Open drain with rock weirs - Stormwater Attenuation guidance needed.

[Patrick Pierard]

Hello, I am tasked with designing an open drain with rock weir stormwater attenuation design for a development. There is 1ha of additional metalled surface area being added. I have to provide stormwater attenuation for a 1 in 10 year storm event. This is a requirement from the authority to allow us to proceed with the development.

The main thing i would like help with is whether there are any relatively simple calculations (where assumptions can be made) that can demonstrate how much flow will go through the rock wall given a specified headwater depth. I have attached some links to calculations, reports and plans which can hopefully be viewed online. I did briefly do some culvert calculations but the client does not want to include any culverts. If you are kind enough to read the report I have highlighted probably the more important part and would love your feedback. I have also hidden any names and places hopefully for confidentiality.

https://4html.net/PDFViewer/#/source/Rock Weir Design.pdf

https://4html.net/PDFViewer/#/source/Stormwater Report_3.pdf

https://4html.net/PDFViewer/#/source/SW Calcs.pdf

Thank you to anyone who responds to this.

 

[GeoEnvGuy]

Based on your description you are looking to make a storm water retention pond or a buried stormwater tank or a propriety stormwater system using plastic and gravel. Local jurisdictions may have a stormwater manual to follow, if you are not familiar with it contact the cities drainage engineer.

For the ditches I know there is an american equivalent to rock flow check dams which are specified in ontario opss specifications and drawings. The american version provides spacing between check dams in a ditch based on the slope of the ditch. The check dams also get filled with sediment and block up during storms so the assumption is they overtop from one pool to the next.

You can also lookup the permeability of a densely graded aggregate. You may also want to lookup bridge and channel scour manuals.