MBB138
Civil/Environmental
- Nov 9, 2015
- 6
Hello everyone,
I'm looking for some guidance on the design of spillways, with riprap at the toe of an embankment. This is specifically pertaining to the riprap.
Background
The project has 2 ponds (pond 1 for irrigation, pond 2 for mitigation), which are connected by a spillway. Since the only means of conveyance to the 2nd basin is this spillway, this spillway both acts as the primary and auxiliary spillway. The first basin is used to collect storm water, which is redistributed through out the project for the purpose of irrigation. This means that my controlling flow rate is the unmitigated 100-year storm, since I'm assuming no storage is provided by this basin. Basin 1 is existing and Basin 2 is proposed. The embankment slope is 3:1, with a vertical difference between the upstream spillway crest basin 2 is 14 ft. The incoming flow is 920 cfs.
What I've been looking for is guidance/equations on designing the riprap at the toe of the spillway. I understand that riprap/rock sizing is very specific to the application, but I can't find literature that specifically deals with this situation. The closest equation/literature relevant to this situation was the "Rock Chutes" by published by ASAE "Design of Rock chutes", however, that appears to be the design procedure for a situation where the spillway/chute is not concrete lined, rather, rock lined all the way to the toe. I also figured I could use shields diagram by determining the shear stress at the toe of the spillway, perform iteration on different rock sizes until the critical shear stress of the rock is greater than the shear stress at the toe from the incoming storm water. I considered using Hec-14 Riprap apron for culverts (equation 10.4), but I feel that also is not correct.
There is so much literature on the subject of rock sizing for erosion and I feel like I may be overthinking this.
I'm looking for some guidance on the design of spillways, with riprap at the toe of an embankment. This is specifically pertaining to the riprap.
Background
The project has 2 ponds (pond 1 for irrigation, pond 2 for mitigation), which are connected by a spillway. Since the only means of conveyance to the 2nd basin is this spillway, this spillway both acts as the primary and auxiliary spillway. The first basin is used to collect storm water, which is redistributed through out the project for the purpose of irrigation. This means that my controlling flow rate is the unmitigated 100-year storm, since I'm assuming no storage is provided by this basin. Basin 1 is existing and Basin 2 is proposed. The embankment slope is 3:1, with a vertical difference between the upstream spillway crest basin 2 is 14 ft. The incoming flow is 920 cfs.
What I've been looking for is guidance/equations on designing the riprap at the toe of the spillway. I understand that riprap/rock sizing is very specific to the application, but I can't find literature that specifically deals with this situation. The closest equation/literature relevant to this situation was the "Rock Chutes" by published by ASAE "Design of Rock chutes", however, that appears to be the design procedure for a situation where the spillway/chute is not concrete lined, rather, rock lined all the way to the toe. I also figured I could use shields diagram by determining the shear stress at the toe of the spillway, perform iteration on different rock sizes until the critical shear stress of the rock is greater than the shear stress at the toe from the incoming storm water. I considered using Hec-14 Riprap apron for culverts (equation 10.4), but I feel that also is not correct.
There is so much literature on the subject of rock sizing for erosion and I feel like I may be overthinking this.
