ICEE cuts holes through seashore pebbles with a powerful waterjet to aid flood protection scheme
Using a powerful 0.8mm diameter abrasive waterjet operating at 90,000 psi pressure, manufacturing services contractor ICEE Managed Services has cut small holes straight through more than 3,500 seashore pebbles for the Eastern Solent Coastal Partnership (ESCP), a scientific research group funded by government grants.
Combining age-old pebbles with ultra-modern radio-frequency identification (RFID) and digital mapping technology, the ESCP has devised and developed a ground-breaking method of tracking and logging the movement of off-shore sediment. Results from a current study will go on to inform beach management decisions which in the long term, aims to improve coastal defence strategies.
In many cases, flooding from the sea arises due to gradual wearing away of the coastline, caused by the action of waves and tides and accelerated by storms. Often, eroded sediment - mostly sand, shingle and pebbles - becomes transported to other parts of the coastline by this action. If the effect is better understood more effective protective steps may be taken.
The innovative method devised and developed by the ESCP involves embedding passive induced transponder (PIT) tags into the holes cut by ICEE and transforming pebbles into 'smart' markers. The markers are placed on the seashore at low tide and over time are transported along the coastline by waves and tidal action.
Using handheld scanners and quadbike-mounted RFID antennae arrays ESCP's coastal engineers comb the seashore at low tide in the direction of the known sedimentary drift to find where the smart pebbles have moved to.
Once found, the identity of a pebble and its location is then logged and uploaded to a geographic information system (GIS) so the path of that individual marker and others may be studied on a digital map. This data enables a far more accurate analysis of movements than has hitherto been possible. It provides information to plan strategies and implement effective measures to reduce coastal erosion and strengthen sea defences.
This high-tech approach has proved far better than previous methods, such as painting pebbles and applying markings (which wore off), manufacturing aluminium pebbles (not the same weight as natural stone pebbles), and casting resin pebbles incorporating copper cores (costly and not durable). The latest development automates tracking, logging and mapping, is more accurate and cost-effective, and increases productivity.
The RFID tags embedded into pebbles by the ESCP are similar to the small tracker devices implanted in pet animals, or used to manage movement of goods in retail warehouses and factories. Featuring passive induced transponder (PIT) technology, the RFID devices are glass-encapsulated. Being battery-less a unique identification number is detected when a signal is received from a handheld RFID scanner’s antennae, or an antennae array mounted on a quad-bike.
Pebbles from the study area are selected by the ESCP according to three sizes, either 30mm, 50mm or 70mm in nominal width and depth. Depending on the size of pebble, two sizes of RFID device are used, both measuring 2.12mm diameter, and either 23mm or 32mm long.
The ESCP has led the development and application of this novel technology, to improve the management of the beaches along their coastline.
The ESCP manages coastal flood and erosion risk across 162km of the Hampshire coastline, stretching from Fareham in the west to Hayling Island in the east. The latest study of the smart pebble system supports part of a £3.3m government-funded project secured by the group to manage healthy beach levels. The project aims to reduce flood risk at Hayling Island, Hampshire, an area that is the responsibility of Havant Borough Council, in effect the client.
Erosion and flooding has blighted the south-facing coast of Hayling Island for centuries. Between 25,000 and 50,000 cubic metres of sediment – sand, shingle and pebbles – may become transported away from the area every year by the naturally occurring action described earlier. This loss leaves the island more exposed and at risk of being inundated by the sea, potentially putting lives at risk and damaging over 1,500 homes, 170 business premises and public infrastructure.
The latest study, still under way, is tracking the movement of 1,500 marker pebbles from Eastoke, Hayling Island, westward along a 4.9-mile (8km) length of coast. Reinstating the loss referred to above is costly. It requires around 15,000 tons of sedimentary material to be recovered from where it has moved to, trucked in and placed back at Eastoke. As an outcome, ESCP’s study of pebble movement will identify ways to mitigate risk, improve defenses and reduce costs on this part of the coast.
“Through the actions described, a pebble may move westwards as much as 120 metres to 150 metres in a tidal cycle, but this is complicated by the fact movement may not always be in one direction,” says ESCP Coastal Engineer Sacha Neill.
“The RFID system coupled to GIS transforms what we couldn’t fully prove before into demonstrable and measurable facts. For example, the longest distance a pebble has been transported, that we have tracked, is 2.74 kilometers, or 1.7 miles. Not only can we see where it originated, but we can track the gross drift,” she explains.
ICEE has cut through over 3,500 pebbles of three different sizes for a total of three trials and studies carried out since 2012 by the ESCP. Over the course of all the work the manufacturing services company has itself been innovative in perfecting a method of safely and securely holding the pebbles during cutting.
“Cutting a small hole up to 6mm diameter clean through an irregular stone object with a high-pressure stream of water only 0.8mm in diameter - at a ferocious 90,000 psi - means holding a pebble rock-steady, otherwise it could end up on the other side of the factory or going through the roof,” says Brian Green, the ICEE manager handling the work.
“As each order was received from ESCP, we gradually developed the best method of holding the widely varying sizes and shapes of pebble work-piece. Waterjet cutting is the easy bit, what’s difficult is working out how to cut as many pebbles as possible in one session - quickly, safely and at least cost to the customer,” he says. “That took a lot of painstaking trial and error, but we now have a proven method where around 1,200 pebbles a day may be processed efficiently and economically.”
ICEE were willing to take on a challenging project and spend time understanding ESCP’s requirements to develop more economical ways to do the job.
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