after interception ceases) increases with mean annual rainfall. Apart from rainfall,
the magnitude of the changes in annual stream flow is also affected by forest type
and the slope aspect. Generally, the largest changes are observed in the case of
clearing conifers, owing to their dense evergreen habit and high interception,
followed by native (but not exotic) forest species, then deciduous hardwoods
which are leafless in winter or dry seasons. Rainfall and runoff data have been
analyzed for May 2008 to December 2018. Flow in the stream was minimum during
March–April and maximum during July–August. Discharge of stream from the
disturbed forest micro-watershed (Tikjuk area) remained negligible for a period of
3 months from March to May whereas discharge of the stream from the undisturbed
micro-watershed remained low but almost steady (0.0028 m
3 /s) during the same
period. Also, the discharge of streams from the semidisturbed micro-watershed
remained low (0.0015 m
3 /s) compared to the undisturbed area. Maximum daily
average discharges in the disturbed and semidisturbed catchment were recorded on
24 August 2010 (0.053 m
3 /s and 0.015 m
3 /s, respectively), whereas maximum daily
average discharge of 0.01 m
3 /s was recorded on 12 July 2010 in the undisturbed
catchment. In terms of runoff per unit area, maximum runoff was 57 mm and 13 mm
in disturbed and semidisturbed catchments, respectively, on 24 August 2010, and
9 mm in the undisturbed catchment on 12 July 2010. Runoff coefficients during the
monsoon period (June to September) were 0.55, 0.25, and 0.20 for disturbed,
semidisturbed, and undisturbed micro-watersheds, respectively.
Standard deviation of daily discharge was 25% higher in the disturbed (0.006 m
3 /
s) than the undisturbed (0.005 m
3 /s) catchment (Fig. 9.8). These results indicate that
runoff was more uniform in the undisturbed catchment. Stream flows from the
undisturbed catchment are perennial whereas streams from disturbed and
semidisturbed forests were intermittent and flowed for only 7–8 months. Stream
flow during the post-monsoon season is supported by subsurface flow in a hilly
watershed, known as the base flow of the stream. Rainfall infiltrates the ground
through intergranular pore spaces, openings, fissures, fractures, joints, bedding
planes, etc., and reappears downslope as springs and seepage. The hydrographs of
three different micro-watersheds (Fig. 9.5) revealed the quick response to rainfall by
stream discharge from the micro-watersheds that results from the small size and
steep slope of both catchments, undisturbed and disturbed. The recession parts of the
hydrographs of the two streams differ. Discharge declined slowly in the undisturbed
catchment during post-monsoon months whereas it declined more rapidly in the
disturbed catchment; the stream dries up in summer months. Streams flowing
through dense forest sustained discharge during non-monsoon months with input
from subsurface flow. Runoffs in the three different catchments were maximum
during August and minimum during May. Total rainfall received in the undisturbed,
disturbed, and semidisturbed micro-watersheds was 2950 mm, 2805 mm, and
2801 mm, respectively, generating runoff of 1470 mm, 1646 mm, and 1517 mm,
respectively, during the year. Total runoff in disturbed and semidisturbed catchments
was found to be 57% and 54%, respectively, whereas 49% was recorded from the
undisturbed catchment.
9 Assessment of Stream Flow Impact on Physicochemical Properties of Water and. . .
217
the magnitude of the changes in annual stream flow is also affected by forest type
and the slope aspect. Generally, the largest changes are observed in the case of
clearing conifers, owing to their dense evergreen habit and high interception,
followed by native (but not exotic) forest species, then deciduous hardwoods
which are leafless in winter or dry seasons. Rainfall and runoff data have been
analyzed for May 2008 to December 2018. Flow in the stream was minimum during
March–April and maximum during July–August. Discharge of stream from the
disturbed forest micro-watershed (Tikjuk area) remained negligible for a period of
3 months from March to May whereas discharge of the stream from the undisturbed
micro-watershed remained low but almost steady (0.0028 m
3 /s) during the same
period. Also, the discharge of streams from the semidisturbed micro-watershed
remained low (0.0015 m
3 /s) compared to the undisturbed area. Maximum daily
average discharges in the disturbed and semidisturbed catchment were recorded on
24 August 2010 (0.053 m
3 /s and 0.015 m
3 /s, respectively), whereas maximum daily
average discharge of 0.01 m
3 /s was recorded on 12 July 2010 in the undisturbed
catchment. In terms of runoff per unit area, maximum runoff was 57 mm and 13 mm
in disturbed and semidisturbed catchments, respectively, on 24 August 2010, and
9 mm in the undisturbed catchment on 12 July 2010. Runoff coefficients during the
monsoon period (June to September) were 0.55, 0.25, and 0.20 for disturbed,
semidisturbed, and undisturbed micro-watersheds, respectively.
Standard deviation of daily discharge was 25% higher in the disturbed (0.006 m
3 /
s) than the undisturbed (0.005 m
3 /s) catchment (Fig. 9.8). These results indicate that
runoff was more uniform in the undisturbed catchment. Stream flows from the
undisturbed catchment are perennial whereas streams from disturbed and
semidisturbed forests were intermittent and flowed for only 7–8 months. Stream
flow during the post-monsoon season is supported by subsurface flow in a hilly
watershed, known as the base flow of the stream. Rainfall infiltrates the ground
through intergranular pore spaces, openings, fissures, fractures, joints, bedding
planes, etc., and reappears downslope as springs and seepage. The hydrographs of
three different micro-watersheds (Fig. 9.5) revealed the quick response to rainfall by
stream discharge from the micro-watersheds that results from the small size and
steep slope of both catchments, undisturbed and disturbed. The recession parts of the
hydrographs of the two streams differ. Discharge declined slowly in the undisturbed
catchment during post-monsoon months whereas it declined more rapidly in the
disturbed catchment; the stream dries up in summer months. Streams flowing
through dense forest sustained discharge during non-monsoon months with input
from subsurface flow. Runoffs in the three different catchments were maximum
during August and minimum during May. Total rainfall received in the undisturbed,
disturbed, and semidisturbed micro-watersheds was 2950 mm, 2805 mm, and
2801 mm, respectively, generating runoff of 1470 mm, 1646 mm, and 1517 mm,
respectively, during the year. Total runoff in disturbed and semidisturbed catchments
was found to be 57% and 54%, respectively, whereas 49% was recorded from the
undisturbed catchment.
9 Assessment of Stream Flow Impact on Physicochemical Properties of Water and. . .
217