# Water flow down a 9% grade for 750' then fills tanks before traveling up 20' over 175'

I'm in hopes that someone far smarter than myself can tell me the answer to my questions.

I am setting up a water capture system for a spring. The spring drains into a pond where I am installing a 525 gallon tank that will essentially be underwater. That tank will feed a 2 inch pipe running 750 feet down a 9% grade where it will fill two consecutive 1700 gallon tanks. The 2 inch pipe will then continue it's run another 175 feet but now going up 20 feet in elevation in that 175 feet before entering the house. Once inside it will downsize to 1" pipe. The two 1700 gallon tanks will be sealed.

Will I have enough pressure from the long 750 foot drop or will I need to put in a pressure pump?

What will the pressure be once it enters the house?

Thank you to anyone who works on my problem and is able to answer my questions.

Be well, Mark

• Static pressure depends on head which is height difference. If you need to know dynamic pressure then you need to specify a flow rate. Your underwater tank will experience an uplift of 1 kg/L (10 N) if there is air in it. You may need to take that into consideration when anchoring it. Apr 25 at 18:09
• Assume the two 1700 gallons tank are full at all time, by gravity flow, you can figure out the flow rate Q1 at the inlet by the head H1, then Q1 becomes the flow rate at the downstream pipe, which has a negative flow rate due to the head H2. Now you can write the continuity equation to get the end flow rate Q2 and determine whether a pump is required to increase the flow rate for the service. Note, you need to include friction losses in the calculations.
– r13
Apr 25 at 23:17

I am not attempted to solve this problem but to express my understanding as a starter. If anything wrong please advise.

Equations:

$$v = \sqrt2g*H$$, Discharge Velocity

$$Q = V*A$$, Flow Rate

$$H_f = f*\frac{L}D*\frac{v^2}2g$$, Friction Head Loss, in which

$$f - f(Re, \frac{\epsilon}D)$$, The Moody, Darcy, or Stanton friction factor, and

$$\epsilon -$$ Roughness Factor of the Pipe

Assume the diagram below is correct, then you can calculate the discharge velocity and flow rate at the points of interest as shown. Then from the output flow rare $$Q_4$$ you can decide whether a pump is required to increase the flow. Note that from point 3 to point 4, the flow is in reversed direction.