Names Abraham and I'm plannin' on diggin' a pond on Johns Island, SC. I'm in the planning phase and hoping to get yalls advice.
First about the project. We plan on digging a 3/4 acre to an acre pond on our 8 acres. The future use would be for farm irrigation, aquaculture, rainwater and flooding mitigation, soil extraction, and general enjoyment. I have a John Deere 120c with a yard bucket available to me for the job. I got a quote of 38k to do this job and hoping to save some money by DIY (cause I don't have 38k). I work 24 hr shift every third day so I can dig 2 out of 3 days. I did 3 years operating work in the past and am an average to above average hoe operator. Dug a bunch of detention ponds and deep ditches, but no retention ponds.
Next about the site. The soil is pretty much straight sand. Won't hit anything else at the depth of the dig. Expecting (and hoping) to hit some shell sand at the further depths of the project The water table is extremely high--less than 2'. The property is flat as an old mans backside. There are old farm drainage ditches on the property. All the surrounding properties had them and they drained to the swamp but some have since been filled in by new land owners and now all the surface water from them and surround properties sits in the 'S" portion of the deepest ditch--where we want the pond to go. There are two ponds north of the site, one an acre and one 4 acres, which are connected and drain to the swamp/river. This will be the overflow discharge space. Both those ponds north of the site didn't require any liner and filled up/stay full from water table alone. I plan on damming up the ends of the ditches and putting a vertical spillway connected to the neighbors ponds for appropriate drainage.
Things I'm unsure about. Has anyone dug in a super high water table with soil like this? I'm going to have to use a trash pump to keep up with the water coming in. Unsure what to use 3", 4" or 6". I have looked at prices of rental and the 4" and 6" are insane (almost 4k a month). I assume I'll be at it at least 3 months weather pending so that's unaffordable. Can I get away with a couple 3"ers? Any other suggestions? Environmental control has rules of 3:1 for banks and 2:1 below water level. This is what I did all my dirt calculations at. I then spoke to an old timer and he stated that those only work for mainland, not sea islands and I'd need to do a 3:1 to 4:1 below water level to keep the banks from collapsing as it repeatedly refills as I'm digging. This would really mess up the shape of the pond. He has also told me some other farming advice that has been disproven too so I'm leery with his advice. Has anyone dug in pretty much sand? What strategies have you used? Finally, it has been suggested to take the pond as close to 20' deep to get to that shell sand. That is incredibly deep. What would be ideal for pond health in a place that has such hot summers? I'd like that good sand to build roads with but with such a small excavator would it even be possible?
I have attached two aerials, one of my future pond shape, and one of the neighbor's to give yall an idea of flow. Any help y'all can give would be most appreciated.
Well, the old timer was correct on the slope. no way to keep sand in place at a 2:1 slope. 3:1 is marginal, 4:1 better.
Here the soil was pure sand to 10', then hit a 12" layer of gravel, then a 12" layer of clay, then another 8' of pure sand, then 12" gravel then blue clay. We dug to 22' depth, and had to pump every day so we weren't digging in water. We had to move the pump down as we dug down, the pump wouldn't suck water up very efficiently. We made a shelf with the excavator, put a sheet of plywood on it and angled it slightly back towards the bank - if we didn't do this the pump would vibrate and walk towards the water.
We also had to put the pump intake thru an inner tube and float in in the pond, keeping the intake about a foot to two feet below the surface and tied with a rope from the other side of the pond to keep it from floating to shore. First time we left it on the bottom the intake hose filled with sand and we ripped it picking it up with the excavator to empty it out.....
You can use a 3" semi trash pump to pump out the water, to get the water moving faster adapt the outflow to 4" pipe as fast as possible, the roll flat hose always kinked on me, I ended up using a very short section of it then transitioned to 4" belled end drainage PVC, thinwall stuff. Drained a 1 ac, 8' max depth pond in 4-5 days with a 3" semi-trash pump. I disconnected the fuel tank on the pump, plumbed it into a gravity fed 6 gallon old metal outboard motor gas tank, sitting higher elevation wise than the pump. I drilled/soldered a fitting to the low point on the side of the tank, I found out that the pump sucks gas so slowly that running it like an outboard motor (out the top of the tank) always developed a slight air leak and lost "prime". The pump would run about 18-20 hours on that 6 gal tank.
As to what is possible with the excavator, that all depends on the operator and the time he has to do the job. We used a Komatsu PC200LC-8 Excavator and had to dig in 2 stages, handling the dirt twice. IIRC it had a 1.5 or 2 yd bucket. This pond is 1.1 or so acres when full, max depth was 22'...... We used a pan scraper in the beginning pulled by a tractor, then the excavator, loading a dump truck to move the dirt away from the pond. An ASV skid steer and a dozer was used to distribute the dirt evenly on site, but we did truck 2,700 cu. yd. to my parents place 7 miles away to build a pad for a pole barn and to level out the ground between the house and the pole barn. We used a backhoe on site to load 2 dump trucks and the ASV at their place to distribute the dirt. We moved that 2,700 yds in a weekend..... (2 LONG days)