Record rainfall at Macquarie Island causes heavy damage to the water supply and some walking tracks.

Macca’s record rainfall event

Last Thursday to Saturday, Macquarie Island received the highest ever recorded rainfall (in something like 65 years). Our Bureau of Meteorology (BOM) senior observer Keon Stevenson provides the following story:

On the 15 January the deep low pressure system that produced significant rainfall over Tasmania drifted towards Macquarie Island from the northeast. We were expecting significant rainfalls here and we had a competition as to who could guess the correct amount over a 36 hour period. After checking the various predictive weather models, the NOAA (USA) model was predicting around 90 mm of rain to which most of us were very skeptical. The European Centre deterministic model was going for more! However, as the NOAA model was spot on for our last rainfall event of 23 mm, there had to be some accuracy and belief there.

Light rain began in the afternoon on 15 January around 1700 hours and increased to heavy rainfall into the evening and the following morning. Rainfall is officially read from 0900 to 0900 over a 24 hour period, and at 0900 on the 16th we recorded 42.2 mm in our rain gauge. This was reported as the second most rainfall in history of a 24 hour reporting period!

The rain was very heavy and consistent between 0900 to midday on the 16 January when the low was very close to Macca — 26.2 mm fell during that three hour period. The rain eased slightly and we had continuous moderate rain for another 12 hours. Mean sea level pressure on the island got as low as 960.3 hpa just after 1500 hours.

To 0900 on 17 January we received 63.4 mm, which is a new record over a 24 hour reporting period. The previous 24 hour record of 52.8 mm was recorded on 14 March 2001. So, over a period of about 36 hours we received a total of 105.6 mm in our tipping bucket rain gauge (primary instrument). During that morning we also discovered landslides and collapses of the coastal escarpment slopes around the Razorback, Gadgets Gully and down at Sandy Bay as reported by the Spirit of Enderby via VHF radio. Unfortunately the landslides filled our small water supply dam at Gadgets Gully with rocks and dirt, and damaged our water supply piping to station, which took the next three days to fix.

Oh yeah, Scotty guessed the closest rainfall figure of 75 mm!

Keon Stevenson 

Rain damage: Gadgets Gully dam and escarpment land slips

After the rain had stopped on Saturday morning, our first indication that it had caused any problems was when Greg checked our water supply and found it not flowing. Our station water supply comes from a small dam about half way up the coastal escarpment going up Gadgets Gully, approximately one and a half kilometres from station. The dam has a catchment area on a plateau shelf which backs onto the escarpment as it continues up to the island’s plateau. The water line to the station tanks runs down Gadgets Gully to the coast, then along the isthmus at the bottom of the escarpment to station. Breaks to the water line pipe are a frequent problem for station plumbers.

Our plumber Greg, with Pete and Ivor assisting, headed out to inspect the line. Our first discovery was an impressive land slip of the heavily tussocked coastal escarpment just past the Razorback steps, and a very scoured out First Gully, which is the gully on the east coast before reaching Gadgets Gully. We repaired breaks in the poly pipe at both locations, but still no water was flowing. Continuing along the coast to Gadgets, we were confronted with a ferociously scoured out gully, where for decades a reasonable walking track up the rocky gully bed, featuring three ladders going up difficult bits, had existed. With some difficulty, Greg and Ivor made their way up the gully, to find one ladder gone, two badly damaged, and the old track absolutely demolished. There were several breaks to the water line poly pipe, which is suspended on the scree slope above the gully on the northern side. But worse was to come.

On reaching the dam after a difficult climb up the deeply scoured gully, we were appalled to discover that our precious little dam was completely filled with dirt, gravel, rocks and matted clumps of tussock grass. This material had been washed down the creek supplying the dam through the dam catchment from a huge land slip at the escarpment above the dam and immediately above the creek. A number of unprintable things were said…

On Saturday afternoon, a work party made our way up to the dam to commence clearing operations. As the Gadgets Gully walking track no longer exists, we went up the alternative Doctors Track route, to discover that it too was affected with one stretch of track washed away and another dangerously undercut by more escarpment landslips. Ranger in Charge Chris quickly marked out new safe track routes. On arrival at the dam, we commenced the difficult task of removing the debris. Fortunately there was still a vigorous water flow. When we got the sluice gate low in the dam wall open, and got a water flow started, the compacted dirt and gravel started to wash out with the sluicing effect. With the aid of much shovelling, we could see a way of clearing the dam.

With literally all on station assisting, this work continued all day Sunday and Monday, until we had a perfectly cleared dam again. Simultaneously, Greg and Pete got to work repairing the water line running on the edge of the gully. As access to the poly pipe in the scoured gully is now much more difficult, in a few places this operation required safety ropes and access from the escarpment above. So another team including some of our search and rescue team people, Scotty, Chris, Mike and Paul set up anchors and rope systems from the escarpment above the gully.

By Tuesday morning our dam had refilled with clear water and Greg had the broken line fixed with water flowing to the station tanks again. It was a fantastic effort by the whole station community. There are still a few ongoing issues but our water supply is assured.

The other major concern now is the land slip damage which has occurred to the coastal slopes around the island. At this stage we know there has been damage in the Sandy Bay and Bauer Bay areas which will have had some impact on the royal penguin colonies in both places. Numerous walking track -'jump ups’ and ‘jump downs’ between the coast and the plateau will be damaged or non-existent. We hope there will not be too many nasty surprises as we assess the impact around the island, but our TASPAWS ranger staff, Chris, Mike and Andrea, will be busy sorting things out for a while yet!