All Designs - Armoring

Below is the decision matrix that considers the four possible armoring techniques: boulders, sheet pile, gabion baskets, and retaining walls. Higher scores represent that the option is a better choice. The option that has the highest score is the rock armoring while the retaining walls have the lowest score. The parameters are defined in the table below the decision matrix.

Current Crossing Armoring
Parameters Weight Rock Armoring Sheet Pile Gabion Baskets Retaining Walls
Cost 0.2 5 3 4 1
Effectiveness 0.3 4 5 4 4
Aesthetics 0.05 2 1 2 2
Safety 0.15 4 3 3 4
Creek Impact 0.15 4 2 4 1
Lifespan 0.15 4 4 4 4
  Total 4.1 3.5 3.75 2.85
Scoring: 1 - Worst
5 - Best

Parameter Definition
Cost Overall cost to construct
Effectiveness Effectiveness to allow debris to pass
Aesthetics Geometry and beauty of the design
Safety Allowability of flow to pass under crossing and threat to public health
Creek Impact Chance of causing erosion and disturbance to creek
Lifespan Longevity of design

Below are pictures of each armoring alternative. A description for each alternative is below each picture.

Rock armoring would be composed of six foot diameter boulders or larger that are shaped in a way to provide the maximum cohesion between the rocks. The rock armoring is the cheapest option because it allows indigenous rocks to be used for the design.

Interlocking metal sheets are used to form a wall in this example. Sheet piling requires the material to be piled straight into the ground, causing a lot of creek disturbance. A footing is not required for sheet piling because it is driven deep into the ground. Any large rocks that may be located underground would cause the installation of sheet piling to be difficult.

Gabion baskets are a collection of wire baskets filled with rocks. The rocks are placed in a particular way so that the void space is minimized within the basket. A step down design, shown above, would need to be implemented in order to provide the needed support. Gabion baskets are not favored by the Forest Service, but it is possible to obtain a permit to install gabion baskets within Oak Creek.

A concrete retaining wall is similar to the sheet piling design except that the ground would be excavated so that the wall could be placed. The retaining wall would also have a footing at the bottom to provide added support. The installation of a retaining wall would cause a large amount of creek disturbance.