Pool deck erosion underneath.

It also looks like the grass area slopes away from the pool deck. The rock area needs to be filled and graded so water flows away from the deck.

This is a two-part fix, as you have a two-part problem. I think Jim is right, you've developed a path for the water build up that is flowing under your deck. Which means it's probably getting to the gunite and eroding dirt from there, too, which is pretty bad.

Pull the rock away from the deck a foot or two. Clean out any loose soil from under the deck. Pack concrete under the deck, as far back as you can get. That will do two things: fill in the gap some, and create a blocking wall that will help some with water getting under there, and it will help support the deck. Don't use dirt, don't use dirt with grass. The grass will eventually decompose and just leave loose soil, but either way the soil will just erode again. Concrete will be the better fix.

But that's not going to solve the problem from coming back. The erosion will just take up again a few feet away. To solve for that you need to reroute the water. So in that 2' gap you created in the rock, you dig a trench. Probably a foot deep. Looking at that last pic, it looks like the yard slopes a bit from right to left. Dig the trench that way. All the way past the pool. Hopefully you can get past that one palm tree in the way. And you extend the trench until the end is lower than where you started. Preferably somewhere that water can find a way to the street or some other drainage system. You lay in corrugated drainage pipe and that pipe will connect up two or three drain basins plotted in that wet corner. The height of the tops of the drainage basins is critical. Low enough to catch the water, but high enough that they don't fill with dirt. At the other end, if you can't connect the pipe to an existing drain system, you can use another drain basin. As long as the top of the exit drain is lower than the tops of the entry drains, the water will find its way away from that wet corner, even if water stays in the pipe. It'll do this:



Check out this page for ideas.


There are several types of drainage basins, here's one:


And several types of caps, here's one:


Back fill the trench, restore the gravel. If you don't build this drainage system, you'll never solve for the erosion.

Lowes or HD will have a selection of parts from which you can build what will work in your yard...

PS. Watering that lawn is a big part of the problem. You're probably getting runoff from the lawn year round, from rain in the winter and from irrigation during the summer. One of the drainage basins should be very close to where the lawn stops. Or do what I did, and replace the lawn with ground cover, watered with drip irrigation. Let's face it, the days of lawn in CA are over. Your deck is being ruined by the sprinklers same as mine was, too. The constant water will eventually create pits in the cream of the deck's concrete, if it's not happening already. I used Myoporum, which is great because its evergreen, never needs mowing (yay!) and grows from a central hub, which means you only have to water the center with drip, not the whole thing with sprinklers. It grows in about 9' circles. So the grass that's showing in that last pic would only need four or five Myoporum plants. Convert the sprinklers to a drip line with five emitters, bobs-yer-uncle. If you tear out the lawn, you can plot drainage basins not only in that wet corner, but all the way around the pool. It'll be a lot of work, but you'll be thankful you did it in a year or two. Just think of all the time and $ you'll save by getting rid of the grass. And no more grass clippings in the pool! It'll still look just as green, just as nice:

An alternate to the drainage basins is to just use corrugated pipe parts, like tees and elbows, that face up, then use these:


or a flat drain cover that fits to the pipe fittings. Might save you a little money.

The advantage to the basins is that they'll catch some of the dirt and crud that will eventually get into the system, which are easier to clean out than trying to flush out dirt that's caught all along the corrugated pipe.

Something like that should have been caught by a home inspector. They're supposed to check all the grades and runoffs and spot any kind of erosion. Oh well.

Like I said, there's nothing that's going to stop that excess water from doing what it's doing unless you reroute it. Here are a few things to try, if you don't think my plan would work.

- If you can't go right, go left.

- I'm not familiar with how palm tree roots work. Many trees can handle having their roots cut through, I'd look into that. Grind a path right past that tree.

- You could solve this with a sump pump. Create a small well in that corner, into which that corner drains, and pump it out of the well. The outlet pipe could then be above ground. As could the electrical conduit to power it.

- You might be able to devise a French drain system that could capture the water, depending on how much rain we're talking about.

- See if the neighbor behind will work with you. They too are enjoying the trees you'd be protecting. That constant moister back there will likely cause premature failure of the fence (posts and/or kickboards), so it is in your mutual best interest to work together on this. If the water is collecting in that corner, it might be causing problems for them, too, which you'd in essence be volunteering to solve for, if they can contribute a few feet of their dirt. Perhaps they'd let you route your drainage pipe on their side of the fence, just enough to get past the palm tree. My neighbor and I have several things we work together on like that: tree trimming, gopher control, fire suppression setups. We're not sovereign countries disputing oil drilling rights after all, we're just trying to live together and help each other out when we can.

Packing under the deck with concrete and then re-grading the soil away from the deck might help with keeping water out from under. But that water's still gotta go somewhere. In essence you'd be developing drainage that would run off into your neighbors' yard(s). Which (1) is not cool, and (2) is actually illegal in a lot of places. Code where I've lived is to provide drainage from your roof and property only to the street, not onto anyone else's property...

I hear ya. I just did something very similar, it wasn't much fun. I have a planting bed near the house that is "trapped" by a walkway. It would fill up with rain and then float the mulch over the walkway. So I dug a trench on the other side of the walkway, enough to run a water blaster under the concrete, to meet a second drainage trench I dug within the planting bed. I used corrugated pipe to re-route both the rain water that collects plus the downspout that dumps into the bed, under the walkway and then out into the garden on the other side. So I know that it works the way I described, and that it was a nasty chore. I also had a second situation elsewhere, where I used the same solution.

This should have all been done by the original contractor, as yours should have been by the original pool contractor. But unfortunately we both got stuck with the problem. It is what it is... Your issue is somewhat more serious in that it's possible the water is eroding dirt from under your pool. There's no way to know for sure, but you don't want to find out the hard way. Remember, the Grand Canyon started out as a little trickle of water. So, ya know, in about 6 million years you're going to have a real problem!

You could get one of these types of businesses to take a look- Corpus Christi, TX Foundation Repair & Concrete Leveling | Baird Foundation Repair

No affiliation & I don't really know 'jack' about concrete (jack...get it?)