Catchment Issues

[Beachboy]

While working in my yard yesterday I noticed one of the waterlines coming off the side of my house was almost brown in color instead of it's usual white color. Didn't put to much thought into it because I was busy at the time. But this morning my wife calls me outside after a brief shower. The pipe I was staring at yesterday wonding about it's discoloration made me realize why the color change! The pipe coming down off the rain gutter along side of house is was fine until the bottom where it elbows out and runs along the ground towards catchment. At the elbow is a joint and that joint is squirting up a lot of water!? I'm wondering is that "backup",happening because catchment is full. Or is it because of debris from rooftop being trapped at elbow? More importantly, what the heck should I do?