Evaporation Rate

[Svengali]

Does anyone know the rate at which a pond - still new, and with not much surface cover - will lose water due to evaporation?
My pond measures approx 25' x 35' with a water tumble about 3' wide x 6' long, with a fall of abou 2' (around 2" deep)
My water loss is beginning to concern me - I have lost about 6" in a week! I know that it's been flipping hot, but is such a loss to be expected, or must I start looking for other causes?

JeremyB

[Svengali]

[djbrenton]

Even with plant cover I lost about 4 inches last week.

[Gadfium]

All number of variables conspire to vary the rate of evaporation e.g. temperature, humidity, wind speed (windy= more evaporation), surface area, atmospheric pressure, amount of shade/in pond shade plants, and water agitation. The waterfall will greatly contribute to evaporation loss... it increases the exposed surface area of the water (plus misting/aerosol drops being blown off course) and allows greater evaporation.

Don't have a formula for calculating the loss rate. Anyone?

There is also the possibility of a leak... this'd be expected to produce a steady decline in level. If cutting the flow rate of the waterfall slows water losses, then that would point towards evaporation as the major culprit, rather than a leak.

Once plants get established, then they'll cut evaporation losses. Even a few aquatic plants should cut the rate by about 10%, but I do think this figure is linked to ponds without waterfalls (lower surface area).

If you have a drainpipe nearby, then a diverter and a hose would be one way to refill the pond (once it rains), avoiding tap water and the likelihood of an algal bloom.

[Garden Manager]

My pond is quite small (about 3' x 4'), with a very shallow area at one end. I too have ben noticing some water loss during the hot weather, when the shallows loose water and the 'tide' goes out!. I have been geting a bit worried about it but now I hear of people with worse evaporation from larger ponds I am encouraged. I should add it is a new pond with little surface cover as yet.

I am led to beleive that small ponds loose water quicker because the water heats up more than a larger pond, but maybe you could also argue that the larger the surface area the more evaporation takes place.


Fortunatley I am not in a hosepipe ban area so can easily top up the pond when required.

PS - Those pond owners loosing alot of water - Are you sure you havent got a leak somewhere?

[libby]

Gadfium
you are full of knowledge,a very good answer :)

[theothermarg]

am I glad I read this , I've a small pond which seems to lose water I don;t think it's leaking but it needs topping up rather a lot my DH says I've too much weed in there and it's drinking it all!! now thats a different explanation isn't
;D ;D ;D ;D

[Svengali]

Leak Identified!
What pointed me in the right direction was that although I lost a lot of water, very quickly, when the pond was full, when I was about 4" down, the water loss slowed.
When I first built the pond, I had a similar problem. I have a waterfall that drops down into the pond proper, with the liner going up a few inches under the waterfall liner and concrete. To give wildlife a "beach", the first couple of feet from the waterfall to the pond goes from 2" to 4" deep, before droping down.. To hide the liner, I put a covering of 4-6" pebbles over this liner, so that the water ripples through the stones.
I discovered last time that these stones caused the water to back up, under the waterfall, and leak away. I sealed the joint with a supposedly underwater mastic, but when I checked the same area today, I found that the mastic had lost all adhesion, & could be pulled straight off!
At least I know where the problem lies, and have ordered a VERY expensive mastic/sealer. I am also going to replace the stones with a piece of the pebble-faced liner that Margaret mentioned, in order to get the water down into the pond more quickly.
Hopefully, it is a case of Problem Solved!

JeremyB