Methodology for migrating basin models from Vflo™ 5 to Vflo™ 6

Vflo™ 6 introduces an enhanced solver for the kinematic wave analogy (KWA). The numerical solution of the KWA for overland and channel cells is performed within Vflo™ using a finite element solution in space and finite difference approximation in time (Vieux et al., 1988)1. Discretization of a real world basin into a network of connected finite elements requires assumptions concerning the interconnectivity at each junction of nodes. Vflo™ 6 has an enhanced method for approximating the $ {\partial\,(uh)\over\partial\,x} $ and $ {\partial\,Q\over\partial\,x} $ terms for overland and channel flow respectively. The previous formulation had introduced dispersion into the model solution. This had the benefit that the model was more tolerant of discontinuities in rating curve cells. However, this dispersion could lead to reduced kinematic wave speeds in steep basins. The reduced wave speed may have been handled in existing models by decreasing Manning's roughness values for channel cells.

 The basic steps in migrating basin models developed in earlier versions of Vflo™ for use with the new solver included Vflo™ 6 are as follows:

  1. Select a group of rainfall events for calibration purposes.
  2. Select a cell or group of cells to serve as the calibration point(s) for the model. For instance, the watch points stored in the model.
  3. Determine the connectivity value of the area upstream of the calibration pointby selecting it and using from the network analysis screen.
  4. Select the channel cells upstream of your calibration point. Adjust the calibration factor for roughness by moving the slider bar for roughness. The calibration factor will be equal to the connectivity value obtained in Step 3.
  5. Compare your new calibrated model with observed peak discharge and time to peak for your group of rainfall events, using each rainfall event as precipitation loaded into Vflo™.
  6. If the error between simulated and observed peak discharge and time to peak is acceptable, then save model for future use.
  7. Otherwise, calibrate the channel roughness using the OPPA calibration technique, discussed in Calibration Methods.
  • 1. Vieux, B.E., V.F. Bralts, L.J. Segerlind, 1988. Finite element analysis of hydrologic response areas using geographic information systems, Am. Soc. Civ. Eng.