Construction Site Inspections by Unmanned Aerial Vehicles (Drones)
For most construction projects, stormwater runoff needs to be controlled and passed through some form of sediment control practice. The practices, such as silt fences and sediment traps, require frequent inspections to ensure that they are functioning properly or if they need maintenance. These inspections and the record of them are very important in remaining in compliance with state and local regulations. In fact, when inspectors arrive at a construction site, usually their first request is to see the inspection records. It can be challenging to conduct inspections by truck or foot because of weather conditions, wet soils, or a remote location, especially right after a substantial storm event. Another option is the use of unmanned aerial vehicles (UAVs), which can quickly fly to each practice and collect images or video of the existing condition. These can provide immediate information as well as documentation needed for audits by regulators. Furthermore, the images can be useful in tracking progress by management and property owners. The use of UAVs for a wide variety of construction site management activities is becoming widely adopted as the technology improves and the cost keeps coming down. Additionally, the images can be processed through “structure from motion” software to generate point clouds from which one can create digital surface models of the terrain. This software processes a series of images of a location, finding common edges and “stitching” them together into a terrain model. These 3D models can be used to determine how surface runoff will flow or accumulate, which in turn can guide decisions on where practices need to be placed. They can also be used to calculate the amount of earth moving that has occurred and which is still needed. Preliminary tests have suggested that the accuracy of these 3D models is close to that obtained by LiDAR (light detection and ranging) instruments. Recently, UAVs with real time kinematic (RTK) surveying capabilities have further expanded UAV surveying potential. Thermal and multispectral sensors can also be used to evaluate vegetation cover to further document regulatory compliance, along with many other potential uses. UAVs with these sensors are becoming very affordable. Much of this technology will be reviewed along with a brief overview of the regulations involved in using UAVs. Examples of actual UAV testing for site inspections of active road construction projects will also be presented and compared to “manual” inspections for accuracy, time, and cost.