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A GIS-based modeling of environmental health risks in populated areas of Port-au-prince, Haiti

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par Myrtho Joseph
University of Arizona - Master in Natural Resources Information System 1987
  

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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

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