Basin results from the melting of high 

 altitude snow during the spring and early 

 summer. The air temperature, therefore, is 

 the controlling factor in establishing the 

 flow in the streams of the Wenatchee River 

 Basin. This fact is shown graphically on 

 figure 5 where it czin be seen that the run- 

 off was dependent upon the air temperature 

 rather than precipitation. This has an 

 important effect on the water quality, for 

 a stream fed mainly by freshly melting snow 

 is low in all types of impurities. 



Geology 



The geology of the Wenatchee River 

 Basin furnishes examples of metamorphic, 

 igneous, and sedimentary rocks (Russell, 

 1900). 



The northern portion of the Cascade 

 mountains is composed of granites and grano- 

 diorites in large areas flanked by metamor- 

 phic rocks such as schists, gneisses, and 

 serpentines (Van Winkle, 1914). On the 

 north and east the Entiat mountains are 

 largely schistose, with mica and hornblende 

 schists predominating (Russell, 1900). On 

 the south in the Wenatchee mountains the 

 rocks are granitic, with large amounts of 

 serpentine representing peridotite (Van 

 Winkle, 1914). In the upper valley sand- 

 stone is abundant except for the portion of 

 the valley cut through granite in Turawater 

 Canyon. In the lower portion, the valley 

 of the Wenatchee is deeply gravel-filled 

 and terraced. 



The geology of a drainage basin is 

 perhaps one of the most important factors 

 in the establishment of the water quality. 

 Water, in contact with the rocks either at 

 the surface or sub-surface, slowly dissolves 

 some of the minerals and puts them in solu- 

 tion. This decomposition of the soluble 

 constituents of the rocks also loosens other 

 particles and mjjtes them available for 

 transport by moving water. The greater part 

 of the minerals in solution in a stream are 

 contributed by ground water since it is in 

 contact with the rocks for a much greater 

 period of time. 



It is significant that the most common 

 rocks in the Wenatchee basin are granite. 

 Quartz is abund ant in granite and is the 

 chief constituent of most sands and sand- 

 stone. Chemically and physically, quartz 



is the most resistant to decomposition of 

 all rock-forming miner culs (Hinds, 1943). 



Soil Mantle 



Soil is formed in many ways and is an 

 extremely complex mixture of mineral debris 

 from rock degradation and decomposition, 

 organic matter, remnants of former plauit 

 and EUiimal tissues, living organisms, soil 

 water, gases, etc. The chief ingredients 

 of most soils are the mineral particles 

 originally derived from rock. Practically 

 all the common rock-forming minerals of a 

 region are found in the soil of the area. 

 The large variety of rocks in the Wenatchee 

 draincige basin causes the valley soils to 

 be formed of a great variety of mineral 

 fragments. These soils derived mainly from 

 granite schist and gneiss, though usually 

 poor in lime, are rich and fertile (Van 

 Winkle, 1914). 



Soil of a drainage basin affects the 

 runoff rate and water quality to a large 

 degree. If a soil is porous, the amount 

 and rate of surface runoff is lessened. If 

 the soil is compact, there is little absorp- 

 tion, and runoff and soil erosion are 

 greater. The solubility of the constituents 

 of the soil are also of importance from the 

 standpoint of water quality. 



Climate 



The State of Washington is divided by 

 the Cascade mountains into two very differ- 

 ent climatic regions. On the west side the 

 prevailing westerly winds from the Pacific 

 Ocean are warm and humid, and supply suffi- 

 cient rainfall to support a dense growth of 

 natural vegetation. Precipitation increases 

 as the westerly winds ascend the Cascade 

 mountains, with some stations averaging 

 over 100 inches of rainfall per year (D. S. 

 Weather Bureau, 1956). The amount of pre- 

 cipitation is abruptly reduced once the 

 divide is crossed. The climate east of the 

 Cascades is characterized by slight precipi- 

 tation cuid much greater extremes in tempera- 

 ture. The modifying effect of the Pacific 

 Ocean is still effective in keeping the 

 climate less severe than similar points 

 inland at compaxcible latitudes. 



The variation in precipitation, a 

 winter mziximum and summer minimum, is about 



