1. grad is a vector q = - K grad h Darcy’s law

2. q is a vector Transient mass balance equation:

3. The dot product of grad and q is div q = 0 grad  q = 0 Steady State Mass Balance Equation with W = 0   q = 0 (del notation)

4. Anisotropic medium: K at a point varies with direction K x  K y  K z or K x = K y  K z Heterogeneous medium: K varies in space

5. Homogeneous, isotropicHomogeneous, anisotropic A A B B Heterogeneous, isotropic Heterogeneous, anisotropic A A B B Characteristics of K in two dimensions Kz Kx Kx  KzKx  Kz   K x = K z = K

6. Homogeneous, isotropicHomogeneous, anisotropic A A B B Heterogeneous, isotropic Heterogeneous, anisotropic A A B B Characteristics of K in two dimensions Kz Kx Kx  KzKx  Kz   K x = K z = K

7. 2 h = 0 Laplace equation homogeneous, isotropic porous medium: K x = K y = K z = K steady state conditions: W = 0

8. Toth Problem (2D) Impermeable Rock Groundwater divide Groundwater divide 2D, steady state

9. i, j j i The 5 point star in a regular grid i+1, ji-1, j i, j-1 i, j+1 xx yy  x =  y

10. Solution by iteration Gauss-Seidel Iteration Iteration indices

11. Iteration planes initial guesses m solution m+2 m+1 m+3 Gauss-Seidel Iteration

12. j i 10 98 98 7 7 6 6 5 5 1 2 3 4 123456123456 2D example with specified head boundary conditions (Assume an initial guess of h =10 for all interior nodes)

13. j i 10 98 98 7 7 6 6 5 5 1 2 3 4 123456123456 Example with specified head boundary conditions 9.75

14. j i 10 98 98 7 7 6 6 5 5 1 2 3 4 123456123456 Example with specified head boundary conditions 8.44 9.75

15. j i 10 98 98 7 7 6 6 5 5 1 2 3 4 123456123456 Example with specified head boundary conditions 9.75 9.94 8.44

16. j i 10 98 98 7 7 6 6 5 5 1 2 3 4 123456123456 Example with specified head boundary conditions 9.94

17. i, j j i Gauss-Seidel Iteration

18. C4=(C3+C5+B4+D4)/4

19. Example of spreadsheet formula Toth Problem