Multiple well systems

In a well field, when cone of depression of one well overlaps with the cone of depression of other wells, then the actual drawdown will be more than the drawdown calculated for the individual well (Fig. 20.1). In this case, the actual drawdown can be calculated using the principle of superposition of linear system.

• Fig. 21.1 Multiple well system

For a well field of n wells, the actual drawdown can be calculated as

                    (21.1)

or,          

Where S_a is the actual drawdown at a distance r at time t , S_i is the drawdown at that point caused by the discharge of the well i at time t, n is the number of wells in the well fields.

Fig. 21.2 explains the interference of cone of depression of two pumping wells. The coordinates of the two wells are (3,5) and (7,5). The individual cone of depression of the two wells are shown on Fig. 21.2 (a) and (b). The combine effect of the two wells can be obtained by adding the individual drawdown of the two wells, i.e. if drawdown of the first well is S₁ and the second well is S₂, the combine drawdown will be S = S₁ + S₂. The combine effect is shown in Fig. 21.2(c).