265

seasonal range in variation are greater under primitive

than under present conditions.

 Figures 62 and 63 give yearly totals for the forcing

functions and simulation results of the model for the 25-yr

period under primitive and present conditions. Each "year"

of the model is the 12-mo period from June through May,

starting with June 1950 and running through May 1975.

Figure 62a shows annual rainfall in the study region, based

on the rainfall record at Ft. Myers from June 1950 through

May 1975. Simulated annual runoff is given in Figure 62b

and simulated annual ET is given in Figure 62c. Variation

between extrenes, i. e. wet year and dry year values for

the parameters, is greater under postdrainage than under

predrainage conditions.

 In order to quantify the regional-scale hydroperiod so

that it could be compared from one year to the next and

under two different conditions, the sum was taken of

surface water area each month for one years period. The

equation was:


A = z A At
c i mi


(28)


where A is simulated water surface area each month; t is
 m
1 mo (time step); and A is cumulative acres of water

coverage in acre-mo for a 12-mo period. This quantity for

primitive and present conditions is graphed for the 25-yr

period of the simulations in Figure 63.