varies between 10 and 19 cubic feet per second per square mile of water- 

 shed, A close relationship exists between precipitation intensity and 

 stream stage. Heavy precipitation falling during the months of October, 

 November, and early December results in many floods which produce a highly- 

 fluctuating hydrograph. Cold weather from December through April is 

 responsible for a declining flow. The hydrograph drops in a long and 

 flattening curve, 



Snowmelt begins in ^iay and produces a gradually rising stream-stage hydro- 

 graph which shows a diurnal peak and trough corresponding to the crest made 

 by melted snow which is added daily to streamflow, V/hen the snow is gone, 

 the flow declines and the hydrograph drops in a long, flat curve on which 

 the occasional summer storm places minor peaks. Storm frequency and 

 intensity generally begins to increase in September, Each stream has its 

 own individual runoff pattern which varies with the general characteristics 

 of its drainage area. 



Relationship between precipitation and runoff 



Fig, 9 shows graphically the average, maximum and minimum monthly stream 

 runoff in inches per square mile of drainage area for the period May 

 through October, Table 6 presents a summary of mean monthly runoff and 

 stream stage values. Maximum water loss takes place through evaporation 

 and transpiration in Southeast Alaska from May through September, This 

 relationship is reflected in fig, 9 which also shows monthly precipitation. 

 During May, at the lower elevations, rainfall rates are high, temperatures 

 increase, vegetation begins to grow, and evaporation and transpiration 

 rates increase. Precipitation generally decreases to its lowest value 

 beginning in June, and increases each month frohi July through October, 

 Though precipitation is greater auring July and August than in June, fig, 9 

 reveals that streamflow for these two months is considerably less than in 

 Jxme, These streamflow differences result primarily from two factors: 

 (l) snowmelt contributing to streamflow beginning in April and generally 

 reaching its peak sometime in Jione; and (2) loss of water through increased 

 evapo-transpiration rates. 



Evaporation and transpiration rates decrease considerably in October and 

 stream runoff swings sharply upward. Precipitation is heavy during this 

 month - generally the wettest month in Southeast Alaska - and quite 

 rapidly satisfies any soil moisture deficit which might have resulted from 

 evaporation and transpirat4.on. Stream discharge generally continues to 

 increase through the months of November, and a portion of December, \antil 

 cold weather and snowfall result in storage of precipitation in the form 

 of snow. Rains are quite common during this season when the watersheds 

 may be frozen and snow-covered. Associated runoff is rapid following 

 these rains. Runoff is also very high during spring when the soils are 

 saturated by snowmelt. Records for the period 1949 to 19!>3, inclusive, 

 show that snow first begins to melt in Maybeso Creek drainage sometime in 

 April, or early May, The stream hydrograph record shows that snowmelt 

 swells stream discharge \mtil sometime in July, Referring again to fig, 9, 

 it can readily be seen that the magnitude of stream runoff during the 

 months of May and June is considerably out of proportion to precipitation 

 intensities received during these months, A considerable quantity of this 

 total runoff comes from snowmelt, 



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