This is one project that I am currently working on and started it this last summer.
Problem: I have a large pond on my property, this pond was built for rain / storm run off. There are areas were erosion has placed large deposits of silt, resulting in maybe a foot of water before hitting mud. I needed a solution to remove the silt with as little impact as possible on the surrounding wild life. There seems to be only one available solution in my area and that is to drain the pond, bring in an excavator, and a dump truck to remove the dirt. This is extremely hard on the wild life in the pond, so I started looking into a different solution. I tried looking for someone that did silt pump / dredging without an excavator but that seems to be more of a coastal service.
Solution: Pull the dirt out of the pond without removing the water. Modern full trash pumps are able to pass large debris, they can not pump dirt but a slurry of dirt and water is consumable by these pumps. I purchase a trash pump that could pass solids no larger then 1.5 inches.
However, I still needed something to agitate the dirt and create a slurry. This was a problem that intrigue me a lot. My mind went wild with ideas of creating a mechanical agitation using the vacuum from the trash pump to power it. Sadly, time does not ever seem to be on my side, digging into creating this mechanical agitation, was more time to invest then I had on hand… So, I looked at different solutions, I finally came to using high pressure water jets to create the agitation needed for the trash pump to pickup. Shamelessly, I purchased a fire hose water pump, it has great water volume transfer and high pressure, so it meets the needs.
I still had one problem to deal with, which has been a little problematic. How to separate the water and the dirt. First trial, started with 8 x 8 x 4 drainage pen utilizing geotextile to separate the silt from the water (Kind of like a sludge tank). Initial test was funny, I had my neighbor helping me out on this and I should have recorded the tests. Have you ever watched a fire fighter fiercely holding a fire hose, trying to put out a fire? I never understood why they would have more then one guy on a hose, well just trying to hold a 3 inch water hose… was fun.. to say at least. This resulted in building a pipe that can be mounted to deliver the water to the pen. Now things were cooking, but… the pump filled up the pen faster then it drained. We were able to pull dirt for about 15 minutes before having to turn it off and allowing the pen the drain. Unfortunately, I needed longer run times as the area of the pond is a lot larger then what I could cover in 15 minutes.
The drainage pen was not going to be an solution even if I scaled up the size. I was thinking that with the drainage pen, I would be able to get decent output with the size of water displacement to fabric coverage, but gravity did not provide enough pressure. I needed to apply more pressure to the water in order to move it through the fabric.
Next Trial Run: Postponed, Schooling and family time has slowed progress on this project. However, to resolve the drainage pen run duration, I will be pumping the slurry into a geotextile bag, this will use the pumps pressure to push the water out. Possible foreseen issues with this transition is the trash pump might not have enough power to pull a slurry and then to push it out. The route to resolution is either a large pump, or just add another pump in series. Looking forward running the next trial and posting pictures.