the same in the upper and lower valleys 

 with the total for the former being much 

 less. As shown in table 1, the amount of 

 precipitation received is roughly propor- 

 tional to the altitude. 



Table 1. — Precipitation in the Wenatchee Valley. 



1/ Not yet established. 



From: U. S. Weather Bureau, 1956. Climatological 

 data, Washington Section. U. S. Department 

 of Conanerce, Weather Bureau, _59 (13) (Annual 

 Summary): 205-216. 



impervious, causing a very rapid runoff 

 should rainfall occur. Temperature is the 

 controlling factor in determining the spring 

 and early summer months' runoff, in the 

 Wenatchee River Basin. This fact is shown 

 graphically in figure 5. Temperature, in 

 conjunction with rainfall also to a large 

 extent determines the character of the vege- 

 tative cover. The amount of rainfall is 

 important from the standpoint of erosion. 



Land Use and Vegetal Cover 



Agriculture is the main land use in 

 the lower Wenatchee Valley, with fruit grow- 

 ing the most important. In Chelan County 

 two out of three farms receive the major 

 part of their income from fruits (Wenatchee 

 Chamber of Commerce i'). 



There are no large stock ranches in 

 the basin, although the watersheds of the 

 Icicle, Peshastin, Little Wenatchee, Chiwawa, 

 and White Rivers provide pasture for large 

 numbers of sheep. Most of the grazing is 

 done within the boundaries of the Wenatchee 

 National Forest and is sytematically con- 

 trolled by trained Forest Service personnel 

 to prevent overgrazing and the resultant 

 erosion and flash runoffs. 



Snowfall in the upper Wenatchee River 

 Basin is heavy during the winter months, 

 with the amounts varying greatly, depending 

 upon the elevation. 



The temperature in the basin is subject 

 to extremes, with January temperatures 

 averaging 27.5' F. , and August temperatures 

 averaging 63.1* F. at Plain, just south of 

 Lake Wenatchee (U. S. Weather Bureau, 1956). 

 There is also a considerable range in daily 

 temperatures, usually producing cool nights 

 even in the hottest summer weather. 



Summer rainfall in the lower valley is 

 not sufficient for agriculture; consequently 

 irrigation has been necessary ever since 

 the ecirliest settlement. 



The climate of a drainage basin, peir- 

 ticularly rainfall, snowfall and temperature, 

 is an ii^jortant influence on the discharge 

 of the streaims in the area. It also affects 

 water quality of the basin, but to a some- 

 what lesser extent. The temperature is 

 important during the winter months, for it 

 may freeze the grounds, mziking it somewhat 



Timber also contributes to the economy 

 of the region, with the most important 

 species being the ponderosa pine, Douglas 

 fir, white pine, and western red cedar. The 

 trees and other vegetation of the forest 

 are also important from the standpoint of 

 soil erosion and water storage, for they 

 break the fall of rain and melting snow and 

 act as a sponge for the moisture. The 

 mosses, interlacing roots of the grasses, 

 brush, etc. absorb the surface water Euid 

 gradually feed the moisture down to the 

 streams, and thereby to some extent equalize 

 the flow. It is well known that disastrous 

 surface water runoffs occur because fires, 

 overlogging, and continuous overgrazing on 

 watersheds have destroyed the ground cover 

 and the ability of the soil to absorb 

 moisture. 



1/ "All about Wenatchee. Apple capital of 

 the world" by Wenatchee Chamber of Com- 

 merce. Mimeographed, 2 p. 



