I have this water outlet from down spout that opens up in my backyard. Because the water collects here and during rains it comes with good speed and causing a sinkhole here. I have filled the hole once with dirt and put a vinyl plank to minimize the impact but I know that is a temp solution. How would you fix it permanently? I have to awkwardly drive my mower around it. It is not in the middle of my yard but also not too far away for me not to notice it everyday. Thanks in advance.
Try adding a pop up drainage emitter.
These are placed with the top being level with the base of the grass. When the rain water comes to the emitter the top pops up and the water flows out similar to a bubbler sprinkler head, but on a much larger scale. This will prevent water washing away dirt or the sod. You can also mow over it.
You will need to bring in some dirt to fill in the valley and some sod, but once the grass is established there will be no more erosion.
A good fix for this may be to extend the drainage pipe further down the slope. It is not clear enough from your photo how much drop there is but the best solution would be that you can extend it far enough and maintain a downward slope to the pipe and still be able to bury it under some dirt and cover it with some sod.
Get a barrel or steel drum, drill some small holes at the bottom of the barrel. Dig a hole and place a bed of stones at the bottom. Place barrel inside hole on top of bed of stones, cut a hole to fit the end of the PVC pipe so that the pipe is inside the barrel near the top. Fill the barrel with 1/2" to 1" stones. Cover barrel with a top and regrade side of hole with top soil. Basically, we are creating a collection area for the water instead of it running free out of the pipe. The size of the barrel (collection area) depends on how much water needs to be drained off.
As @Michael has said, you could also extend the pipe and create a drainage bed as the water is moving down the pipe. (Similar to barrel concept)
Another idea is to create some obstructions at the end of the pipe to re-direct the water or slow it down, then there would be less erosion. Even a bed of stones or large rocks at the end of the pipe would help with the erosion as the water would hit the stones/rocks first and disperse before hitting the soil. Those are less work. A nice arrangement of rocks and pebbles could do the trick.
If you want to hide it, then a more elaborate drainage system would be needed.
