A Tale of Two Windfarms, Mt Barker vs Denmark
Mt Barker is located 50km inland, just a few kilometres north of the township of Mt Barker on a private sheep farm, just west of Albany Highway. Denmark is located on an uncleared parkland and recreation reserve on Wilson Head, 10km south of Denmark town at the southern end of Ocean Beach Road.
In Mt Barker, the sheep farm is half cleared with about one and a half kilometres of existing track. The vegetation is 10 to 12m tall jarrah and marri which were never cleared because of the coffee rock (lateritic gravel) and somewhat eaten out by the sheep. The site consists of a smooth L shaped hill. The orange lines are 5m contours.
In Denmark, the peninsula is made up of heavily vegetated sand dunes with ridges running east west. On the ridges, the vegetation is wind blown, low and sparse. In the valleys, it is quokka country and very hard to walk through. There are a number of tracks through it including an old surveying track to the highest point. We used this track for the monitoring mast but there was nothing we could include in the access road route for the windfarm itself.
Before contracts for the foundations could be tendered, core drilling to depth of 10 to 15m had to be done to determine the soil conditions under each foundation. In Mt Barker, the drilling rigs just drove over the paddocks.
Whereas, in Denmark , a road had to be scrub rolled and a major cut through a ridge had to be dug. This could only be done once clearing permission was obtained and we knew where the road was to go. Even then, the excavator still had to tow the drilling rigs through the sandy cut.
As Denmark being uncleared meant not only the access road for the cranes and oversized delivery trucks had to be cleared, but space for the switchroom and the crane hardpoints adjacent to the turbine sites also had to be made. The area cleared was about 3 hectares, half of which was rehabilitated. Interestingly, the topsoil in Denmark was roughly 60cm deep, adding to the cost, but improving the rehabilitation. In Mt Barker, only a 200m section of bush 5m wide had to be cleared and two existing tracks could be used.
The access roads for both projects had to be straight enough, strong enough and all slopes gentle enough for semitrailers carrying the overlength, overwidth and overweight turbine components. In Mt Barker, we simply asked the road builders to join the dots using existing tracks.
In Denmark, the rolling sand dunes covered in vegetation meant we spent much time and effort in designing the road, to fit into the landscape with minimum disturbance. Exposure to wind and water erosion were all key considerations. We saw clearing as having the greatest negative environmental impact from the windfarm and so we were particularly keen to keep the clearing to a minimum.
The entrance for Mt Barker is off Albany Highway, just before the speed limit drops from 110km , but with good lines of visibility. The trucks delivering the turbine components came up from Albany and for the bottom tower sections, took over two whole minutes to get off Albany Highway and completely onto site, taking up the entire shoulder to do so. Access to the Denmark site was from Ocean Beach Road, south past the quarry entrance, past where the road becomes gravel and even up the hill , so steep there is a small sign saying no caravans. The cost of reducing the gradient to specification was considered to be much more than the extra time and money than it would take to push the heavy trucks up with extra earth moving equipment. On the day, all the delivery trucks made it in without help.
Why so big?
The large amount of coffee rock in Mt Barker meant all gravel for the road was sourced onsite, a welcome saving in costs. Just to the north of the site in Denmark is a limestone quarry which is why there is a 22kV powerline almost to site and a key reason we had thought a modest windfarm would be feasible. In the end, we were unable to use the quarry and as there was very little limestone on site, all gravel was imported.
The wind resource