COMMISSION

culverts, heavy equipment operators excavated
the culverts and replaced them with a hardened
crossing. This type of crossing is intended to
act as a reinforced streambed that matched the
natural drainage profile. The project was completed
during the 2016 rainy season. The true gauge of
the management strategy effectiveness will come
from the park’s water quality monitoring gauges.
The gauges have been calibrated to measure the
amount of suspended sediment coming through the
creek downhill from the project site. This project
Olive Orchard culvert
is an example of how Hollister Hills SVRA staff implement soil conservation practices and
design monitoring studies to gauge the effectiveness of implemented management actions.
Bonanza Gulch Restoration
The Bonanza Gulch trail is located in the park’s Upper Ranch area on the southern extent
of the park boundary. The property is designated for four-wheel drive recreation. The
soil type in this area is comprised of parent granitic material interspersed with carbonate,
limestone, and dolomitic rocks. These types of rocks have a tendency to break down
because of the chemical reaction caused by acid found in rainwater. In the upper reaches
of Bonanza Gulch trail, the rocks became acid-bleached due to trail alignment that
subsequently led to the inability to shed water. The resulting loamy clay substrate produced
a mass wasting of the trail tread and eventually caused the trail to become incised.
Hollister Hill SVRA returned the incised section of the trail back to grade using soil captured
from a sediment detention basin located downslope in the watershed. Then, staff realigned
the trail to follow the natural contour of the trail to promote increased drainage capabilities.
Finally, the section of trail was revegetated with native plant species to ensure the soil
would stay intact and eventually sustain viable wildlife habitat.
Bonanza Gulch before restoration
Bonanza Gulch after restoration
2017 Program Report 145