Rockfall Protection Systems In St Helena – Tackling A Natural Hazard

We’re perched on a slope just above Ladder Hill road watching rockfall protection systems being put in place.  Dust flying, I shield my eyes and brace against the warm downdraft of the Eurocopter AS350 squirrel helicopter aka an Airbus H125 that’s hovering noisily above our heads. The proximity of helicopter blades to the rock face is a little alarming to witness up close like this.  Hearts racing, we watch the pilot deftly manoeuvre and slot into place a rockfall barrier post that’s hanging from a long rope beneath the helicopter.  All the while he’s making constant adjustments to keep the aircraft ‘rock’ steady.  Talk about multi-tasking, the man is a ninja.

 

The French Rock Stars Are Back | Sharon Henry

A team of six CAN France rope access technicians, wearing their distinctive red trousers, are on the ground reaching upwards to grab the suspended cargo.  They bolt the post into position, connect stay wires to secure the load and supervisor, Samuel, gives the signal for the AS350 helicopter to unclip and fly off.

This is specialist work; the threat of a sudden gush of wind or sway of the load keeps everyone well focused to get it right.

 

 

Go Where Scaffolding Can’t Go

But these guys are highly experienced rope access specialists and pioneers in their field of geotechnical work, accessing difficult to reach locations, they go ‘where scaffolding cannot be erected.’  And they make it look easy, like fitting together a kids K’Nex toy set.  Quickly, like mountain goats, the ground crew scamper on to the next anchor point.  I love it that Saints, Terry ‘Rocker’ Crowie and Martin Constantine are part of the team.

With the first post in, the squirrel helicopter collects another from the pre-loaded truck parked a few metres below on Ladder Hill road.  The driver (Antonio Williams, another Saint) hooks it to the rope and gives the rotating finger signal for the lift. They’ve clearly done this a few times already.

This procedure is repeated about six times, swiftly and super-efficient, everyone working with precision.  Exactly 15 minutes after starting, the aerial work is done and the AS350 helicopter returns to base in Rupert’s Valley.  It’ll be back once the truck has been reloaded, and will lift in the final set of Ladder Hill rockfall barriers.  Netting will later be suspended between the newly installed uprights.

Wow, we’ve just had front row seats to the best show in town and it’s been brilliant.  Darrin, who’s always wanted to be a pilot, (like most little boys, I suspect) is just buzzing.

 

The Early Morning Commute

For the past few days, we’ve been given ‘backstage passes’ to photograph this work up close – and man, is it impressive!  Our ‘passes’ came courtesy of contractors, Arthur Bourret and Catherine Inglis.  Arthur’s the Contracts Manager for French company CAN, and Catherine is Supervising Engineer for Scottish-based, Fairhurst.

Yesterday, at the crack of dawn we hiked Munden’s Hill to photograph another team of rope access technicians install Spider netting above Rupert’s jetty, observing for the first time the operation in close-up, awe-inspiring action.

Those guys too, make what they do look effortless and I was thrilled to pick out the face of fellow Saint, Philip Isaac, in the CAN team of six.  Their transport to the work site at first light, was the AS350 helicopter (#socool) which landed on a makeshift helipad on the tip of Mundens.  After the necessary prep-work, the guys were soon suited-up for rope access with safety lines, harnesses and anchor points in place before the first rockfall netting arrived.

 

St Helena Rockfall Protection Systems

Long lengths of Geobrugg Spider netting, neatly assembled in the CAN France compound down in Rupert’s Valley, were then lifted by the helicopter to the top of Munden’s.  The dangling bottom end was carefully hovered within reach for the guys on the hill to grab and bolt into place.

Throughout, there was radio communications between the pilot and Jean-Baptiste, supervisor of the hill crew.  With one end now secure, diligently the pilot draped the length of netting downward to evenly blanket the rock face, before releasing the ‘clip’ and flew off to fetch the next section.

A minute later another panel was being airlifted, this time further down the hill where the top one ended.  Again the proximity of the helicopter rotor blades to the hill was spine-tingling, there’s no room for error.  They’re carrying out complex work in super precarious positions.

 

A Head For Heights

Catherine had told us earlier, the wind in Rupert’s can cause problems, “François the pilot, says it is very challenging.  It rushes down the valley.”

The single engine A350 B2 Squirrel has an external load lifting capacity of 800kg at the altitude of 500m.  A 20m Spider netting panel weighs 203kg, a 50m drape net weighs 322kg.

It was fascinating to watch; the intense focus and skill, in the air and on the ground.  Especially with us being level and directly in line with the helicopter pilot, we could see right into the cockpit and watch him controlling the aircraft whilst keeping an eye on the ground crew below.  Quite sensational.

Like a quilt, each section of netting was methodically and manually knitted together with shackles, fitting the rockfall mesh to the crags like a silvery second skin.  This is designed to retain and channel any fallen rocks safely to the base of the netting.  Installation is strenuous and physical work, and the team went non-stop, clambering over vertical crags like Spidermen.  Nobody on this job is afraid of heights.  Being a rope access technician seems an incredibly exciting job, it’s certainly not your regular 9 to 5.

 

Living With A Natural Hazard

For centuries, Jamestown inhabitants have lived with the all-too-real, dangerous, natural hazard of rockfall, with little choice but to block out scary thoughts whenever heavy rain fell.  The St Helena rockfall protection works from 2008, 2010 and now 2020, (all by Fairhurst and CAN) have significantly reduced the risks and brought a welcome peace of mind for residents going to bed at night.

The western hillside (Ladder Hill) now has rockfall barriers running from Donny’s Nightclub at the seafront all the way up to Maldivia at the top of town.

In 2014 an estimated 20-30 tonne of rock fell 200m from an outcrop above Maldivia, in the middle of the night. Luckily no one was hurt.

Back in 1984, a mother and her baby daughter were killed in their sleep from a rock fall near China Lane.  The tragic story was broadcast on BBC World Service. There have been other incidents but thankfully that’s the last with a fatal outcome.

 

The Geological Hazard of Rockfall In St Helena

So, to have this rockfall mitigation put in place is worth the inconvenience of temporary road closures on Ladder Hill, the Wharf and Rupert’s beach.

Rockfall stabilisation works on St Helena in the valleys of Jamestown and Rupert’s are now almost complete.

Fairhurst designed the island’s rockfall protection systems and Catherine, an engineering geologist, is the company’s on-island representative overseeing the work.  “St Helena is so unique in terms of the actual geography and landscape,” she told us earlier when we sat down for a chat at the Wicked Wahoo bar.  “It’s just brilliant but my goodness – the rockfall!”

The company she works for carried out a series of rockfall modelling.  “They looked at the trajectory of how rocks fall and behave specifically on St Helena,” said Catherine.  “These coarse bands (of rock) tend to be at the top of the valleys, like basalt.  This gets eroded underneath because there are softer layers underneath.”

 

Putting The Brakes On And Reduce The Risk

“That’s what releases, or allows the block to be released, generally when it rains.  And rather than it coming down as one rock, it breaks up as it goes because it hits all these different layers on the way.  So if you model it, you’ve got this massive block, by the time it gets to where the fences are, it’s actually smaller.

“That’s why we keep the fences as low down the valley as possible, then you get more chance of rocks smashing up.”

On either ends of the fences are brakes, or lateral anchors, that activate to resist loads whenever the fence or post gets hit.

 

Made In Switzerland

The Wharf cliffs were the first area to be worked on in 2008, then Jamestown valley in 2010 and now 2020, Jamestown and Rupert’s.  “That’s where rockfall hazards and consequences are the highest and biggest,” said Catherine.

The rockfall netting used on the catch fences are TECCO, a super-strong, high-tensile steel wire, that can withstand impacts without sustaining damage.  It’s made in Switzerland by a company called Geobrugg.  It’s used worldwide for rockfall, avalanche and landslide defences, in mines and tunnels, and even on motorsports race tracks.

 

Drilling Anchors To Last A Century

It’s low profile and doesn’t spoil the look of our Georgian town (in my opinion).  All materials used in the project has a life span of 120 years and they are constantly checked and maintained by the St Helena Rock Guards who clear out rocks and “patch” any warped netting.

Funding for the St Helena rockfall protection systems has come from DFID.

Since January 2020 when the third phase started, more than 1,300 catch fence and netting anchors have been drilled and grouted, some as deep as 5m most at 2m.  All in preparation for the helicopter’s delayed arrival in April on the MV Helena.

“The helicopter really speeds up the process,” said Catherine, “and it cuts down on the manual handling.”

 

Going Back To Base

AS350 B2 Squirrel helicopters are known as workhorses in the field, and this one comes from Jet Systems Helicopter Services in France, who are specialists in aerial work, flight training and private transportation.  This is the first trip to St Helena for pilot, François Gillet (‘ninja’ I’m calling him) and second for mechanic, Olivier Merchat who was here in 2010.  The helicopter is going to be shipped back at the end of the month.

Working on this project are 10 CAN personnel from France, three from South African company, ‘ASC,’ two Jet Systems guys, Catherine from Fairhurst and 10 locals from Johnny Isaac Contractors and a few who’ve previously worked with CAN.

Delays due to shipping and the coronavirus have pushed the project back a few weeks, but if all goes to plan everything should be completed in July.

 

Rockfall Protection Built In 2020

Which is:

Ladder Hill – six rockfall barriers above the junction with Shy Road

General Hospital – three rockfall barriers

Maldivia – rockfall fences totalling 440m in length

Munden’s Path – a lightweight 360m catch fence running from the Customs building to the end of the wharf.

Rupert’s Jetty – rockfall barrier above Lower Mundens Path.  A rock trap adjacent to the jetty.  Spider netting and draped netting on the crags and slope.

Rupert’s Valley – catch fences.  One was put to use on St Helena Day (21 May) catching a falling block following heavy rainfall.

Haul Road – draped netting at the bottom hairpin.

Bulk Fuel Installation – catch fences

Power Station – catch fences.

 

Guardians Up On The Hill

Anyway, back to us perched up on Ladder Hill.  Darrin’s reviewing the shots on the back of the camera and I have time to take in our surroundings and figure out, how on earth we’re getting down from here?  (Uphill is so much easier).

Directly below is the Baptist Church that was badly damaged by rockfall in 2008, that day rocks had also landed in the playground of neighbouring Pilling Primary School.  Luckily it was class time and no one was hurt.

Thankfully, now for 120 years at least, we have these high-tensile steel defenders, solidly wired to hold firm and stand guard over the citizens below.