Surveying a Sewage Outflow

Fort William survey

Commendium were asked by Veolia to survey a kilometer of sewage outflow pipes near Fort William. The weather was cold, with a sprinkling of snow, but visibility was excellent. So we headed off to Bonnie Scotland with LiDAR scanners, a Trimble GNSS and a Hagglund BV206 to assist with the often wet and boggy terrain. 

Measuring gravity based flow

The aim ‘to measure the drop’, in a treated sewage outflow pipe. This is to ensure that planned improvements would maintain or improve the gravity-based flow of treated sewage. In addition to the measurement of the pipe, we performed a visual inspection along the pipes with ROVs equipped with sonar and video.

Survey Stations

After visual inspection, we established a GNSS fixed ground control network of survey stations. These were located between the two access portals and the high tide level on the beach. We carried out a LiDAR survey using a Riegl scanner, between the stations and the two outflow pipes to the sea. Our measuring positions ensured the production of a highly accurate, geolocated surface model.

Surveying the pipes

To survey the levels in the pipes, we lowered a GEOSlam ZEB-Horizon portable LiDAR unit into the access portals. With an accuracy of 6mm and a range of 100 meters, it was perfect for the job at hand. The ZEB negated the need and accompanying risk, of having to enter the portals ourselves; definitely a bonus! The base of the portals where still covered in about 0.8m of water, despite being pumped clean. In order to measure the base level we placed a precision Trimble GNSS unit on top of an 8m pole to gain an accurate GNSS fix of the base level.

Data results

The final data results showed a healthy gradient throughout the length of the pipe down to the exit point. In addition, detailed scanned outputs provided Veolia with accurate engineering drawings illustrating the pipes condition. These will be useful to assist with future plans and works.