
natural occurrence where areas or land that is normally dry abruptly becomes
submerged in water (Magami et al., 2014). Flooding has many extreme negative social,
economic and environmental impacts (Kolawole et al., 2011). Some of the negative
impacts of flooding include; damage to properties, crops and livestock, loss of
human life, health problems, damage to roads, bridges, and power plants (Adetuji and Oyeleye,
2018). Despite these negative impacts of flooding, it still has some
important role to play in the environment. It recharges groundwater systems,
fills wet lands, moves viable nutrients and contribute to the dispersal of
seeds of plants e.g., such as coconut, water lily, lotus etc. around the
ecosystem, increases fishing activities and triggers dispersal, migration and
breeding (Jeffrey et al., 2020).
Flooding occurs in three forms; coastal flooding, river
flooding and urban flooding also called flash floods. Coastal flooding occurs
in the low-lying belt of mangrove and fresh water swamps along the coast. River
flooding occurs in the flood plains of the larger rivers while urban flooding
is linked with rivers in the inland areas. It is often short-lived and the
sudden heavy rains in the inland areas can change them into a destructive
torrent (Oruonye
et al., 2017). Many factors are responsible for
flooding which include; dumping of refuse in water bodies (Magami et
al., 2014), constructing buildings on flood
plains and poor maintenance of drainage facilities and breakage of dams (Adetuji and Oyeleye, 2018). Removal of vegetation, increase in the
size of water channel and increase in erosion also contribute to flooding.
Flooding can also be caused by excess rainfall when the absorption capacity of
the soil is exceeded. Other
causes of flooding include; climate change, excessive precipitation, rise in
sea level and development of unplanned cities.
Types of Flooding and Causes
Many conditions result in flooding (Magami et al., 2014).
Hurricanes, clogged drainages, and rainfall are some of the conditions that
have led to flooding in various regions across the globe. Here are the leading
types of floods:
v
Flash Flood:
This is the type of flooding caused by heavy rainfall. The flood conditions
develop rapidly because the rainfall is so heavy the ground is incapable of
absorbing the water quickly enough, resulting in a very high runoff rate. The
events are generally locally intense and damage is usually restricted to a
limited area.
v
River Floods: Rivers or streams can
overflow their banks. This happens when the river or stream holds more water
upstream than usual, and it flows downstream to the neighboring low-lying
areas, typically referred to as the floodplains. As a consequence, this creates
a sudden discharge of water into the adjacent lands leading to flooding.
Dams
in rivers may also at times overwhelm rivers when the carriage capacity is
exceeded, causing the water to burst and get into the floodplains. Flood caused
by river overflow has the potential of sweeping everything in its path
downstream.
v Lakes and Coastal Flooding: Lake and Coastal flooding
occurs when large storms or tsunamis causes the water body to surge inland.
These overflows have destructive power since they can destroy ill-equipped
structures to withstand waters strength such as bridges, houses, and
cars. In the coastal areas, strong and
massive winds and hurricanes drive water onto the dry coastal lands and give
rise to flooding. The situation is even worsened when the winds blowing from
the ocean carry rains in them. Sea waters from the tsunami or hurricane can
cause widespread damage.
v Urban floods occur when the drainage
system in a city or town fails to absorb the water from heavy rain. The lack of
natural drainage in an urban area can also contribute to flooding. Water flows
out into the street, making driving very dangerous. Although water levels can
be just a few inches deep, urban floods can cause significant structural
damage.
v Pluvial floods form in flat areas
where the terrain can’t absorb the rainwater, causing puddles and ponds to
appear. Pluvial flooding is similar to urban flooding, mainly in rural areas.
The agricultural activities and properties in areas where pluvial floods have
occurred can be seriously affected.
Effects of Flooding on the
Environment
v
In the agricultural sector, flooding
can ruin crops, delay harvests, spoil produce, remove or contaminate valuable
topsoil and cause death of livestock (Olajuyigbe et al., 2012). These
effects can cause great emotional stress and financial loss to farmers.
v
For the general public, food
shortages and higher costs of produce can result.
v
Flooding also destroys wildlife
habitats, depletes fishery stock and alters biodiversity and ecosystem
functions critical to socio-economic development.
v
Flooding Disrupt economic and social
activities.
v
It set back the nation's security and
development by damaging or destroying roads, buildings and other
infrastructure.
v
A secondary effect of floods is the
contamination of floodwaters with chemicals and sewage. This can pose a threat
to the health of people and animals and can increase the risk of contracting
waterborne diseases.
v
It also causes death by drowning.
Ways to Manage Flooding
v
Design A Good Drainage System: The
design and layout of a town’s drainage system can build a great foundation for
preventing floods and cause less headache overtime (Emeribeole, 2015).
A drainage system should be well-mapped and properly covered to prevent
leaves, debris and large items from clogging the system. Water should be able
to drain freely and quickly to avoid pooling in streets and low-lying areas.
v
Plant Vegetation: While trees, shrubs
and even different varieties of grass can be decorative and scenic, they serve
an even greater purpose when it comes to flood prevention (Hansson et
al., 2008)
Extra vegetation can absorb excess water into the soil and can prevent land
erosion by slowing down heavy water flow.
v
Create Retention Basins: Also known
as retarding basins, detention basins provide a pathway for water runoff and a
temporary holding place for floodwaters. Vegetation and large rocks are often
used to line the edges of the basin for additional absorption and to slow the
rapid flow of water and prevent erosion. (Nkwunonwo et al., 2016).
v
Building of well planned
environmentally sustainable dams.
v
Desilting and canalization of rivers
and natural drainage channels
v
Provide Education: It is important to
educate people that live in the town and ensure they understand the importance
of keeping drainage systems clear. This can help reduce the amount of litter
and debris that clogs culverts and water ways. (Evans et al., 2017). In addition to prevention, it is important to
educate people on what to do if a flood occurs to stay safe and minimize
damage. Providing contact information for a flood cleaning service can be
helpful to businesses that are impacted by storms.
Effects
of Flooding on the Depletion of Plants
Flooding can have a significant impact on
terrestrial plants that cannot withstand inundation for extended periods of
time (Nkwunonwo et
al., 2005), although Some plants are perfectly okay growing in wet
places e.g., rice, bulrushes or water lilies, water hyacinth, etc. However,
when flood water rise, the submerged vegetation is deprived of oxygen which is
necessary for photosynthesis and respiration in the roots leading to the
build-up of carbon dioxide, methane and nitrogen gases (Najeeb et al., 2010).
Ultimately, the roots can suffocate and die. Toxic compounds such as ethanol
and hydrogen sulphide can also build up in the soil and damage plants. If
leaves and stems are submerged, photosynthesis (absorption of energy from the
sun to produce sugars) can be inhibited and plant growth can slow or even stop.
Plants that are
suffering from excessive-water stress are more prone to infection by
disease-causing organisms such as fungi or insects. (Sperber, 2014). Also,
excessively wet soil tends to favour the growth of soil-microbes such as Fusarium spp., Phytophora spp. and Rhizoctonia
solani, which can infect
plant roots leading to diseases such as root and crown rot. The damage caused to plants by flooding differs
depending on the time of the year and the age of the plants. Here are some of
the ways flooding enhances the reduction or destruction of plants;
v
Suffocating Soil: When soil is saturated by excessive flooding,
soil pores are completely filled with water and have little to no oxygen
present. Much like humans, plants need oxygen to survive, with the gas taken
into plants via leaves and roots. Also identical to humans, plants such as farm
crops can’t breathe underwater (Najeeb. et al., 2010). Essentially,
excess and prolonged flooding kills plant roots because they can’t breathe.
Dead plant roots in turn lead to death of aboveground plant, or crop, growth.
v
Nutrient
depletion: Flooding can wash away
nutrients from the soil which can lead to nutrient depletion, beneficial
microbes in the soils die and anaerobic organisms take over and produce toxic
byproducts that may further kill the plants. Plants require nutrients to grow,
and if the soil is depleted of nutrients, the plants will not be able to grow.
v
Salinization: Floodwaters can bring in saltwater from the
ocean, which can lead to salinization of the soil. This can make it difficult
for plants to absorb water and nutrients, leading to their depletion.
v
Soil
compaction: Flooding can cause soil
compaction, which can make it difficult for plants to grow. Compact soil can
prevent water and air from reaching the roots of plants, leading to their
depletion.
v
Causes
Plant diseases: Flooding can create
conditions that are conducive to the growth of plant diseases. Plant diseases
can weaken plants, leading to their depletion.
v
Loss
of biodiversity: Flooding can lead to
the loss of biodiversity, which can have a negative impact on the ecosystem.
The depletion of plants can lead to the loss of habitats for animals, which can
lead to a decline in biodiversity.
v
Reduced
crop yields: Flooding can lead to
reduced crop yields, which can have a negative impact on food security. The
depletion of plants can lead to a reduction in the amount of food that can be
produced.
v
Economic
losses: Flooding can lead to
economic losses, particularly for farmers who rely on crops for their
livelihoods. The depletion of plants can lead to a reduction in income for
farmers, which can have a negative impact on their livelihoods.
v
Environmental
degradation: Flooding can lead to
environmental degradation, which can have long-term consequences for the
environment. The depletion of plants can lead to soil erosion, loss of
biodiversity, and other environmental problems.
v
Additionally, Flooding can
mechanically uproot plants, break stems and branches and wash away seeds and
seedlings, leading to a decline in plant density and plant diversity.
Role of Flooding in the Dispersal of
Plants
The transfer
of seeds from a parent or mother plant to a different location is called seed
dispersal. Seed dispersal through water is called hydrocolloid. The seeds of
plants that grow in or near running water are usually dispersed by water (Wenny and Levey, 2000). Common examples are coconut, palms, water lily seeds of
mango, oranges and lotus etc. These fruits and seeds have several adaptations
for floating in water. Coconut fruits have a light and fibrous fruit wall and
are carried over long distances by water. Lotus has flat, spongy thalamus
containing seeds. Kohai and mangrove trees are located on the banks of rivers
and estuaries. Therefore, the seeds float on the surface of the water and the
stream carries the seeds away. Plant seeds growing in water are spread to
water, but there are many other ways to play a part of water when dispersing
seeds. Plants growing by water often relied on water and transport their seeds.
You can produce floating seeds, or it may be a thread that helps buoyant. Flooding is likely to have several benefits
for different plant species. Seed survival is often higher away from the parent
plant. This higher survival may result from the actions of density-dependent
seed and seedling predators and pathogens, which often target the high
concentrations of seeds beneath adults (Manzaneda et al., 2005).
Competition with adult plants may also be lower when seeds are transported away
from their parent.
Flooding helps in the dispersal of plants through the
following ways:
v
Facilitates seed distribution: Flood waters can carry seed pods and grains far away
from their source. This helps to disperse plants so that they can grow in areas
that they might not have been able to reach otherwise.
v
Increases habitat diversity: Flooding can create new habitats for plant species by
depositing sediments, nutrients, and organic matter in areas that were
previously inaccessible.
v
Increases genetic diversity: As plants are carried away by flood waters, they mix
with other specimens, leading to increased genetic diversity.
v
Provides nutrients: Flood waters often bring nutrient-rich soil and other organic matter to
areas that are in desperate need of it. This helps to jump-start the growth of
plant species.
v
Reduce competition: Flood waters can wash away invasive species or competing vegetation,
clearing the path for native plants to establish themselves.
v
Improves soil quality: Flood waters can carry sediment and organic matter from
upstream areas, which can then be deposited on soil. This helps to enrich the
soil and improve its overall quality for plant growth.
v
Promotes germination: A sudden surge of water can trigger the germination of seeds that have
been lying dormant for extended periods of time.
v
Supports wetland ecosystems: Flooding can help to preserve the integrity of wetland
ecosystems by providing the moisture and nutrients necessary for plant species
to thrive.
v
Promotes biodiversity: Floods can lead to the creation of new habitats and
environments, leading to the growth of a more diverse range of plant species (Green et al., 2021)
v
Flood waters allows plants to reach
specific habitats that are favorable for survival, a hypothesis known as
directed dispersal. It may also allow plants to colonize vacant habitats and
even new geographic regions.
FEATURES THAT ENABLE SEEDS DISPERSAL
THROUGH WATER
There are
several features that enable seeds and plants to disperse a long distance and
still survive. (Manzano and Malo, 2006):
- Buoyancy: Seeds that
can float on water are more likely to be carried away by water currents.
- Water-resistant
coatings: Seeds that have a waterproof or water-resistant coating around
them are less likely to absorb water and sink to the bottom.
- Air pockets: Some
seeds have air pockets that help them float on water.
- Hooks or barbs:
Seeds with hooks or barbs can attach to fur or feathers of animals that
come in contact with water, which can then transport them to new
locations.
- Slimy or
mucilaginous coatings: Seeds with slimy or mucilaginous coatings can stick
to water-dwelling organisms such as fish and amphibians that move between
water bodies.
- Long dispersal
periods: Some seeds can remain viable for extended periods, which allows
them to travel long distances through water currents.
CONCLUSION
Flooding
being a disaster is unavoidable but can be managed if appropriate measures are
instituted. Notably, flooding is caused by excessive
rainfall, poor environmental planning and management and weak policy
implementation by institutions concerned with flood management. Flooding is
also caused by increasing deforestation and inability of developers to adhere
to physical development plans and scheme. Flooding has negative implication on
the environment, economy and social lives of peoples living at flood prone
areas. Flooding affects physical and natural developments such as houses,
plants, trees, roads, bridges and other structures. In the cases of serious
flooding, lives can be lost in the process. Flooding destroys and alter the
ecosystem and a wide variety of terrestrial plants. More so, it enhances the
spread and survival of most aquatic plant and some terrestrial plants that
their seeds freely float on water.
Combination of hard infrastructural solutions and
ecosystem-based adaptation should be employed. Examples include the
construction of Dams and reservoirs to hold excess water, riverbank protection,
construction of levees and spillways, appropriate drainage systems and storms
water management, and dredging of major rivers. Appropriate measures should be
put on ground to stem the level of flooding occurrence. Specifically, governments should ensure that
environmental management policies are properly enforced in the country.
Development control activities should be taken seriously to avoid the erection
of developments on flood plains and flood prone areas. Awareness raising, education on flood risk, communication and
messaging need to be strengthened to minimize flooding effects. Ecosystem-based solutions such as
reforestation in important river catchments, planting native vegetation on
flood plains that have been claimed for cropping, and creating buffers through
vegetation should be serious considered.
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