Site Suitability Analysis for a Central Wastewater Treatment Plant(S) In Accra Metropolitan Area Using Geographic Information System

Paulina Ansaa Asante (paulina.asante1989@gmail.com)

Alex Owusu Barimah (owusuba@yahoo.com)

Remote Sensing and GIS Laboratory Department of Geography and Resource Development, University of Ghana, Legon

 

This study presents the use of Geographic Information Systems (GIS) in

selecting suitable sites for the construction of a central wastewater treatment

plant(s)

For this purpose, several variables were analyzed using GIS technology.

This method present here, can also be used in checking the suitability of

selected sites or new areas for the purpose of constructing wastewater treatment

plants.

The study was conducted in the Accra Metropolitan Area (AMA)

AMA is a primate city in Ghana with a total land surface area of approximately

231km2

Has a total population of 3.9 million, population density 69.3 persons per hectare

and growth rate of 3.36% (GaWC, 2010)

It lacks of wastewater treatment facilities

The study was to help solve the problem of siting wastewater treatment plants

Study Area

Is not likely to pose any health threat to the environment as

well as the people.

Large enough for locating central wastewater treatment

plant(s).

Accessible

No negative aesthetic effect to the city

Gain the support of the people

A Suitable Location

The study also considered the following sub objectives.

Ascertain the factors that are considered in selecting a site.

Determine what would be the best site(s) based on multi-criteria decision

making algorithm

Examine the attitude, knowledge and perceptions of residents on

wastewater treatment plants

Objectives.

The study was approached in two ways.

1. stakeholder interviews and criteria assessment to identify common criteria that need to be considered in suitable site selection.

2. the application of GIS (multi-criteria decision making) in modelling these factors in order to arrive at locations that are suitable for locating wastewater treatment plants.

The result is a composite map, which highlights the areas that satisfy all suitability criteria.

ArcGIS software was used

Methodology:

The process was divided into two steps,

A. Selection of variables and criteria with stakeholders; Key variables include

1. slope,

2. land cover,

3. distance to existing major roads,

4. distance to rivers and lagoon,

5. distance to existing major populated communities and

6. distance to airport facilities.

Multi-criteria decision making Variable and Criteria

B. the second step looked at the actual analysis using

variables and criteria to determining suitable and not

suitable locations

The final analysis of each variable was used to create

maps showing only the areas of interest.

The study applies exclusionary criteria.

Multi-criteria decision making Variable and Criteria

Digital Elevation Model

Mild slopes would result in, higher hydraulic residence times and thus higher

pollutant removal capacity.

To minimize pumping costs and improve the overall efficiency of the wastewater

treatment plant a maximum slope value of 10% was considered based on officials

guidelines.

Methodology: Slope

Slope grid of the study area

Selected areas in terms of slope less than 10%

A 2000-m buffer around existing populated areas

3000-m Buffer Around Airport in AMA

Land Cover Map of the Study Area

Selected Areas Based on Land cover.

A 90-m river, 300-m lagoon Buffer Zone.

A 300-m road buffer zone

Having examined all the different variables in the study area and maps

created for each based on criteria identified,

The final analysis was carried out using the overlay function in ArcMap

provided by the ArcGIS program.

The result is showing the areas that meet all the previously specified criteria

and are suitable for the construction of a central wastewater treatment plant

in the Accra Metropolitan Area.

Methodology: Analyzing the Variables

Selected Areas for Central Wastewater Treatment Plant in AMA

The total land area of AMA suitable for central wastewater treatment plant

is about 20km2.

This is the parcel of land north of AMA

Most residents living around treatment plants have no knowledge about the

essence of treatment plants.

They are indifferent

Major Findings

Any final decision at the sub-metro level should be based on more detailed

examination on each selected sites, involving a ranking of all possible sites using

non-exclusionary criteria.

The opinion of the people in the local communities should be taken into consideration

in making the final decision to use any site for the construction of the treatment plant.

Education of the local people is also very vital as it informs them on the essence

of the installation of the treatment plants and how they would have to handle them.

Conclusions

End Of

Presentation

Thank You.