Local Retention Dam

Near where we live (they are common along the whole front range) is a small dam, with a retention pond behind it that's almost always empty. These are designed to hold back water in the huge thunderstorms that we get in the summer, to prevent flooding downstream.

On the upstream side where the water collects there's usually a pipe sticking out of the ground, so that the water can flow in a controlled manner. Obviously these pictures were taken when it was dry.

I found this log a little downstream of the dam.