The term yield of the well is used to indicate the rater of with drawl of water without causing failure of well. It is the rate at which a well can supply the water.

**YIELD OF AN OPEN WELL**

The term
yield of the well is used to indicate the rater of with drawl of water without
causing failure of well. It is the rate at which a well can supply the water.

The factors which influences the
yield of an open well are:

1. Well dimensions

2. Location of nearby wells

3. Porosity of aquifers

4. Quantity of water available in
aquifers

5. Slope of water table

6. Coefficient of permeability of soil.

7. Rate of pumping water.

**CO-EFFICIENT OF PERMEABILITY (k)**

It is
defined as the velocity of flow which will occur through the total cross sectional
area of soil (or Aquifer) under a unit hydraulic gradient.

**CO-EFFICIENT OF TRANSMISSIBILITY**

It is defined as the rate of flow of
water in m^{3}/day through a vertical strip of the aquifer of unit
width and extending the full sanitation height under unit hydraulic gradient at
a temperature of 60^{0}F.

T = BK

Where

B = Aquifer thickness

**DARCY'S LAW**

The percolation of water through
soil was fist studied by darcy(1856) who demonstrated experimentally that for
laminar. Flow conditions in a saturated soil, the rate of flow or the discharge
per unit time is proportional to the hydraulic gradient.

i.e
Q = Ki.A

V = Q/A = Ki

WHERE,

Q = Discharge

K= Darcy?s Co-efficient of
permeability i = hydraulic gradient

A = Total C/S area of soil V = Flow
velocity.

**EXPRESSION**
**FOR** **YIELD** **OF** **AN** **OPEN** **WELL** **OR** **DISCHARGE** **FROM** **AN UNCONFINED
AQUIFER**

Let,

H= depth of water before pumping h=
depth of water after pumping

i = slope of hydraulic gradient - ^{dy}/* dx*

r = radius of well

R = Radius of circle of influence K=
coefficient of permeability S = draw dawn at the well.

Consider any point „P? on the draw
down curve (cone of depression) whose co-ordinates are(x,y). THEN from DARCY?S
law

Q = KM.Ax ix

Where

Ax = Area of C/S at the saturated
part of Aquifer at „P?

Ax
= (2Pi x)y = 2 xy

Ix
= hydraulic gradient

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