3.4.2.6 Pollution from water
bodies
Urban and peri-urban population health is equally affected by
wastewater from urban drains and municipal dumping of waste, especially human
excreta (Nsiah-Gyaabah et al 2004). River pollution is particularly found to
be worse where rivers pass through cities and the most widespread is the
contamination from human excreta, sewage and oxygen loss (UNEP 1986). Canals
and rivers are also used as an outlet for trash, particularly at locations
where waste collection is lacking. Stagnating water transmits bilharziose or
triggers malaria. Additionally, where potable water is rare, poor people
often use the polluted rivers to wash their clothes, contributing to the
pollution, and exposing themselves to multiple pollution hazards. Lastly,
polluted water bodies represent a source for the breeding of disease vectors
(WHO 2001).
In addition to distance to rivulets, which was classified into
four levels from 0 to 400 meters, slope was integrated as a vulnerability
factor. Low slopes were deemed more favorable to water pooling, mosquitoes
breeding, and a higher concentration of pollutants, therefore correspond to a
higher risk. That is, for the same threshold distance to the channel (e.g. 100
meters) people living in areas located in lower slope were more at risk than
those living on steeper slopes. These two factors were summed with a greater
weight assigned to distance to channels. The result was reclassified with the
geometric interval technique as it appears on Table 6.
Water body risks = 0.7*(distance to rivulets) + 0.3* slopes
Table 6: Pollution from
water bodies - Risk Levels
|
Distance(0.7)
Slope (0.3)
|
>200
|
101-200
|
51-100
|
0-50
|
|
1
|
2
|
3
|
4
|
|
> 25%
|
1
|
1.0
|
1.7
|
2.4
|
3.1
|
|
15 - 25%
|
2
|
1.3
|
2.0
|
2.7
|
3.4
|
|
5 - 15%
|
3
|
1.6
|
2.3
|
3.0
|
3.7
|
|
0 - 5%
|
4
|
1.9
|
2.6
|
3.3
|
4.0
|
|
Risk Levels
|
|
1 - Low
|
2 - Moderate
|
3 - High
|
4 - Very High
|
|
1 - 2.4
|
2.4 - 3.05
|
3.05 - 3.35
|
3.35 - 4.0
|
3.4.2.7 Proximity to the sea
The area immediately contiguous to the seashore is the last
repository for all type of waste, mud, household and human refuse, and
industrial waste. In developing countries, people in poor households living in
proximity to the sea and who do not have a toilet or latrine don't
have any other alternative than to unload their defecation either in
the sea shore or vacant plots and open drains (Olanrewaju 1990). In
addition, discarded cans, bottles, waste incoming from all activities are sinks
and places for mosquitoes breeding, which spread diseases such as malaria and
dengue (SKAT 2002). In Haiti, as reported by UNEP (1996), several shantytowns
have been built in proximity to the seashore in recent years. Some of them are
erected on dumping sites which often block water flowing to the sea, and
generating ponds. The wind blowing from the sea may dissipate the effects of
pollutants or it may spread them across a larger area. These locations have a
high dose of pollutants and expose their residents to very harmful effects. A
2001 Panamerican Health Organization (PAHO 2001)) report on health in Haiti
stated that the transmission of malaria occurs mainly in coastal areas
coincident to altitude lower than 300 meters.
A Euclidean distance surface was calculated with a threshold of
1000 meters from the sea divided into four vulnerability levels as shown in
Table 7. The impact may not be linear and may vary in function of some factors
such as the disposition of the slums, local variation in elevation,
canalization or conditions of the canalization (which is a temporal variable),
amount and types of debris (vehicle carcasses for instance may block the
movement of waste towards the sea), etc. For simplicity, we assumed that the
phenomenon is linear in its materialization.
Table 7: Distance to the
sea and Risk Levels
|
Distance (in meters)
|
Risk Level
|
|
0 - 300
|
4
|
|
301 - 500
|
3
|
|
501 - 700
|
2
|
|
> 700
|
1
|
| 
