How do you calculate total head in ground water flow?

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SUMMARY

The total head in groundwater flow is calculated using the formula H = p/(ρg) + (z - z0), where p is pressure, ρ is fluid density, g is gravitational acceleration, and z - z0 represents the elevation above a datum. Pressure head is defined as the height of fluid that would produce the same pressure due to gravity, expressed in meters of fluid. The discussion emphasizes the importance of understanding the relationship between total head, pressure head, and pore water pressure, particularly in the context of steady flow conditions and hydraulic conductivity, which is noted as 10^-4 m/s.

PREREQUISITES
  • Understanding of fluid mechanics concepts, specifically pressure and elevation.
  • Familiarity with the formula for calculating total head in groundwater flow.
  • Knowledge of hydraulic conductivity and its significance in groundwater flow.
  • Basic grasp of the relationship between pressure head and elevation in fluid systems.
NEXT STEPS
  • Research the concept of hydraulic conductivity and its role in groundwater flow analysis.
  • Study the derivation and applications of the total head formula in hydrogeology.
  • Explore the differences between pressure head and elevation head in various fluid contexts.
  • Learn about steady-state flow conditions and their implications for groundwater modeling.
USEFUL FOR

Hydrogeologists, civil engineers, environmental scientists, and students studying groundwater flow dynamics will benefit from this discussion.

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Its attached below. I don't understand how you work out the total head. Can someone explain how you do it? I'm really struggling.

I know how to do the elevation, which is just the height above/below the datum level. And I've checked the solutions as well, it seems like you're supposed to work out the total head before the pressure head.
 

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What are the "total head", "pressure head" and "pore water pressure"?
Can you explain that to you grand-mother?
 
maajdl said:
What are the "total head", "pressure head" and "pore water pressure"?
Can you explain that to you grand-mother?

'head' is simply stress (or pressure) mulitplied by depth

for total head is the total pressure as it were
 
Do you think your grand mother could understand?
Could you explain those things in a tangible way?
For example, by comparing what you measure if free water versus water in a soil?

In addition, I don't think that "pressure x depth" is related to the "head".
As I am from Belgium, I am not used with this terminology.
However, I looked at http://en.wikipedia.org/wiki/Pressure_head and it looks like that "pressure head" is the height of fluid that would produce by gravity the same pressure. In some way, it is the pressure expressed in meters of fluid.

In a "Pressure Casserol", the pressure is unrelated to the depth of water insided the "Pressure Casserol". Yet, it can be expressed in head of fluid, and the numerical value might be meters while the "Pressure Casserol" would only be 20 cm high.

See also this picture, where head is shown by the measuring tubes.

320px-Venturifixed2.PNG
 
Last edited:
The head is defined as H=\frac{p}{ρg}+(z-z_0), where z-z0 is the distance measured upward from the Ordinance Datum z0. So, at points P and C, the head H is 1 meter (there is no flow resistance between points P and C). At point A, the figure shows that the head is 6 meters above the Ordinance Datum. At point B, because the flow is steady, the head is the average of points A and C, or 3.5 meters. The upward seepage velocity is given by:

v=- K\frac{(H_A-H_C)}{(z_A-z_C)}

where K is the hydraulic conductivity (10-4 m/s).
 

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