For sizing riprap for erosion protection above a stream bank stabilization wall. It is a 3H:1V slope and is well above the 100 year flood line, so the only erosive forces to be concerned about are storm water flows. It seems like most of the guidance for riprap sizing is for scour protection from river flow or in a channel. How would I go about sizing the riprap for this application? My thought is to use the Rational Method to get average velocity of the storm water flow over the area, or maybe try to use the guidelines for riprap subject to overtopping flow from dams for this application.
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Riprap sizing for erosion from storm flow / sheet flow 1
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BridgeSmith
Structural
For sloped bank protection at our bridges, we typically specify an erosion control geotextile under gabions (riprap filled wire baskets), but we usually only run the bank protection to 1' above the 100 year flood level.
Are looking to protect the slope from flows from the top of the bank running down the slope into the channel? Where we have concentrated flows down a slope, we usually do a ditch lined with standard class 1 riprap (4"-6" stones), also with an erosion control geotextile. Our slopes are usually 2:1 (H:V). On a 3:1 slope, unless we were collecting runoff from a sizable area and concentrating it, our normal approach would be to vegetate the slope (get some grasses growing on it) and leave it be.
Rod Smith, P.E., The artist formerly known as HotRod10
Are looking to protect the slope from flows from the top of the bank running down the slope into the channel? Where we have concentrated flows down a slope, we usually do a ditch lined with standard class 1 riprap (4"-6" stones), also with an erosion control geotextile. Our slopes are usually 2:1 (H:V). On a 3:1 slope, unless we were collecting runoff from a sizable area and concentrating it, our normal approach would be to vegetate the slope (get some grasses growing on it) and leave it be.
Rod Smith, P.E., The artist formerly known as HotRod10
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