Accessing the Critical Storm Analysis Wizard

You can access the critical storm analysis wizard from three locations:

Open the scenario manager (see Opening Managers); click the New button and then click the Critical Storm Analysis Wizard menu item.

Click the arrow below the compute button on either the Home or Analysis tabs and click the Critical Storm Analysis Wizard menu item.

Critical Storm Analysis Wizard

The critical storm analysis wizard assists in streamlining the process of creating scenarios, alternatives, calculation options and storm events for a specific set of return periods and durations. It provides an easy method to run a series of unsteady state calculations on an initial design. For example, you may have created a conveyance system using steady state (or peak flow) calculations, and perhaps ensured that there is no surcharging for the design storm. The next step might be to see how that system copes with a range of storm events and durations, and this wizard will guide you through this process.

The set of scenarios, alternatives, and storm events are created virtually and then calculated. After each virtual scenario is calculated the results are retrieved and cached. Once all virtual scenarios are calculated, the results are used with the Critical Storm Analysis tool.

Analysis Options

The base scenario is used as the parent of any scenarios exported from the critical storm summary results table. It is also used to initialize the default assignment for the catchment prototype and calculation options. This is done if the base scenario is a non-rational method-based scenario. The calculation options must use the implicit, explicit or GVF-Convex (using EPS) solver. The active catchment prototype must use a non-rational method-based runoff method.

Catchment Prototypes

The critical storm analysis wizard uses catchment prototypes to apply non-Rational runoff data to catchments in your model. The catchment prototype may be left unassigned if the base scenario already uses non-rational method catchment settings.

The data copied from the assigned prototype to each active catchment in the model include the following attributes:

• Runoff Method
  • Applies to all runoff methods
    • These attributes are never copied
      • Area Defined By
      • Use Scaled Area?
      • Area (User Defined)
      • Tc Input Type
      • Time of Concentration
      • Tc Data Collection
  • EPA-SWMM Runoff
    • Characteristic Width
    • Storage (Impervious Depression)
    • Storage (Pervious Depression)
    • Storage (Depression)
    • Manning’s n (Impervious)
    • Manning’s n (Pervious)
    • Manning’s n (Pervious) Pattern
    • Percent Impervious
    • Slope
    • Percent Impervious Zero Storage
    • Subarea Routing
    • Drying Time
    • Infiltration Pattern
  • ILSAX
    • Percent Impervious
    • Subareas
    • Antecedent Moisture Condition
    • Soil Type
    • ILSAX Soil value
  • Time-Area
    • Percent Impervious
    • Time-Area Diagram Type
    • Ignored Attributes
      • Time-Area Table
  • SCS Unit Hydrograph
    • Percent Impervious
    • Drying Time
    • Unit Hydrograph Method
    • SCS Unit Hydrograph Method
    • Ignored Attributes
      • Generic Unit Hydrograph
  • RTK Unit Hydrograph
    • Percent Impervious
    • Unit Hydrograph Method
    • Ignored Attributes
      • RTK Set
  • User Defined Hydrograph
    • Runoff Hydrograph
• Loss Method
  • Ignored for following runoff methods
    • ILSAX
    • RTK
    • <none>
    • User Defined Hydrograph
  • The loss method and properties for the selected loss method are always copied from the prototype to each active catchment.
  • If the loss method is not listed in the prototype property grid, then the losses are part of the subareas collection which is not copied other than for ILSAX.

Return Periods, Storm Events, Durations and Climate Change

A return period is defined as the probability that an event, such as a rainstorm, will occur.

Storm Events are a collection of return periods typically starting at 1 year and ending at or above 100 year. The typical return periods include 1, 2, 5, 10, 25, 50, and 100-year events. Though additional events of 200, 500 and 1000-year events may be included. The return period is not restricted to the typical values but can be whatever is required.

A duration defines the length of the storm event. This can be defined from 5 minutes to several hours or days depending on the data available.

The climate change factor is applied on top of a storm event. If a factor of 25% is used, it is applied at the time of calculation on top of the selected storm event. The data itself is not modified.

Calculations

Once the profiles are set and the finish button is clicked, the virtual scenarios are calculated. After each calculation, the results are retrieved and cached.

The status bar shown here will show the status of the calculation. The lower bar is the overall status and shows the current virtual storm out of the total number of storms. The top progress is used when there is a set of temporal patterns per storm.

You can stop the calculation at any time. The results stored up to the point when you clicked Stop will be used with the Critical Storm Analysis tool.

If a virtual scenario fails to calculate, you are prompted to export the problem scenario for further review. Clicking Yes will create the scenario, necessary alternatives and the storm data. You can then compute that individual scenario, and review the resulting User Notifications, to determine the cause of the problem.