A Surface Water Model for the Orinoco river basin Technical Report P.P. Schot A. Poot G.A. Vonk W.H.M. Peeters 2 A Surface Water Model for the Orinoco river basin Technical Report P.P. Schot A. Poot G.A. Vonk W.H.M. Peeters Utrecht, March 2001 Department of Environmental Sciences Faculty of Geography Utrecht University P.O.Box 80.115 3508 TC Utrecht The Netherlands e-mail: [email protected] 3 4 Contents LIST OF FIGURES ................................................................................................................. 6 LIST OF TABLES ................................................................................................................... 7 1 INTRODUCTION ............................................................................................................ 9 2 STUDY AREA ................................................................................................................ 10 2.1 General description................................................................................................ 10 2.2 Climate .................................................................................................................. 10 2.3 Hydrology.............................................................................................................. 12 3 GENERAL MODEL DESCRIPTION.......................................................................... 16 3.1 Model concept ....................................................................................................... 16 3.2 Model input ........................................................................................................... 18 3.2.1 Water balance input.................................................................................. 18 3.2.2 Routing input............................................................................................ 21 3.3 Model output ......................................................................................................... 23 4 MODEL COMPONENTS.............................................................................................. 24 4.1 Method of model selection .................................................................................... 24 4.2 Precipitation........................................................................................................... 24 4.3 Snow...................................................................................................................... 25 4.4 Potential Evapotranspiration ................................................................................. 27 4.5 Actual Evapotranspiration, linear.......................................................................... 29 4.6 Actual Evapotranspiration, exponential ................................................................ 30 4.7 Groundwater.......................................................................................................... 31 4.8 Casiquiare diversion .............................................................................................. 33 4.9 Model Selection..................................................................................................... 34 5 CALIBRATION AND VERIFICATION..................................................................... 36 5.1 Calibration ............................................................................................................. 36 5.2 Evaluation of the calibration ................................................................................. 37 5.3 Verification............................................................................................................ 38 5.3.1 Verification at Puente Angostura ............................................................. 39 5.3.2 Verification at other locations .................................................................. 41 5.4 Evaluation.............................................................................................................. 44 6 LIMITATIONS AND SCENARIOS............................................................................. 45 6.1 Limitations............................................................................................................. 45 6.1.1 Limitations due to spatial and temporal resolution .................................. 45 6.1.2 Limitations due to calibration and verification ........................................ 45 6.2 Scenarios ............................................................................................................... 46 6.2.1 Interventions............................................................................................. 46 6.2.2 Example 1: Construction of a dam........................................................... 46 6.2.3 Example 2: Diversion of a part of the water towards another river basin 49 7 EVALUATION AND RECOMMENDATIONS.......................................................... 52 7.1 Evaluation.............................................................................................................. 52 7.2 Recommendations for future model improvements .............................................. 52 REFERENCES....................................................................................................................... 54 APPENDIX I: DATA SOURCES AND FEATURES ......................................................... 55 APPENDIX II : ADDITIONAL VERIFICATION RESULTS.......................................... 56 5 List of figures Figure 2.1 The basin of the Orinoco River (Source: MacKee et al, 1989). ............................. 10 Figure 2.2 Mean monthly precipitation in mm and temperature in degrees Celsius during the dry and wet season. ................................................................................................. 11 Figure 2.3 Mean discharge in the Orinoco river basin (Source: Meade et al, 1990). .............. 12 Figuur 2.4 Hydrographic measuring stations in the Orinoco river basin included in this study. ................................................................................................................................. 13 Figure 2.5 Temporal variation in monthly averaged river discharge at Puente Angostura (1925-1990)............................................................................................................. 14 Figure 2.6 Flow duration curve for Puente Angostura measuring station (1925-1990). ......... 14 Figuur 2.7 Long term yearly total discharge at Puente Angostura and 65-year average discharge (1925-1990)............................................................................................. 15 Figure 3.1 Flow diagram of the Orinoco surface water model concept ................................. 16 Figuur 3.2 Maximum water storage capacities of the soil in mm in the Orinoco basin. ......... 19 Figure 3.3 Land cover map of the Orinoco basin derived from the GLCC-database. ............. 20 Figure 3.4 Pre-processed land cover map of the Orinoco basin, based on figure 3.3.............. 20 Figure 3.5 Digital elevation model (DEM) of the area in which the Orinoco basin is located.21 Figure 3.6 Map with local drainage directions (LDD) in the Orinoco basin. .......................... 22 Figure 3.7 Streamorder network according to the Strahler classification and basin boundaries of the Orinoco basin before modification of the digital elevation model. .............. 22 Figure 3.8 Streamorder network according to Strahler classification and basin boundaries of the Orinoco basin after modification of the digital elevation model....................... 23 Figure 4.1 Monthly averaged measured and simulated discharge of the model with direct generation of discharge from precipitation. ............................................................ 25 Figure 4.2 Monthly averaged measured and simulated discharge of two models. .................. 26 Figure 4.3 Monthly averaged measured and simulated discharge of three models. ................ 28 Figure 4.4 Monthly averaged measured and simulated discharge of four models................... 30 Figure 4.5 Monthly averaged measured and simulated discharge of five models. .................. 31 Figure 4.6 Monthly averaged measured and simulated discharge of six models..................... 33 Figure 4.7 Monthly averaged measured and simulated discharge of seven models. ............... 34 Figure 5.1 Monthly average simulated discharge before and after model calibration and monthly average measured discharge at Puente Angostura. ................................... 37 Figure 5.2 Simulated and measured discharge at Puente Angostura for verification run 1..... 39 Figure 5.3 Simulated and measured discharge at Puente Angostura for verification run 2..... 40 Figure 5.4 a-d Simulated and measured discharge used for verification. ................................ 41 Figure 5.5 Simulated discharge (m3/s) in the Orinoco basin during the month with highest simulated discharge (July), logarithmic values. ...................................................... 43 6 Figure 5.6 Simulated discharge (m3/s) in the Orinoco basin during the month with lowest simulated discharge (March), logarithmic values. .................................................. 43 Figuur 6.1 Estimated reservoir area of a dam with hypothetical characteristics in the Ventuari River. ....................................................................................................................... 46 Figuur 6.2 Effect of dam on basin scale. Simulated