53

 The coefficients, or "k" values for the equations of

 the model were computed by dividing the flow by the

 upstream stock. Thresholds were estimated based on

 literature values and measurements from the study. The

 differential equations were the basis for an analog diagram

 that served as a guide for patching the analog board. Pot

 settings were calculated from "k" values. Differential

 equations are given in the legend to Figure 10.

 Outside inputs, or forcing functions of the model,

were solar radiation and surface water area, calculated as

percent of maxima and represented by sinusoidal curves with

surface water area lagging solar radiation by approximately

3 mos. The water area curve was approximated from the

simulation for the June 1974-May 1975 year from a water

model, which will be described later in this section. It

was possible by means of the water model to determine how

drainage changed the seasonal expansion and contraction of

surface water area. This change was approximated by

adjusting the mean and the amplitude of the sinusoid.

Several other levels of drainage were also tested for their

effect on fish growth and concentration and bird biomass

and breeding.

 The model in Figure 10 (Model I) represents the

simplest possible interpretation of the system. It assumes

that seasonal expansion of fish biomass is a function only

of sunlight and water area and that initial fish stock, or

the parent population at the beginning of the wet season,