The I/I Normalization tool uses regression analysis to predict the inflow and infiltration for a specified site under storms of various return periods (e.g., a 1:10 or 1:25 year return period storm). Typically, proper usage of this tool requires at least five (5) measured rainfall events above a defined threshold volume.

From the Monitoring Station pop-up menu, select the bottom icon (Analysis Tools) and I/I Normalization from the drop-down menu. Alternatively, you can select I/I Normalization under Tools in the hamburger menu, in which case you would have to define the Organization, Project, Service, and Monitoring Station in addition to the configurations noted below.

Upon opening the tool, the user is prompted by a “Select Sensor Information” pop-up; this sets up the sensor used for normalization. This setup includes:

  • Flow Sensor
  • Rain Gauge
  • Catchment Area (total area of contributing catchment, defined in Station Details under the “Attributes” tab)
  • The Time of Concentration of the catchment (the time needed for water to flow from the most remote point in the catchment to the outlet), in minutes (defined in Station Details under the “Attributes” tab)
  • Pipe diameter of the sewer at the monitoring site (defined in Station Details under the “Attributes” tab)
  • Total pipe length (the sum of the lengths of all connected sewer pipes within the catchment), if known (required if you want to see the rainfall-derived inflow and infiltration per pipe footprint in the output)
  • Options to define start and end dates for the normalization analysis, or to use the entire range of monitored data
  • Defining the minimum storm volume used to run the regression analysis (defaulted to 15mm volume events and higher)

A red asterisk denotes required inputs.

The user is then taken to the “Configuration” tab, where they have the options of:

  • Adding further sensors to the regression (these are differentiated for comparison purposes)
  • Defining the X Axis of the normalization graph (peak rainfall intensity or total rainfall volume)
  • Defining the Y Axis of the normalization graph (peak I/I flow, peak I/I rate, I/I volume, or volumetric coefficient)
  • Selecting the design storm to be used as a benchmark, with choices to display 1:2 year, 1:5 year, 1:10 year, 1:25 year, 1:50 year, and 1:100 year storm thresholds (in terms of peak rainfall intensity or total rainfall volume) on the graph
  • The user can determine whether the line of best fit for the regression analysis is constrained to the origin, intercepting (0,0)

The resulting I/I Normalization regression graph is interactive: the user can hover over any of the points (representing the wet weather events included in the analysis) and view the event’s date and the two variables defined by the user for both axes of the graph.

Below the graph is a summary of the site ID, the sensor utilized, the regression equation, and the correlation coefficient (values less than 0.4 generally indicating poor curve fit, and values greater than 0.7 generally representing acceptable correlation).

Finally, each of the wet weather events included in the analysis is presented in tabular form, along with key metrics:

  • Event Date
  • Total Precipitation
  • Peak Rainfall Intensity
  • Peak Precipitation Intensity over Time of Concentration
  • Peak I/I Flow
  • Peak I/I Rate
  • Total I/I Flow Volume during Event
  • Volumetric Coefficient (the percentage of the volume of rainfall that became I/I in the sewers)
  • Instantaneous Wet-Weather Peaking Factor (the ratio of peak wet weather flow to average daily dry weather flow)
  • I/I per Pipe Area

The user can apply a thematic color ramping based on defined thresholds to the table’s columns. Based on a green, yellow, orange, and red color ramp, the user can set a “theme” based on ascending threshold for a specific parameter.

The graphical output can be exported as a PDF, .jpeg, or .png. The table can be exported as a .csv.


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