To increase interest and involvement of people in protecting and improving the Ribble River, the Ribble Rivers Trust recently commissioned a bathymetry survey of a notable section of the riverbed. A robotically controlled 1.2-meter twin-hull shallow draft vessel powered by a twin jet system was used to survey approximately a hectare of the river’s bed. Aboard the vessel was a depth recording sonar and a tracking prism that enabled a Spectra Precision FOCUS 35 total station to lock onto and robotically follow and record the location of the vessel.
Echo soundings from the sonar were transmitted back to a tablet PC ashore via long-range bluetooth and time stamped, while the boat’s position was continuously recorded by a FOCUS 35 total station and sent back to a tablet PC also using long-range bluetooth and time stamped.
The tablet PC ran, 4Site, a program that formatted and processed the data from the sonar and the total station into a DWG drawing. Each point was positioned in real-time on the screen of the tablet, so the operator of the vessel could see gaps in the data in real-time, and navigate the boat back to them to ensure complete coverage.
A mesh of the survey area, a 200-meter section of the 50-meter wide river with the deepest depth 3.5 meters, was created and combined with aerial Lidar information and a topographic survey and provided to the Ribble Rivers Trust for its education outreach efforts.
According to Jack Spees, CEO Ribble Rivers Trust: “The challenge with rivers is that much of the beauty and interest is hidden from view beneath the waters surface, and so we selected a location for a bathymetry survey that is adjacent to a heavily used public footpath, and is thought to have some interesting features.The location is a pool at the confluence of the Rivers Hodder and Ribble, known as Hodder Foot. A famous angler (Hugh Falkus) is said to have declared, ‘If god was an angler he would fish at Hodder Foot’. The confluence of two large rivers such as these leads to interesting river processes that create interesting features. This includes scouring the riverbed to surprising depths. We hope to use the survey to reveal these Hidden Depths on interpretation boards, but also digitally by augmented reality and also video media.”