In March we conducted some gravity cores off a barge with the help of the boys from Dynamic Dredging. Conventionally this coring technique is used with deep sea vessels where a steel barrel pipe is lowered close to the sea floor with 200+kg’s of lead weights mounted on top, and then released, letting gravity ‘pile-drive’ the core barrels into the ground. A piston within the core barrel and core catcher prevent the sediment from falling out of the barrel as it’s winched up from the seafloor.
We gave this a go on the Murray at Younghusband near D.Brinkley’s Sand Supplies, at the channel margins and in the centre of the river channel. In principal it worked, however the age of our gear (from the 1960’s) prevented any deep cores, and with a 6 metre core barrel we only retrieved around 3 metres (piston basically got stuck halfway up the barrels preventing more sediment retrieval). We are keen to try it again, however with ‘newer’ gear, and will probably try Vibrocoring on our next trip. Vibrocoring involves attaching a vibrating head to an aluminium barrel which acts to shake the sides of the barrel reducing side-barrel friction allowing ‘easy’ penetration into the soil. Its commonly used in sandy environments, however we’re going to try it on the Murray muds to see if it will help us get through some stiff and organic rich layers. Previously we’ve been using percussion coring manually hammering in PVC pipes, with our longest retrieval in 2013 off East Front Rd Mannum at 4.2m.