The rainwater that acquires high downward velocities causes consequent erosion which can be reduced by provision of berms.
The provision of berms serves following purposes ?
? It behaves like a good lining for reducing losses and leakage
? They provide protection against erosion and breaches due to wave action
? They help channel to attain regime conditions as y help in providing a wider waterway
? It can be used as borrow pits for excavating soil to be used for filling.

If height of dam is up to 7.5 m n top width value according to Strange?s recommendation is 1.85 and if height is in between 7.5 to 15 m, n recommended value is 2.5. If height is in between 15 to 22.5 m n top width is 3.0 m.

When re is appreciable flow through dam body below phreatic line, it reduces effective weight of soil and also shear strength of soil due to pore pressure. The capillary tension in water leads to increased intergranular pressure as insignificant flow through fringe leads to greater shear strength. Hence, effects are neglected.

The entire dam may slide or just one face slides over foundation when foundation of earth dams is made of soft soils. Then foundation bulges out on side of movement. The top of embankment gets cracked and lower slope moves outward forming large mud waves near heel.

The toe filter consists of three layers of fine sand, coarse sand, and gravel with stone size or rock chips varying from 15 to 20 mm. It acts as a transition zone and prevents choking of toe and height of rock toe is kept between 1/3 to 1/4 of dam height to achieve good results.

In this method, an embankment is created by water and earth slurry which is discharged inwards to form a central pool at site. When water is pumped to site it spreads coarser material drops out first and finest at last. Thus core material settles within central pool forming a zoned embankment and high pore pressures develop in core.

Equipotential lines are lines of equal energy. Every point on upstream face of an earth dam will be under equal total energy, this line acts as an equipotential line. Similarly, upstream floor of a weir acts as an equipotential line.

There is a possibility that water may boil up near toe of dam when large scale seepage takes place through pervious foundation overlain by a thin less pervious layer. Relief wells or drain trenches and d/s berms beyond toe of dam are all provided to control sand boiling.

The outer zone is made of fairly pervious material like grit, gravel, and murrum. The innermost zone is done with fairly impervious material. The central core is covered by comparatively pervious transition zone which prevents piping through cracks which may develop in core.

Swedish circle method is also called as method of slices and Fellenius method is a modified version of it. Swedish circle method assumes condition of plain strain with failure along a cylindrical arc. The location of center of possible failure arc is assumed and earth mass is divided into slices.