Inquiry Regarding Flattest Slope for 44m PVC Stormwater Drainage Pipe at Fuel Dispenser

[T-jay]

Seeking professional advice regarding the design of a stormwater drainage system for a fuel dispenser facility with a small car wash at a small organization. I have planned to install a 44-meter run of Class 6 PVC pipe for this purpose and wish to minimize excavation costs. Therefore, I am inquiring about the flattest possible slope that would still ensure sufficient flow capacity for the stormwater runoff. Anticipated flow rate is 0.35l/s, pipe is of diameter 110mm and I am from a British standards using country. My primary concern is adhering to all relevant safety regulations and best practices for stormwater management.

 

[gbam]

Hi T-Jay, I would first consult your design requirements for the approving agency. Second, If no design requirements then consider minimum self scouring velocity in my area that value is 2-2.5 ft/sec which translate to 0.6 - 0.75 m/sec. One can use a nomograph or Manning's Eqn. to compute the velocity based on your pipe size, slope and material. Hope that helps.

 

[T-jay]

hi gbam, so, we dont expect any solids in the pipe, it's coming just after a junction manhole serving as a grit chamber. so i wanted to find out if there's a lower slope i can use.

 

[CarlB]

Typical recommended minimum slope for a sewer pipe of that size is 2%.
But since clean water, should be able to go flatter without it becoming a maintenance nuisance.
That flow is pretty small. It will actually flow okay at 0% (water depth will slope in pipe to generate flow).
I see 0.5% often used as a minimum, which will facilitate complete draining.

 

[KaBone]

Where I see trenching costs really jump is when you need to bring in shoring. Not sure what your starting cover is, or when you need to shore, but you if start at 0.5m deep and ended at 1m you’d have 1% slope on that length, and that should suit you just fine. Is it possible to use slotted pipe? Then you’d be fine at 0%.