In situ biophysical data analysis establishing the draining process of
Central African lakes whose origins are hypothetica...
Location:
Northwest of Congo Basin
Rainforest
Tri-National Park of Sangha
(UNESCO – World Heritage of
Humanity)
Central Af...
Issues :
 Dense rainforest, hardly accessible
 No mapping
 Isolated area covered with lakes with
hypothetical origins
N...
1891 : 1st exploration by Alfred Fourneau
2012 : Sangha 2012 team
2009 : Beginning of Sangha 2012 project
2010 : Prelimina...
Context Sensors Method Results Hypothesis Conclusion
Lake 1
Lake 2
Lake 4
Lake 5
Lake 6
Lake 7
Lake 3
15 months of data !
...
Comparison with ancillary data
Pressure and temperature : recording
every 30 minutes
Brightness and temperature : recordin...
Mean daily pressure inside the lakes
95
97
99
101
103
105
107
109
29/09/10 18/11/10 07/01/11 26/02/11 17/04/11 06/06/11 26...
15
17
19
21
23
25
27
29
95
97
99
101
103
105
107
109
18/11/10 07/01/11 26/02/11 17/04/11 06/06/11 26/07/11 14/09/11 03/11/...
Supposed rainy events occur in high rainfall estimate periods
Context Sensors Method Results Hypothesis Conclusion
The beginning of flood moves back or forward depending on the lakes
Context Sensors Method Results Hypothesis Conclusion
Context Sensors Method Results Hypothesis Conclusion
2
4
5
7
Isolated
watersheds
Context Sensors Results Hypothesis Conclusion
Simultaneous responses to major rainy events regardless the period of the ye...
Conclusions
Context Sensors Results Hypothesis Conclusion
This analysis over the Sangha rainforest demonstrates the
comple...
Geo212 – 25, rue Jean Dolent – 75014 Paris – www.geo212.fr
benedicte.navaro@geo212.fr
Thank you for your attention
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Sangha 2012 Biodiversity in Pigmy Land - Presentation at Geomorphology 2013

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In situ biophysical data analysis establishing the draining process of Central African lakes whose origins are hypothetical: complementarities with an original small scale satellite based study
Presentation at Geomorphology 2013 - Paris - August 2013

Publié dans : Technologie, Business, Voyages
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Sangha 2012 Biodiversity in Pigmy Land - Presentation at Geomorphology 2013

  1. 1. In situ biophysical data analysis establishing the draining process of Central African lakes whose origins are hypothetical: complementarities with an original small scale satellite based study Bénédicte Navaro, Gilles Lerouge, Camille Netter, Thierry Rousselin Geo212 – 25, rue Jean Dolent – 75014 Paris – www.geo212.fr contact@geo212.fr
  2. 2. Location: Northwest of Congo Basin Rainforest Tri-National Park of Sangha (UNESCO – World Heritage of Humanity) Central African Republic South of Bayanga A data analysis conducted by Geo212 within the scientific program « Sangha : Biodiversity on Pygmy land - Insects of the World in Central African Republic » (2010 -2012) Context Sensors Method Results Hypothesis Conclusion
  3. 3. Issues :  Dense rainforest, hardly accessible  No mapping  Isolated area covered with lakes with hypothetical origins Necessity :  Understanding the environmental distribution of fauna  Understanding the river system organisation (location / distribution / communication) An old hypothesis : Through photointerpretation, some lakes were interpreted as sinkholes of a paleo cryptokarst above continental sands. Context Sensors Method Results Hypothesis Conclusion Image Spot-5, résolution spatiale 5m
  4. 4. 1891 : 1st exploration by Alfred Fourneau 2012 : Sangha 2012 team 2009 : Beginning of Sangha 2012 project 2010 : Preliminary field mission : installation of 17 sensors in strategic locations 2012 : Principal field mission : collect and analysis of the sensors data Context Sensors Method Results Hypothesis Conclusion
  5. 5. Context Sensors Method Results Hypothesis Conclusion Lake 1 Lake 2 Lake 4 Lake 5 Lake 6 Lake 7 Lake 3 15 months of data ! Prosensor®
  6. 6. Comparison with ancillary data Pressure and temperature : recording every 30 minutes Brightness and temperature : recording every 2 hours Lakes area GDEM ASTER 2 Rainfall Estimate per dekade on a 10x10 km grid Context Sensors Method Results Hypothesis Conclusion
  7. 7. Mean daily pressure inside the lakes 95 97 99 101 103 105 107 109 29/09/10 18/11/10 07/01/11 26/02/11 17/04/11 06/06/11 26/07/11 14/09/11 03/11/11 23/12/11 11/02/12 01/04/12 Pressure(kPa) Date Synchroneous responses of the lakes regardless of the water level Context Sensors Method Results Hypothesis Conclusion
  8. 8. 15 17 19 21 23 25 27 29 95 97 99 101 103 105 107 109 18/11/10 07/01/11 26/02/11 17/04/11 06/06/11 26/07/11 14/09/11 03/11/11 23/12/11 11/02/12 01/04/12 Temperature(°C) Pessure(kPa) Date Mean data for lakes 2 4 5 7 Mean pressure Mean temperature Hypothesis : response of the lake to a rainy event 0 10000 20000 30000 40000 50000 60000 70000 18/11/10 07/01/11 26/02/11 17/04/11 06/06/11 26/07/11 14/09/11 03/11/11 23/12/11 11/02/12 01/04/12 Brightness(lux) Confirmation by brightness data Context Sensors Method Results Hypothesis ConclusionContext Sensors Method Results Hypothesis Conclusion
  9. 9. Supposed rainy events occur in high rainfall estimate periods Context Sensors Method Results Hypothesis Conclusion
  10. 10. The beginning of flood moves back or forward depending on the lakes Context Sensors Method Results Hypothesis Conclusion
  11. 11. Context Sensors Method Results Hypothesis Conclusion 2 4 5 7 Isolated watersheds
  12. 12. Context Sensors Results Hypothesis Conclusion Simultaneous responses to major rainy events regardless the period of the year BUT Not a hydromorphic soil : - No streaming observed above the ground : Lakes drained by underground flow, surfaces are free piezometrical surfaces. -During swelling or flood, simultaneity caused by saturation - During low water period simultaneity caused by direct rain contribution Deferred starts of respective floods Not just one common watershed : Aquifere loading time different from one lake to the other
  13. 13. Conclusions Context Sensors Results Hypothesis Conclusion This analysis over the Sangha rainforest demonstrates the complementarity between local in situ measures interpretation and a small scale geomorphological analysis.  Proof of a non hydromorphic soil  Draining process explained by independent aquifers  Link between lakes and deep karst not confirmed and unlikely … The protocol of the mission and the use of Aster GDEM v2 explore the prospects to highlight river patterns with fairly simple logistics.
  14. 14. Geo212 – 25, rue Jean Dolent – 75014 Paris – www.geo212.fr benedicte.navaro@geo212.fr Thank you for your attention

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