Saturday, January 30, 2016

Flash floods in our cities and on our highways

The increased hard surfacing of soil in our cities  comes at a high price when it comes to localised flooding risks.

Higher than normal short term intensities ( up around 75 mm per hr -3inches per hour ) are common for localised thunderstorms but affect small areas;  such events usually last less than an hour and are usually quite localized  .
The more normal high intensity for rainfall we experience down here each year is more  around 25mm per hour (" 1"per hour).,

The worst and biggest type of floods occur , not when we have these localized cloud bursts,  but when moist air is unlifted for many hours by the local topography and wind direction( as can easily happen on the Otway Range and happened on the Toowoomba range recently)      
Huge floods occur only when many hours of rain are involved as many soils can  take in the 25mm per hour for the first hour.
What happened in Geelong last week can happen in lots of places where roofs paths and roads cover the landscape .
Here are some things to think about  to avoid the risk of damage and danger where you are . As well some ideas on how you can help .

We can't do much about the huge swathes of roads except to ALL drive much much slower or , when possible and safe , get right off the road  if a storm hits ( assuming that they will not last long )

Wide tyred vehicles are most at risk from slipping and skiing on accumulating patches of water on roads( whatever the tread depth)  Why have them ?

A small dense beautiful part of our back garden survives quite well without much extra watering through the summer because it receives summer rain off the garage roof .
The stormwater system does not need this water when storms like the one that hit Geelong last week

Put in your rainfall figures in here  and see also the water requirement required to keep the precious parts of your  garden alive here   shows  Litres per m2  per month on average.

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Thursday, January 21, 2016

Lakes dry out

A series of dry years and low runoff sees even lakes with some catchment in a high rainfall zone like  Lake Colac about to dry out. This drying out is nothing new as the hills to the east and south east of the many such temporary water bodies in the area shows .

The ambition to make this "lake" function for fishing and boating could be a reliable reality if Vicroads and the local community decide to create two lakes in the area.( some where even further out than existing water level on photo ) There is a considerable catchment to the lake making further lake management involving permanent water a possibility.

The water level is only ever as much as 2 metres deep with playa type flatness a feature.  The shallow depth  means its still too choppy to enjoy for boating and too hot for the 36 Murray Cod and most other fish planted in there in 1858 . The shallowness is a hazard as aquatic  life is easily killed when a period of growth is cut short by turbidity from wave action.
As a eutrophic lake with a salinity level around 2000 its also prone to deadly blue green algal blooms

The last Regatta was held over 100 years ago because the depth of the water is unreliable and generally insufficient . There are no prospects for an improvement unless something changes drastically to maintain a depth of at least 3 metres in at least a portion of the lake.

A bypass bank could change all that with permanent deep water spots and places for rowing swimming and fishing at this picturesque expanse withing 2 hrs of Melbourne.see sketches