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How to Calculate and Solve for Length of Well Screen | Water Budget

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The image above represents length of well screen.

To compute for length of well screen, three essential parameters are needed and these parameters are Maximum Expected Discharge Capacity of Well (Qo), Effective Open Area per Metre (Ao) and Entrance Velocity at the Screen (Ve).

The formula for calculating length of well screen:

L = Qo / AoVe

Where:

L = Length of Well Screen
Qo = Maximum Expected Discharge Capacity of Well
Ao = Effective Open Area per Metre
Ve = Entrance Velocity at the Screen

Let’s solve an example;
Find the length of well screen when the maximum expected discharge capacity of well is 12, the effective open area per metre is 24 and the entrance velocity at the screen is 18.

This implies that;

Qo = Maximum Expected Discharge Capacity of Well
Ao = Effective Open Area per Metre
Ve = Entrance Velocity at the Screen

L = Qo / AoVe
L = 12 / (24)(18)
L = 12 / 432
L = 0.027

Therefore, the length of well screen is 0.027.

Calculating the Maximum Expected Discharge Capacity of Well when the Length of Well Screen, the Effective Open Area per Metre and the Entrance Velocity at the Screen is Given.

Qo = L x (AoVe)

Where;

Qo = Maximum Expected Discharge Capacity of Well
L = Length of Well Screen
Ao = Effective Open Area per Metre
Ve = Entrance Velocity at the Screen

Let’s solve an example;
Find the maximum expected discharge capacity of well with a length of well screen as 21, effective open area per metre as 10 and entrance velocity at the screen as 5.

This implies that;

L = Length of Well Screen = 21
Ao = Effective Open Area per Metre = 10
Ve = Entrance Velocity at the Screen = 5

Qo = L x (AoVe)
Qo = 21 x (10 x 5)
Qo = 21 x 50
Qo = 1050

Therefore, the maximum expected discharge capacity of well is 1050.

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How to Calculate and Solve for Hydrostatic Pressure of a Dam | Water Budget

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The image above represents hydrostatic pressure of a dam.

To compute for hydrostatic pressure of a dam, two essential parameters are needed and these parameters are Specific Weight of Water (γ) and Depth of water (h).

The formula for calculating hydrostatic pressure of a dam:

Hn = γh² / 2

Where:

Hn = Hydrostatic Pressure of a Dam
γ = Specific Weight of Water
h = Depth of Water

Let’s solve an example;
Find the hydrostatic pressure of a dam when the specific weight of water is 10 and the depth of water is 5.

This implies that;

γ = Specific Weight of Water = 10
h = Depth of Water = 5

Hn = γh² / 2
Hn = (10)(5)² / 2
Hn = 10(25) / 2
Hn = 250 / 2
Hn = 125

Therefore, the hydrostatic pressure of the dam is 125.

Calculating the Specific Weight of Water when the Hydrostatic Pressure of the Dam and the Depth of Water is Given.

γ = Hn x 2 / h2

Where;

γ = Specific Weight of Water
Hn = Hydrostatic Pressure of a Dam
h = Depth of Water

Let’s solve an example;
Find the specific weight of water when the hydrostatic pressure of a dam is 30 and the depth of water is 6.

This implies that;

Hn = Hydrostatic Pressure of a Dam = 30
h = Depth of Water = 6

γ = Hn x 2 / h2
γ = 30 x 2 / 62
γ = 60 / 36
γ = 1.667

Therefore, the specific weight of water is 1.667.

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How to Calculate and Solve for Entrance Velocity | Darcy’s Law | Water Budget

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The image above represents entrance velocity.

To compute for entrance velocity, one essential parameters are needed and these parameters are Hydraulic Conductivity (ki).

The formula for calculating entrance velocity:

Ve = ki

Where:

Ve = Entrance Velocity
ki = Hydraulic Conductivity

Let’s solve an example;
Find the entrance velocity when the hydraulic conductivity is 8.\

This implies that;

ki = Hydraulic Conductivity = 8

Ve = ki
Ve = 8

Therefore, the entrance velocity is 8.

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How to Calculate and Solve for Storage Co-efficient for a Confined Aquifer | Water Budget

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The image above represents storage co-efficient for a confined aquifer.

To compute for storage co-efficient for a confined aquifer, five essential parameters are needed and these parameters are Unit Weight of Water (γw), Confined Aquifer Thickness (H), Compressibility of the Aquifer Material (α), Porosity of Aquifer Material (n) and Compressibility of Water (β).

The formula for calculating storage co-efficient for a confined aquifer:

S = γw(α + nβ)H

Where;

S = Storage Co-efficient for a Confined Aquifer
γw = Unit Weight of Water
H = Confined Aquifer Thickness
α = Compressibility of the Aquifer Material
n = Porosity of Aquifer Material
β = Compressibility of Water

Let’s solve an example;
Find the storage co-efficient for a confined aquifer when the unit weight of water is 8, confined aquifer thickness is 12, the compressibility of the aquifer material is 21, the porosity of aquifer material is 18 and the compressibiity of water is 14.

This implies that;

γw = Unit Weight of Water = 8
H = Confined Aquifer Thickness = 12
α = Compressibility of the Aquifer Material = 21
n = Porosity of Aquifer Material = 18
β = Compressibility of Water = 14

S = γw(α + nβ)H
S = 8(21 + 18(14))12
S = 8(21 + 252)12
S = 8(273)12
S = 26208

Therefore, the storage co-efficient for a confined aquifer is 26208.

Calculating the Unit Weight of Water when the Storage Co-efficient for a Confined Aquifer, the Confined Aquifer Thickness, the Compressibility of the Aquifer Material, the Porosity of Aquifer Material and the Compressibility of Water is Given.

γw = S / (a + nβ)H

Where;

γw = Unit Weight of Water
S = Storage Co-efficient for a Confined Aquifer
H = Confined Aquifer Thickness
α = Compressibility of the Aquifer Material
n = Porosity of Aquifer Material
β = Compressibility of Water

Let’s solve an example;
Find the unit weight of water when the storage co-efficient for a confined aquifer is 20, the confined aquifer thickness is 10, the compressibility of the aquifer material is 8, the porosity of aquifer material is 3 and the compressibility of water is 4.

This implies that;

S = Storage Co-efficient for a Confined Aquifer = 20
H = Confined Aquifer Thickness = 10
α = Compressibility of the Aquifer Material = 8
n = Porosity of Aquifer Material = 3
β = Compressibility of Water = 4

γw = S / (a + nβ)H
γw = 20 / (8 + (3 x 4))10
γw = 20 / (8 + 12)10
γw = 20 / (20)10
γw = 20 / 200
γw = 0.1

Therefore, the unit weight of water is 0.1.

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