The combination of steep slopes, heavy precipitation and limited water- 
holding capacity of watersheds in Southeast Alaska results in fairly 
unstable characteristics of flow. This is especially true in streams 
without sizeable lakes in their watersheds which afford natural regula- 
tion of streamflow. Discharge responds quickly to rainfall intensity 
and fluctuates quite rapidly between maximum and minimum values within 
relatively short periods of time. The flashy nature of storm runoff 
is shown by an analysis of a storm which deposited 1.25 inches of pre- 
cipitation within a 16-hour period on the Maybeso Creek drainage (11). 
The stream rose from a height of 0.8 feet to a height of 2.6 feet within 
a few hours after the first rain fell on the watershed. 
Heavy precipitation during October, November, and early December causes 
numerous floods which produce a highly fluctuating discharge hydrograph 
(fig. 6). Cold weather and snowfall from December until April are 
responsible for a declining flow and the shaping of a hydrograph which 
drops in a rather long and flattening curve. Snowmelt generally begins 
in May and produces a gradually rising hydrograph which shows a diurnal 
peak and trough corresponding to the crest made by melted snow. When 
the snow is gone, the flow declines and the hydrograph drops in a long, 
flat curve on which the occasional summer storm of June, July, and 
August places minor peaks. Storm frequency and intensity generally begin 
to increase in September. 
Each stream has its own flow characteristics which vary with general 
characteristics of its drainage area. Drainage characteristics include; 
shape, size, topography and gradient of watershed; presence or absence 
of lakes; vegetational density and type; depth and character of soil; 
and geological formation. Land-use practice plays a major role in the 
pattern of stream runoff. 
Characteristics of Streamflow 
Fig. 9 shows graphically the relationship between runoff and precipita- 
tion for Maybeso Creek8/ from May to October, inclusive. Table 2 
presents a summary of mean monthly discharge and stream level at the 
gage station. 
Maximum water loss takes place through evaporation and transpiration in 
Southeast Alaska from May through September. During May, especially at 
the lower elevations, rainfall is generally heavy, air temperatures 
increase, vegetation begins to grow, and evaporation and transpiration 
rates increase. Precipitation generally decreases to its lowest value 
in June, but snowmelt holds the runoff pattern up. Rainfall increases 
each month from July through October. Though precipitation is greater 
during July and August than in June, fig. 9 reveals that streamflow 
for these two months is considerably less than in June. This results 
primarily from loss of water through increased evapo-transpiration rates. 
8/ The watersheds of Maybeso Creek, Harris River and Indian Creek react 
to precipitation in an almost identical manner. Discussion is there- 
fore limited to Maybeso Creek to avoid repetition. The relationship 
between precipitation and runoff cannot be determined for Old Tom Creek 
at this time because a stage-discharge rating curve has not yet been 
deve loped. 
- 14. 
