Hydraulics Handoff Memo.pdf

Memorandum

Western Federal Lands Highway Division 610 E. Fifth Street

Vancouver, WA 98661-3801

MP 52 CULVERT REPLACEMENT

HYDRAULICS CONSTRUCTION HANDOFF MEMO

To: Brandon Stokes, WFLHD Project Manager From: Sven Leon, P.E., WFLHD Hydraulics Engineer Date: January 12, 2021 Project: AK NPS DENA 10(48) – Culvert Replacement MP 52 and Rockfall

Mitigation

Background

Denali National Park (Park), Alaska, is installing a concrete box culvert for the Bugstuffer Creek crossing on the Denali Park Road at milepost 52. The proposed work includes installing a CMP riser on the existing 30-inch diameter CMP culvert and installing new precast concrete box culverts with precast concrete headwalls. The Park wants the completed culvert installations to have a color and texture that blends into the surroundings and does not noticeably detract from the views along the road. The Park owns and maintains the road and culvert structures. Western Federal Lands Highway Division (WFLHD) is designing the culverts. Construction related issues and recommendations are presented.

Recommendations

• Install precast concrete box culverts with 10 feet span and 4 feet rises.

• Ensure the precast concrete box culvert has a removable lid as shown on the drawings and that lid segments can be removed and reinstalled with conventional backhoe equipment.

• Install four 12 feet long by 10 feet high precast concrete headwalls, angle walls 45 degrees.

• Install 12-inch high removable precast concrete curbing over the box culvert crown at both inlet and outlet.

• Install 4 feet high precast concrete cutoff walls below both inlet and outlet.

• Set the culvert invert elevations as shown on the culvert profile, slope culvert 0.13 ft/ft.

• Regrade new channel for 135 feet upstream at 0.14 ft/ft.

• Regrade new channel for 190 feet downstream at 0.13 ft/ft.

• The new channel must have a 10 feet wide bottom and 2(h):1(v) side-slopes.

• Smoothly transition the constructed channel and banks to the natural channel and banks.

• Install riprap Class 3, method B (FHWA FP-14), 2 feet thick, and 5 feet wide along headwalls.

• Use sub-rounded to sub-angular riprap having a color approximately matching the existing natural stone in the project area.

• Place the riprap on a geotextile filter, class 1, type C.

• Cover the placed riprap with conserved material matching the existing road embankment

Memo to: Brandon Stokes, WFLHD Project Manager January 12, 2021 material.

• Apply both color finish and color additive to all precast concrete elements visible from the ground surface.

• Use stain color and color pattern matching the existing natural stone.

• Use form liner finish matching the existing natural stone for all precast concrete elements visible from the ground surface.

• Have the Park approve the form liner finish and color.

• Install CMP riser on existing 30-inch diameter culvert, including CMP riser, steel base plate, CMP connection pipe, CMP coupling band, connection bolts, and trash rack grate.

• Fabricate and assemble all components in the shop.

• Paint trash rack grate, riser, and connection pipe according to Paint System 1, Table 563-1.

• Submit four color options to CO for approval before painting.

• All welds to be shop welds.

• All coatings to be applied in the shop under controlled conditions.

• All perforations and connection bolt holes to be completed in the shop with appropriate drilling equipment.

• Cover steel base plate with 6 inches of conserved streambed material.

• If any of the culvert design parameters cannot be met, contact WFLHD Hydraulics.

Construction

Apply color finish to the concrete culvert headwalls outside faces, side edges, and top edges. Apply color finish to all interior and end wall surfaces of the outlet and inlet precast concrete culvert end-sections.

Match and coordinate color stain and staining pattern with the natural river rock in the existing culverts gabion basket headwalls.

Apply colored concrete additive to the precast concrete culvert curbing, headwalls, and culvert sections.

Use color approved by CO. Produce consistently colored concrete culvert components. Base dosage rates on weight of portland cement, fly ash, silica fume, lime, and other cementitious materials but not aggregate or sand. Match curing compound color to concrete color. Cure with clear curing compound and use only non-chloride admixtures. Match fiberglass form tie rod color to concrete color. Minor adjustments of water and air-entraining agent are allowed. Do not vary quantities, types, or source of materials. Other changes require mix re-approval. Perform finishing operations consistently to avoid color variation. Do not begin finishing while bleed water is present. Do not allow plastic sheeting to come in contact with colored concrete. Protect the colored concrete from damage.

Complete a Class one finish according to Subsection 552.16(a). Apply form liner finish to the precast concrete culvert curbing, headwalls outside faces, side edges, and top edges.

Conform concrete form liners to a pattern like river rock with a 2-inch maximum relief. Match and coordinate concrete form liners with the natural river rock in the existing culverts gabion basket headwalls. Build five 24- by 48-inch concrete form liner sample panels to obtain a color and form liner pattern acceptable to the CO. Protect the approved pattern panel. Match the finished pattern with pattern of the approved sample.

Memo to: Brandon Stokes, WFLHD Project Manager January 12, 2021

Use reusable form liners, made of high strength urethane and not compress more than ¼” when concrete is placed at a rate of 10 vertical feet per hour. Remove form liners without causing deterioration of surface or underlying concrete. Use release agent compatible with the form liners, simulated stone masonry, and with the color stain system, as recommended by the manufacturer. Design form ties to separate at least one inch back from the finished surface, leaving only a neat hole that can be plugged with patching material.

Color additives containing carbon black are acceptable. Do not use calcium chloride admixtures.

Divert stream flow as needed for completing culvert and riser installation work. Diversion sandbags can be filled with material mined from the floodplain if such material is replaced at end of the project. Small amounts of in-stream material can be moved to help seal and secure diversion structures. Leakage through and under the barrier must be small enough to allow for proposed work.

The existing 30-inch diameter CMP culvert may be used for conveying the diverted stream flow.

After installing diversion and any temporary de-watering facilities, begin reducing the water level through the isolated work area. Do not de-water isolation area entirely until all fish and aquatic life have been removed. Fish passage upstream or downstream through the temporary flow diversions is not required.

Span the active stream channel and floodplain as needed to divert all flow through a diversion with a minimum flow capacity of 10 cfs from July 15 to October 15 and 52 cfs from October 16 to July 14.

Upstream barrier must have sufficient height to effectively force the diverted water through the diversion channel, have a minimum height of 3 feet above the stream bottom, and be stable assuming 8 feet per second parallel flow and 2 feet maximum water depth. Prevent overtopping of the diversion structure and isolation berm for all flows less than or equal to the minimum design flows. Contractor must provide capacity calculations for the diversion system.

Maintain and control water flow downstream of the isolated work area for the duration of the diversion to prevent downstream de-watering. Stabilize channels and dissipate flow energy at the bypass outflow to prevent damage to riparian vegetation or stream channel. Regularly inspect and clean any coffer dams, culverts, or water-proof lined diversion ditches of excess debris or sediment accumulation.

Upon project completion, monitor downstream conditions during re-watering. Maintain sufficient stream flow and prevent stranding of aquatic organisms below the construction site. Slowly re-water the construction site to ensure adequate flows downstream as the construction site streambed absorbs water.

Controlled re-watering will also prevent a sudden release of suspended sediment.

Restore damaged stream banks to match pre-existing conditions.

Construct diversions such that the ends are left plugged until the main stem of the new channel is completed. Open the outlet end before the inlet end to minimize the introduction of silty water into the stream.