The location of three observation wells is as shown in the following figure. If the total head in Well-1. Well-2 and Well-3 are 20.8 m, 20.4 m and 20.6 m, respectively. then the hydraulic gradient should be _______________.

Figure

A

$$\frac{1}{\left(500\sqrt{2}\right)}$$

B

$$\frac{\sqrt{2}}{500}$$

C

$$\frac{1}{\left(1000\sqrt{2}\right)}$$

D

$$\frac{\sqrt{2}}{1000}$$