How to use the Optimal Storm Duration tool

The Optimal Storm Duration tool can be used to allow the user to find what the duration of a storm would be required to achieve a maximum level or discharge at a location of interest. 

The Optimal Storm Duration, also known as the Critical Storm Duration, should be identified and used when assessing flood risk, either as part of a flood risk assessment, flood risk mapping or developing models to test flood mitigation options, to assess the impacts at maximum level or discharge. Running design events using the Optimal Storm Duration should assess the maximum impact for that scenario.

The tool calculates the Optimal Storm Duration by creating many 1D simulations with varying storm durations, in which all other model settings (including all other hydrological unit parameters) remain the same.

1. Load the data of interest - this should include a river network (or event) file and a simulation (.ief) file. This simulation should be an unsteady type and have a long enough simulation time to cover the range of storm durations which will be analysed in the OSD tool.
2. To open the OSD tool, navigate to the Hydrology tab and click the Optimise Storm Duration button.
   
   Note

   The active network or any files associated to the active network should not be edited when the OSD tool is open.
3. Select one or multiple hydrology boundaries to determine which node(s) storm duration will be optimised. To select all of the available options, deselect the Apply only to selection box.
4. Select one single downstream node to optimise at. The node can be selected by searching in the list of downstream nodes present, or manually entering the desired nodes name in the (case-sensitive) or manually enter label here box.
5. Specify the optimisation process which you wish to run. In the Variable field, select whether the flow or stage is being optimised at the node in question. In the Optimise field, select whether a maximum or minimum of this variable is to be calculated. In the Optimising Method field, select whether the Brent or Exhaustive method is to be used. 
6. Input the mandatory Maximum and Minimum (upper and lower limits) of all the duration values to be tried by the OSD tool in the Storm Duration box.
7. A different start point in the range for the analysis to begin may also be chosen; enter this in the Initial field. The Use Current check box uses the storm duration value contained in the data file while using Brent’s method. For the Exhaustive search, an initial value is not required.
8. Select the 1D simulation file prepared earlier. Ticking the Generate run convergence bitmap option allows for the run-time graphics window to be shown at the end of a simulation. 
9. To begin the OSD simulations, select the Optimise button at the bottom of the tool. The simulations can be aborted by pressing the Escape key when the Storm Duration graph window is open.
   
   Note

   You can run the tool in double-precision by checking the box to the right of the Optimise button.
10. The calculated optimum storm duration obtained from running the OSD tool may be viewed in tabular or chart forms. Each format can be viewed via the Data (tabular) or Graph (chart) tabs respectively.
    
    Note

    The storm duration of your boundaries can be edited using the global edit tool or overwritten at simulation runtime via settings in the hydrology tab.

Download the sample dataset used in the video to try it yourself: