For the success of the earth dam, its U/S and D/S slopes have to be properly maintained.
U/S slopes have to be protected against wave action, and sudden draw down conditions whereas D/S slopes against heavy down pours, and action of burrowing animals.
Following are some of the measures used for slope protection.
1. Turfing.
Down stream slopes of the dams can be protected against erosion by developing turf.
This measure is quite effective for slope protection.
2. Counter Berms.
Down stream protection of the dam can be achieved to some extent by providing counter-beams.
This measure is usually adopted for very high dams.
Counter beams break the rhythm of the velocity of rain water, flowing down the berm.
This is the only measure of protecting the U/S slope against the action of wave erosion and sudden draw down.
This measure can equally be used for protection of D/S slopes also.
Rip rap is a layer of systematically dumped blocks on the slope.
A gravel filter layer 40 to 50 cm thick is applied before blocks are laid over it.
A survey conducted by US Corps of Engineers revealed that dumped rip-rap failed in 5% cases, hand packed rip-rap in 30% cases, and concrete pavement in 36% cases.
It can very easily be inferred from this that dumped rip-rap is the most successful measure of slope protection.
Thickness of rip-rap excluding the thickness of gravel filter is about 1 m.
The performance of rip-rap depends upon the weight and size of blocks, quality of rick of which blocks are made, thickness of rip-rap, and slope of the embankment on which rip-rap is laid.
The rip-rap thickness is adopted from following criteria.
Rip-rap, revetment and pitching all mean the same thing.
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