Flood basins are critical components of water management systems. Surveyors can take charge of their monitoring and ensure that their retention capacities are consistent with original design values. Virtual Surveyor includes tools to measure water capacity directly from your drone data. For example, it may be necessary to measure the actual retention capacity after several years of sedimentation in a basin, or to validate the exact volume of a pond for an as-built survey. 


Note: This workflow only works with an empty flood basin. Photogrammetry cannot "see" through water surfaces.


Overview


Drone Surface Cleaning

Before proceeding further in the flood basin analysis, the first thing you'll want to do is clean your Elevation Terrain so it only contains the ground surface. 

  • Use Remove Object and Replace Terrain tools to delete machines and other small size structures. 
  • Then, you can use Modify Terrain tool to remove large structures that could sit on top of the basin floor, e.g., a bridge.

  • Lower portions of the basin can be filled with small ponds or some standing water that may create terrain noise, so you'll want to Flatten their noisy surfaces.


Determining the Water Level

Use the Create Water tool available in the HOME tab. If you know the overflow level, create a Water item exactly at that elevation level. You can also determine the level by creating a Water item at an arbitrary elevation level within the basin and then adjusting it through the settings available in the TOOLS for Water tab until you get the water to the basin's capacity. You'll want it to be just below the overflow level so you can create a clean boundary around the water.


Creating the Water Surface

Select the Water item and click on the Intersect Terrain button available in the TOOLS tab. This tool creates boundaries at each intersection between the water level and the Elevation Terrain on the entire dataset. You'll want to keep the boundary that represents the basin you are working in and remove the rest. To quickly remove any extra boundaries or lines that remain within the basin, select the basin Boundary, go to the TOOLS tab, and use the Select Within function. Then press Delete. 


Note: As shown in the example vid above, you can quickly delete additional boundaries and lines using the Project View to quickly select multiple project items and delete them all at once, then renumber your boundary item.


You can now turn the water item off in the Project View, as you only need the Boundary item to generate a Cut and Fill. You can also create a layer for your cut and fill items and move your boundary into that layer to help organize your project.


The last step before you create your surface for the Cut and Fill, is to Simplify your boundary in order to help the Cut and Fill calculate much more quickly. Select the Boundary item and go to the TOOLS tab to see the Simplify tool settings. There you can set the Method and Threshold so that it works best for your specific data set.


To create the water surface, select the flood basin Boundary and go to the TOOLS tab. Then use the Triangulate Within feature to create the water surface.


Volume Calculation

Select the water's Surface and go to the TOOLS tab. Click on Cut/Fill to calculate the volume. A progress bar appears in the lower-left corner. When completed, results are available in the Selection box. The retention capacity is equal to the fill value displayed in the box.