How much water evaporates per day?

   #1  

Alan L.

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I know there are many factors, but can someone give me a rough idea how to figure how much water will evaporate from my 1-acre pond in a day. Temps in upper 90s, light breezes usually, humidity at hottest part of the day probably 45-55%.

I am trying to figure out how much and how often I need to pump into it just to keep status quo for the long hot dry summer.
 
   #2  

gordon21

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I have seen my pool lose up to .33" per day. The wind and wave action will cause more loss than the temperature. 9-10 days of high heat and wind could cost you 3" of pond. 3" times one acre is a lot of water. 50,000 gallons or more. Someone on TBN will have the formula for acre/feet of water. A well pumping 20GPM out of a fire hose assembly would take a day and a half to replace that much water. Hopefully you will be looking at a lot less loss than .33" per day.
 
   #3  

Dargo

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There was one area of my property that was always wet. You could count on getting a tractor stuck there about every year. I decided about 12 years ago to dig a lake in that spot. I don't have a background in engineering, but I do have a background in carefully plotting out actions and making the appropriate contacts to allow me to achieve the proper engineering and calculations.

I have a 1 1/2 acre lake there that is 20 to 22 feet deep at the deepest and carries a 7' average depth. I calculated that I moved something like 35,000 cubic yards of dirt when I dug that lake. That is quite a bit of dirt to move, but it becomes more when you figure that every yard had to be trucked to a different area of my property and then spread and levelled. That means that I basically had to handle the dirt twice; moving around 70,000 cubic yards of dirt.

Anyway, even with a mild natural spring feeding the lake, I will still lose about 1' of water every month during the hot summer months if we don't have any rain. We have had droughts where we have not had any measurable rain in over 4 months; last year being one of those years. My lake was down right at 4'. I used that opportunity to line the banks on one side with rip rap rock.

Taking standard calculations and measurements, that would mean that I would have roughly 3,421,425 gallons of water in my lake at any given time. Based on the apparent rule of thumb of losing about a foot a month, and knowing that one acre foot of water is equal to 325,850 gallons and my lake is 1 and 1/2 acres in size, I'm losing about 16,293 gallons of water a day to evaporation in summer months. In the winter months, the evaporation rate seems to be practically nil.

In your case, with a 1 acre lake/pond (some call it a pond and some call it a lake - I don't care), and for calculation sake assuming that you will have about the same evaporation rates I have, you will lose about 10,862 gallons of water per day. Just rounding up to accomodate for the continued evaporation during water replacement, that means during the hottest dry season that you will need to replace water at a rate of roughly 500 gallons per hour, or about 8 and a half gallons per minute.

Whew! Hopefully that all makes sense to you. The formulas and calculations are all based on scientific fact other than the evaporation rate. That has too many variables for me to be able to give you any accurate measurement other than what I experience. The rate will vary with the hours of sunshine, the relative humidity, the average temperature of your water, the average ambient temperature of your air, the wind speed, as well as the amount of algae and even the turbidity of your water; complicated to say the least. Anyway, hopefully that will answer your question.

Oh yeah, this is all based on my lake which does have a small natural spring feeding it. I have no idea how much water is put out by that spring. Since you are in a generally hotter climate and you made no mention of a spring feeding your pond, take my calculations at a bare minimum for your needs. Also, I am familiar with the estimated evapotranspiration calculations using the Priestly-Taylor method, the Penman method, the DeBruin-Keijman method and the Papadakis method. However, for my response here, I opted to use my actual measurements of evaporation loss method. /forums/images/graemlins/wink.gif There are just too many variables in any particular method to give you an accurate guide for your particular pond.
 
   #4  

DaveNay

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Take a look at this page, it has a good explanation of evaporation and rates for various parts of the U.S. At the bottom is a calculator that you can put in your numbers to get a good idea of how much your pond will evaporate.

Evaporation
 
   #5  

Pilot

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The annual pan evaporation rates reported on that web site won't do you much good for summer evap rates. You might just set out a pan and check it yourself for a few days.

When I was a kid in So. Cal. we lost about 1/8" per day in the summer from our unheated swimming pool.

Are you in east humid Texas or west dry Texas? West Texas with it's dry winds would probably lose a lot more than we lost in southern California, but east Texas would probably be less.
 
   #6  

stevenf

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Alan, I tried to do exactly what your attempting, make sure the bottom is water proof to start with so that you have no loss thru absorbtion, bentonite is a good bet. I didn't and after burning up my old well decided that I'd wait for rain. I did learn some important lessons before the well seized. I have an acre or so hole it is at its deapest about 16' deep there is a lower section in it where the water collects as its drying up I ran a 3/4 inch line to it and had the well running 24 hours a day it got to a point at about 50' wide and 100' long and 4' deep where absorbtion and evaporation kept up with input water and never got any deeper. I still have not done the bentonite application as to do it correctly takes a D6 with a commercial tiller and till it into the bottom and sides 18" deep it would take 50,000lbs of bentonite to even get close the one bid I got to have it done was around $12,000 including the bentonite. Good luck with your project and another lesson I learned is find out how much water you can pump and how fast to set the valve so that you don't run your well dry like I did and burn your pump up, a timer also would work.
Steve
 
   #7  

sendero

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I have a 1.5-1.75 acre pond in Grayson county. It loses about 1/4" to 3/8" per day, depending upon conditions. Obviously, wind is a big factor.
 
  
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#8  
OP
A

Alan L.

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Thanks for all the replies. I am discouraged by the answers /forums/images/graemlins/confused.gif. My pump is rated 20 gpm, but I have a 1.5 inch water run to the pond/tank/lake and if I open the gate valve I loose all the pressure in my pressure tank. I close the valve down just to the point where the pressure stays at 50 and let it run all night with the pump running, but not losing pressure.

I stuck a stick right on the edge at 7:00 PM last night and and 8:30 this morning I could only barely tell the level had gone up, maybe 1/4 inch at the most.

I had thought maybe I could do that once a week, but sounds like thats not going to put a dent in it.

Looks like I am going to lose my pond this year, as its not supposed to rain all summer and its already half gone. There are nice bass and 36 inch long channel cat in there that I feed and so its a shame I can't keep enough water in there to keep them a live.

I suspect I will try to pump water in there a couple of times a week and track the level on my stick to see if I am at least slowing it down.

I don't think there is any significant seepage, the tank has held water real well for 6 years, up until the last year which has been a pretty bad drought period. It usually fills up and overflows every spring. I cuss about it being so high, I'll never complain again if I could just get the level back up.

Since my well is supposedly producing 30 to 35 gpm and my pump is only 20 gpm it would seem that I'd not be likely to pump it dry, but I suppose it could happen. Just spent $2600 on a new pump a couple of months ago, so I sure don't want to burn it up.

I am in North Central Texas where we have moderate humidity, if you are from West Texas you would say its very humid, if you are from east or southeast Texas you would say its very dry.
 
   #9  

stevenf

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Alan, Don't be discouraged my dry hole/lake has been dry since last year and yep I lost 200 catfish and 2000 bull head minnows. Talk to your well folks if you just had a well pump put in they will have current data on the well, how much it draws down, flow rate, pump still in warranty etc etc. By the way my primary well pump burnt up last Sunday I haven't gotten my bill yet but I'm expecting a $3,500 bill or so its at 550' and is a 3hp Gould now.
I talked to my well folks about using it to irrigate and subsidize water in the lake and they went thru a thorough discription of how to do it. You need to keep the pump running its not the running its the start and stop that kills pumps OR the well running dry which was the case on my old Gyp well. On my good well the pump is at 550' the water level is at 400' and in 3hours it drew down 10' the well folks believe that I couldn't run my well dry with a 10hp pump. They also said that if I weren't using the well for the house and in need of pressure its would be best to have no pressure tank that way the pump would just be churning away with no chance of stopping. I don't know if that is an option for you but they said that would really extend the life of the pump for sure but since I needed the well for the house's and such they showed me how to do it. You need to have enough hoses/taps turned on so that the pressure tank and booster pump can't keep up in my case it takes 4 3/4" hoses running full blast and I have to drain about 750' out of my storage tank to get it started. Give your well guys a call, sorry for my original discouraging post I was in the middle of making decisions on the deep well replacement equipment and I was rather discouraged myself.
Steve
Sorry I edited this I reread it and discovered I said well pump couldn't keep up its the above ground 10hp booster that shouldn't be allowed to keep up that way both pumps are running full time if the well pump couldn't keep up that'd probably be a problem /forums/images/graemlins/grin.gif
 

CharlieTR

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Sorry I don't have an answer to you question but I thought you might be interested to know the recent discovery on evaporation. Apparently from two separate studies (Russian, and I think Britsh??) they found that the heat, humidity, wind, all have little or no affect on evaporation. The "Pan Evaporation" study over 50 years confirmed the Russian results that the number of Photons striking the water surface is the cause of evaporation. They came to this after find the the temp on earth are going up and the evaporation is decreasing. Thus they concluded the sun in getting weaker or at least sun's rays are reaching the ground weaker.
 
 
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