1A2: Monitoring Sediment Build-up or Scour at Intake Structures of Hydroelectric Power Plants and Dams
July 13, 2022
Civil Works and Dam Safety
Problems can arise in day to day operations of hydroelectric power plants and dams, whereby there are events of high aggregation of bedload and suspended sediment at intake structures. Although this problem is usually taken into consideration by incorporating use of settling basins in the design, the actual sediment loading can still be underestimated especially in run -of-river types of power station. Even when hydrology and geomorphology assessments have been thoroughly investigated, forces of nature are unpredictable especially in the extreme and changing climate conditions that are occurring more frequently these days. Extreme changes in the weather can create highly complex flow conditions, involving significant variations in both water levels, river flows and bedload material. Unsettled sediment which passes through the turbine runners can cause an erosion process and damage the turbines. Any further impact or shutdown causes losses of thousands of dollars in revenue per day as well as additional costs for manpower for clearing possible blockages in pipes and valves, repairs or necessary replacement of damaged equipment. The effect of scour or erosion of sediment at outfalls can potentially be detrimental to the stability of the structure and its fatigue life. The core point of monitoring sediment build-up or scour is to understand the problem and carry out intervention work before it becomes unsolvable or the damage costs becomes multiple times more. When there is intense blast of moisture from heavy storms and also during spring freshet as snow and ice melts, the high sediment loading often makes the waters murky with low or zero visibility. Underwater inspections suffer from considerable limitations due to poor visibility with high riAs sonar technologies improve, interest in applying these tools for underwater inspection is increasing. A series of field tests and trial inspections both in the US and UK have been carried out using sonar and laser technology with favourable results. International Civil Engineers UK, (ICE) proceedings (ref 1) and Federal Highway Administration (FHWA), USA (ref 2) described in great detail on the findings of using sonars for purposes of underwater inspections. The sonar is typically deployed at an optimal location for creating a 3D map of the survey area in both horizontal and vertical planes. The rugged design of the dual axis scanning sonar, providing 3D point cloud, is ideal for long-term deployment in harsh environments. Since the sonar is deployed permanently, it can capture critical changes especially in dynamic conditions which can easily be missed when conducting surveys or inspections periodically. By combining the permanently deployed sonars with a fully autonomous system, critical parameters of the surrounding riverbed at the intake can be scanned, at pre-defined and variable time intervals. This allows for a timely action/intervention for necessary remediation work. As the data collected is also time stamped, records of historic time series can be readily accessed through a web browser. The real-time data can be shared between multiple users at different locations, with the owner’s security and permission.