Figure 5. --Mean weekly 

 temperatures and 

 evapo transpiration 

 for the Chicken Creek 

 Watershed. 



' ' ' III III III 



OND JFMAMJ JAA 



MONTH 



snow. Average soil profile depths to limiting horizons were assumed to be 5 feet. Aver- 

 age weekly temperatures and potential evapotranspiration fluctuated according to the 

 patterns shown in figure 5. A series of annual hydrographs for observed CCW streamflow 

 were analyzed and the model coefficients in table 1 were adjusted until a predicted 

 hydrograph was produced that agreed closely with past watershed behavior. During the 

 calibration process, the only coefficients to be adjusted were those coefficients not 

 easily estimated from a knowledge of watershed characteristics but to which the model 

 is sensitive. Table 2 presents the values for model coefficients set according to the 

 best available knowledge from the literature. The purpose of this calibration procedure 

 is not to model CCW, but to develop a reasonable point of reference against which 

 hydrologic changes attributable to vegetation changes may be estimated. 



Once an acceptable hydrograph was obtained, all coefficients except the vegetative 

 cover parameters were held constant throughout the remainder of the study. Thereafter, 

 the areal cover of vegetative types on the watershed (CVG , CVA, and CVC, table 2) was 

 sequentially altered to simulate the entire grass-forb to aspen to conifer sere. Water- 

 shed response to relatively wet and dry years was examined for five different vegetative 

 combinations by increasing or decreasing the amount of annual precipitation. Input: 

 wet year = 58.8 in (125 percent of normal), dry year = 55.3 in (75 percent of normal), 

 and drought year = 23.5 in (50 percent of normal). 



9 



