You can control storm water runoff with gravel bags to minimize sediment and other pollutants from entering the storm drain system. The idea is slow rain related run-off long enough that the sediments settle or dropout behind the bags. The photo above shows a check dam. Berms are gravel bags stacked along contour lines, which reduce erosion by slowing runoff. Controlling runoff is required on large scale jobs like subdivisions or industrial sites. It might be worth doing this on single residence DIY projects.
Photo credit: Storm Water Thoughts
Here is an image of a swirling eddy behind a natural wing dam. Note the direction of the swirl, and compare that with the direction of the light reflected off of the swirl shown above.
http://www.mr-ideahamster.com/howto/kayak/images/seddy.jpg
Please note that the water flow in the photograph is moving from right to left. The wing on the check dam points downstream, creating an eddy that sucks the sediment in behind it where it is deposited in the slower current. I have seen large check dams installed on the Colorado river just for this same purpose. BTW, the check dams make great fishing spots, too, if they are installed on a stream or river.
I’m pretty sure the water is flowing from left to right. Note how most of the water is behind the check dam (left) and almost none below (right). Sediment is building up and overflowing around the right side.