InStream Conservation

The Roman Arch Concept

Roman Arch Concept
300 B. C. Pont Ambroix Bridge, France

The Roman Arch, mans 2,500 year old engineering marvel is still working today

Over 2,500 years ago a new building concept allowed man to design, engineer and construct bridges that span rivers, aqueducts that moved water to cities and fields and built churches, to unprecedented heights.

More recently, the Roman Arch concept is helping to restore endangered salmon and steelhead.

Whether the Roman Arch is used to span a stream, or is integrated into a riverbed, the same basic engineering principals apply. The weight of the structure pressing down, or pressure of flowing water, forces each building block of the structure to support and reinforce the rest of the structure, thus allowing river structures to be built with a minimum of materials and blend into the natural environment.

Roman Arch Concept
Wood/rock cross vanes help provide deep water habitat


Roman Arches create deep pool habitat for endangered salmon and steelhead

In the summer during critical low flows and high temperatures, deep holding plunge pools provide cool upwelling oxygenated water, cover and feeding areas for juveniles and resting places for returning wild salmon and steelhead. Upwelling pressure from groundwater and deep pools also enhance flows through tailwater gravel, where wild salmon and steelhead seek to spawn. This prime habitat increases survival of eggs and emerging fry. When creating deep holding pool habitat, wood and rock are used to mimic the natural environment, restore proper stream functioning, remove stress from banks and move current energy to the middle of a stream. This helps banks heal and allows growth of new trees and vegetation.

Combining deep pools, riffle run tail-out habitat with increasing nutrient distribution, either with salmon carcass or analog pellets, plus restoring side channel holding areas for juvenile fish, can go a long way toward improving our threatened and endangered wild salmon and steelhead populations.

Stream restoration projects need to be monitored for:

  • How successful the project is in providing deep cool water pools and spawning/rearing habitat.
  • A transparent, audited, monitored system of how the project met its goals overtime, and how tax and rate payer, as well as endangered salmon and steelhead, benefit.

Note: All projects shown are monitored for success

Roman Arch Concept

Roman Arch Concept

Roman Arch Concept

Roman Arch Concept

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