Invaluable InSAR : Allen Cadden, PE, ASCE
Monitoring large infrastructure requires operational and risk based decisions to identify the elements of greatest interest. However, the structures are only a piece of a much larger system. This is particularly salient for water storage reservoirs and flood control structures. The surrounding features often include steep slopes around the reservoir, access roads and bridges, pump stations, riser towers, spillway and associated riverine features, marinas, etc. Many of these features can have detrimental impact on the performance of the main structure. It is obvious that we must monitor the dam structure for critical operational and performance metrics.
The emergency response to the main structure could be impacted by where the access roads or bridges become damaged. If a slope failure happens around the reservoir, water level rises could cause overtopping. Changes in the downstream riverine areas can have impact on downstream elements of the dam. Further, these structures are often very large, and therefore it’s difficult to perform regular observations on every part of the structure itself, the abutments or spillway.
With this recent AP article showing more than 1,800 dams at risk across the United States this topic is more important now than ever.
Individual monitoring points are just that, isolated and singular indications of possible changes around these points. Often regularly scheduled terrestrial surveys, periodic drone or areal based photogrammetry, and LiDAR can be used for change detection. However, none of these can keep an eye on the entire system. PS InSAR is that tool. A compliment to the traditional monitoring system, PS InSAR utilises the already available satellite based data to determine motion at the millimetre scale from 2015 to today forward without the need for a site visit.
Focused intermittent site specific monitoring programs are valuable data. Calibrating point data to regional changes brings comfort to our understanding of the datasets and helps us define the response plan to observed changes in the InSAR systems.
InSAR allows us to monitor the big picture of the system. Having this ability with regular data streams allows operators and engineers to factor this insight into risk management tools, operational management and maintenance programs.
Our guest author, Allen Cadden
Allen Cadden, P.E., D.GE is a Principal with Schnabel Engineering, Inc in Chadds Ford, PA where he leads the companies GeoStructural Practice. He is an active member of the ASCE Grouting Committees and ICOG and is a Past President of the Geo-Institute of ASCE. Mr. Cadden received his BSCE and Masters of Engineering from Virginia Tech, Blacksburg, Virginia and is a licensed engineer in ten states.