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runoff volumes and outflow hydrographs (Table 14.1). Routing coefficients for different tributary areas varied with the directness of runoff flow to the main drain, as more distant areas were assigned higher routing coefficients than those draining directly to the channel. |
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14.2.5
Model Calibration and Verification |
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Definition of Storm Events |
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The SPIDA model was calibrated and subsequently verified using rainfall, flow and level data collected as described above. Storm events were identified as those having a maximum rainfall intensity average over a 30 minute period of at least 4 mm/h. (A review of level and flow data showed that rainfall of intensities less than this resulted in no significant hydraulic response in the drains.) Using the above definition, 21 storm events were recorded; these accounted for 86 per cent of the total recorded rainfall. These events were subsequently used for both calibration and verification of the model, and for computer simulation to test the sensitivity of performance to different solids levels. |
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Initial Calibration Using Smaller Storms |
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Seven storms known not to cause major flooding were used for initial calibration. The objective of this work was to tune the hydrological variables of catchment response without the complications of flooding. Predicted and observed level and flow hydrographs were compared at the sites of the two recording level and flow gauges, and adjustments were made to various parameters of the model. Close correlation between observed and predicted volumes and hydrographs showed that the hydrological coefficients assigned to each portion of the catchment were sufficiently accurate. |
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Second Stage Calibration with Flood Events |
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Modification of the model to reflect performance during floods only started after satisfactory agreement had been achieved with the smaller storms. Shapes of the flood cones were estimated |
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