The project is part of Rio Tinto’s ongoing efforts to proactively manage potential effects of mine subsidence. The program will quantify any effects subsidence may have on the stability of the creek’s bed and banks, allowing for early detection and remediation works of any adverse effects.
Whilst pre-subsidence monitoring was completed mid-last year, actual subsidence is not expected to potentially impact the creek until 2009, lasting until 2012.
Further pre-subsidence monitoring is currently being undertaken following significant natural flow events at Crinum Creek to gather background data to understand natural erosion processes.
Reaches of Crinum Creek are being mapped using AutoCad computer assisted drafting software and photographed. The key outcomes of the surveys are reports which contain mapping, photographs and qualitative and quantitative assessments.
Gilbert and Associates Hydrology and Water Management Consultants were commissioned by Kestrel to conduct the first of the pre-subsidence monitoring surveys in July 2003.
Prior to commencing the survey, Gilbert and Associates conducted a thorough investigation of other similar studies conducted within Australia and offshore to develop a rigorous and practical methodology for conducting these surveys.
The method involved splitting reaches of Crinum Creek to be subsided into 200 metre "blocks" marked with bank markers.
During the initial survey information such as bed cross section and profile, vegetative cover, bank profile, slope and height and overall bed and bank condition was recorded, photographed and mapped.
Repeat surveys will involve updating these records to allow for the identification of any changes.
Erosion pins are also being used in areas of specific interest to quantify deposition or erosion of sediment within the bed of the creek.
Kestrel said it was unlikely subsidence would have an effect that caused any harm beyond that already caused by the highly erosive flood events of the creek that occur naturally. If adverse effects did occur remediation required would be determined on a case by case basis in consultation with the Environmental Protection Agency and the department of Natural Resources and Mines.
