HEALTH EFFECTS OF DAM CONSTRUCTION

Dams are massive barriers built across rivers and streams in order to impound

water. There are three main types o f dams, concrete dams, earth dams and

rock-filled dams. The first known dam was built in 2900BC across the Nile river to

protect the city of Memphis from flooding. Dams are usually constructed because

of their numerous beneficial effects to man. Some of these benefits include

GENERATION OF ELECTRICITY
A dam is built to trap water, usually in a valley, where there is an existing lake.

Water is allowed to flow through the tunnels in the dam to turn turbines and thus

drive generators. Hydro-electric power stations can produce a great deal of power

e.g the huge Hoover dam on the Colorado river supplies much of the electricity of

Las Vegas in the USA. The Kainji and Shiroro dams in Nigeria generate a large

volume of electricity which is supplied to a large number of cities and villages.

Although, hydro-electric stations are expensive to build, once the station is built,

the water comes free of charge.

The provision of electricity has enhanced productivity in many industries hence

increasing man's earning ability and thus, purchasing power. This enables him to

afford basic neccessities of life like good nutrition and shelter, which inturn

promotes good health. He is also now able to afford the cost of treatment in the

various health facilities. Electricity itself improves health care provision in the

various health care facilities since many modern equipments used in diagnosis

and treatment are largely dependent on supply of adequate electricity.

IRRIGATION
By constructing a dam across a river, a large reservoir of water can be held back

and later released at any time of the year to feed adjacent farms. Such perrenial

canals can irrigate vast areas throughout the year e,g the Sacramento and San

Joaquim irrigation schemes of California, the Murray-Snowy rivers scheme of

Australia, the Aswan dam project in Egypt and the various irrigation schemes on

the river Indus in Pakistan. Large dams can also help to improve the aesthetic

value of the environment e.g Western Rajasthan in India was transformed into a

green area by the Indira Gandhi canal which draws water from the Bhakhra dam.

This project apart from allowing farmers to grow crops in the desert, also helps to

check the spread of the Thar desert in adjoining areas of Punjab and Haryana.

Periyar dam reservoir has become an elephant sanctuary with thick green forest

all around while at the same time, the famine that used to haunt the district of

Madurai in Tamil Nadu before its construction has become a thing of the past.

Also, the Mandya district once covered with shrubs and home to many wild beasts

has been transformed into a prosperous place with green paddy and sugarcane

fields through the Krishnarajasagar dam.

With irrigation, there is increased food production which enhances nutriton and

promotes positive health.

FLOOD CONTROL
Control of flooding is ensured by damming. Such dams, which either stop or slow

down the flow of water in a river are called detention dams.

The control of flooding protect farmlands from destruction hence promoting

good nutrition and in effect good health. It also prevents loss of life and property.

WATER SUPPLY TO THE POPULACE
Provision of adequate portable water supply can be achieved through damming.

The water impounded by the damming is pumped to the treatment plant for

purification and supply. The Ikpoba dam, a subunit of the Edo state urban water

board in Nigeria, supplies 70% of the portable water distributed within Benin-City

and its environs.

The provision of portable water from dams has no doubt improved the health of a

large segment of the human populace. The morbidity and mortality associated

with water borne diseases is reduced to the barest minimum.

DAMMING HAS ALSO BEEN USED FOR RECREATION AND SILT AND DEBRIS COLLECTION
Recreational activities are known to promote good health.

It is obvious from the above that numerous socio-economic and health

advantages are derivable from damming. Ironically, damming also inadvertently

creates other problems viz:

DOWNSTREAM ARE DEPRIVED OF NUTRIENT-RICH SILT
Silt that would normally make its way down the river gets trapped behind the

dam. The silt can therefore not get to farmlands downstream. This causes

farmlands to be less fertile. The resultant fall in food production may lead to

malnutrition with its associated negative implications on health.

SPECIES EXTINCTION
Dams have harmful effects on fish and marine mammals. Majority of dams do not

include proper bypass systems for these animals, interfering with their life cycles

and sometimes forcing species to extinction. For instance, in the USA, dams block

fish passage upstream to areas where Salmon once reproduced and spent their

early lives. Grand Coulee on the Columbia rivers and Hells Canyon on the 'Snake'

permanently block 1200 miles of the mainstream rivers once used by salmon.

Dams also reduce the number of salmon that migrate downstream to the ocean.

On the Columbia-Snake system, juvenile salmon that remain in the river on their

downstream migration must pass eight dams. An estimated 10-15% die passing

through the turbines at each dam, which means 60-70% of those fish will never

reach the ocean.

The nutrients derivable from thi source will therefore, be unavailable to the

people.

FLOODING
Dams as stated earlier, can be used to control flooding. Ironically, they can also

cause flooding. There may be flooding of a vast expanse of land, including

farmlands behind the dam. The lake Nasser is an example where many people

were moved and rendered homeless as well as lossing their farmlands because of

damming.

Flooding leads to destruction of farmlands and decreased food production with

its attendant adverse health consequences. There may also be disruption of

health services occasioned by the flood disaster.

DISPLACEMENT OF PEOPLE
Apart from flooding, the construction of dams in itself may necessitate

relocation of a large segment of the population. The creation of the reservoir now

known as lake Nasser necessitated the relocation of approximately one million

Egyptians and Sudanese Nubians. They lost their farmlands and were dispersed to

less fertile government lands in Upper Egyypt and Eastern Sudan.

Displacement of persons may lead to inadequate access to health care. People

may also lose their occupations, which decreases earning power. The incidence of

malnutrition may increase thus promoting increased morbidity and mortality.

SPREAD OF DISEASES
As the water in the reservoir and the irrigation channels is contained, this

promotes the build-up of water snails which are vectors of schistosoma. There

may also be the build-up of mosquitoes, since the stagnant water favours the

breeding of mosquito larvae and pupae. This increases the incidence of malaria

and other mosquito-borne diseases in the affected area.

The larvae and pupae of the insect vector of onchocerciasis(river bindness), the

black fly thrive in highly oxygenated water attached to submerged vegetation and

stones. The upstream area which is fast-flowing and well oxygenated is thus a

favourable breeding area. This may result in increased incidence of river

blindness. The Volta lake is upstream to the Akosonbo dam in Ghana. One of the

largest endemic areas for onchocerciasis is the Volta river basin, incorporates

parts of Benin Republic, Ghana, Mali, Togo, Burkina Faso etc. This is the area of

the onchocerciasis control programme.

DAM FAILURE AND SAFETY
Inspite of the high technology and safety measures involved in construction of

dams, failure occasionally occurs with disastrous consequences.

The Malpasset dam in France collapsed suddenly in December 1959. The ensuing

flood wave resulted in 421 deaths and great damage. The Vaoint catastrophe of

October 1963 in Italy resulted from instability of the banks of the reservoir. A

large abrupt rockslide into the reservoir caused water to pass over the Vaoint dam

at a depth of more than 70m. The dam was undamaged but the resulting flood

wave inundated a downstream village causing the death of 2600 people.

Apart from deaths that may result from dam failure, the resultant flooding may

cause other problems associated with flooding as already stated.

It is obvious from the foregoing that while a lot of advantages are derivable from

dam construction, the negative consequences are also numerous.

A number of anti-dam and pro-dam groups have sprung up in various parts of

the globe canvassing their various positions.

The important lesson from all of these is that a lot of assessment should be done

and a lot of factors considered before embarking on dam construction in a

particular area.