365 Challenge #276 - the floodgates at Wivenhoe Dam

Happy New Year! Woke up hangover free, and decided to venture out to Toowoomba for a day trip. We drove past the sign to the Wivenhoe Dam, and decided to go check out what a dam at 125% capacity looked like - personally, I thought someone had got their percentages wrong....I mean in my mind, 125% means 25% more full than the dam is capable of holding. But more about that in a sec.

It took a few attempts to get to the Spillway Lookout - couldn't quite find the right road to take, but we eventually made it, along with every other man and their dog.

According to Seqwater, "Wivenhoe Dam (Lake Wivenhoe) is built on the Brisbane River, approximately 80 kilometres from Brisbane.  It was designed by the Water Resources Commission and built in 1984. Its primary function is to provide a safe and reliable water supply to the south-east Queensland region."

As I mentioned earlier, thanks to the massive volume of rain in South East Queensland recently, the dam is currently at 125% capacity - so they'd recently opened the floodgates to let some of the water out. And spew out it did! The mist played havoc with the camera gear, so it was a case of get in, get a few bracketed shots so I could do some HDR processing, then get outta there!


Here are some facts about the Wivenhow Dam:

• Wivenhoe Dam consists of an earth and rock embankment 2.3 kilometres long and 50 metres high, measured from the lowest foundation to the crest, with a concrete spillway section on which five steel crest gates have been installed. 
• The gates measure 12 metres wide and 16.6 metres high and are among the largest of their type in the world.
• The dam has a total storage capacity of 2.6 million megalitres.  At full supply level it will hold 1.15 million megalitres, or about 2000 times the daily water consumption of Brisbane.

And what about that 125% thing? Well..this explanation on the Seqqater site helped to clarify it for me.

"During a flood situation, Wivenhoe Dam is designed to hold back a further 1.45 million megalitres as well as its normal storage capacity of 1.15 million megalitres. Floods may still occur in the Ipswich and Brisbane areas but they will be rarer in occurrence. Wivenhoe’s flood control facility, together with the existing flood mitigation effect of Somerset Dam, will substantially reduce the heights of relatively small floods.

 

It is anticipated that during a large flood similar in magnitude to that experienced in 1974, by using mitigation facility within Wivenhoe Dam, flood levels will be reduced downstream by an estimated 2 metres.

 

Full supply level or 100 percent capacity (in the water level analysis) is indicative of the optimum level intended for town water supply, and does not take flood mitigation levels into account."

So - looks like a dam can be more full than 100%. This is reassuring living so close to the Brisbane River!

The Wivenhoe Dam is an impressive structure, and well worth the drive out to see it, particularly now while the flood gates are open. It would just be nice if this damn rain would let up a bit! :)