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Joined: Aug 2003
Posts: 17
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Joined: Aug 2003
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I found a piece of land for sale that currently has a 1 acre pond. If I buy the land, I would want to increase that to about 4 acres. This pond is basically a dammed up ravine and I calculated the watershed to be about 120 acres, most of which is cropland. Is 120 acres enough to fill a 4 acre pond? I would want the 4 acre pond to have a max depth of at least 25 feet to control winter kill (northern midwest). My calculations tell me yes, but I'd hate to be wrong. What is the best way to determine this?
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Joined: Oct 2005
Posts: 6,934 Likes: 2
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Chet, There are a number of criteria that go into determining the watershed for any given area...it can be taken to the level of a somewhat complicated mathematical equation. I have said this before, and I will say it again...Pub 590 contains all the basic formats for the elements of this equation. If you care to take this calculated route, you will need to know the hydrological types of the soils that make up this watershed and a snapshot of the method of crop planting within. This, combined with your avg precip in your area and some other basic criteria will provide the required calculation elements. If your NRCS office is "pond-friendly", you will be doing yourself justice to get their input and opinions(this forum has reported various levels of competance and interest by the NRCS...hope your's is pro). From the hip, I gotta guess that you get a good level of precip. Assuming this, even with medium to highly permeable watershed soils, 120 acres of farmland water shed will be plenty to feed a 4 ac pond. 30:1 is strong. FWIW, I think Meadowlark in TX has a 1 ac "sky" pond with virtually no drainage and he says it does fine (hard to believe, eh?...ML is a straight shooter). (edit a Pub 590 link) Pub 590
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Chet, Below Dennis does a good job of answering your question: dennisinponca
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posted May 03, 2005 08:49 PM
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Jack,
"Basic Pond Management" by Bob Lusk and Mark McDonald (available from this site) gives the correct answer.... Depends on the evaporation rate vs. the rainfall.
Step 1. Determine if you need watershed.
If evaporation for your area is 50 inches per year and your annual rainfall is 50 inces inches per year, you have enough rain to keep the pond full. Too bad rainfall is not consistent throughout the year. If you have dry summers, you have to create a reservoir to maintain water during drought.
Suppose your evaporation rate is 24 inches more than your rainfall in the two hottest summer months, you have to have enough watershed to make up for the missing 24 inches during those months or your pond will drop 24 inches.
2. Calculate the amount of watershed to fill your pond.
To calculate the amount of watershed to fill your pond you need to know the total amount of runoff you will be getting in the time frame you are concerned with.
1 ac. times 10 ft. times 12 inches per foot equals 120 inches of runoff needed to fill the pond.
Say in July, you want to have the pond filled and you only get 4 inches of runoff after the trees and grass soak up the water. You will need 30 acres of water shed to fill the 1 acre ten foot deep pond. 120 inches needed divided by 4 inches equals 30 acres.
The problems are numerous... for example, in northern Oklahoma we only get 2.5 inches of rain in April and then 6 inches of rain in May and 6 inches in June (interfers with the wheat harvest). Then it gets very dry again. The average for the three months is 4.8 inches per month but the &*&*(%%$ wind in March and April evaporates the heck out out the ponds during the time we don't get very much rain so we end up dropping our pond levels in March and April by 6 to 10 inches and then flooding them in May and June.
I think the best thing to do is do the calculations but also check out the other ponds in the area for how much watershed they require. The pond owners will most likely be more than happy to get long winded about their problems, which reminds me..... Good luck
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Dennis
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Posts: 89 | From: Ponca City, Oklahoma | Registered: Jan 2005 | IP: Logged | Just a FYI, there's an unbelievable amount of info on this site! You can do a search & not have to wait for many answers. I would make sure the existing dam is suitable to hold back the additional 4 ac of water. I will be in envy of your 5 ac pond!
Pond Boss Subscriber & Books Owner
If you can read this ... thank a teacher. Since it's in english ... thank our military!
Ric
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