Dynamique hydrolog ique, s édimentaire et g éochimique des zones d inondation en Amazonie: résultats et perspectives 1
Floodplain surface area estimation for the whole Amazon basin: between 3, and 6, km² (±67,) (Martinez et al.,27) 6 km 2
Floodplain and River interactions Landsat Image, High waters (8/July/21) Role of floodplains: attenuation of floods zone of sediment deposition modification of water chemistry (sorption & redox processes) 3
Study area: The Curuaí floodplain -8-7 -6-5 Location: 55.43 W / 2.18 S System size: 126 x 2 km Iquitos U % # U % # U % # Manaus Santarem - N W Km S -2-8 -7-6 -5 River level fluct. River slope : 7m : 1.4 cm.km-1 Watershed Area E Altitude (m) - 5 5 - - 25 25-5 5 - - - 15 15-2 2-35 35-5 5-65 65-7 OCEAN -2 : 366 km² 4
Riverbank Aquatic-Terrestrial Transition zone Local Watershed 5
Methodology 6
Várzea lake hydrological modeling :Available data Bathymétrie -8 - - 2.7 2.7-3 3-4 4-4.5 4.5-5 5-5.5 5.5-6 6-7 7-8 8-9 9 - - 11 11-12 12-13 13-14 14-16 16-18 18-2 2-25 25-3 3-35 35-45 45-6 6-7 7-8 8-85 85-9 9-95 95 - - 544.81 No Data Surface-water level relationship 3 N 3 3 6 Kilometers W S 2 (km²) SRTM + MOSAIC JERS DEM => relationship between the inundated surface area and water level 2 Flooded area: 575/243km Aquatic Terrestrial Transition Zone: /1855 km2 E 2.5 5. 7.5 1 (m) S=(216 ± 9.2)(Z-Z )+(551±46)7 12.5
Várzea lake modeling: available data for water discharge $ AI3 AI2$ $ $ AI $$$ $ AI7 $ $ $ AI8 $$ ATS AC -1 2 3 Width (m) 3 19 déc. 27 2.5 Width Depth Max. depth(m) Discharge m.s 4 2 5 5. 7.5 1 Water level (m) 12.5 5 6 7 8 9 Water level (m) 11 8 12
Várzea lake modeling: available data for rainfall -1 mm.day 12 8 6 4 2 Annual rainfall (mm) 9-3 3-3 9-2 3-2 9-1 3-1 9-3- 9-99 3-99 35 Humid year 3 Curuai 25 Orixima 2 Juruti 15 Obidos 5 9-98 around the varzea lake 3-98 9-97 Rainfall recorded at 4 rain gauge stations Time Dry year 97-98 98-99 99- -1 1-2 2-3 Water year 9 76-year average of rainfall
Várzea lake modeling: available data for evaporation 5 Riou, 75 (Empirical transfert de masse formula) 4.5 Mass transfer (Dalton law) 4 3.5 mm.j -1 3 2.5 2 1.5 1.5 mars févr janv déc Good agreement between the 2 formulas Seasonal variations of evaporation are weak. Evaporation accounts for 5 to 73 % of rainfall. nov oct sept août juil juin mai avr mars
Várzea lake modeling: Analyses procedure Channel Local runoff Bank overflow Rainfall/evaporation AI2 Bank seepage Heva Model Rainfall t+ 1 L V Evaporation = V + QR QE + QWN + QWS ± QG ± t L Runoff from the aquatic-terrestrial transition 19 déc. 27zone QwN = Max( ( P E )( S BVN S L ),) Upland local discharge i Qci t Groundwater flow from bank-seepage dh dx K=-2m.s-1 QG = KL * dz Amazon- varzea channels discharge 11
Várzea lake modeling: Analyses procedure At each step of time Δt (daily time step) the hydrological mass balance is expressed as: t+ 1 L V = V + QR QE + QWN AI3 + QWS ± QG ± AI2 t L i Qci t B = Qci + QR + QwN + QwS ± QG QE i Evaporation Amazon- varzea channels discharge Rainfall Runoff from the aquatic-terrestrial transition zone Groundwater flow from bank-seepage dh dx K=-2m.s-1 QG = KL * dz QwN = Max( ( P E )( S BVN S L ),) Upland local discharge 12
Model calibration and validation Computed and measured water levels at Curuai station 12 measured computed.3.1 cm 8 Water level (m) Differences between observed and computed values -.1 6-4 -.3 2 calibratio n validation -.4 -.5 Sep-3 Mar-3 Sep-2 Mar-2 Sep-1 Mar-1 Sep- Mar- Sep-99 Mar-99 Sep-98 Mar-98 Sep-3 Mar-3 Sep-2 Mar-2 Sep-1 Mar-1 Sep- Mar- Sep-99 Mar-99 Sep-98 Mar-98 Sep-97 Sep-97 validation Time mean absolute differences and standard deviations: 97-98 98-99 99-2 2-21 21-22 22-23 9 6 6 4 5 7 7 6 5 4 5 4 13
9 8 7 6 4 3 2 5 wn G Month 11 9 8 Month 7 6 5 4 3 2 1 12-6 2 9-4 P wn 8 2.5 VL 4 3) -2.5 7 5. 6 QG 6 I 5 QE 8 in 4 QwS 3) Cumulative fluxes (km QwN 7.5 in Volume (km I-O V/Σ Volume (km 2 Σ 3 3) QP b 2 4 1-2 1 a 12 1-2 1. 1 Fraction of each source term 6 1 12 Cumulative volume and fraction of the water flux components Month year 21-22 (regular year) 11-6 Groundwater related flux 14
11 7 6 5 4 3 2 P wn 6 2 wn G Net contribution from the floodplain to the river: 6.7 km3 9 8 Month 7 6 5 11 9 8 Month 7 6 5 4 3 2 1 12-6 = 95% = 4% = 1% 4-4 8 4 3 VL in I 2-2 Σ 3) Sink terms: Amazone River Evaporation 2.5 Seepage.5 b = 78% V=/Σ9% in = 5% = 5% =3% 1 3) 3) Cumulative fluxes (km Volume (km I-O 1-2 Volume (km a Source terms: Amazone River Q DirectP rainfall 7.5 Local QwS water basin QwN Runoff on ATTZ QE Seepage QG 5. 12 1-2 4 2 1. 1 Fraction of each source term 6 1 12 Cumulative volume fluxes of the water Monthflux year 21-22 (regular year) 9 8-6 15
Cumulative volume related to source and sink terms for the 6 water years study 3 year Inflow 97-98 98-99 99- -1 1-2 2-3 Average SD % Source terms (km ) Rainfall Runoff wn Runoff ws Seepage Sink terms (km3) Outflow Evaporation Seepage Water mass balance (km3) Ra Rw m SD % m SD % m SD % m SD % m SD % m SD % m SD % m SD % m SD % m SD % 13.3 2 2.4 3 1.8 4 1.6 4.7 2 17.6 19. 1.6 13..4 2-4.2 3 6 55.6 16. 3.4 3 1.8 4 1.9 4.6 2 6.8 13. 2.1 13..4 2-5.2 3 6 4.6 19. 4. 3 2.2 4 2.3 4.7 2 47.3 13. 1.9 13..1 2-6.7 3.5 6 36.8 19. 3.9 3 2.1 4 2.2 4.6 2 44.2 13. 1.8 13..1 2-7.3 3 -.5 6 28.6 18. 3.3 3 1.8 4 1.8 4.9 2 34.4 14. 1.8 13. 2-5.8 3.1 6 22.6 19. 32.9 45. 3.8 3 2.2 4 2.2 4.9 2 29.5 15. 1.9 13. 2-6.9 3 6 3.5 17.3 2. 11.5 2. 12.8.7 17. 39 38.8 2 7.8.7-6 -19.6 34 16
Inter-annual variation: temporal mixture in the lake.1 98-99 38 32 26 2 14 3 2 2 1 1 38 3 32 4 26 4 2 5 14 5 1 6 6 6 Day 97-98 Groundwater G& bank seepage 38 32 Day 1 6.1 38 32 26.4 26.4 2.6 14.6 1 1..8 6 38 32 26 2 14 1 6.1 in.8.1 1..3 Day /Σ Mixture Vfrom year-1.3 Day I ws Local Basin discharge.4 Days 2 14.1.4.1 1 6.3 wn Runoff ATTZ P Rainfall.4 38.4 32.4 26.6 2.6 14.8 1.8 6 1. I Inflow Amazon 1. Day 99-2-3 17
Inter-annual variation: temporal mixture in the lake.8 38 32 26 2 14 2 2 1 1 38 3 32 3 26 4 2 4 14 5 1 5 6 6 38 32.4 26.4 2.6 14.6 1.8 6.8 98-99 1 32 26 2 38 G 6 Day 97-98 -1 in 1. Day Day 1. 38 32 26 2 14 1 6.1.1.1.1 V/Σ Day I ws.3 14 1.1.3 6.1 Days.4 6.3 38 32 26 2.4 14.6 1.4.4 Input from the groundwater system represents between 7 and.3 times (1 and 5%) the maximum volume of stored water in the floodplain system. 3 Local Basin The discharge Curuai floodplain contributes to 9.3 km Mixture from year for 6.3 Groundwater & bank seepage to the Amazon flow Mean water residence time is about 3 ± months 6.6.8 wn ATTZ Runoff P Rainfall.4 1. I Inflow Amazon 1. Day 99-2-3 Bonnet et al., in press 18
Suspended solids mass balance 4 12 Flux liquide net (Mm3) Flux solide net (^3 t) Flux entrant 3 Cote Amazone 2 8 Flux sortant Nov-3 Sep-3 Jul-3 May-3 Mar-3 Jan-3 Nov-2 Oct-2 Aug-2 Jun-2 Apr-2 Feb-2 Dec-1 Oct-1 Aug-1 Jun-1 Apr-1 Feb-1-6 Dec- (cm) 4-2 -3 Une forte remise en suspension en période de basse eaux Un stockage de sédiment entre 14 et 5% des flux entrant Un taux d accrétion de 1 à 2 mm par an -4 Bourgoin et al., 27 2 19
Bilan de certains éléments chimiques K T/an Ca T/an Sr T/an Mn T/an Fe T/an Ba T/an Cu T/an U T/an Q 3 m /s Flux moyen entrant dans la varzéa 24245 161666 987 744 2798 679 52 2 947 Flux moyen sortant de la varzéa 27874 185479 9 17 1467 778 58 2 11 Bilan de transfert 3629 23813 2-727 -1331 6 1 162 Temps de résidence dans la varzéa pour le cycle 22-23 (jours) 126 133 133 1471 234 122 141 122 122 Barroux, 26 A l échelle annuelle, seuls le Mn et le Fe semblent non conservatifs 2
Variations saisonnières de Ca2+ 2 Recharge par la nappe ou dégradation de la 15 végétation RCa 5 Uptake par la végétation Sale -5 Em Ec R= cl - -15 12-3 11-3 -3 9-3 8-3 7-3 6-3 5-3 4-3 3-3 2-3 1-3 12-2 11-2 - 2 Comparaison du comportement du chlore (conservatif) avec celui du Ca2+ 21
Primary production in floodplains and impact on CO2 emission Lago de Curuai Lago de Janauaca about 16 km² Solimoes floodplain Clear and black waters Objectives : To quantify primary production and it s controlling factors in floodplains To track primary production fate and evaluate it s impact on CO2 emissions Method: Study of two contrasted sites to help extrapolation : Method based on in situ survey, water color and modelling program EC2CO 27 22
Thanks for your attention! 23