Ground-water Depletion 
The principal source of water for streamflow during rainless periods 
is the ground-water flow resulting from infiltration of precipitation 
during storms. Minimum streamflow is a sensitive indicator of change 
in stream regimen and watershed characteristics resulting from the re- 
moval of trees from the watershed. Ground-water depletion curvesll/ 
were prepared for each of the study streams using a somewhat modified 
procedure from the methodl2/ used by Johnstone and Cross (12). 
Depletion curves for Maybeso Creek, Harris River, and Indian Creek are 
shown in fig. 1l. Base flow for Maybeso Creek decreases from approxi- 
mately 35 .c.£.s. after 10) rainless days to Ws eres. ec Ee daysi3/. 
Harris River from 64 c.f.s. after 10 days to approximately 26 c.f.s. in 
30 days; Indian Creek from approximately 5 c.f.s. after 10 days to 
3 c.f.s. after 30 days. Base flow has not yet been determined for Old 
Tom Creek. Base flow values for the three study streams vary according 
to size of watershedl4/ and indicate that base flow characteristics are, 
among other factors, a function of watershed size. 
The effect of deforestation on the minimum flow of streams is variable. 
Deforestation may decrease interception and transpiration more than 
evaporation is increased, thus augmenting streamflow whether at flood 
or at minimum stages. In other cases, denudation has been found to re- 
duce minimum flow because of an increase in surface runoff with a 
resultant reduction of infiltration. Date of summer minimum flow may 
be later as a result of deforestation (13). 
Continuing observations will show what effect, if any, clearcutting 
has on magnitude and date of occurrence of minimum flow. 
1l/ Presumably representing the hydrograph that would result from 
ground-water flow alone over a protracted dry period. 
12/ The lowest arc (ground-water flow) of the daily flow hydrograph 
was traced backward in time from the lowest discharge to a period of 
surface-water runoff. The tracing paper was then moved horizontally 
until another arc of the hydrograph coincided in its lowest part with 
the arc already traced. The second arc was plotted on top of the first. 
This process was continued until all the available arcs were plotted 
on top of one another. The upswinging portions of the individual arcs 
are disregarded as they are presumably affected by surface runoff or 
channel storage or both. The remaining continuous arc is a "mean" 
depletion curve. Stream stage values were than converted to discharge 
values and plotted on semi-log paper. 
13/ Johnstone and Cross (12) caution that the best that can be said 
in any given case is that the base flow is probably not less than about 
» nor more than about A 
14/ Size of watershed in square miles: Harris River - 31.8; Maybeso 
Creek - 15.2; Indian Creek - 8.6. 
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