|
Because an accurate flow
rate at the top of the waterfall or feature is critical to choosing a pump,
please take you time in calculating the flow.
There are two ways to
establish the answer.
1) How to measure flow rate using hose/s and a bucket
This formula can be used to measure the flow rate of the pump you require.
With a container
of known volume (i.e. a 25 litre bucket), measure the period of time
(in seconds)
taken to
fill the container
by the flow that you
wish to measure . Then divide 3600 by the number of
seconds taken to fill the container and multiply by the volume (litres) of
the container. The result will be the flow rate in litres per hour.
Example: It
takes 10 seconds to fill a 25 litre bucket.
3600 divided
by 10 seconds x 25 litres = 9,000 LPH
You can also use
this formula to decide how much flow you would like over a waterfall. Simply
place a hose at the top of the waterfall and adjust the volume of water
until you find the flow that you like. Measure this flow and you will have an
idea of the volume required to get the effect you desire.
2) Waterfall weir rates using
water width and thickness
The most important consideration
in setting up a waterfall is it's appearance. The volume of water
required to achieve different effects, from a robust waterfall to a modest
trickle, will depend upon the width of the waterfall lip (weir) or stream and
the material that it is constructed from. The chart below will tell you how much
water is required per 100mm (10cm) of waterfall width to achieve different
depths of water over the entire width of the waterfall weir. Once you have
calculated the total head of the waterfall, it becomes quite easy to determine which pump
to use.
|
Desired
Water
Depth |
Required
LPH for every
100mm of waterfall width |
|
1mm |
144 |
|
1.5mm |
216 |
|
3 mm |
432 |
|
5 mm |
720 |
|
7 mm |
1008 |
|
10 mm |
1440 |
|
13 mm |
2270 |
|
20 mm |
2880 |
|
25 mm |
3600 |
Example
You have a
1-meter high waterfall
(measured from the pond surface), and will have 4 meters of
tubing run between the pump and the top of the waterfall. The
total head is thus 1.4 meters. To achieve a 7mm water depth over the width of a 250mm
wide waterfall weir, you would require a pump producing 2,520
LPH (1008 LPH
per 100mm x 2.5 (250mm) total width) at a total head of 1.4 meters.
|
