VO uses the results of one pre-development scenario to calculate the confidence interval for hydroperiod analysis. Therefore, before doing the hydroperiod analysis, we should select one scenario from all the scenarios in the project as the Pre-Development Scenario.

To do that, select and right-click on the scenario “Existing” under the Drainage Network Scenarios group in the Project Manager. In the opened context menu, click on Set as Pre-Development Scenario

Click the Scenario Comparison button in the Simulation toolbar.

A Scenario Comparison window will pop-up. Keep the scenarios with long-term simulation checked on. Select “SL26” in the Command window. Click Hydroperiod tab to view the hydroperiod of all the three scenarios.

You can change the Year to be compared and the desired Confidence Interval (%) from the drop-down list.

The grey lines in the Graph are the upper and lower boundary lines for the confidence interval. Below the graph is the Statistics table summarizing the days when the Storage depth of the RouteWetland is out of the confidence interval for each scenario in the selected year.

Keep the scenarios with long-term simulation checked on and “SL26” selected in the Command window. Click Inflow Mass Curve tab to view the cumulative inflow mass going to the wetland. From the figure, we can see that after the new development, there is less water flowing into the wetland. To compensate the water loss, a part of roof water is collected and re-directed to the wetland via a pond.