Flow regulating functions of natural ecosystems for Dam synchronization in the Zambezi River Basin

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Transboundary Water Management Workshop held in Johannesburg, South Africa from April 29-30, 2014.

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Flow regulating functions of natural ecosystems for Dam synchronization in the Zambezi River Basin

  1. 1. Photo:DavidBrazier/IWMIPhoto:TomvanCakenberghe/IWMIPhoto:TomvanCakenberghe/IWMI www.iwmi.org Water for a food-secure world Xueliang Cai 29/04/2014, Johannesburg, South Africa Flow Regulating Functions of Natural Ecosystems for Dam synchronization in the Zambezi River Basin
  2. 2. www.iwmi.org Water for a food-secure world Outline • Introduction • The Zambezi river basin • Flow duration curves for analysing hydrological functions • Results • Conclusions
  3. 3. www.iwmi.org Water for a food-secure world Introduction – why does it matter • Africa, and to less extent Asia, landscape largely characterized with natural vegetation and untamed areas; • Forests, wetlands and floodplains big influence on hydrological processes; • Natural ecosystems into water resources planning and management (e.g. dam operations) for green economy; • Lack of understanding on hydrological functions of ecosystems.
  4. 4. www.iwmi.org Water for a food-secure world Mixed findings of wetland hydrological functions • 30/66: headwater wetlands reduce flood peaks, but 27 concluded the other way around. • 11/20: headwater wetlands increased flood event volumes. • 48/77: wetlands increase evaporation or reduce river flow. • 47/71: wetlands reduce downstream flows during dry periods but in 20% of cases verse visa. • 23/28: floodplains reduce or delay downstream floods Bullock and Acreman, 2003, based on review of 169 studies
  5. 5. www.iwmi.org Water for a food-secure world ESA GlobCover GLWD The Zambezi River Basin
  6. 6. www.iwmi.org Water for a food-secure world The Zambezi River Basin 102 stations with 25 years or more data 18 sites identified
  7. 7. www.iwmi.org Water for a food-secure world The method Downstream gauge Upstream gauge Reference gauges
  8. 8. www.iwmi.org Water for a food-secure world Establishing reference (no ecosystem) flow duration curve Standardized FDCs derived from mean daily flow measured at gauges located in the vicinity of the Luswishi floodplain 0.01 0.1 1 10 0.1 2 12 22 32 42 52 62 72 82 92 99.3 Q/Qmean % time flow exceeded Normalised reference FDC Regional FDC (avg) GRDC 1591500 (Reference) FRIEND 60334250 (Reference)
  9. 9. www.iwmi.org Water for a food-secure world Transferring the reference flow duration curve to the site of interest 0.1 1 10 100 1000 0.1 0.5 0.9 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 88 92 96 99.1 99.5 99.9 Flow(m3s-1) % time flow exceeded Reference FDC GRDC1591440 (Downstream) Comparison of the “reference” FDC and the observed FDC at the gauge downstream of the Luwishi floodplain FDCdestination = FDCreference * Qdes. mean
  10. 10. www.iwmi.org Water for a food-secure world Generating the reference flow time series Pdes = (Pupstream + Pdownstream)/2 0.1 1 10 100 1000 0.1 2 12 22 32 42 52 62 72 82 92 99.3 Q/Qmean % time flow exceeded Reference FDC downstream of floodplain Regional FDC (avg)
  11. 11. www.iwmi.org Water for a food-secure world Results 0 20 40 60 80 100 120 1-Oct-84 1-Nov-84 1-Dec-84 1-Jan-85 1-Feb-85 1-Mar-85 1-Apr-85 1-May-85 1-Jun-85 1-Jul-85 1-Aug-85 1-Sep-85 1-Oct-85 1-Nov-85 1-Dec-85 1-Jan-86 1-Feb-86 1-Mar-86 1-Apr-86 1-May-86 1-Jun-86 1-Jul-86 1-Aug-86 1-Sep-86 Flow(m3s-1) Daily flow with and without floodplain: HY1984 and HY1985 Without floodplain (simulated) With floodplain (observed) Upstreamfloodplain (observed) Flood plains
  12. 12. www.iwmi.org Water for a food-secure world Results Base flow index Mean annual minimum (m3s-1) 1-day 10-day With floodplain 0.994 2.96 3.04 Without floodplain 0.886 2.02 2.13 Return period (yrs) Flood Magnitude (m3s-1) % reduction With floodplain Without floodplain 1.1 27.3 37.0 26.3 1.5 41.0 62.0 33.9 2 47.3 73.3 35.5 5 56.2 94.3 37.2 10 65.2 104.6 37.7 25 71.4 115.3 38.0 50 75.4 121.9 38.2 100 78.9 127.8 38.3 200 82.0 133.0 38.3 0 20 40 60 80 100 120 140 1 10 100 Peakfloodflow(m3s-1) Return period (yrs) Flood Frequency With floodplain Without floodplain (simulated) Extrapolated 0 20 40 60 80 100 120 140 1 10 100 Peakfloodflow(m3s-1) Return period (yrs) Flood Frequency With floodplain Without floodplain (simulated) Extrapolated Flood plains
  13. 13. www.iwmi.org Water for a food-secure world Results Headwater wetlands 0.00001 0.0001 0.001 0.01 0.1 1 10 100 0.1 0.5 0.9 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 88 92 96 99.1 99.5 99.9 Q/Qmean %time flow exceeded RegionalFDC (avg) - inc 65312102 FRIEND65312602 (downstream) 0 50 100 150 200 250 300 350 400 450 500 1-Oct-85 1-Nov-85 1-Dec-85 1-Jan-86 1-Feb-86 1-Mar-86 1-Apr-86 1-May-86 1-Jun-86 1-Jul-86 1-Aug-86 1-Sep-86 1-Oct-86 1-Nov-86 1-Dec-86 1-Jan-87 1-Feb-87 1-Mar-87 1-Apr-87 1-May-87 1-Jun-87 1-Jul-87 1-Aug-87 1-Sep-87 Flow(m3s-1) Daily flowwith and withoutheadwaterwetlands: HY1984 and HY1985 Withoutheadwaterwetlands(simulated) Withheadwaterwetlands(observed) Percentile Flow (m3s-1) % difference With wetlands Without wetlands 99 0.0 0.1 - 95 0.0 0.5 - 90 0.0 0.8 - 75 0.2 2.1 980.4 50 2.2 5.3 142.1 25 20.1 17.1 -15.3 10 70.3 46.2 -34.3 5 107.0 73.5 -31.4 1 152.9 208.2 36.2 Bua River in Malawi Total catchment area: 4,777 km2 Area of wetlands: 823 km2 (17.2% of total catchment)
  14. 14. www.iwmi.org Water for a food-secure world Results Headwater wetlands BFI Mean annual minimum (m3s-1) 1-day 10-day With wetlands 0.96 0.028 0.032 Without wetlands 0.74 0.389 0.443 Return period (yrs) Flood Magnitude (m3s-1) % reductio nWith wetlands Without wetlands 1.1 31.9 15.0 -112.7 1.5 75.0 24.8 -202.4 2 96.5 47.8 -101.9 5 140.5 161.8 13.2 10 164.4 272.2 39.6 25 190.8 439.6 56.6 50 208.3 579.2 64.0 100 224.3 728.3 69.2 200 239.2 885.9 73.0 0 100 200 300 400 500 600 700 800 900 1000 1 10 100 Peakfloodflow(m3s-1) Return period (yrs) With headwater wetlands (observed) Without headwater wetlands (simulated) Extrapolated
  15. 15. www.iwmi.org Water for a food-secure world Results Miombo forest Luchelemu River in Malawi Total catchment area: 261 km2 Area of wetlands: 244 km2 (93.5% of total catchment) 0.01 0.1 1 10 100 0.1 2 12 22 32 42 52 62 72 82 92 99.3 Flow(m3s-1) % time flow exceeded Regional FDC (avg) Downstream (65312505) 0 5 10 15 20 25 1-Oct-72 1-Nov-72 1-Dec-72 1-Jan-73 1-Feb-73 1-Mar-73 1-Apr-73 1-May-73 1-Jun-73 1-Jul-73 1-Aug-73 1-Sep-73 1-Oct-73 1-Nov-73 1-Dec-73 1-Jan-74 1-Feb-74 1-Mar-74 1-Apr-74 1-May-74 1-Jun-74 1-Jul-74 1-Aug-74 1-Sep-74 Flow(m3s-1) Daily flowwith and withoutforest: HY1972 and HY1973 Withoutforest(simulated) Withforest(observed)
  16. 16. www.iwmi.org Water for a food-secure world Results Miombo forest BFI Mean annual minimum (m3s-1) 1-day 10-day With forest 0.79 0.552 0.628 Without forest 0.67 0.465 0.508 Return period (yrs) Flood Magnitude (m3s-1) % reductio nWith forest Without forest 1.1 6.5 7.9 17.7 1.5 9.6 17.0 43.3 2 11.7 19.7 40.6 5 16.8 30.6 45.1 10 20.4 38.3 46.7 25 25.3 48.5 47.8 50 29.1 56.2 48.2 100 33.1 64.2 48.4 200 37.3 72.4 48.5 0 10 20 30 40 50 60 70 80 1 10 100 Peakfloodflow(m3s-1) Return period (yrs) With forest (observed) Without forest (simulated) Extrapolated
  17. 17. www.iwmi.org Water for a food-secure world Conclusions • A simple yet effective approach proposed and tested capable of application in the Zambezi with limitations; • In the Zambezi: • floodplains decrease the magnitude of flood flows and increase low flows; • headwater wetlands increase the magnitude of flood flows and decrease low flows; • miombo forest, when covering more than 70% of the catchment, decrease the magnitude of flood flows and also decrease low flows.
  18. 18. www.iwmi.org Water for a food-secure world Conclusions Some further potential developments to separate other factors: • Land use, topography, climate soil, geology; • Society development (Population, infrastructure, farming, deforestation); • Groundwater contribution. • And feed into synchronized operations.
  19. 19. www.iwmi.org Water for a food-secure world Thank you!

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