Timnath hears engineering update on County Road 5 bridge, recommends phased build and 25‑year flood protection

Engineers and town staff briefed the Town of Timnath council and planning commission on May 11 on progress for the County Road 5 corridor study and recommended improvements that include replacing the existing bridge and raising portions of the roadway.

The JUB Engineers project team said the preferred, cost‑balanced alternative would provide protection against flows up to a 25‑year event, expand the river crossing to a roughly 240‑foot span and include four 3-by-20 box culverts under the roadway toward the south end of the project. "We are proposing the 25 year storm event which would be a 240 foot bridge with 4 box culverts," the project team said during the presentation.

Why it matters: most of the corridor lies inside the Poudre River regulatory floodplain and has overtopped multiple times historically; the recommended design aims to reduce frequent overtopping while limiting impacts on adjacent properties and construction cost. Staff and consultants said the 25‑year standard balances resilience and cost because a viable alternate route exists at Whitesell Street, allowing the town to avoid the much larger expense of providing 100‑year protection at this location.

Key details and supporting information

- Scope and limits: the study examined the corridor roughly from just north of Harmony Road down to Whitesell Street, including the bridge immediately south of the Harmony intersection; consultants performed topographic survey, utility locates, environmental assessments and traffic projections to 2045.

- Bridge and hydraulics: consultants reported the existing bridge span is about 60 feet and recommended replacement with a roughly 240‑foot span to satisfy river hydraulics and to avoid constructing two structures with different lifespans and maintenance challenges. The existing bridge width was reported at about 40 feet; consultants said a wider crossing will be needed to accommodate future traffic and multimodal elements.

- Flood design: the preferred long‑term alternative was described as providing roughly 25‑year event protection rather than 100‑year protection. Consultants modeled more than 32 alignment and structural alternatives (including larger bridges, levees, culverts and overbank grading) and concluded the 25‑year solution reduced costs while still protecting primary access. Consultants noted the road would still overtop in events larger than the 25‑year design and recommended measures to avoid washouts during rarer high‑magnitude floods.

- Roadway alignment and ancillary work: the team examined three horizontal alignments and recommended shifting the roadway slightly west in places to reduce encroachment into the river channel; final horizontal alignment will be refined in final design after additional stakeholder and property owner coordination. The project scope also includes rebuilding the Harmony Road intersection and tie‑ins to Timnath Parkway and Cornhusk.

- Environmental considerations: staff said wetlands were not found in the first phase but that riparian and bird habitat (a rookery and an eagle nest nearby) exist and will require coordination with Colorado Parks and Wildlife and appropriate mitigation during the design and permitting phases.

- Construction staging and impacts: consultants said replacing the bridge in a single closure is likely more time‑ and cost‑effective than extensive phasing; they estimated the bridge replacement portion could take about six months of active construction and would likely require closing County Road 5 south of the bridge during that period. The team warned that extensive phasing could double or triple schedule and cost.

- Schedule and next steps: the project team said alternatives analysis is wrapping up and that a future work order would be brought to council for final design funding in a subsequent meeting (staff referenced a potential work order in April or May during the presentation). Consultants and staff said a transportation project fair was scheduled for May 12 to provide public engagement and that, pending construction funding in the capital improvement program, construction could begin as early as 2027 to meet timing commitments with adjacent developments.

Questions raised by council and commissioners included requests for more detail on cost tradeoffs among the 10‑, 25‑ and 100‑year design options; how much private right‑of‑way acquisition would be required for a westward shift; whether park‑dedicated land near the bridge would be affected; the project’s bicycle and trail connectivity; and how long the bridge closure would last. Consultants replied that the 100‑year alternative would require roughly eight box culverts (versus four for the 25‑year design), noted an approximate $2 million difference in one comparison they would confirm in writing, and confirmed trails are planned on both sides of the bridge with provisions to accommodate future 10‑foot paths on the structure.

Community and funding context

Staff said the preferred phased approach reduces near‑term CIP demands by building only the capacity needed for near‑term development and future tie‑ins; later phases could raise the roadway south of the bridge and shift alignment if and when traffic or funding justified the work. The project team emphasized coordination with adjacent property owners will determine final horizontal alignment and any right‑of‑way needs.

Provenance: JUB team presentation and council Q&A (transcript May 11, 2025).