Quote Originally Posted by mansworld View Post
That large pipe is a main contributor to soil erosion. Water is the biggest eroder. At some point in time, the large pipe will end up hanging on its own weight with no soil underneath, crack and accelerate erosion.
Bote the even larger pipe at the bottom where the water and soil are exiting must have been a riser pipe and either elbows or a T involved at one time in the past

The biggest problem in storm drains is what is required to get from ground level down to the main line the risers and down tubes have to be designed to account for natural heaving and settling