16 BULLETIN 950, U. S. DEPARTMENT OF AGRICULTURE. 



WATER POWER. 



The following extracts from an article by J. G. Hoyt, Geological 

 Survey Bulletin 442, indicate the general water-power situation in 

 southeastern Alaska : 



Owing to topography, the streams, with the exception of a few of the larger 

 rivers which come through the mountains from the interior, have small and 

 precipitous drainage areas. Their courses are short and they have a large 

 fall : in fact many of the streams are made up of a series of cataracts. 



In the northern part of the area most of the streams head in the glaciers 

 which cover a large portion of the country. In the lower southern part of the 

 area many of the streams head in small lakes which occur a short distance 

 back from the shore line in the hanging valleys that are characteristic of this 

 area. Most of the streams flowing from these lakes are precipitous and many 

 of them empty into the ocean with a cataract at the shore line. These lakes 

 afford excellent opportunities for storage, as the topography near them is such 

 that a dam can usually be constructed for raising their water level. The most 

 successful powers already developed depend on such storage during a large 

 part of the year, and further development in this region will depend on the 

 availability of such lakes. 



The run-off from the streams in this area results principally from direct rain- 

 fall, melting snow, and melting glaciers. In view of the large rainfall, the ex- 

 cellent forest cover, and the glacial areas, the general deduction would be that 

 this section should have many large streams with an abundant and well-sus- 

 tained run-off. This, however, is not the case, as the catchment areas are small 

 and, although the total yield per square mile is considerable, the streams are 

 not large and they fluctuate very rapidly. 



The streams which .head in lakes have a much better sustained flow and are 

 practically the only ones in the area which are of much value for power, as 

 any large development must depend on storage, both for the winter months and 

 during dry parts of the summer. 



The principal defect in the water supply, so far as the production of power is 

 concerned, is the extremely low flow during the winter months. On the smaller 

 streams, which have no storage, there is practically no flow in winter, and even 

 on the streams having lake storage the flow is extremely low, as shown in the 

 records for Turner River, which empties into Taku Inlet near Juneau. This 

 stream has a drainage area of 60 square miles and heads in Turner Lake, which 

 offers excellent facilities for storage. A portion of the area is also covered with 

 glaciers. The scantiness of the winter flow is due largely to the meager amount 

 of storage capacity in the ground, which freezes to bed rock, thus holding back 

 the water. 



The winter flow is particularly slight when freezing weather comes 

 before the heav}' snowfall and in those inland locations at the head 

 of inlets or passages where the ameliorating influence of the Japan 

 Current is less effective. It has been estimated that on several sites, 

 no storage being provided, the ratio of low winter flow (which 

 involves two, three, or four months) to usual summer flow is only 

 about 2 to 5 per cent. On the other hand, it should be noted that 

 the high-flow period in Alaska coincides with the usual low-flow 

 period in other locations which causes so many of the pulp mills 

 to shut down in the late summer. 



