Geography Reference
In-Depth Information
Precipitation inputs can vary by up to 50% from year to
year in this region and the timing of snowmelt can vary by
months. Annual and seasonal evaporation vary signifi-
cantly as a function of snowmelt timing and summer rains
since it is a strongly water-limited, as opposed to energy-
limited, system.
Trees in TCEF are mostly lodgepole pine, a highly
adaptable tree that can grow in a wide range of environ-
ments, from water-logged bogs to dry sandy soils. The
presence of sagebrush in the area, however, suggests a
semi-arid environment. Analysis of widely available topo-
graphic and surficial geology data indicate that TCEF
ranges from north-facing to south-facing; the main drain-
age runs east to west with north- and south-facing sub-
catchments; the slopes are moderate for mountainous
terrain; the hillslopes are relatively planar; and the riparian
valley bottoms are limited to 2
Figure 3.14. Tenderfoot Creek Experimental Forest catchment.
Note the gentle mountain topography and forested landscape that
includes areas of disturbance (forest harvest). Photo: F. Nippgen.
4% of the landscape. The
catchments show little evidence of glaciation and therefore
soils were likely formed on local shale, sandstone and
granite from low to high elevation, suggesting differential
permeability and bedrock weathering that could exhibit a
broad range of conditions from intact to highly weathered
and fractured bedrock. The landscape form suggests some
disequilibrium with current climate conditions.
Tenderfoot Creek is a tributary of the Smith River,
which has a downstream real-time stream gauge main-
tained and served on the Internet by the USGS. Historical
and real-time runoff conditions that include contributions
from TCEF and other nearby mountain catchments corrob-
orate inferences drawn from hard and soft
-
its peak varies by up to a month or more. This forms the
dominant runoff event of the year. The timing and intensity
of snowmelt delivery to the catchment soil strongly impact
the magnitude of dynamics of the runoff hydrograph. Add-
itionally, the temporal intersection with available energy
and vegetation productivity lead to differential evaporation
from year to year in this water-limited environment.
Following snowmelt, the seasonal recession declines rap-
idly due to the shallow soils and steep slopes that promote
rapid soil water drainage. Additionally, strong evaporation
further reduces catchment storage and thus water available
for runoff. Summer rainstorms produce only modest
increases in runoff due to unrequited catchment storage.
Decreased potential evaporation and vegetation productiv-
ity in the autumn lead to small increases in runoff into the
winter snow accumulation period.
Seasonal low flow occurs in late August and early
September, with peak snowmelt runoff occurring in April
through June. Annual runoff ratios (ratio of runoff to
precipitation) fall by between 0.2 and 0.4 in these high-
elevation snowmelt-dominated semi-arid environments.
Nationally available topography data indicate that
TCEF's catchment area is 22 km
2
, elevation ranges from
1900 to 2400 m, and it contains first- through third-order
streams that form distant headwaters of the Mississippi
River system, which drains to the Gulf of Mexico. National
vegetation products indicate that the forested catchment
is predominantly lodgepole pine (Pinus contorta). The
location of the catchment at high elevation in the northern
Rocky Mountains, USA, corroborates that it is a snowmelt-
dominated hydrological system with 40
information
described above.
The value of field visits to TCEF is largely a function of
the time of year (hydrological season) and the spatial
extent of the observations. Regardless of season, initial
observations confirm that the landscape is of moderate
relief and complexity with relatively gentle convex slopes
and moderately planar uplands (
Figure 3.14
). Open lodge-
pole pine forest and wet riparian meadows are readily
apparent, and simple depth to bedrock probing confirms
that the soils are shallow (
1 m). Little evidence of over-
land flow is present, suggesting subsurface flow dominated
hydrology. Stream morphology and streambed material
size indicate moderate peak runoff magnitudes. Taken
together, these observations suggest that the hydrological
dynamics are moderate and likely lack a flashy response to
snowmelt and precipitation. Evidence of recent forest dis-
turbance from logging suggests that the response of some
tributaries will be more rapid during spring snowmelt and
sustain higher levels of summer baseflow due to altered
snow energy balances and decreased evaporation. Summer
dry season observations indicate low runoff and therefore a
steep recession from spring snowmelt (
Figure 3.15
). Dry
uplands and wet riparian soils imply riparian and perhaps
~
90% of annual
precipitation in the form of snow and a short snow-free
growing season of 3
-
-
5 months.
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