Saturday, December 10, 2011

Sensitivity Analysis in InfoSWMM and H2OMAP SWMM

Subject:  Sensitivity Analysis in InfoSWMM and H2OMAP SWMM

Sensitivity Analysis in InfoSWMM and H2OMAP SWMM

by dickinsonre
Subject:  Sensitivity Analysis in InfoSWMM and H2OMAP SWMM   
It is easy to perform sensitivity analysis in InfoSWMM and H2oMAP SWMM using the Scenario Manager, Dataset manager, Block Edit in the Database Editor, Batch Simulation and theReport Manager.  For example, we will do a sensitivity analysis for the Subcatchment Width (one the physical parameters in the Subcatchment analysis of SWMM 5 – see Figure 1).  The width is normally the area divided by the overland path length but there are many common means of calculating the width.

Figure 1.  Physical Data used in the Calculation of Surface Runoff using the Non Linear Reservoir Routing method in SWMM 5.
Figure 2.  The base scenario for our sensitivity analysis.
There are seven main steps in the sensitivity analysis of the width:
Step 1.   Use the Scenario Explorer to make Child Scenarios from the Base Scenario.  For ease of understanding we will name each of the Child Scenario's the percent change in the width parameter.  Thus, W-50, will be the Base Width Plus 50 percent.
Step 2.   Use the Dataset Manager to create different Subcatchment Sets that will be used for each of the Scenario's.  Again for ease of understanding we will use the name S_W+50 etc for the Sets to match the change in the Width Parameter.
Step 3.   Use the Scenario Manger to choose the right Subcatchment Set for Each Scenario.
Step 4.   Use the Database Editor to Edit and modify the Width of Each Subcatchment Set.
Step 5.   Use the Block Edit tool to multiply the Base Width Value by the needed value, 1.25, 1.50, 0.75, 0.50
Step 6.   Use the Batch Simulation Command to run all of the Scenario's.
Step 7.   Use Report Manager and the tool Compare Graphs to graph the results of Each Scenario together.
Step 8.   In Report Manager you can produce a table that shows the runoff for each of the different scenarios.

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