Thanks Algernon, Nametag 
The city water commission pamphlet is all wet about dripping faucets:
There are 86400 sec/day,
190 gal = 760 L = 760,000 mL
So to lose 190 gallon in 86400 drops, each drop would have to be ~8.8 ml. That’s HUGE ! At a more typical drop size of 0.1 ml, 1 drop per second works out to ~2.2 gallons per day.
Good point Squink.
I was so focused on my pond that I never even thought to question the information in the brochure. It’s probably one of those false statistics that keeps making the rounds through all the local municipalities, and even the water engineers supported by my tax dollars don’t even bother to validate the statement of “fact” themselves.
There’s a good lesson in here somewhere.
Those calculatins are a waste of your time. Put a bucket of water by your pond and mark the water level in the bucket. If the water level in your pond goes down faster than the water level in the bucket, you have a leak.
If you want to be more precise, you can put the bucket in the pond so the water in the bucket is at the same temp as the pond water.
I’m a mech engr. Those calculations would be hard for me, and they are not necessarily accurate. We always look for an easy, common sense solution before going to the theory.
Good luck!
zombie or no
a bucket and pond will not evaporate at the same rate.
In low humidities like 25% the air movement can have a big difference on the evaporation. I would make sure the bucket was real full to minimise the wind break effect of the sides.
Why not? It looks sound to me.
a bucket is shallow and has reflective sides. it has characteristics that will cause it to heat differently from a pond.
OK, so you partially submerge the bucket in the pond, like FS2020 suggested, which will keep it at the same temperature regardless of radiant properties (convection is much more efficient than radiation, for water under Earthly conditions).
Go to the 99 cent store and get a cheapo plastic drop cloth and cover the pond for a day. Turn off the waterfall. No evaporation = real world answer
Yup - you could stand the bucket on bricks in the pond, so the water levels start out exactly the same. It’s a beautifully simple idea, and worth resurrecting the thread for.
That only works if the drop cloth is air tight and doesn’t heat the water, and if you don’t mind killing any fish.
The bucket idea is a good one - I’d definitely make sure it was partially submerged to match temperature, light, wind, etc.
I know it’s way to late to help the OP, but my koi pond with a similar surface area (perhaps 150 sqft) can lose as much as half an inch on a hot, dry day. Furthermore, I only lose that much water when it’s hot. A cooler, cloudy day will see no noticeable change in water level.
But it is worth considering a third option: another pond owner I know was frustrated by the amount of water lost and insisted it must be a leak. What he eventually discovered was that deer had decided to use the pond watering hole. They were drinking upwards of 100 gallons a day, especially on warmer days.
That’s just a 2D polynomial fit to empirical data. They use each combination of constant, linear, and quadratic variation in temperature and relative humidity, and find coefficients to best fit that data over some range of temperature and humidity. Very little thought required, just a MatLab code to do the fit. Such a fit will generally fail miserably outside the range data it was fit with, and doesn’t give much insight into the physics involved.
(Pretty sure Whack-a-Mole is still around.)
They keep trying to knock him down, but he always seems to pop back up again.
Wow. I don’t post much anymore, but in the old days my threads usually disappeared without a trace. To have a 12 year old thread of mine become a reanimated zombie is quite thrilling actually.
The tarp idea would not work – my pond is too big and strangely shaped.
The bucket idea seems to be a reasonable approach. But the math was more fun.
Turns out that it indeed was simple evaporation. Over the years I’ve experienced similar rates, depending on conditions. And so far (knock on wood), no leaks.
If I ever suspect a leak in the future, I will try the bucket method and report back. Is there a name for a thread that gets resurrected more than once?
double zombie
do a bucket for fun, for science, for the dope.
Such fits are very useful and in many cases the norm even if the physics is not well understood. Here are some examples :
1> Antoine equation for vapor pressure
2> Ergun equation for pressure drop through packed beds.
Sometimes, Physicists successfully explain the physics behind these equation fits :
1> Stefan–Boltzmann law for black body radiation
2> Van der Waals equation of state for non ideal gases
Although matlab can do great curve fits, the form of the equation is still a matter of art/experience of the user.
How can I resist?
I will have to wait until the water level drops to “normal”. A recent heavy thunderstorm has drenched the ground so much that the water level is currently above the overflow drain opening, which simply empties into the ground.