1. Case Study Atankwidi Catchment (Westafrica, Volta Basin)

2. real gauge (No.1) fictive gauge (No.2) fictive gauge (No.3) Fictive irrigation field N 51015 km0 3 2 Subcatcment 3 Subcatchment 2 & implemented fictive reservoir 1 2 3 1 Subcatchment 1 Study Area: Atankwidi Catchment (Volta Basin)

3. Example of the model application: Reservoir volume: 100000 m³ Reservoir area:81701 m² Irrigation system command area:50 ha Maximum number of iterations:4 Area maxArea minOptimization Value Wet Rice1513 Dry Rice1012 Tomato1012 Onion1513

4. Red Line Constraint: Reservoir Volume>1000 m³ Constraints not fullfilled Reduction of the irrigated area Increase of the Reservoire Volume

5. Results

6. Reduction of the Irrigation Field Area

7. Reduction of water withdrawal

8. OBSERVED VALUE = resVol month 1= min : 3400.95000| max : 4073.12000--- true month 2= min : 285.22300| max : 345.55500--- failed month 3= min : 33.31420| max : 66.95770--- failed month 4= min : 100000.00000| max : 100000.00000--- true month 5= min : 5140.90000| max : 6755.63000--- true month 6= min : 100000.00000| max : 100000.00000--- true month 7= min : 100000.00000| max : 118030.00000--- true month 8= min : 100000.00000| max : 100000.00000--- true month 9= min : 100000.00000| max : 100000.00000--- true month 10= min : 42.46340| max : 85.18110--- failed month 11= min : 41.93220| max : 84.50180--- failed month 12= min : 93.86200| max : 188.85400--- failed OBSERVED VALUE = resVol month 1= min : 1888.34000| max : 2259.77000--- true month 2= min : 63.58550| max : 267.02400--- failed month 3= min : 33.36820| max : 67.00810--- failed month 4= min : 100000.00000| max : 100000.00000--- true month 5= min : 114.66100| max : 1744.76000--- failed17 times month 6=min : 100000.00000| max : 100000.00000--- true month 7= min : 100000.00000| max : 118065.00000--- true month 8= min : 100000.00000| max : 100000.00000--- true month 9= min : 100000.00000| max : 100000.00000--- true month 10= min : 42.52880| max : 85.30950--- failed month 11= min : 42.19190| max : 84.84340--- failed month 12= min : 94.64700| max : 189.78500--- failed Optimization: Reservoir Volume

9. GAMS: Agricultural Profit

10. Discussion … still many problems : in the actual WaSiM-ETH version concerning reservoirs and irrigation, i.e. not adapted for irrigation of big areas & no consideration of evaporation and percolation from the reservoir Optimzation only possible by reducing / expanding the irrigated area Reservoir size (semi-arid areas)