- Why Bridges Don’t Sink (practical.engineering)
The essence of a bridge is not just that it goes over something, but that there’s clear space underneath for a river, railway, or road. Maybe this is already obvious to you, but bridges present a unique structural challenge. In a regular road, the forces are transferred directly into the ground. On a bridge, all those forces on the span get concentrated into the piers or abutments on either side. Because of that, bridge substructures are among the strongest engineered systems on the planet. And yet, bridge foundations are built in some of the least ideal places for heavy loading. Rivers and oceans have soft, mucky soils that can’t hold much weight. Plus, obviously, a lot of them are underwater.
- Chehalis River Surge Plain Natural Area Preserve (dnr.wa.gov)
This large wetland area is spread out at the lower end of the Chehalis River, just upstream from where it empties into Grays Harbor. Sitka spruce and western redcedar thrive in the wet soils where fresh and salt water mingle on this 4,494-acre site. This preserve contains the largest and best quality tidal surge plain wetland in the state, including sloughs that shelter young salmon and other fish. The surge plain also supports osprey, bald eagles, and state-listed sensitive Olympic mudminnows. Vegetation communities represented in the Chehalis River Surge Plain preserve are Sitka spruce/red-osier dogwood/skunk cabbage vegetation, lady fern coastal herbaceous vegetation, softstem bulrush herbaceous vegetation, red-osier dogwood-willow species shrubland, Lyngby’s sedge herbaceous vegetation, and cattail surge plain herbaceous vegetation.
