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, make sure your elevation terrain contains only the ground surface. Use Remove Object and Replace Terrain tools to delete machines and other small size structures. Lower portions of the basin can be filled with water ponds. Flatten their noisy surfaces. Finally, you can use Modify Terrain tool to remove large structures that could sit on top of the basin floor like a bridge.




Determining the Water Level

Use the Create Water button 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 see the water overflowing from the basin.



Creating the Water Surface

Select the water item and click on the Intersect Terrain button available in the TOOLS for Water tab. This tool creates boundaries at each intersection between the water level and the elevation terrain on the whole dataset. Keep only the boundary that represents the basin you are interested in. To quickly erase boundaries which remain within the basin, select the basin boundary, go to the TOOLS for Boundary, and use the Select Within function and then press Delete. 



Select the flood basin boundary and go to the TOOLS for Boundary tab. Use Triangulate Within feature to create the water surface.



Volume Calculation

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