returning to gwondanaland

returning to gwondanaland
Originally uploaded by imageo.

It has been a while since I have blogged about my Cretaceous garden, because it has been left to solider on by itself. A classic case of gardening by neglect and in fact it has looked after itself rather well, albeit becoming a touch overgrown.

Admittedly the weather has been very kind, lots of rain, but i am impressed with how fast the ferns have recovered from the drought conditions of the past few years.

Wet, Wet, Wet

Well the rains have come (at last) and Gwondanaland is more like a river than a garden. Also some water restriction have been lifted but now no one needs to water their garden.
It is amazing how the ferns have come to life. Everything is gushingly green again

Position, Position, Position

Rain gauges, like most meteorological instruments, should be placed far enough away from structures and trees to ensure that any effects caused are minimised. The Nylex Rain Gauge 1000 instruction leaflet suggest the gauge should be located twice as far away as the height of nearby buildings and trees (ie if your house is approx. 3m high then the gauge should be 6m away!) I have two of these rain gauges (normally at different locations) but I have already noted that then can give different readings with only small separation. The main culprit is wind. nearby obstacles can cause shadows and eddies and if the gauges is too exposed eddies in strong winds can carry away up to 20% of the rain. Finding a good site is a standard suburban block can be a challenge and using two gauges (these can be homemade) at various locations is a good way to select best location to permanently mount your rain gauge.
Swalim (the Somalia Water & Land information Management) project has put their comprehensive Rainfall Observers Manual on the net.
The rain gauges that come in most weather station kits are based on tipping buckets. These are generally not as accurate at the conventional graduated cylindrical collectors, for a couple of reasons. A certain amount of rain is needed to tip the buckets and the rain event may finish before the bucket is tipped, where the rainfall is infrequent and low this can be an issue. Also the tripping mechanism may have considerable tolerance (most are made of molded plastic) and it may be wise to "calibrate" the readings against a convention gauge (using a few decent rain events of perhaps 2mm of more)

rain

Well decent rain is falling, and we may even get close to our normal march average. With the long term predictions still suggestion better than average rains through autum. If you are interested the Australian Bureau of Meterology has a great area on their website to graph and compare a number of key climate measures.

Where did the cretaceous weather come from?

The anwser is simple it came dowm from the tropics. Looking at the lastest satellite image, which I got from the Bureau of Meterology's satellite page. You can see the big band of cloud coming down the east coast of Australia. A tropical Low (low pressure area) in Northern Australia had connected with low coming acrosss the Great Australian Bight and it just sucked all the hot moist air south (where it is needed)

Where did the water go?

The water levels of Melbourne's dams are now published daily, and a surprising number of people are well informed on the levels. Today "The Sunday Age" had a story about the bit dry (it has actually rained for two days now) and mentioned that the dam levels fell 0.1%, in a sidebar, strangely the article only indicated 8mm of rain in the past 24 hours and the rainfall section back a bit only showed 1.5mm. I can tell you it rained more than that. Checking on the net I could see that the average around melbourne was 24mm and some place over 40mm in some places (mainly the areas were our water catchments and dams are). This which is closer to what I expected.

So what is going on here. Well I found one likely cause, the news paper story is probably not basing its discussion on up to date data. It appears to be based on Melbourne Water's website (which at the time of writing had not been updated for the recent rains.)

This melbourne water conserve water website is interesting, it gives all the dam levels and also mention that melbournes consupmtion (on average, and that means without water restrictions is 500 giga litres, which is 500,000 megalitres). The full capacity of our dams from this source is 1,773,000 megalitres which is about three and a half years supply. We are now down to 66,577 megalitres and that thens leave close enough to 1.32 years of unrestricted use. Sorry haven't managed to track down the about of water that is expected to be saved by the restrictions.

The inaccuracy of the newspaper report asided, does all the panic about water and water restrictions really seem like we are despeate and about to run out of water? Over a years worth does seem ok to me when much of northern victorian has virtually none left, but to me it is even harded to justify expensive TV adds to dob in water wasters.

Or is the urgency perhaps more to do with political spin!

Some excitement

The humid weather, and being given a spell out in the rain, has prompted a littel growth spurt on my wollemi pine. At this stage I'm not sure if its buds for new braches or perhaps some cones developing. I'll keep you posted

soaking rains, at last

Well overnight and this morning we have had some decent soaking rain. Perhaps not enough to fill the dams or put out the bushfires, but the plants certainly liked it (and so have the birds). It is still hot and humid, I would imagine this is perfect cretaceous weather.

Waiting for the rain

So the heat (over 40 C) continues, the serious bushfires continue and the weather bureau is forecasting "chance" of rain and "risk" of thunderstorms. I think that is just bureau spin for a few drops of rain, which unfortunately evaporates soon after landing. The drought drags on.

Without doubt the best way to deep water your garden is via natural heavy rain. However the continued dry conditions can cause soils to become hydrophobic (literally it means afraid of the water) which in physical terms it means that the soil gets a skin that repels water. How soils are affected depends on the soil type. In Melbourne the most sandy soils will quite quickly become hydrophobic, the surface affected with waxes from plants, air fall of hydrocarbons and oily polutants and possibly some natural near surface fungal and baterial actions. Melbourne more clay soils (>30% clay) areas will also be affect but only after the clay has started to dry out. First it becomes very hard, and then surface with start get powdery and large shrinkage cracks will open up. This occurs because the clays are loosing their formation water (water that makes up part of clays crystal structure). The fine powder particles of this dehydrated clay are then on the look out for water and will stick to water droplets rather than staying attached to other clay particles. The clay coated droplets soon coagulate and form a mat that forces any further water to run-off.(This drying of clays has the potentially to damage structures, like your house, via subsidence but this will need to be a separate post)

The best way to fix this in the long term is to add lots of organic matter to the soil to change its structure, and add a surface mulch.(when mulches are too thick and allowed to dry out they can apparently themselves become hydrophobic)

In the short term there is a group of materials called Surfactants (or wetting agents). They work by reducing surface tension of water, and are generally complex organic compounds which have one end which is water loving (hydrophilic) and the other water averse(hydrophobic), they work by acting as a joining agent. Soap and detergents are good surfactants, so using soapy grey water on areas that seem to be becoming hydrophobic has some merit as a good way to pre-wet the surface.(but the affect may only last a few hours).