The following is a list of suggestions and warnings to consider when calibrating an unsteady flow model:

  1. Calibrate mostly to stages. Flow data is derived from stage. Be wary of discharge derived from stage using single value rating curves.
  2. Do not force a calibration to fit with unrealistic Manning's n values or storage. You may be able to get a single event to calibrate well with parameters that are outside of the range that would be considered normal for that stream, but the model may not work well on a range of events. Stay within a realistic range for model parameters. If the model is still not calibrating well, then there must be other reasons why.
  3. If using a single-valued rating curve at the downstream boundary, move it far enough downstream so it doesn't affect the results in the study reach.
  4. Discrepancies may arise from a lack of quality cross-section data. If you are using cross sections cut from a 10 meter DEM, then you should not expect to be able to get a good model calibration with such poor terrain data.
  5. The volume of off-channel storage areas is often underestimated, which results in a flood wave that travels to fast and will generally have to high of a peak downstream. Try to closely evaluate all of the areas that water can go and include them in the model.
  6. Be careful with old HEC-2 and RAS studies done for steady flow only. The cross sections may not depict the storage areas. Defining storage is not a requirement for a steady flow model to get a correctly computed water surface elevation.
  7. Calibration should be based on floods that encompass a wide range of flows, low to high. Be careful, to low of a flow can cause an unsteady flow model to go unstable. This is general caused by flow passing through critical depth between pools and riffles.
  8. For tidally influenced rivers and flows into reservoirs, the inertial terms in the momentum equation are very important. Adjusting Manning's n values may not help. Check cross sectional shape and storage. Also, setting Theta towards a value of 0.6 will often help with the numerical accuracy in tidal situations.
  9. You must be aware of any unique events that occurred during the flood. Such as levee breaches and overtopping.