Risings and floods from Rivers Tomi, Gribingui and Fafa in Central and Central-North of  Central African Republic Dr. Cyri...
Introduction <ul><li>Located on both sides of the  Interfluve Chad-Congo  i.e. on upper Chadian (Fafa and Gribingui) and C...
Problem & Aims <ul><li>Survey carried out over extreme events,  floods  = most marked event, followed by  drough t  in the...
Applied Methodology   <ul><li>Maximum daily mean and annual flows data from Tomi at Sibut (1951-1995), Gribingui at Kaga-B...
RESULTS   3rd International Disaster and Risk Conference IDRC Davos 2010, 30 May - 3 June 2010 ¦ Davos, Switzerland
Fluvial  regimes  and appearance of risings’ peaks 3rd International Disaster and Risk Conference IDRC Davos 2010, 30 May ...
Discharge of historical or flood’s risings from Rivers Tomi, Gribingui and Fafa over 1951-1999 period 3rd International Di...
Frequencies of historical risings from studied rivers 3rd International Disaster and Risk Conference IDRC Davos 2010, 30 M...
Frequencies of historical risings from studied rivers (Cont.) Weather/Climate  perceptions in past time: others characteri...
Frequencies of historical risings from studied rivers (Cont.) 3rd International Disaster and Risk Conference IDRC Davos 20...
Risings and floods manifestations, and flows index Complexity of Rivers’ dynamics in time and space according probably to ...
Recorded modifications in time over local importance of maximum flow 3rd International Disaster and Risk Conference IDRC D...
Conclusion <ul><li>S take for local management of the flood’s phenomenon = the districts’ extent regularly affected per st...
<ul><li>Coupling these data with calculated flow frequencies = support a base of local management of these phenomena  </li...
Thank you! 3 rd  International Disaster and Risk Conference IDRC Davos 2010, 30 May - 3 June 2010 ¦ Davos, Switzerland
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Risings and floods from Rivers Tomi, Gribingui and Fafa in Centre and Centre-north of Central African Republic

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Risings and floods from Rivers Tomi, Gribingui and Fafa in Centre and Centre-north of Central African Republic

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Risings and floods from Rivers Tomi, Gribingui and Fafa in Centre and Centre-north of Central African Republic

  1. 1. Risings and floods from Rivers Tomi, Gribingui and Fafa in Central and Central-North of Central African Republic Dr. Cyriaque-Rufin Nguimalet Department of Geography, University of Bangui, Central African Republic (CAR) & CMRT Project, Egerton University , Kenya 3 rd International Disaster and Risk Conference IDRC Davos 2010, 30 May - 3 June 2010 ¦ Davos, Switzerland INTERNATIONAL SECRETARIAT
  2. 2. Introduction <ul><li>Located on both sides of the Interfluve Chad-Congo i.e. on upper Chadian (Fafa and Gribingui) and Congolese (Tomi) basins </li></ul><ul><li>Soudano-Guinean variant of the wet tropical climate (1,200-1,400 mm) </li></ul><ul><li>River Tomi basin = 2,380 km 2 ; Gribingui basin area is 5,680 km 2 and River Fafa’s one covers 4,380 km 2 </li></ul><ul><li>Average bed’ slopes are respectively 0.0024 m m -1 (Tomi), 0.0014 m m -1 (Gribingui) and 0.0011 m m -1 (Fafa) </li></ul><ul><li>Rivers Tomi, Gribingui and Fafa normally are perennial flow and tropical mode of transition </li></ul>3rd International Disaster and Risk Conference IDRC Davos 2010, 30 May - 3 June 2010 ¦ Davos, Switzerland Risings are seasonal/annual demonstrations able to affect communities in flood’ shape These are streams’ powerful and occasional hydrometric swellings, difficult episodes to envisage by their causes, demonstrations and consequences
  3. 3. Problem & Aims <ul><li>Survey carried out over extreme events, floods = most marked event, followed by drough t in these studied basin </li></ul><ul><li>Although reducing regularity in space and time, violence of 1999’s event that some inquired compare to 1961’s in terms of installation and phenomena’s local management, considers population growth and especially uncontrolled soil occupation </li></ul><ul><li>Reconsideration of the rivers risings and floods’ last dynamics of their respective outlets (Tomi at Sibut, Gribingui at Kaga-Bandoro and Fafa at Bouca) </li></ul><ul><ul><ul><li>(i) give an account the past risings of floods’ width and their space-time regularity </li></ul></ul></ul><ul><ul><ul><li>(ii) predict future phenomena by taking account climate change incidences </li></ul></ul></ul><ul><li>This is the interest of the floods’ study. </li></ul>3rd International Disaster and Risk Conference IDRC Davos 2010, 30 May - 3 June 2010 ¦ Davos, Switzerland
  4. 4. Applied Methodology <ul><li>Maximum daily mean and annual flows data from Tomi at Sibut (1951-1995), Gribingui at Kaga-Bandoro (1951-1995) and Fafa at Bouca (1958-1995) </li></ul><ul><li>Interview conducted for those having 50 years old and above focusing on their observed changes and past floods’ events </li></ul><ul><li>Using statistical tests: frequencies analysis with HYFRAN Plus Software (GEV, Gumbel, Weibull and Gauss distributions), flow index, A coefficient for appreciating the risings’ power </li></ul><ul><li>Determination of the appearance periods of risings’ peaks by HYFRAN Plus Software </li></ul><ul><li>Comparison of risings’ daily modes in various periods for typifying their spreading out in space and time </li></ul><ul><li>Spatialization of flooded areas by GIS approach for supporting management plans . </li></ul>3rd International Disaster and Risk Conference IDRC Davos 2010, 30 May - 3 June 2010 ¦ Davos, Switzerland
  5. 5. RESULTS 3rd International Disaster and Risk Conference IDRC Davos 2010, 30 May - 3 June 2010 ¦ Davos, Switzerland
  6. 6. Fluvial regimes and appearance of risings’ peaks 3rd International Disaster and Risk Conference IDRC Davos 2010, 30 May - 3 June 2010 ¦ Davos, Switzerland Dynamics of maximal risings from Tomi, Gribingui and Fafa (1951-1995) Appearance dates of risings’ peaks from Fafa at Bouca Appearance dates of risings’ peaks from Tomi at Sibut Appearance dates of risings’ peaks from Gribingui at Kaga-Bandoro
  7. 7. Discharge of historical or flood’s risings from Rivers Tomi, Gribingui and Fafa over 1951-1999 period 3rd International Disaster and Risk Conference IDRC Davos 2010, 30 May - 3 June 2010 ¦ Davos, Switzerland
  8. 8. Frequencies of historical risings from studied rivers 3rd International Disaster and Risk Conference IDRC Davos 2010, 30 May - 3 June 2010 ¦ Davos, Switzerland River Tomi basin = 2,380 km 2 Highest recorded Q in studied area Rivers Gauging stations location Basin area (km 2 ) Q (m 3 s -1 ) Break Observation date GEV distribution Gumbel distribution Weibull distribution Gauss distribution Fafa (n = 31) Bouca 4,380 312.5 196.5 1969-1970 Sept. 30, 1961 Oct. 12, 1988 105 years 10 years 190 years 10.5 years 1400 years 9 years 4250 years 10 years Gribingui (n = 35) Kaga-Bandoro 5,680 168 138 1969-1970 May 27, 1980 October 8, 1961 150 years 13,5 years 19 years 8.3 years 75 years 13 years 85 years 13 years Tomi (n = 30) Sibut 2,380 154 150 1969-1970 Augt. 27, 1966 Oct. 3, 1955 and Oct. 20, 1964 30 years 25 years 15 years 14 years 30 years 25 years 35 years 27 years Return periods GEV distribution Gumbel distribution Weibull distribution Gauss distribution Average of estimated Q Recorded Maximum Q 2 years 5 10 14 15 20 25 27 30 35 50 100 200 500 1000 83,1 114 132 146 150 154 162 173 182 192 199 79,7 115 139 150 154 162 191 213 235 264 286 84 116 133 147 150 154 162 173 182 194 202 85,6 116 132 145 150 154 160 169 178 189 197 83.1 115.25 134 150 154 150 150 150 154 154 168.75 182 194.25 209.75 221 154 m 3 .s -1 le 27/08/1966 150 m 3 .s -1 les 3/10/1955 et 20/10/1964 140 m 3 .s -1 le 29/08/1967 113 m 3 .s -1 les 30/09/1960 et 26/09/1968 110 m 3 .s -1 le 30/09/1975 108 m 3 .s -1 le 13/09/1961 107 m 3 .s -1 le 18/09/1986 106 m 3 .s -1 le 11/10/1971 102 m 3 .s -1 le 29/08/1991 98,7 m 3 .s -1 le 16/08/1963 96,7 m 3 .s -1 le 24/09/1973 85,5 m 3 .s -1 le 20/09/1962
  9. 9. Frequencies of historical risings from studied rivers (Cont.) Weather/Climate perceptions in past time: others characteristics 3rd International Disaster and Risk Conference IDRC Davos 2010, 30 May - 3 June 2010 ¦ Davos, Switzerland Gribingui basin area is 5,680 km 2 Return periods GEV distribution Gumbel distribution Weibull distribution Gauss distribution Average of estimated Q Recorded Maximum Q 2 years 3 5 7,5 8,3 10 10,5 13 13,5 19 20 50 75 85 100 150 200 500 1000 86,1 102 117 133 138 145 157 164 168 170 176 180 80,6 119 133 138 145 168 170 202 226 250 281 305 84,5 116 133 138 147 162 168 172 182 193 201 86,2 102 117 132 133 138 145 160 168 170 179 190 198 84.35 102 117.25 133 138 135.75 133 138 138 168 151.75 170.25 168 168 183 168 195.25 210 221 168 m 3 .s -1 le 27/05/1980 138 m 3 .s -1 le 8/10/1961 133 m 3 .s -1 les 23/09/1953 et 16/10/1955 123,5 m 3 .s -1 le 1 er /10/1951 122 m 3 .s -1 le 3/09/1966 114 m 3 .s -1 les 25/10/1952 et 25/09/1956 112 m 3 .s -1 les 30/09/1967 et 6/10/1975 109 m 3 .s -1 les 19/10/1959 et 2/10/1974 108 m 3 .s -1 le 30/09/1960 102 m 3 .s -1 les 3/10/1962 et 17/09/1968 94,8 m 3 .s -1 le 24/10/1954 88,1 m 3 .s -1 le 31/10/1979 87,4 m 3 .s -1 le 26/10/1964
  10. 10. Frequencies of historical risings from studied rivers (Cont.) 3rd International Disaster and Risk Conference IDRC Davos 2010, 30 May - 3 June 2010 ¦ Davos, Switzerland Fafa’s basin-area covers 4,380 km 2 Return periods GEV distribution Gumbel distribution Weibull distribution Gauss distribution Average of estimated values/Q Recorded Maximum Q 2 years 5 8 9 10 10,5 20 50 100 105 190 200 500 1000 1400 4250 118 163 196 228 274 310 312 348 401 444 120 164 194 196 202 259 287 312 314 350 378 126 174 192 196 200 222 246 262 276 294 306 312 129 173 196 215 237 251 264 280 291 312 123.25 168.5 192 196 196.5 196 216.75 254 277.5 312 312 300.5 331.25 354.75 312 312 312 m 3 .s -1 le 30/09/1961 196,5 m 3 .s -1 le 12/10/1988 192,5 m 3 .s -1 le 3/09/1992 182 m 3 .s -1 le 12/10/1975 174 m 3 .s -1 le 29/09/1963 173 m 3 .s -1 le 6/10/1962 169 m 3 .s -1 le 5/09/1960 168 m 3 .s -1 le 31/08/1967 149 m 3 .s -1 le 13/09/1966 147 m 3 .s -1 le 29/10/1970 145 m 3 .s -1 le 16/09/1959 134,5 m 3 .s -1 le 21/08/1974 133 m 3 .s -1 le 20/10/1964 123 m 3 .s -1 le 18/08/1965 120 m 3 .s -1 le 10/09/1968 117 m 3 .s -1 le 16/09/1971
  11. 11. Risings and floods manifestations, and flows index Complexity of Rivers’ dynamics in time and space according probably to catchment area, beds’ slope and elevation but changes’ occurrence is noticeable 3rd International Disaster and Risk Conference IDRC Davos 2010, 30 May - 3 June 2010 ¦ Davos, Switzerland
  12. 12. Recorded modifications in time over local importance of maximum flow 3rd International Disaster and Risk Conference IDRC Davos 2010, 30 May - 3 June 2010 ¦ Davos, Switzerland A Coefficient is calculated by dividing risings maximum flow to root squared of drained area.
  13. 13. Conclusion <ul><li>S take for local management of the flood’s phenomenon = the districts’ extent regularly affected per studied area </li></ul><ul><li>Flooded districts = a respective proportional urban surface of 30% to Sibut, 31% to Kaga-Bandoro and 36% to Bouca </li></ul><ul><li>I ncreasing human densities = respectively 544.88 persons km -2 , 1,054.94 persons km -2 and 1,762.12 persons km -2 ; </li></ul>3rd International Disaster and Risk Conference IDRC Davos 2010, 30 May - 3 June 2010 ¦ Davos, Switzerland
  14. 14. <ul><li>Coupling these data with calculated flow frequencies = support a base of local management of these phenomena </li></ul><ul><li>Leading public authorities to change to prevention methods of floods’ management by discouraging the occupation, settlement as well as socio-economic activities in floodplain </li></ul><ul><li>Application of legal framework and the provision of the means to the management structures of the catastrophes make that the flood’s risk management be random </li></ul><ul><li>Which would imply for the populations and their goods to be affected by a rare but more destructive flood? </li></ul>Conclusion ( cont .) 3rd International Disaster and Risk Conference IDRC Davos 2010, 30 May - 3 June 2010 ¦ Davos, Switzerland
  15. 15. Thank you! 3 rd International Disaster and Risk Conference IDRC Davos 2010, 30 May - 3 June 2010 ¦ Davos, Switzerland

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