Weathering a storm

A category one cyclone is not a devastating storm. But it does test every thing mankind makes. Architects and engineers can learn a lot by examining what failed.

Friday started at 4am with the ratting through of a storm. I battled the resulting tiredness to prepare for TAFE teaching, wrapping the student's work to protect it from the rain. I thought it would be wet, but just another routine day.

The first architectural lesson was one that I knew well. All through the first lesson on the top floor of the 1938 TAFE building there was a loud drip, drip, as water came from the ceiling from three places, including down the light fitting and dropped with a 'plop' onto the wet carpet. Flat roofs were popular with architects in the early era of Modernism. And flat roofs with box gutters often leak. I knew to watch the light fitting, as water and electricity don't mix. It kept raining, and I still thought nothing of it. I sent the students to lunch. One went to see the bulk
carrier washed onto Nobbys beach, they'd heard about via SMS. It started hailing and a pool of water formed on the floor beside the window. About to eat, while entering attendance data, the siren sounded loudly and a voice was heard "evacuate immediately".

I looked at ceiling and wondered if the hail had been greater than I had thought and it was going to collapse. I slammed the lid on my lunch box, ran to the room to check the students, but they had left. I picked up everything I could carry in an instant and ran down the stairs, still thinking the ceiling was collapsing (why else would they evacuate?) Down there many were gathered, none leaving the building. I saw why. It was white with wind driven drenching rain. It was clearly worse out there than in. We waited. Then firemen burst in. Was it a fire? Then a female staff member raced down the stairs saying the upper floor was flooded with water. I thought that's ok, if the water has come through the ceiling won't collapse. They turned the alarm off and I returned to the room. It looked ok. The ceiling was still dripping, it had been dripping all morning. We were told to send the students home. I saw no reason to do so, but I knew I must follow directions. I cleaned the board and in a leisurely way packed up. Then we were instructed to evacuate the building, they were evacuating the campus.

Buildings subject to rain like that would leak. If there was any fault, they will fail, and leak. Our house leaks, every office I've worked in has leaked, I've owned a Truimph Stag (in rain I took up the carpet). Buildings leaking in heavy rain is normal (at least in Australia where construction tends to be rather 'she'll be right').

I still did not believe there was anything to be concerned about.

Until I walked out and saw the stormwater drain was full. And this stormwater drain was over 2m deep and 6m wide. Actually, it was over the edge and into the carpark. And it was still raining. It was about 1pm.

In Mayfield one side of the street was flooded and in a carpark two cars were in up to the floor. They were going nowhere.

A fallen tree blocked a street.

Industrial Drive into town was slow and I wondered why until I came to the lights and saw ahead the road was covered with water. I u-turned, only to find more water the other way. I knew my low 'sports' car was not up to it. There were cars parked to the side, then I saw the median strip was just above and drove one wheel up on it and crossed at a reasonable speed. From there it took half and hour to get to Maitland Rd. I rang home 'what's going on?'. I was told don't take Bennetts Green, it's slow. It was slow where I was. After 5 minutes I found the problem was another new river to be forded.

Two things. Everywhere the roads looked like a mulcher had been down and left a trail. And there were so many cars. Where did they all come from? An hour and a half to get home, when usually it was 25 minutes.

And I didn't know it then, I was lucky.

There was a message on my computer from my brother telling my father not to go into town to see the ship, as it was gridlocked. I had a phone message. One line was out. There was a thunderstorm. I rang out on the other, thinking I was a fool as lighting struck somewhere. I solved a problem taking some time and the storm stopped.

That wasn't the only problem. My brother rang, 'How deep is the water at the front gate, can I drive through?"

Water! at our Gate?!! I looked out. The front gate to the Pacific Highway it was a lake up and over the footpath! It was dusk.

My brother drove home on the footpath, just fitting between the power pole and the fence. He was the last car to enter, or leave the property that night. 4WD only after that. The water kept rising over the bricks (that was 200mm over the footpath), and there was a river into the service station opposite heading though Bunnings. A few cars broke down and dad got out the 4WD and he and my brother towed them off. One person who works here took of their shoes and walked home, another two were rescued by a friend in a 4WD.

Lesson two: No city drain can cope with continous heavy rain for 12 hours. Water will take the easiest path and it fills any low spot.

It was filling a hollow in our entry and rising to go into my office on the lower level. We swung into action. I baled, Dad used a crowbar and my brother grabbed a jackhammer. They broke through the sill of the door, and a volume of water you would expect from a small stream went through the lower floor of our house in the channel and came out our front door to travel eventually to the rising lake at our front gate.

We were watching this water rise when my sister came and said there was water in her office. Checking the source of this, my brother climbed the roof and saw the neighbours yard behind under half a meter of water. Water was just seeping though the walls at this height into the office. We moved everything paper or electronic onto desks.

Water had come over the edge of the detention basin for the subdivision up the street.

Lesson three. Every hard surface collects water. But with his kind of deluge every soft surface was also collecting it. Nothing was absorbing any water. At the base of the hill the detention basin for the newer subdivisions on the hills was filling with water run-off from every surface. But it was never designed to take this much water and people had eroded the edge. One section of the edge failed. Like a mini dam breaking. And downstream the already overloaded stormwater system could take no more. It went to half a metre in depth as a flood surged down the street. Water can come almost as a wall as it flows on the surface of the earth.

After stablising everything we could. We ate, very thankful we had power. Many people did not. It was still raining.

The eye of the storm came through about midnight. My brother saw if on the BOM site. He was up as there was a tremendous bang as some flashing blew off the roof in winds that rocked the house.

The fourth lesson was seen the next day. The water had gone down. But power was out. Power poles had fallen as the earth around their base had turned to slush or trees had pulled the lines down. Earth loses its ability to carry load when saturated. And life stopped. Shops could not open. Our society is now dependant on electricity. And it was cold. Bitterly cold that day. To not be able to heat anything. But worse. It was still raining. Off and on.

The fifth lesson was about Trees. Beautiful trees. We don't cut then down. But they get old. They get weak. They become dangerous. They kill. This tree below is a case in point. It looks healthy. But its roots were bound against the concrete kerb.
It failed. They fail suddenly. Trees are dangerous. Trees are even more dangerous where their root system is interfered with. Measure the height of a tree against the distance from the nearest building. If the main trunk is 200mm at the point it will hit the building if laid flat- It could cause major damage. Trees never look as tall as they really are.

Also some Australian gum trees are wonderfully designed. They drop branches. The tree may sacrifice a limb rather than falling over. They also in dry drought years starve certain limbs to drop them to reduce the need for water for the tree. And it has been dry recently: very dry. The weak branches with the wind will fall. The reason some species are called "widow makers" is that even with no wind the branch can fall. Branches can be over 100mm in diameter at the base. They can kill.

Lesson six was that just as wind can blow something as huge as a bulk carrier onto the beach, it can push in a poorly made wall.

A category one cyclone shows up and eliminates poorly made fences, including ones in un-reinforced brick. A wall 2m high of brick can be pushed over by the wind. In fact the higher it is the more likely it will fail. Fences are perfect in offering big flat surfaces like sails to the wind. Sails on boats are designed for wind, most fences aren't. Colorbond fences failed everywhere. Colorbond is a lovely light material solid that offers no gaps for 'spill' for the wind. If the footings are poor, or if the soil is so water logged it cant carry the load it will fall. They tend to fall as one at least, whereas brick fences may fall and break.

Retaining walls without adequate agg. lines will also fail. I saw a small brick retaining wall sitting on the footpath, liquid earth behind it.

And after the rain stops somewhere it is flooding still.

Lesson seven is that water can go up a stormwater system. First image is last week. The second is the same drain with no sign of the concrete culvert, instead the wind is pushing water up the drain. The lake has no capacity to take any more water.

A good outcome is the creativity of people.

Without power there is still something to do. This is a cubby house from found objects.

These two saw an opportunity in salvage of found objects.

Inside had a floor and a roof, and two living compartments made with shopping trolleys.

It was going to be up the tree, but they told me that that had presented technical problems. I concluded there had not been enough structural bits found and they had no tools. Candidates for Survivor.

Humans are weaker than nature. A huge boat under full power can be pushed backward by wind and huge waves onto shore to be left like a toy, or a shell, on the beach. A tall tree can fail suddenly and crush a car and kill the person who happens to be there. Water can soak earth an make it liquid and carry huge sections of it away, suddenly. And nothing, nothing, can stand in the way of a wall of water. It only needs 300mm of water on the roads in a few places to throw a city into chaos.

And once upon a time the world did not know electric power, not so very long ago. However, now 'normal' life stops when trees fell power lines. If you are reading this, you have electricity.