DAM 1. RIGID DAMS: (a) Timber Dams (b) Steel dams (c) Arch dams (d) Buttress dams (e) Solid gravity dams 2.NON-RIGID DAMS: (a) Rock fill dams (b) Combined rock and earth fill dams (c) Earth dams

(a ) According to hydraulic design dams may be classified as: (i) Non-overflow dams (ii) Overflow dams.  In non-over flow dams the height of the dam is so chosen that under no circumstances water is allowed to overtop the dam. Almost all dams are made non-overflow type with provision of surpassing the excess flow through outlets or over a short and selected stretch of the part of the dam designed to allow over- topping.  Overflow dams allow the surplus water to pass over the body of the dam. A most common example of this type of dam is a concrete or masonry spillway.

(b) According to stability considerations dams may be classified (i) Gravity dams (ii) Non-gravity dams. Gravity dams are those in which the external forces like water pressure, uplift pressure, earthquake pressure etc. are resisted mostly by the weight of the same itself. Concrete and masonry dams are best examples of this type.  In non-gravity dams the weight of the body of the dam is not the main stabilising factor. For example, in such dams principal part of the water pressure is taken up by the abutments of the dam by arch action.

According to the functions the dams may be classified (i) Diversion dams (ii) Detention dams (iii) Storage dams. A common example of diversion dam is that of a weir or a barrage. It is clear that such a structure is small and does not store water to create a reservoir but it simply raises the water level to facilitate diversion of water. The main objective of a detention dam is to withhold flood flows temporarily so that area downstream do not get inundated by flood waters when the river is already running full

ARCH DAM  A dam resisting the pressure of impounded water by an arch principle, especially a dam having in plan the form of a single arch abutted by natural rock formations.  Arch dams require a high level of stress and force analysis in order to create a sufficient design.  The main force against an arch dam is the hydrostatic pressure provided by the reservoir behind it, uplift, which is water pressure beneath the dam, the weight of the dam itself, and all the forces combined.  Other forces that affect a dam include, but are not limited to, temperature, chemical reactions, settling, silt accumulation, and earthquakes

 Arch dam is made of concrete and placed in a "V"-shaped valley.  The foundation or abutments for an arch dam is very stable and proportionate to the concrete.  Two basic designs for an arch dam: o Constant-radius dams, have constant radius of curvature, o Variable-radius dams, have both upstream and downstream curves that systematically decrease in radius below the crest. o A dam that is double-curved in both its horizontal and vertical planes may be called a Dome dam. o Arch dams with more than one contiguous arch or plane are described as Multiple-arch dams

 In general, arch dams are classified as thin, medium, or thick.  If width of an arch dam's base is 2/10 of the dam's height or less, it is thin.  Any base and height ratio greater than 2/10 but less than 3/10 is considered medium.  Thick is a ratio of 3/10 or greater.  An arch dam's base is historically just as thick as the crest, but often it is twice as thick as the crest  Contraction joints are normally placed every 20 m in the arch dam and are later filled with grout after the control cools and cures

o Arch-gravity dam, curved-gravity dam having the characteristics of both an arch dam and a gravity dam. o It is a dam that curves upstream in a narrowing curve that directs most of the water against the canyon rock walls, providing the force to compress the dam. o It combines the strengths of two common dam forms and is considered a compromise between the two. o They are generally made of reinforced concrete which provides more strength compared to normal concrete. o A gravity dam requires a large volume of internal fill. [ An arch- gravity dam can be thinner than the pure gravity and requires less internal fill

The Idukki Dam, located in Kerala is a m (554 ft) tall tall arch It supports a 780 MW hydroelectric power station. It is built on the Priyar River, in the ravine between the Kuravan and Kurathi Hills in Kerala It is one of the highest Arch dams in Asia and third tallest dam in India.AsiaIndia It started generating power on 4 October Technically, the dam type is a concrete double, curvature parabolic, thin arc dam.