72

 Interflow equation. Both ground water flow to sea and

 interflow between soil and surface water are governed by

 Darcy's law (Lindsley et al., 1958). The equation for

 Darcy's law used as the basis of the interflow equation

 was:



 QDI = K i An (9)


where Q is flow rate, i is gradient, A is cross-sectional

area normal to water flow (seepage plane), and K is the

hydraulic conductivity (permeability) of the soil and

substrate. In the interflow equation of the model, both i

and A are functions of elevation of the water table and

change as the water table fluctuates. i is equal to h/dW ,

where d is the distance of water flow and h is the

absolute difference in elevation of groundwater and surface

water. An is equal to h x p, where p is the width of the

cross-sectional area normal to flow. For simulations under

primitive (predrained) conditions, p was the total gross

perimeter of the ponds, strands, and sloughs. For

simulations under present conditions, it was double the

length of drainage ditches plus the gross perimeter of the

natural drainage-ways.

 Equation for groundwater flow to sea. Another form of

the equation for Darcy's law was used as the basis of the

equation for groundwater flow to sea. This form was: