|Abstract or Summary
- During the summer of 1980 an infiltration/sedimentation study was
conducted on the Oregon Range and Related Resource Validation Project
Work Area in the Blue Mountains of east-central Oregon. A modified
Rocky Mountain infiltrometer was used to simulate a 28 minute high
intensity rainfall event to determine mean infiltration rates and
average potential sediment losses on 19 improved resource units consisting
of various combinations of productivity and condition classes.
Such improvements included seedings, thinnings, herbicide spraying,
mechanical brush control and certain combinations of 2 or more practices.
Natural or unimproved resource units of similar soil type and
ecological expression were sampled and used as controls.
On 4 of 9 seeded mountain grassland ecosystems sampled, the
control had significantly higher infiltration rates for the entire
run. On 2 others, no significant difference in infiltration rates
occurred during the 3 -8 time interval. Thereafter, the control had
significantly higher infiltration rates. In another instance, the
control had significantly higher infiltration rates only for the 3-8
minute time interval after which no significant differences were
found. In another case, significantly higher infiltration rates
occurred only during the 3-8 and 23-28 minute time intervals for the
treated and control areas, respectively. For the remaining site there
were no significant differences in infiltration rates between the
treated and control areas throughout the storm. The control had a
significantly higher average potential sediment loss in all cases
except 4. In 3 of these no significant differences in sediment loss
was found. On the remaining site the treated area exhibited the
significantly higher sediment loss.
On the sagebrush ecosystem sampled, where sagebrush was mechanically
removed and the area seeded, the treated area had significantly
lower infiltration rates than the control and a lower average potential
sediment loss. The control for a thinned pine-mixed fir-sedge
ecosystem in fair condition not only had a significantly higher
average potential sediment loss but also had a significantly higher
infiltration rate than the treated area for the 3-8 minute time interval
after which no significant differences in infiltration rates
On a thinned and seeded pine mixed fir-sedge ecosystem in good
condition, on which seeding establishment appeared unsuccessful,
infiltration rates were significantly higher for the treated area for
the entire storm. However, no significant differences in average
potential sediment loss were found.
A thinned larch ecosystem was divided into a pinegrass, a seeded
and a bareground area and each area was sampled separately. In all 3
cases, the control had significantly higher infiltration rates throughout the storm as well as a significantly lower average potential
On 1 of the 2 pine-sedge ecosystems the treated area had significantly
higher infiltration rates for the entire storm as well as a
significantly lower average potential sediment loss. On the other
pine-sedge ecosystem, divided into non-vegetated and vegetated areas,
the control of non-vegetated portion exhibited significantly higher
infiltration rates and a lower average potential sediment loss than
the treated area, whereas, no significant difference in infiltration
rates or sediment loss was found between the control and treated area
on the vegetated portion.
On a thinned ponderosa pine-bunchgrass ecosystem although
infiltration rates were significantly higher for the treated area
during the entire run, no significant difference in average potential
sediment loss was found.