Stream Bank Armoring/Channel Armoring

Protective covering, such as rocks, vegetation or engineering materials used to protect stream banks, or fill or cut slopes from flowing water.

Purpose: Stream bank and channel armoring is done to prevent erosion of channel banks and bottoms during runoff events. In some hydrologic systems stream banks are a major source of sediment.

Relative Effectiveness: Not enough interviewees rated this treatment. Comments on armoring indicated that it functions well in small, ephemeral drainages or near the heads of larger ephemeral drainages, and lower gradient areas. In steep terrain, sloughing of upslope materials can bury the bank armoring.

Implementation and Environmental Factors: Stream bank armoring requires proper design, a well-developed implementation plan, and experienced crews for maximum effectiveness. Other implementation factors that contribute to success include proper sized materials, use of geotextile fabric, avoiding overly steep areas, and the use of energy dissipaters.

Overflow Structure Implementation 

OBJECTIVE

To provide a means of keeping water in its natural channel in the event of a culvert failure
To provide an alternative to a culverted crossing, maintain access and prevent loss of soil and loss of water quality
To prevent downcutting into and through the roadbed and loss to downstream values

PRESCRIPTION

Use Overflow structures in cases where overtopping of the embankment is expected. Two types of overflow structures as a fail safe measure are possible. One is driveable to the dimensions of a rolling or intercepting dip the other can be a non-driveable excavation, or a culvert bypass. Both are installed immediately below (downgrade) of the culvert and have sufficient cross section handle the expected flow. Another structure is included in this section and that is the ford crossing.

Armoring

Armor the structures to reduce the erosive effects of the kinetic energy in the flow. Use rip rap to cover raw soil especially on the embankment and bring water over the rip rap to vegetated or rocky natural ground. When the natural ground is not very rocky and downcutting is expected, use a grade stabilizing type of reinforcement to this new "artificial" channel. 

LOCATION

Culvert Bypass

Use the culvert bypass in situations where the road does not need to be open to traffic. Also, look for situations where the stream crossing does not lend itself either physically or economically to other treatments. For example, if there is a 36", diameter pipe or larger in a deep embankment and you expect plugging or overtopping, it may not be feasible to install a riser and very prohibitive to remove the culvert. However, if you excavate and armor a channel below and around the pipe, you can provide reasonable protection from a massive failure and/or a loss of control of water. This type structure is also easily and economically restored after the emergency has passed.

Armored Ford Crossings

Consider armored ford crossings where embankments are small and where hydrologic analysis indicates pipe sizes that are too costly or that do not fit the roadway cross section

Overside drains (berm drain and downdrain)

Consider overside drains (berm drain and downdrain) in stream crossings where no culvert exists and the embankment needs protection berm drains can also protect embankments in cases where, the burn below the road was high intensity, where the berm is a part of the original road design and where removing it would be impractical. maintain control of water (often in a concave topography) with berm drains by directing it to the natural channels

CULVERT BYPASS

This term is used to describe a crude yet effective trenching through the road to allow control of flows that may be expected to overwhelm a culvert. By this description these structures are not intended to be passable to vehicles. Excavation can be done with dozer, or backhoe and should be sloped so as not to have vertical banks that will easily erode. This structure will protect the investment in the culvert you expect to fail and therefore should be located beside the culvert and not directly over it. Leave the excavated material mounded up and out of the path of where water will flow. Provide for outlet on natural ground or insure adequate armoring is done to prevent downcutting.

ARMORED FORD CROSSING

Many design possibilities exist for these structures, the simplest being a rip rap armored bottom to a sag crossing. Another simple structure is the gabion ford. Anything more sophisticated than these may have difficulty meeting ESR application criteria. The concept of these simple "natural" ford crossings is to employ a downstream endwall that will establish a leveling layer backing up the stream gravels and sand that will serve as the road prism. Endwalls that have been successful include logs tied into each bank and loose or grouted boulders. Insure that endwalls are buried deep enough, or provide for an erosion resistant splash pad, so that they will not be undermined. Use U.S. Department of Agriculture, Forest Service (USDA-FS). Use of Gabions For Low-Water Crossings on Primitive or Secondary Forest Roads, Engineering Field Notes, Volume 5. May-June 1973.

OVERSIDE DRAINS

Overside drains can be metal spillways or rip rap embankments. Metal spillways collect water from the road surface in what are commonly referred to as "Big Macs" and "Little Macs" which guide the water into the metal downdrain. The rip rap embankments receive water guided by the berms and discharge onto natural ground. Build these structures to the dimensions of the typical drawings. Rip rap embankments may need to be increased in size to insure that the rip rap is not outflanked. Metal spillways may need to be placed a little further down the slope to make sure they do not encroach on the traveled way.

COSTS (1992 costs)

Materials and Labor Cost
Equipment Dozer, D6  $43.36/hr
Grader, 12G  $31.62/hr
Water Truck $33.6/hr
Service Truck $9.80/hr
Dump Trucks (transfer, belly dump, semi-dump) $60-75/hr
Stakeside (boom)  $1.01/mi
Equipment Operator  $52.51/hr
Equipment Operator $56.15/hr
Truck Driver (water truck) $40.30/hr
Laborer (swamper)  $35.31/hr

COST FACTORS

Material consistency (common, rip, blast)
Amount of rip rap required to armor exposed and erodible slopes
Distance from material source (i.e. ,from rock plant)
Depth of fill or embankment

SAFETY CONSIDERATIONS

Working around moving equipment
Muscle and back strain from lifting heavy rocks or materials