Water – Filling an outdoor drain with concrete to reduce standing water

One frequent cause of backups is that a root from a tree or large bush has grown into the pipe. If that's happened to you, you'll need to dig up the clogged area to sever the root and then repair the pipe, or if it's a porous drain pipe, wrap it in a landscaping fabric.

As Tester says, use a snake to see what you can find. You can also measure the distance until the snake gets stuck to get an idea of where you need to dig. Pay attention to any bends you feel the snake making on the off chance it isn't a straight run to the front.

Once you have an idea from one side, I'd fill the drain up with water on a dry day and see if you can find the outlet. Then try snaking from that outlet as well since the clog may be a long one from sediment building up over time. Again, measure the distance, and now you'll have an overall area to check.

There is a concrete that I have used, and it is regular concrete, and perhaps it can have gravel in it, but the type I have installed did not use any gravel/aggregate. Dry pack is what I have learned to know it by, and stone setters use it for building walls and laying flagstone sidewalks. I have used it for shower bases over PVC liner and coated it with Redguard for waterproofing. That is where I learned that it took on water real fast. I was to dampen the dry pack slab I set 2 days before. What water I poured on to move around just fell into the concrete, did not stand at all. I even had a decent troweled surface.

The mix is the same, just add enough water to get the concrete to form a ball when compressed in your hand, and I mean just enough, too much will screw it up.

This may be worth a shot, but be careful, this may clog too from atmospheric dirt, decayed debris settling in etc.

The pipe since it is covered with concrete can be black corrugated drain tile or perforated sch 35 set in a gravel bed. Holes in the pipe are slits in the black drain tile and gravel size will not matter. In the Sch 35 the holes are larger so you do not want to use a small gravel there, #57 crushed stone or something larger than 3/4" washed gravel depending on your area. You may want to consider using a different type of area drain. The way you describe "shower drain", sound like it get clogged pretty easily. Replacing the drain you have with something that has a much larger grate or trap included that allows debris to collect, but not clog, may do you well too.