Hydrology of Alaska— Waananen 153 



returns to the atmosphere by transpiration from plants and 

 trees, or (3) evaporates directly back into the atmosphere. Hy- 

 drology is still a relatively new science; it is based upon meteor- 

 ology, geology, hydraulics, soil physics, chemistry and ecology, 

 and on the constantly increasing store of data obtained by 

 observation and measurement. The student of Alaskan hy- 

 drology thus would be particularly interested in studies of pre- 

 cipitation, temperature, snow, glaciers, permanently frozen 

 ground, seas, rivers, underground waters, erosion and alluvia- 

 tion as well as evaporation, transpiration, and the relations of 

 runoff or streamflow to rainfall, snow melt, and glacier ice melt. 

 His interest would also extend to the effects of geology, land 

 management practices and vegetative cover on runoff and floods. 



Hydrologic studies are of particular significance in the de- 

 velopment of water resources. Through them we can determine 

 the capacity or extent of our water supplies for, though surface 

 and underground reservoirs may be drawn down or emptied 

 they will fill again if rainfall and runoff are sufficient. Adequate 

 hydrologic studies are the means for determination of the safe 

 point for development and use of our water supplies. 



Observation, measurement and appraisal programs in the 

 United States have provided a large number of hydrologic data 

 which are of tremendous help to the hydrologist studying the 

 occurrence and distribution of water supplies, frequency and 

 distribution of storms and floods, and related studies. Though 

 there are important deficiencies the hydrologist nevertheless is 

 able to make appropriate interpretations and adaptations of the 

 available information for many localities and so work out rea- 

 sonable and acceptable results. In Alaska not only is there a 

 great lack of comprehensive hydrologic data but the situation 

 is further complicated by the effects of glaciers and permafrost 

 on runoff which preclude application of the assumptions and 

 procedures utilized in the more southern latitudes. 



To review briefly the general hydrology of the Territory, the 

 climate of Alaska may first be summarized as follows: 



1. Southeastern Alaska has a mild, moist climate with re- 

 corded precipitation ranging from annual averages of about 26 



