Your Dam Your Responsibility (PDF~1.2MB)

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C
Appendix C
Adjustment may require addition of water by spraying, or removal of water by drying
(loosen to allow sun and wind to dry soil). The material should be mixed to achieve
uniform moisture content before placement on the embankment.
Embankment materials should be placed in layers no thicker than 150mm when
compacted. These layers should not be allowed to dry out prior to the next layers being
placed above them.
An additional amount of 5% of the embankment height should be allowed over and
above the freeboard to allow for settlement (consolidation) of the fill material after initial
construction.
A self propelled or towed tamping foot roller should be used to compact the
embankment material. Adequate compaction is generally achieved when the tamping
feet “walk out” of the fill without further disturbing the compacted layer.
Relying on track rolling with a dozer for compaction of the materials is not suitable
for most types of materials and proper compaction equipment should be used,
notwithstanding common practice to the contrary. Track rolling for dispersive materials is
not acceptable under any circumstances, and for these materials very careful control of
moisture content is also required.
Embankment Crest Width
The embankment crest width should be suitable for vehicle traffic (minimum 3.5m) to
cope with emergency maintenance should it be needed. Day to day vehicle access on the
crest should be avoided, unless the surface has been capped with gravel, as wheels ruts
can pool water and accelerate deterioration of the dam.
A 150mm capping layer of well-graded gravel on the crest of the dam provides a
trafficable surface and protects against drying out of the soil, helping to prevent cracking
of the embankment material.
Erosion Protection
Erosion protection of the embankment can be achieved by spreading topsoil and sowing
grass over the upstream and downstream slopes of the dam. If gravel is available it can
be used to provide erosion protection for the water-face slope of the embankment.
Spillways
General
Spillways are an essential part of the farm dam construction. Without a spillway, dams
will overtop and fail when high inflows occur. Dams are at greatest risk when full.
The spillway crest level must be set such that there is adequate allowance for flood
overflow to occur without the dam overtopping, and to cope with any wind induced
waves that can also overtop the dam.
The nature of the discharge channel from the spillway crest should be both sized and
protected against erosion occurring.
Location
Spillways must be located in the natural abutment material and not in the embankment
(refer Figure C-1). Where an earthen spillway is provided, some protection against erosion