I have a new 1.5 acre pond in Iowa and want to try and prevent silt from the neighbor farmer's 70 acres from accumulating in my pond over time. I am considering building a 10 foot long rock "Dam" out of clean 3 inch rock that would be deeper than the creek that feeds the pond. My hope is the water entering the pond will deposit any sediment prior to entering the pond.
Should I be concerned about silt with the ratio of watershed compared to my pond size? Would the plan be effective? Building an actual silt pond would be ideal, but the lay of the land would make that difficult.
Is the 70 acres plowed fields, no-tilled, or what?
I'm no farmer, but there's corn or beans every year. I'm guessing they plow it, till it, do whatever it takes to get their 200 bu of corn or 60 bu of beans each fall.
As long as the inflow is not to strong to wash out the dam it will diffently help. If the dam is big enough to slow down the inflow and spread it out it will at least slow down the sediment build up. You will need to consider that the area behind the dam will have to be cleaned out annually or when ever it fills with sediment You might want to put chain link fence or similar wire mesh over the rock dam to hold it in place.
The secret to filtration is to use various layers of gradually smaller media or a mix or mixed media of various size distribution. Small particles are trapped in te void space between the rocks. If you have too uniform of rock, then filtration holding capacity is reduced.
I have seen the road construction industry use silt dams on sloping ditches effectively using a mix of 1-3" rock sloped in the opposite slope angle as the ditch in a long angled slope, followed by gradually smaller rock dams spaced along the ditch. they usually include an overflow pipe to prevent wash out of the rock in heavy rains. These dams seem to collect sand and silt in front of the dam over time which acts as a pre-filter. This can be dug out occasionally.
Look around in your area and you can probably see ones constructed that will give you a better idea of what I am trying to describe.
All good ideas. I have PERSONALLY found that upstream brush piles grab an awful lot of junk before it gets to the real silt dam. No matter what you do, it has to be occasionally maintained.
ICHawk, you might check out this thread, i built a sediment dam, maybe give you some ideas.
http://www.pondboss.com/forums/ubbthread...b20b8b#Post5736only the middle portion of sediment dam is below water, surveyed in 1 foot below spillway elevation. it works good. welcome to pondboss and good luck.
I think I would be interested in this for my pond. Since our property was clearcut we have a bad erosion problem and we don't have enough room to put in a silt pond.
As M Spinhirne eluded to 3" rock is not going to technically "filter" silt out of runoff. You would use it to create a rock check dam. These are what you see on construction sites. When properly installed they stair step down a ditch so that the pool created by one touches the check dam upstream of it. They create slow moving pools of water that allow the silt to fall out of suspension. They don't have any "filtering" properties. They are really velocity control structures.
Dave in el dorado's design is very effective at slowing the water, and may have slight filtering properties due to his addition of smaller and smaller mediea (rocks). He's really created a slow fore-bay that he can clean out before the silt impacts his larger pond.
Erich
ICHAWK, I'm from Iowa City and am looking to build about a 1.5 acre pond this year as well. I also have one area where I'm concerned about silt and have limited room. Have you decided on what you'll do yet? I would like to see how you use the rock silt damn if possible.