CASE STUDY

When is a bridge better than a culvert?

CASE STUDY:
When is a bridge better than a culvert?



When a Bridge Reduces Environmental Impacts & Satisfies Water Flow Restrictions Better than a Culvert


Our vehicular project, Inspired Living, shows how a bridge reduces impacts to the environment and water flow. The bridge was built at 40 feet above a flood plain to enter a senior living community. Originally, this project was considered to have several culverts installed rather than a bridge. However, with costs of mitigation included, the culvert project budget was going to be significantly higher than a bridge project. There was also significant fill required to raise the road nearly 20 feet in elevation to be above the 100-year flood level. Even with this planned increase in elevation, the 100-year flood flow test was not passed, and the culvert option was eliminated altogether. The final and accepted bridge solution reduced the impacts by 50,763 square feet, limiting environmental impacts to erosion control under the bridge and the fill areas to the bridge ends only. The natural flow is left uninhibited, and the area of flood impacts was limited to two 18 inch piling faces, ultimately increasing the flow clearance by 237 square feet within the flood area.

Not only was the bridge project less expensive, but it also allowed a large amount of land to be left to its natural state, which is key to maintaining undisturbed ecological systems. In turn, this leads to reduced environmental risks or repercussions at the bridge and downstream.

Permitting


CULVERT
Failed 100-year flood test
TIMBER BRIDGE
Permitted

Environmental Impacts & Mitigation


CULVERT
81,823 sq ft
TIMBER BRIDGE

31,060 sq ft
(reduced by 62%)

Cost


CULVERT
$150K more than the bridge due to mitigation costs
TIMBER BRIDGE

Less expensive due to low environmental impact

Maintenance & Risk


CULVERT
Limited to 192 sq ft of flow within flood area & caused rise in 100-yr flood elevation
TIMBER BRIDGE

Provides 429 sq ft of flow within flood area

Aesthetics


CULVERT
Dirt & sod
TIMBER BRIDGE
Custom design options


Timber Bridge Alternatives to a Culvert