Old Route 99 Road to Trail Sediment Reduction Project

Summary of Featured Structures

Culvert sleeving, replacement and upgrades

The plugged and rusted out culverts at Crossings 2, 3 & 4 were sleeved with smooth-sided culverts, which will increase culvert longevity and hydraulic conveyance. In addition, another culvert found plugged up and buried beneath the roadbed was excavated, cleaned out, and sleeved. All sleeved culverts also received Energy Dissipation structures at their outlets, as well. The two 24” culverts at the Lost Lane crossing were removed and replaced by 3-36” concrete culverts. The adjacent banks upstream of these culverts were protected with vegetated riprap.

During construction – you can see the old squashed culverts		During construction
After – conveying a flow that would have exceeded the capacity of the previous culverts

Before		During installation of vegetated riprap
After

The abandoned 36” concrete culverts that were plugging the channel in Hwy 99 Creek were removed, along with both old house sites that were located in the floodplain of the creek. Unfortunately, we were unable to remove the swimming pool buried underneath the creek in the upper end of the restoration area, as we almost lost an excavator in the quicksand there. The restoration of this reach involved the removal of over 5,000 CY of sediment, clearing over an acre of invasive Himalayan Blackberry and Vinca major, and outsloping the historic Beltline Road above the target reach. These restoration actions together should greatly reduce the potential for flooding downstream, and for sediment production to Sulphur Creek. In addition, we hope that with the installation of the biotechnical structures, we have increased the diversity of both aquatic and terrestrial habitat in and immediately adjacent to the stream channel.

Biotechnical Erosion Control

After the sediment plugs were removed from the channel, biotechnical streambank stabilization techniques were implemented to stabilize the restored channel segments. Two cross vane structures were installed, one near each removed homesite, and pole planting was liberally applied near the stream channel. In addition, all disturbed area not directly in a stream channel was seeded and mulched with native grass species, and native shrubs were planted throughout floodplain areas. Biotechnical work coincided with the dormant stage of native riparian species (November through March).

Cross Vanes

Before – note abandoned culvert channeling water		During construction – culvert has been removed, and Beltline pilings are being placed
After construction – the channel is adjusting to the new structure

MRE Wall

Before		During
During		After
A wide variety of grasses and forbs have established themselves in the soil of the MRE wall

Vegetated Rock Buttress

A vegetated rock buttress was installed adjacent to the MRE wall to provide some trail support amongst the trees, and to dissipate energy from any water that overflowed the curb inlet.

Before		After