Submarine Outfall For Storm Water Drainage Pipe

[Point Conception]

Would a water pump for pressure be required for a submarine outfall for storm water drainage ?
Diameter of pipe 2 meters
Gradient 5⁰
Horizontal distance from shore to outfall 200 meters depth about 16 meters, sine 5⁰

Or would the pressure from gravity gradient be sufficient to overcome pressure from depth : Pressure = P₀ +ρgh

 

[Nidum]

(1) If we very roughly assume that densities of sea water and of storm water with mud are about the same then you will need a pump to definitely ensure out flow under all conditions .

(2) You may not have to meet the 'all conditions' requirement in practice though :

What happens without a pump depends a lot on your local tidal rise and fall pattern .

At high tide you will get little or no outflow . As tide drops you will get increasing outflow . If tide drops far enough you may get completely adequate outflow .

You therefore need to plot tidal height against time using local information about tides and work out the proportion of time that tidal height has dropped far enough to get required outflow .

(3) Storm water surges can occur at any time so you may need to use statistical analysis to decide risk of worst surges coinciding with highest tides over say a ten year period and a further risk analysis of consequences .

Since storm water surges generated by heavy rainfall often coincide with rough sea conditions you may have to take into account swell and sea water wave surges in you analysis .

(4) In gravity systems there is always the danger of back flow at high tide and in rough conditions . Usually self opening/closing flap valves are used to prevent backflow .