Friday, 16 July 2010

Assessing water flows in Whiskers Creek


This post covers a few thoughts about how to assess the rate of flow in Whiskers Creek where it goes under (or occasionally over) the drive into our property.


I originally had a range of designations based upon the proportion of the pipe which was 'filled' by the water. However this was very difficult to assess (and even when flooded the pipe was only 50% full). So I developed the set of designations below. The words were chosen so as:

  • to have relevant meaning; and
  • to be able to be sorted into a relevant sequence.
After a while Frances commented on the use of the sound of the water as an objective means of distinguishing between trace and light flows. So that is included as well.


At present we are finding the Visual and Aural measures are correlating well.


The basic assessment is made in the morning each day when we first cross the creek, either in an exercise walk or driving out. If however the road is flooded later in the day I will use that as the measure . I will also use flood if it is obvious, from the vegetation, or debris left on the road or erosion of the road, that the creek has flooded overnight but dropped to 'heavy' flow status by the time we get there.

Designation
Visual
Depth at mouth of pipe(mm)
Aural
Znotobservedn/a
n/a
n/a
ZeroPipe dry
0
silent
tracewater dribbling out of pipe
< 2
silent
LightWater running out of pipe
< 25
running water audible close to pipe
HeavyWater gushing out of pipe
25 +
Running water audible 30+m
FloodWater flowing over road
300
running water audible @100m

  I will, from time to time - perhaps every 6 months  - summarise what has been observed.


 

2 comments:

Denis Wilson said...

Is it not simpler to assess the quantity or "attitude" of the rain, or even in extreme cases its "trajectory"?
In Robertson, we have a range of quaint rural expressions which are not necessarily fit for your Blog (which is probably read by a more genteel clientele than mine).
It starts with mist, Fog, Bloody thick fog, and goes on through "pissing down" to other far more explicit phrases, which I shall spare your readers.
If the main road in town is flooded, then you know we have had in excess of 6 inches of rain in half an hour. We have the deepest gutters of any street in Australia that I have ever seen.
Cheers
Denis

Flabmeister said...

As always, an interesting comment Denis.

In many years we are a little more rainfall-challenged than Robertson (but see a forthcoming page for some comments on current moisture levels in our vegie garden). This means that we can get quite a bit of rain, but it all goes into the soil with little run off. On other occasions if we get a strong thunderstorm when the ground is baked as little as 20mm of rain can get the Creek over our drive (ie Flood status). I'll be having a lot at that relationship when I have enough data to analyse.

The other point to make - which I should probably have put in the post - is the original reason for making the assessment. This was to provide some information to our local CMA who measure water quality about 2 km downstream. I thought, and they agreed, that it might be interesting to have a measure of flow from upstream to see what it adds to knowledge of the catchment.

Martin