Sydney Gas Update
Date: 11-Jul-08
Author: Dana Hollis
Update for Wollombi and Paynes Crossing Residents
9 July 2008
Paynes Crossing site progress
The preparation of the core hole site at Paynes Crossing is expected to be finished by the end of this week.
We have commissioned a new multi-million dollar drill rig, which is considered the quietest and most efficient on the market.
Due to the sensitive tourist areas of Paynes Crossing and Wollombi, we have prioritised use of this new rig for those sites.
We will notify you when the drill rig arrives at the Paynes Crossing site and keep you updated.
Flood level update
During the Wollombi meeting on June 7, many residents raised their concerns about potential flooding of the site we had selected for an exploratory core hole.
Since then we have been assessing data to determine the potential impact on the site.
We were also forwarded pictures from some residents, to help us in the analysis, which we greatly appreciated.
Following is a letter I sent to a concerned resident, which you may also find helpful:
Thank you for bringing the magnitude of the flooding issue to our further attention.
Certainly it is in everyone's interest to ensure that flooding will not impact negatively on the exploration process and the surrounding environment.
First, I should explain that we understand that the access to the site will be restricted if the floods you have described do occur. We recognize that this will cause us some inconvenience and delay and that we will need to wait for things to dry out before being able to re-enter the site. We have focused our investigation on the area where the rig will be sited as we understand that your concern is around the site itself being flooded and the resulting damage which maybe caused.
We have checked all existing data on flood levels in relation to the site where we will be drilling a core hole, including evidence from the landowner, your photos of a recent flood, records from the Cessnock City Council and survey data.
We have based most of our assessments on the 2007 floods and a one in 100 year flood height, provided by Council. To clarify, a one in 100 year flood event (1:100 Annual Recurrence Interval) is a projection made by hydrologists, which anticipates floods of such magnitude that statistically it would only be expected once every hundred years. These projections are calculated based on historical records of rainfall events and flood levels in the region, which includes flash flood events.
Cessnock City Council has confirmed that the 1:100 Annual Recurrence Interval (ARI) flood height at the Wollombi corehole site is 100.3 metres Australian Height Datum (AHD). Incidentally, the Australian Height Datum is the standard reference used for measuring elevation.
The height of the site is 102.0 metres, which provides a 1.7 metre buffer. A flood of 102 meters would be considered a flood of extreme magnitude, the chances of experiencing a flood of this size would vastly exceed a 1:100 year event.
We examined your photos and contour mapping and it showed that the flood level, at the time of you taking the photograph, was approximately 97.5metres AHD.
If there is any further evidence that we have not considered, we would be glad for you to bring it to our attention and we can add this to the current data for the area.
After a more detailed assessment of the frequency and the height of the floods in this area I better appreciate the concern of some residents about the impact of flooding on this site.
I hope that the data we have researched and been able to give to you is reassuring.
