I&I Studies: Set Data Intervals and Fill Data Gaps (Using FACE)

Overview:

If you are getting errors related to I&I studies, your RAINFALL channel(s) or FLOW channel(s) may be the cause of the issue when generating your Dry Weather Patterns and/or Storm Event Groups. To successfully run an I&I study, the data in your raw or calculated channels being used should be (1) in uniform time intervals (5, 10, 15 minutes etc.) and (2) free of data gaps with respect to the date ranges you have set in your study. This article provides an overview on how to setup a CALCULATED channel which can set your data into uniform intervals (timestamps) and fill any data gaps with a value of your choice.

Summary:

Using 3 calculated channels, we will set our data up in 15 minute intervals and replace data gaps with a constant value of 0. This is to help ensure we can run an I&I study with uniform data, free of data gaps - which is a requirement of generating dry weather patterns and/or storm event groups based on the relevant data. Note: The value you choose to set your data intervals (5, 10, 15 minutes etc.) as well as the value you choose to set to fill your data gaps (can be '0' or data pulled from another site/channel) is variable - your choice. 

The 3 step approach is to fill any gaps in a channel we are going to use called "Rainfall" with NULL values where there is a gap. Then we will replace any occurrences of NULL with values from another channel (ex: nearby rain gauge) or use an assigned constant – such as a value of 0 as is common practice.

IMPLEMENTATION: 3 Step Process

  1. Create a new channel “Rainfall_FilledRain”. Use the SUM function with a 5-minute interval. This will fill any gaps with NULL values, but it will also shift all of your values 5-min forward.

    NOTE: You can set this channel to HIDDEN to avoid future confusion with your site in terms of presentation / graphing etc.


  2. Create a new channel “Rainfall_FIlledRainShift” that uses the previous channel as a source component. Use the SHIFT function with a 5-minute back setting. This re-aligns your values.

    NOTE: You can set this channel to HIDDEN to avoid future confusion with your site in terms of presentation / graphing etc.


  3. Create a new channel “Rainfall_Final” that uses the previous channel as a source component.  Use a formula:    IF(A == NULL, 0, A)
    Note: A = Rainfall_FIlledRainShift as your source component

    This formula says that when our FilledRainShift channel is NULL, then replace it with the value 0. Else, use the rain from the FilledRainShift channel. Note: to replace NULL's with values from another rain gauge, simply swap the 0 in the last formula with a rainfall channel another gauge. This is your FINAL RAIN channel and ensure it is VISIBLE for presentation / graphing etc. Do ensure this channel is set to RAINFALL ENABLED and units are assigned accordingly (inches in this case), in order to run the I&I tool with this FINAL edited channel as a selection. You may also want to set the interim channels in step 1 and 2 to not visible to reduce clutter.

References:

Before we begin, here are some reference articles that we will be using for this 3 step process:

 

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