How much water?

[roda]

I live on an 80 acre lake in central FL that has had the water level dropping over the past year due to the lack of rain. What is the best guess on how much water (and pump HP) it would take to maintain 80 acres at a fixed level if you had zero rain and were losing water from just evaporation? We understand that we also would lose some back to ground seepage but are just looking for rough orders of magnitude to start with.

 

Thanks

 

[Boody]

You first need to find your evaporation rates in your area which should be availabe online for farming purposes. Where I am at in Oregon the rate maxes at .33 of an inch a day in the summertime.

 

Next you need to be a math wiz to figure out an average evaporation x acres (80) x days (365)

[lottawatta]

If my math is correct, you have 2,172,192 gallons of water in every inch of depth in an 80 acre lake. Assuming an evaporation rate of 1" a day, you would need a pump capable of 1508.5 gallons a minute. A typical 6" centrifugal pump available at any contractor's rental place should be in that rage. An electric pump is WAY cheaper to run that a gas or diesel fueled pump. I have a 50hp electric powered pump capable of 2200 gpm I can make you a deal on if you have access to 3 phase electric service. I bought a 6" gas powered irrigation pump to pump water into my lake for tournaments during a couple of dry years. For reference, it cost me close to $1000 in fuel to raise my 17 acre lake 1 foot.

[ForrestGump]

Man, that gas pump is expensive. Using our 6" diesel pump to raise our 12 acre lake 18 inches only cost us $350 in diesel.

[lottawatta]

I should probably clarify the fact that I can never really pump water in to my lake for any period of time as my lake is the water table, I can only "borrow" water from a neighboring lake as it just seeps right back out through the sand/gravel almost as fast as I put it in. When I raise my level 1 foot, if I stop the pump, I lose 4" the first day, 2-3" the second day, 1-2" the third, etc. So in order to maintain that 1' of water pumped in, I have to run the pump at speed for 2.5-3 days, then at idle for 2-3 days during the tournament. My gas powered pump uses around 3 GPH at speed, and 1 GPH at idle.

[eleeski]

From a 2008 USGS report I googled, Florida has an evapotranspiration rate for open water of about 4.5mm/day. That's nothing compared to our socal deserts. But (assuming I didn't screw up the math) that works out to about 260 gpm. Lots of California wells pump at that rate (Stan's shallow 10 hp well pump does about that). My shallow small wells pump at 40 to 100 gpm on 3 hp. Keeping your lake full is not unreasonable.

 

I am suspicious of my math. My 12 acre lakes take 100 gpm (running 24/7) in the summer to keep full - barely. That suggests more like 600 gpm - thats a big (but available) pump. If your lakes are dropping there is probably none of the rain that figures into the ET rate. Plus it is hard to play catch up (will you notice if the water recovers by 4mm?). Still, even at a higher ET rate, commercially available ag pumps should work.

 

Or you could wait for the rains...

 

Eric