As I've posted before, I'm digging a small pond on my 1 acre property (see attached picture). It's probably 3000-4000 sqft surface area. I'm on the banks of the Arkansas River so I only have sandy loam to work with in this deep and steep holler. I'm skipping to Plan C to fully line it with a heavy duty vinyl liner. I'm planning to buy them in manageable pieces and weld/cement them together in place, customizing each section as needed for nooks and crannies and anchoring the edges in a trench 1' above water line.
I've spoken to TJ on the phone a couple of times and he provided valuable help and good advice on this project, as I'm trying to achieve the most bang for my buck. I have three questions that TJ suggested I pose to the forum:
1. If I have a bed of solid sand with no rocks or sharp objects, do I need an underlayment for 20 or 35 mil material? 2. My contractor quoted me Qty 2 20" culvert pipes as overflow through the top of the dam. TJ thought that was wayyyy overkill and I agree after thinking about it. Anyone have a better gauge at rightsizing the outflow pipe? I have about an acre that drains this one spot, including my roof downspouts and several catch basins that move a ton of water. I'm obviously on a steep slope so erosion has been a problem. 3. Anyone have experience is fabricating a pipe sleeve/bib/collar (using same material as liner) to fit around the outflow culverts and then weld/seal to the main liner?
The only one I can offer some advice on is #1 and #2.
1) All it takes is one puncture to have the liner fail. They are talking about that mil underlayment (which has been run through a screen to ensure the size of the material) to ensure that there are no pokey things in it that could put a hole in the liner. Have you ever filled a swimming pool and had to adjust the liner so it would be smooth? There is a LOT of PSI pushing down on the liner, and all it takes is one forgotten rock or stick to create a hole in the liner over time.
2) Talk to your counties NRCS office and ask them about the culvert pipe size. You want enough to be able to discharge as much rain as will fall in a 100 or 500 year flood. Are you positive that you only have one acre of land that drains to this one spot? Some areas of OK either today or yesterday had 5" of rain. That's only just shy of 136,000 gallons of water. BUT if you actually have 10 acres that drain through that one spot, that is 1,360,000 gallons. You want to dump the water out just about as fast as it runs in. If the dam gets topped by the rain event, then the dam could potentially wash out.
On the drainage it could be as much as 1.5 acres. Most of my 1 acre, and some of each of my adjoining neighbors' properties drain to my lot due to how our area is graded. I have this steep and deep canyon and most of my property sits lower than theirs, so I get a lot of their water too. I'm managing it with catch basins, buried downspouts, trench drains and corrugated 4" pipe, all of it feeds to this pond area.
I'll work with my contractor to make sure I have enough outflow capacity.
FishinRod that's a great idea. However this area is so steep I really have nowhere to realistically divert it. It's either going to flow naturally off my neighbors' and my property from the point of origin to this spot, or I can move the problem further down the slope in this area with all my basins and plumbing. When I moved in here I chose to just kick the can down the road so-to-speak and move the erosion problem to where I now want to start capturing it for a pond. I'll rightsize the outflow and put rip rap with underlayment on the back side of the dam to prevent erosion there.
Yep, I was just trying to add some "out of the box" additional options for you.
If you cannot divert water to some adjacent areas with gentle, grassy slopes, then I agree that your pond plan is the best solution.
Erosion by water is strongly controlled by the "base level" of that moving water. Your new pond will greatly elevate the local base level of the water running down your draw above the pond. You will be reducing erosion in the watershed above the pond location, merely by constructing the pond.
If you have some other erosion problems in that draw further down the slope, you could even build a second small pond (while you have construction equipment on site).
That pond wouldn't even need a liner. All you have to do is create a "still" pool to reduce erosion. If the water leaks outs over 1-2 weeks, there would still be plenty of critters that would benefit.
On the drainage it could be as much as 1.5 acres. Most of my 1 acre, and some of each of my adjoining neighbors' properties drain to my lot due to how our area is graded. I have this steep and deep canyon and most of my property sits lower than theirs, so I get a lot of their water too. I'm managing it with catch basins, buried downspouts, trench drains and corrugated 4" pipe, all of it feeds to this pond area.
I'll work with my contractor to make sure I have enough outflow capacity.
Thank you!
It's better to have outflow pipes that are too big than too small. You have to plan for the worst, and even if that only happens once the whole time you own the property, it's money well spent.
We are seeing "100 year rain events" happening more frequently than every 100 years now, (might be twice in 5 years) and we are seeing the normal rain events disappearing.
Take my property for instance. When I bought the place 20 years ago the woods was classified as a "wooded wetland". Every Spring there would be water standing in the woods, up to 18" deep, from spring melt until mid June. I couldn't access the back of the property without driving through water. After the first 3 years, it's only happened once since then.
Hurricane Ike rolled through here not a month after I finished the renovation on the pond. I had to build up the East side of the pond to stop water from running into the pond from the neighbors, which it did over a 120' long stretch. It still runs into the pond from the East, but now it only runs into the pond through the culvert that we installed. Hurricane Ike washed 24" of sand into the pond too, which was never removed.
