276


Validation

 A crude estimate of actual runoff from the study area

 during some of the latter. years of the simulation was

 obtained by totalling runoff measurements from all

 monitored flow-ways from October 1969 through September

 1974 (U. S. Department of Interior. Geological Survey,

 1972-75). Appendix Table A-10 lists monitored sites.

 Monitored flows do not represent total surface water runoff

 because many channels are not monitored, and water also may

 leave'- the area as sheet flow, particularly in wet years.

 In addition, measurement techniques may cause an

 underestimation of runoff in wet years and an

 overestimation in dry years.

 Figure 65 allows comparison of simulated runoff from

the model with total monitored runoff from the study

region. Simulated runoff is higher in wet years and lower

in dry years than monitored runoff. The timing of peaks

and ebbs is approximately the same.

 Figure 66 allows comparison of monitored runoff with

the rainfall input to the water model, based on rainfall at

Ft. Myers for June 1970 through September 1974 (U. S.

Department of Commerce. National Oceanic and Atmospheric

Administration, 1970-74). In the figure monitored runoff

is very low in 1972, despite high rainfall. Runoff is

higher in the dry years of 1971 and 1973 than in 1972.

Figure 67 compares simulated monthly runoff from the model