74

 Equation for surface water runoff. Runoff in the

water model is governed by the Manning equation (Lindsley

et al., 1958):


 = 1.49 hw 5/3 L (sin 0)1/2 (11)



where QW is flow rate, hwis depth of the surface water, L

is the width of overland flow, and 8 is h/d, or the land

elevation gradient between upper and lower ends of the

flow-way. One quarter of the water depth at the deepest

local point (from the curve relating depth at deepest local

point to total surface water volume) was the estimate of h

used in the model. Runoff values simulated with the use of

this estimate of h were very similar to those simulated

with the use of "average depth," a value determined by

dividing total water volume by total area of surface water.

The first estimate, however, yielded a more realistic

simulation of seasonal change in surface water area. The

equation is:


 hw= c h, (12)


where h' is depth at local deepest point and c is 0.25. In

the model L was a variable that changed according to a

power of the proportion of the total wetlands area

containing surface water. The equation is: