Storm Drainage on steep slope in northern California 1

[beautifulhills]

Junior engineering designer here working on a storm drains for residential project in Bay Area California, with very few other similar recent projects generally undertaken by any entity on steep slopes. For storm drainage, I m specifying Concrete V drain, with catch basins every so often down the slope, picking up the V drain water and transporting it in HDPE. HDPE runs close by, buried. I have one or two appropriately sized energy dissipators. Slope is 40 pc to 50 pc, presently storm water is limited of course but as we know it is to be planned for. Anything I m missing?


Not a regulator, despite what my unchangeable profile states

Designer, Specifier (I don't regulate anything despite what my profile says)

 

[1503-44]

Ditch breakers? Anchor the pipe and prevent water running inside the ditch from washing trench backfill out of the trench.

https://duckduckgo.com/?q=ditch+breakers&t=brave&iax=images&ia=images

Try to grade the surface so that water is not going to run parallel to the pipe over the trench surface.

Discussed a bit here.

https://www.eng-tips.com/viewthread.cfm?qid=487110

There may be other erosion control mitigation measures you might wish to investigate.

 

[cvg]

debris, slough walls

https://www.ladbs.org/docs/default-...all-(4-foot-high-or-less)-ib-p-bc2014-002.pdf

 

[zahid106]

If you are using the Mannings equation to design your pipes and ditches, be aware, at 40 or 50 PC slopes, you are outside the intended range for this equation. I would suggest oversizing the channel or pipes, maybe design for 50 to 60% of full capacity.

 

[eea]

Are you trying to control velocities in the pipe? I have stair stepped the storm sewer, using drop manholes to avoid a steep, straight-line grade. I would offer that the flow impacting the opposite side of the manhole and free fall dropping to the outflow invert is also a decent energy dissipater.

 

[beautifulhills]

275 & 281 COLEMAN DR -44-45 SETS for stamping.pdf

Thank you much for your input. We ended up doing the attached - for Planning Permit purposes.
A combination of concrete v ditch, HDPE picking up through inlets from the v ditch, and an energy dissipater before crossing the new road. The project is on private land, so that does save some of the more hard core arrangements.

Designer, Specifier (I don't regulate anything despite what my profile says)

275 & 281 COLEMAN DR -46-47 SETS for stamping.pdf
275 & 281 COLEMAN DR -44-45 SETS for stamping.pdf