How much rain is too much rain

[samh]

I just wonder what people consider too much rain to go on a walk. ie when would you call of a walk due to rain. obviously that depends on the length of the walk, and if the walk can be done at another time . Most ofthe time in tassie the forecast shows at least some rain but i never really know how much is too much. I haven't quite figured what amount in mm is a lot and what is only a drizzle ie is 20mm much or little or medium. i guess there is no definite answer and everyones interpretation is different but i'm keen to hear any thougts and advise

[Ent]

Hi

With rain bit of care is needed to work out if any creeks will become impassable. Having struck them almost dry at times it can be a shock to see them in flood. Often bit of local knowledge can go a long way.

Cheers

[wayno]

i've had 300mm in a day and a half... that might have been a bit much, anything less doesnt seem like that much....

[alanoutgear]

In 1995 my then young daughter and I camped at Fed Hut. Also there were a school group from Wangaratta High School as I recall, in their school tents. We had a Salewa Sierra Leone tent, which was a pretty good tent at the time (still got it somewhere too). The weather changed immediately the sun went down and overnight we had around 250mm of rain in a land gale with incredible winds.

It was a pretty rough night for us with heaps of close thunder and lightning, but the Salewa handled it well. When we got up in the morning, all the school tents were flat on the ground on top of very wet kids, or tents had been torn asunder by the wind. The ground was awash and we decided to head down rather than continue on.

Time has probably played with my memory, but I recall getting increasingly worried as more and more water flowed off the mountain and over the Bungalow Spur track as we got lower and lower. We got to the bottom and the car, and the Ovens River was already out of its banks. We drove home, and later that night on the news it was reported that the Ovens had flooded Wangaratta, and I remember seeing news film with 5' of water flowing through the Benalla town centre.

So in my view, 250 mm in a night is too much rain.

[Tortoise]

I just wonder what people consider too much rain to go on a walk. ie when would you call of a walk due to rain. obviously that depends on the length of the walk, and if the walk can be done at another time .

It also depends on the elevation, exposure, track surface etc. i avoid lots of places with significant rock scrambling if there's likely to be lots of rain. Other more sure-footed people might be okay, but as those places tend to be good for views when there's some visibility, I'd go with a plan b anyway. Harder if very limited with time/ opportunity for a particular walk.

I haven't quite figured what amount in mm is a lot and what is only a drizzle ie is 20mm much or little or medium.

I guess I got the hang of it with a rain gauge at home. Drizzle vs showers, heavy showers, torrential rain. You could also check out how many mms of rain are reported where you live on a day of drizzle vs rain all day.

[Wollemi]

From the paper presented 'The Potential Risk of Phytophthora Dieback in the Greater Blue Mountains WHA'
- Variable condition and optima; Increasing risk with increasing wetness.
- this is to say; don't go bushwalking after rain.

I put 'rain phytophthora' into Google, and got the above (which I helped with the remote-area soil collection/mapping and to a lesser degree, SEM analysis). I also got the below, from around the world. You would have to agree that 400mm p.a. is very low rainfall...

...Excessive rain paired with poor drainage can cause more than just floods – it also creates the ideal environment for Phytophthora root rot.

Where is Phytophthora Dieback? Areas receiving greater than 400mm of annual rainfall in the south west of Western Australia are most affected.

Foliar blight is also a symptom of Phytophthora sojae, especially when the plant has recently experienced heavy rain.

Phytophthora ramorum – help keep it out of Australia! Many consider that the impact of Phytophthora ramorum in ... spreading its spores in rain and mist.

[madmacca]

25 mm is an inch in the old scale, and is steady rain in anyone's language. Across southern WA, SA and Vic, 25-50 mm in 24 hours would probably be heavier rain, with 50-100 mm in mountain areas in those states being not uncommon. In tropical and sub-tropical areas (Qld, coastal NSW), falls of 200-300mm in 24 hours are frequent. Someone from Tas can chime in on conditions there, but my understanding it is the frequency, rather than amount of rain that really is the issue.

I am assuming that you are well enough equiped in terms of clothing and tentage that the rain itself is not an issue. So really there are two things you need to be concerned about:

* track conditions - clay surfaces can become slippery, while heavy mud (you know, the stuff strong enough to suck the boot off your foot) can really slow you down. Mud is probably as much an issue of traffic levels (frequently used tracks can get really churned up), and existing soil moisture (25mm is unlikely to cause problems, but if it rained another 25 mm yesterday and the day before as well, then there may be issues) and topography (low lying areas drain slowly), rather than just the amount of rain.
* river and creek levels. Again, the size of the relevant catchment area is probably more of a factor than the amount of rain, so a bit of map study can help here. A creek draining a few km2 is unlikely to be a major issue, one draining a few 10's of km2 may rise and become temporarily impassible but also falls pretty quickly too, while a river draining a few hundred km2 (remembering 10 x 10 = 100 km2, but 15 x 15 = 225 km2) can be more of an issue, and can carry sufficient debris to trash the area even after it has fallen. With a ridgetop walk, you might be completely untroubled by heavy rain.

[north-north-west]

If the gear can't cope with it, it's too much.

It really depends on the area. I don't mind forest walking in the rain, but there's nothing worse than pushing through wet scrub for hours.

[madmacca]

Oh, and in terms of getting a feel for rainfall, and seeing how much rain has fallen in your intended walking area, try http://www.bom.gov.au/australia/flood/