Task 3 – Override Combine TIN Method.

By default, the temporal combination method is either Aggregate or Average, depending on the data type. However, the default method can be overridden with another method. For example, if the dataset represents temperature, it will be averaged by default, but the user might be interested in the maximum or minimum values over the time period.

Task 3 will demonstrate how to override the default TIN combination method using precipitation data.

Copy a New Map Window.

• Right-Click on the "Extent Constraints" Map Window and select "Map Window" → "Copy Map Window..."
• Name the new Map Window "Combine TIN-Max" and select Ok.
• Open the DSS Data Reader by expanding the "Combine TIN-Max" Map Window Node in the HEC-MetVue Explorer Window.

Override Combine TIN Method to Maximum.

• Right-Click on the TIN node and click on "Select DSS paths…"
  

The LMRFC precipitation grids are already selected since we created a copy of the "Extent Constraints" map window.

• Expand the "Active Read Constraints/Overrides" options and select "Override TIN Temporal Combine Method."
  

Notice that the data reader has identified that the selection is precipitation data and the combine TIN method is set to Aggregate by default.

We are interested in the intensity of the precipitation event so would like to see the maximum hourly precipitation (ie, the greatest intensity) during the 29-31 August 2021 event.

• Override the default combine TIN method to "UseMax" to identify the maximum precipitation intensity during the 29-31 August 2021 event.
  
• Select "OK" to view the data within the Map Window.
  
  

Question: Which subbasin received the most intense hourly precipitation during the 29-31 August 2021 event?

Next, let's use HEC-MetVue to determine the average hourly precipitation intensity within the Pearl River watershed.

Copy a New Map Window.

• Right-Click on the "Combine TIN-Max" Map Window and select "Map Window" → "Copy Map Window..."
• Name the new Map Window "Combine TIN-Avg" and select Ok.

Override Combine TIN Method to Average.

• Right-Click on the TIN node and click on "Select DSS paths…"
  

Again, the LMRFC precipitation grids are already selected since we created a copy of the "Combine TIN-Max" map window.

Determine Average Hourly Precipitation for Entire Event.

• Expand the "Active Read Constraints/Overrides" options and select "Override TIN Temporal Combine Method."
• Override the default combine TIN method to "Average" to identify the average precipitation intensity during the 29-31 August 2021 event.
  
• Select "OK" to view the average hourly precipitation for the 29-31 August 2021 event within the Map Window.
  

Question: Which subbasin has the highest average hourly precipitation during the 29-31 August 2021 event?

Determine Average Hourly Precipitation for 1 Day.

Try reducing the time window selected to see how it impacts the average hourly precipitation.

• Create a new map window by right-clicking on the "Combine TIN-Avg" Map Window and select "Map Window" → "Copy Map..."
• Name the new Map Window "Combine TIN-Avg-1 Day" and select Ok.
• Right-Click on the new map window's TIN node and click on "Select DSS paths…"
• Remove all of the selected paths except those for 30 August 2021.
• Select "OK" to view the average hourly precipitation for just 30 August 2021 within the Map Window.
  

Question: Hourly precipitation averages for just 30 August 2021 are much higher than the full 29-31 August 2021 event. Why is that?

Question: Which subbasin has the highest average hourly precipitation on 30 August 2021?

Prior Task(s):

Task 1 - Spatial Extent Constraints

Task 2 - Override Default Time Zone

Current Task:

Task 3 - Override Combine TIN Method

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