Question 13.12: A flow net for part of a confined aquifer is shown in Fig. 1......
A flow net for part of a confined aquifer is shown in Fig. 13.24. At point P the permeability is estimated as 2.5 m/d and the corresponding distance (L) between successive contours is 3 km. The aquifer is approximately 45 m thick. Estimate the flow though the aquifer.
The contour interval Δh = 10 m, so h = Δh/L = 10/3000 = 0.00333.
Assuming that the ‘square’ of the flow net has a width of 3 km, then the cross-sectional area of flow A = 3000 × 45 = 135000 m². Thus the flow through one streamtube of the flow net is:
q = khA = 2.5 × 0.00333 × 135000 m²
= 1125 m³/d
Since there are four streamtubes in Fig. 13.24, the total flow through this part of the aquifer = 1125 × 4 = 4500 m³/d. Note that this flow will vary seasonally. As in the previous example, it is unlikely that wells could abstract all of this amount, nor would it be desirable to do so.