I have said this before in a few of the threads you have on the subject; if the the equipment is not in the hole...and your pump arrangement is doing it's job....then you don't really need to fill it. But in either case (and especially if you fill it) you need to put filter fabric around the walls to catch that soil. The gravel will hold up the fabric once it is filled in;....... or you will need to rig something if not filled. About acorns and stuff: if there is an old broken pipe back behind that hole, chipmunks etc. could be using it for storage or shelter and the shells are washing out into your crawlspace.
The pumps do their job, but the water is so nasty/gritty that it isn't good for the pumps. The old skim layer of concrete that they put on the floor is breaking up. The hole is just so nasty, has mold issues, etc. The pedestal pumps are very noisy. At the time when those were put in, they were used because the submersible pumps had such a high amp rating and the pedestal pumps used less power. The situation with the breaker and how much power was available was unknown at that time, so pedestals were used. Now, they make low powered submersibles that can pump way more water, but I basically don't want to spend the money on nice submersible pumps and then throw them in that gritty mess to destroy them. A lot of them say that they are for harsh sump pits, but it seems like a bad idea to me. Those pedestals are attached to a floor joist with a board. The smallest one is annoying. When both come on for flow over about 35-40 gallons per minute coming into the hole, the whole bedroom above that jars because they're attached to the floor joist, of course. The catch-22 is that there's nowhere else to affix them. The torque on that 1/2HP pedestal pump (cast iron) that is down there right now...there's no way that thing could be supported by a rock in the hole or braced by the wall on each side.
It bothers me that there isn't a properly enclosed sump setup for the pumps to be in. I could dimple board the inside of the wall and flap it over the top of the cinderblocks (which are open on top all the way around with visible water in them that can go as high as halfway up the wall or about 1.5 feet deep during hard rains). Yet the dimple board setup is still "open" to the air and allows moisture, which I'm trying to get rid of. Even using dimple board, the back of the wall between the dirt and wall...all of that is open. I can put filter fabric around the inside of the wall before I fill it with gravel. I would think that the gravel itself behind the wall, inside of the holes of the cinderblocks and inside of the wall would kind of filter out most of the dirt and only allow water to pass before reaching the sump basin. The perforated sump basin in the top of the gravel would also be wrapped with filter fabric before it is put in, just as a backup.
Given how serious this problem seems to be with the water, it seems to me that filling the hole completely kind of helps with the entire integrity of the crawlspace. It holds everything in place, keeps any more dirt from moving around and washing out from under the crawlspace foundation behind the wall and just makes everything "neater" in general. Granted, at the sacrifice of space. I'd lose the room to stand up in there, but gain a drier crawlspace and have an actual pump setup that would be better and functional. I'm fine with that. It was the size of a regular crawlspace before they dug it out that way, anyway. Gravel seems to be my only option. I have had people before tell me that I should fill it with dirt. If there's that much water in the surrounding ground and existing water flow holes are already there, I think it would seriously mess with any dirt that would be filled in and still loose on the bottom. Granted, it couldn't move it too far, but I think it would cause problems.
If there is an old pipe somehow under the ground, I'm going to have to leave it. I have pretty much given up with digging and looking for anything else outside. Since the house has a raised rock and mortar foundation that is just sitting on top of the ground and nothing else below that, the ground will always have a way to let water into the crawlspace areas that are below the outside ground level.
At this point, I don't really care whether the pumps trigger or not after it is filled in. If they do, fine. If they don't, that's fine, too. I'm not trying to keep them from triggering. It would be nice, but...at the end of the day, I'm just trying to do this to seal this disaster off and make the crawlspace more normal. I don't want a bunch of open water running across the floor into a little pool anymore. Even if the equipment was out of the hole, I'd still be concerned about letting the entire hole flood to see how deep it would get. That would tell me how far it would flood (which I'm confident would be nearly up to the top of the wall due to the hydrostatic pressure), but I'd also have an enormous haven for mold shortly after that.
I'm not knocking anyone's help. I appreciate everyone helping out so much with this. Just trying to nip it in the bud and be done with it. Even if I relocate the equipment...if I put a new tankless water heater in the crawlspace, the moisture is bad for the electronics. The moisture is bad for the furnace electronics, as well. I need more quotes on flipping the furnace (and possibly moving it completely off to the side in the crawlspace). If their quote for flipping furnace meets or exceeds that of a new and possibly smaller furnace setup, they'd rip that one out and start over. Even more so in that case, I wouldn't want it to be moist down there. So...I'm 90% sure that I'd like to fill it to within inches of the top of the wall and do the concrete to seal it off for good.