Characterization of shallow aquifers in Guinea Bissau to support the - - PowerPoint PPT Presentation

Characterization of shallow aquifers in Guinea Bissau to support the promotion of manual drilling at country level

• F. Fussi*, F. Asplund**, L. Fumagalli*, M. Caruba,

M.Rotiroti*, T.Bonomi* (Italy) *University Milano Bicocca – Italy ** UNICEF Guinea Bissau fabio.fussi@usa.net

GUINEA BISSAU

I

Fussi et al. - 44th IAH 2017 – Groundwater Heritage and Sustainability

Geology of Guinea Bissau is characterized by a division in two main sectors:

 West part of the country (Mesozoic Basin) including

Quaternary-Tertiary groups

 East part including Paleozoic and Crystalline formations

Extension: 36,125 km2 Morphology: flat or slightly

• ndulated

Climate: warm all year. Average yearly temperature: 26.3 °C Intense precipitation concentrated from June to September. Yearly rainfall in Bissau: 2024 mm

WHY PROMOTING MANUAL DRILLING IN GUINEA BISSAU?

In Guinea Bissau still 35% of rural population has no access to safe water (2012). Most of them are living in small villages UNICEF and DRGH (Direção Geral de Recursos Hídricos) wants to assess the potential of manual drilling as a low cost solution to provide safe water to these areas In 2016 a preliminary study to assess the suitability for manual drilling in the country and identify those regions with favourable conditions has been carried out. This study is the continuation of the mapping of suitable zones for manual drilling already completed by UNICEF in 16 African Countries (www.unicef.org/wash/index_54332.html, plus Zambia, Burundi, Guinea Conakry and Guinea Bissau)

Fussi et al. - 44th IAH 2017 – Groundwater Heritage and Sustainability

SUITABILITY FOR MANUAL DRILLING

Suitability for manual drilling is a combination of 2 factors It takes into consideration other two aspects:

 Presence and thickness of hard laterite  Water quality

FEASIBILITY

possibility to drill a hole using manual drilling techniques

POTENTIAL FOR EXPLOITATION

Semi-quantitative assessment

• f potential yield

and size of the user’s group

Fussi et al. - 44th IAH 2017 – Groundwater Heritage and Sustainability

METHOD OF ELABORATION



MAP OF GEOLOGICAL GROUPS (FROM GEOLOGICAL MAP) MAP OF ENVIRONMENTAL GROUPS (BASED ON DTM) MAP OF GEO- ENVIRONMENTAL UNITS INPUT AND CODIFICATION OF STRATIGRAPHIC LOGS HYDROGEOLOGICAL PARAMETERS AND ASSESSMENT OF FEASIBITY AND POTENTIAL AT LOGS POSITIONS SPATIALISATION OF FEASIBILITY AND POTENTIAL SCORES MAP OF SUITABILITY MAP OF COMBINED APTITUDE

Fussi et al. - 44th IAH 2017 – Groundwater Heritage and Sustainability

GEO-ENVIRONMENTAL GROUPS

ENVIRONMENTAL GROUPS Coastal areas Plateau (slightly ondulated) GEOLOGICAL GROUPS Sedimentary Cristallyne

Fussi et al. - 44th IAH 2017 – Groundwater Heritage and Sustainability

EXTRACTION OF HYDROGEOLOGICAL PARAMETERS FROM STRATIGRAPHIC LOGS

DATA SOURCE Stratigraphic logs obtained from national water authority (DGRH), UNICEF and local drillers DATA PROCESSING The method is adapted from the previous experience in Senegal and Guinea (Fussi, 2014. 37th WEDC Conference, Hanoi)

 Manual input of data in a specifically designed spreadsheet  Assigning standard terms to describe each geological layer  Extraction of percentage of different texture classes at 1m regular steps  Extraction of hydrogeological parameters for each log (up to 30 m deep)

Fussi et al. - 44th IAH 2017 – Groundwater Heritage and Sustainability

HYDROGEOLOGICAL PARAMETERS AT LOGS POSITION

Fussi et al. - 44th IAH 2017 – Groundwater Heritage and Sustainability

FROM HYDROGEOLOGICAL PARAMETERS TO THE ASSESSMENT OF FEASIBILITY AND POTENTIAL



DEPTH TO WATER

DEPTH TO HARD ROCK THICKNESS OF HARD LATERITE THICKNESS OF COARSE LAYERS (HIGHLY PERMEABLE)

FEASIBILITY AT LOGS POSITION POTENTIAL AT LOGS POSITION DISTRIBUTION OF FEASIBILITY AND POTENTIAL BY GEO ENVIRONMENTAL UNITS

Fussi et al. - 44th IAH 2017 – Groundwater Heritage and Sustainability

SPATIALISATION



Fussi et al. - 44th IAH 2017 – Groundwater Heritage and Sustainability

Weighted average of class of feasibility, potential and presence of laterite at borehole logs, aggregated by geo-environmental group

SUITABILITY FOR MANUAL DRILLING

Fussi et al. - 44th IAH 2017 – Groundwater Heritage and Sustainability

ESTIMATION OF COMBINED APTITUDE

% OF TERRITORY BY CLASS OF APTITUDE

Fussi et al. - 44th IAH 2017 – Groundwater Heritage and Sustainability

RESULTS AND CONCLUSION

In Guinea Bissau 53% of the territory has good

• r excellent aptitude for manual drilling

366.000 inhabitants are using unsafe water

• sources. 90% of them live in areas with suitable

condition for manual drilling

Manual drilling is a valid low cost option to cope with some of the major problems concerning access to safe water in Guinea Bissau

RESULTS AND CONCLUSION

At the end of the research, the information of 500 borehole logs is available, organized in a well structured geographic database and suitable for automatic extraction of hydrogeological parameters for shallow and deep aquifers. This dataset shows the potential relevance of converting to numeric database of more than 5000 stratigraphic logs stored in hard copy in national institutions in Guinea Bissau. Data processing and map production has been done with free and open source software. This makes easier to promote further data analysis and mapping for a large group

• f users.

Thanks for your attention Fabio.fussi@usa.net