Soils 456 Notes Chapter 2

1. Static water pressure is based on height of water level above outlet.
Pressure= force/ area= F/A

P = lb/inch^2
F= lb
A= square inches.

Force= weight of water

Pressure= W/A = 62.4 lb/ft^3*1ft^2/144 in.^2= 0.433 lb/in.^2 for1 ft of water height

Pressure for two ft of water height

P=W/ A= 62.4lb/ft^3*2 ft* 1ft*/144 inch^3=0.866 psi for2 ft of water height

If the area increases but the height remains the same then the pressure which is force / unit area remains the same.
1 lb/in.^2/0.433 lb/in^2/ ft of water = 2.31 ft of water or each ft of water creates 2.31 psi

E= p(2.31 ft/ 1 psi)

Example Water tower 200 ft high = 86.6 psi of pressure

Dynamic water pressure or working pressure differs from static pressure because it varies throughout the system due to friction loss, as well as elevation gains or losses. The dynamic water pressure is the pressure at any point in the system with a given quantity of water flowing pass that point.

Velocity is related to flow and the pipe cross-sectional area

Where q= flow ft^2/ sec
v= velocity ft/ sec
a= area ft^2

q= 2.45 v d^2
where q= gal/min
v= ft/s
d= inside diameter of the pipe.

Friction Loss equation in book.

hf= 0.2083 [100/c]^1.852 q^1.852/d^4.866


hf= frictions loss ft 100/ft
q= flow gal/min
C= Hazen-Williams coefficient
d= pipe inside diameter (in.)

Hazen-Williams equation  calculator      Table of Hazen-Williams coefficients

2. Friction loss uses the Hazen-Williams equation and friction loss of fittings can be expressed in equivalent pipe length.

Calculate the friction loss with outlets by calculating the friction loss in a pipe and then adjusting the friction loss using a correction factor.

3. Open channel flow can have water measuring devices installed in the channel. The simplest device to construct is a circular flume PDF file for figure 1.

4. Bernnouli Equation. V^2/2g +P/w + h= Constant  Where v= velocity( ft/sec)  P= pressure (lb/inch^2)  h= elevation (ft)  w= density or weight of water (62.4 lb/ft^3) g= gravitational acceleration (32 ft/sec^2)

5. Pitot tube used to measure flow of water in a pipe.

6. Orifice equation Q= 0.61 A (2gh)^1/2    see calculator