Chris Graham, sales director at Sykes Pumps, discusses the challenges of managing water levels at a wind farm installation in Essex.

In the construction sector, demanding site conditions are not unusual. And in the renewables sector, the challenges are often multiplied because it’s in the nature of wind farm projects that they are frequently in remote locations where increased wind velocity provides optimum conditions for power generation and maximises capacity and return on investment.

Demanding site conditions call for a robust turbine installation to maximise service life and minimise maintenance. However, accessing sites like these with turbine components and the plant required to carry out the project can be arduous, particularly if the site is off the road network and prone to flooding.

That was the scenario when engineering and construction specialist, VolkerFitzpatrick, erected 10 wind turbines for RWE npower at a wind farm in Bradwell-on-Sea, Essex and the company had to grapple with both logistical and construction challenges to complete the scheme.

Challenging Site

Bradwell-on-Sea is located on a flood plain in an area of arable farm land on the Essex coast at sea level. The site for the wind farm is just 300m from the sea wall in places and the construction team was aware that flooding was a potential issue in the area before the project even began.

The high water table had to be addressed for both the site of each turbine and for the 4.5km access road that was essential for bringing personnel, materials and equipment to the wind farm during construction.

The wind farm was designed as a 20.5MW project, which was calculated to meet the energy needs of some 12,000 homes. To deliver this energy generating capacity, VolkerFitzpatrick’s remit was to erect 10 turbines.  Each turbine was to have a 40m x 25m crane platform adjacent to it, which will provide a permanent, stable surface. The platform was used as a solid base for construction equipment during installation and will serve the same purpose for future maintenance projects and inspection visits.

The foundations for the turbines themselves were constructed using pre-cast concrete piles and a 330m3 reinforced concrete base at levels below mean sea level. The turbines were then installed in sections, with an 8m hub supporting three 40m long blades for each turbine.

As Dion Smith, general foreman at VolkerFitzpatrick commented, “While the design of the wind turbines and the construction methods used were not out of the ordinary, the water levels and the potential for excess water to disrupt both the programme and access to site presented considerable challenges.

“The Environment Agency has a fixed pump permanently at the site to pump water from drainage dykes over the sea wall into the sea but we were conscious that we needed to have pumping capabilities on site to manage water levels across our works during the construction programme.”

Pumping Strategy

To add to the flood risk, there was heavy rainfall prior to work commencing on site, which significantly increased the ground water. To address this, VolkerFitzpatrick turned to Sykes Pumps as a pump hire specialist to advise on a pumping strategy, which involved supply and installation of pumps on site and provision of maintenance throughout the programme. Sykes Pumps provides routine maintenance visits from a skilled engineer on a fortnightly basis as a standard part of its hire agreements.

Following a site survey, the Sykes Pumps team initially investigated using  electric submersible pumps but a lack of power supply and the possibility of losing an untethered pump in the boggy ground meant that this approach was not viable.

Instead, the Sykes Pumps team opted for a diesel pump strategy but this also involved significant challenges. The team had to specify pumps that were sufficiently powerful to enable VolkerFitzpatrick to dig the 2.5m foundations for each turbine and keep the haul road safe and operational. However, the pumps also had to be sufficiently light to cope with the ground conditions on both the road and each turbine site, otherwise there was a risk that they might sink in the boggy ground.

In response to these conditions, Sykes Pumps provided up to five 6” diesel pumps for the project at any given time and these were moved around the site throughout the 18-month programme to manage the water levels in the areas where work was taking place.

The pumps were used to extract water from the excavation sites for the turbine foundations, the crane platforms and the 1.5m deep cable trenches. The water was transferred via hoses through a series of sediment tanks to the drainage dykes to ensure that no sediment from the ground-works was pumped into the dykes. These dykes were then drained by the permanent Environment Agency pumps over the sea wall.

As Dion Smith from VolkerFitzpatrick added, “Sykes Pumps’ expertise was vital both during the initial specification of the pumps and throughout the project as we reconfigured the pump layout on site to meet the demands of the programme.”