Selection of Site-specific Stabilization Techniques
Although stone which is not submerged below the winter freeze line can be damaged
by freezing and thawing, that is not necessarily a deterrent to the selection of stone as the
erosion protection material in cold climates. The primary measure to combat stone
deterioration is to insure that high quality stone is used, as demonstrated by local experience
or tests. In severe applications, consideration can be given to increasing stone size beyond
that which is adequate for hydraulic stability in order to partially compensate for later
fracturing.
Ice floes uplifting and removing stone and other armor or dike and retard materials
may be a problem to be considered in the light of local experience.
Rigid armors are more susceptible to damage from heaving than are adjustable
armors, flexible mattresses, and indirect techniques.
Permanent submergence greatly reduces deterioration of wooden components from
wetting and drying, and damage to synthetic materials from sunlight. These materials are
often used above low water line, but special treatment is usually required. Manufacturers of
synthetic materials can provide information for their products.
5.1.1.4 Debris Loads
Debris, in the form of uprooted trees or ice carried by the flow, can cause such
extensive damage on some streams as to rule out some techniques entirely, and may make the
cost of others prohibitive if they are designed to withstand debris loads. However, debris can
also affect bank stabilization work positively. Examples of this are:
Debris can increase the effectiveness of structures in reducing near- bank
velocities and accumulating sediment, but debris can also fail structures which
accumulate large debris in zones of high velocity, and can make the structures
more vulnerable to fire.
Comprehensive stream stabilization will eventually reduce debris loads, but
structures must usually be designed for the heavier interim loads.
Debris accumulated by stabilization works may provide habitat for wildlife,
but in populated areas the debris may be considered unsightly, and the wildlife
it attracts may be pests to nearby residents.
Whether the net result of these interactive events is positive or negative must be
determined by applying engineering and environmental judgement to the particular site
conditions and project purposes. The sum is often negative, and so the selection of a
technique which is likely to accumulate debris, such as permeable dikes or retards, must be
approached cautiously if a stream carries large debris loads.
9
89
Previous Page
