Often times, raw precipitation data may cover a much larger area than your area of interest. Trimming the extents of the data can reduce file sizes and allow you to focus on your area of interest. Task 2 will demonstrate how to trim, factor and save precipitation data as well as view the effects of the changes to streamflow in the watershed within HEC-HMS. 

Copy the Map Window.

Return to the "HEC-MetVue_Overview" project. 

Right-Click on the "Radar" Map Window

From the "Map Window" option, select "Copy Map Window..."

Name the new Map Window "Radar – Trimmed – Factored"

Trim the Precipitation Data Extents.

Use the Polygon tool to draw a boundary around the Bald Eagle watershed perimeter.

Right-click on the polygon when done drawing

From the "Ad-Hoc Polygon Operations" option, select "Polygon Operations → "Delete Points outside polygon"

The TIN values outside of the selected polygon will be removed, trimming the extents of the precipitation grids.

Notice that a "History" of edits window will pop up.

This window keeps track of all user edits to the data and allows the user to turn edits off or on, or clear edits altogether.

Factor the Precipitation Data.

Right-click on the trimmed TIN and choose the option to Ad-Hoc Operations → Entire TIN Operations → Adjust Measurement Values for entire TIN...

Multiply by a constant of 2.5

The precipitation volumes will be scaled up by the specified factor of 2.5.

Factoring precipitation data can assist with answering questions like, "what if we get more (or less) rain than the current forecast?" The precipitation totals can be scaled upward or downward easily within HEC-MetVue. The new, factored gridded precipitation can then be saved to a DSS file and applied to an HEC-HMS model to assess the impacts of the factored precipitation volumes. 

Save the Factored Precipitation Grids.

Use the "Save Current TIN" tool to write out the modified TIN images.

  • Select Save to "DSS: SHG 2000.0 meter grid in DSS file"
  • No need to save the aggregate TIN (uncheck this option) or apply a time shift when saving the TINs
  • Only Check the box next to "Apply edit changes to base TINs"
  • Fill out the DSS Path Parts (A: SHG, B: BALDEAGLE, C: PRECIP, F: NEXRAD-FACTORED)
  • Browse to and select the DSS input file for the HMS model:

...\HEC-MetVue_Overview_Workshop\HEC-MetVue_Overview_Start\HEC-HMS\BaldEagle\dss\BaldEagle.precip.2018.09.dss

  • Press OK

Run HEC-HMS (Factored Precipitation). 

Return to the HEC-HMS model and compute the "Sep2018 – Factored" Gridded Mod Clark Simulation Run.

  • Open the "BaldEagle" basin model
  • From the HEC-HMS Compute Selection menu, select the "Run: Sep2018 – Factored"
  • Select the Compute All Elements () icon to compute the Sep2018 -Factored model which utilizes the Factored precipitation grids.

View HEC-HMS Results (Factored Precipitation).

Right-click on the Outlet element, "Lock Haven SNK" → View Results (Sep2018-Factored) → Graph.

You can also select the "Summary Table" option to view quantitative metrics (peak flow, peak timing, volume, etc.) from the simulation.

Question: What is the Peak Flow of the September 2018-Factored event (using the 2.5x factored gridded precipitation) at the Bald Eagle watershed outlet? 

The peak flow at Lock Haven SNK was about 86,000 cfs for the Sep2018-Factored event when HEC-HMS was run with the factored gridded precipitation data.

Question: How does the Sep-Factored Peak Flow compare to the initial Sep2018 event with the original gridded precipitation data? 

The Sep2018-Factored peak flow (86,000 cfs) is just over 4 times greater than the initial Sep2018 event's peak flow of 20,000 cfs.

Factoring gridded precipitation can assist with assessing possible impacts of variable precipitation volume, but what if a storm event was to change course? The next task will demonstrate how to trim and translate gridded precipitation data to address this concern.

Tasks

Part A – HEC-MetVue Orientation:

Part B – HEC-MetVue Data Input:

Part C – HEC-MetVue Precipitation Preprocessing for input into HEC-HMS :