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<br />58% of dams are privately owned, 1 C% are owned by local govermnents, 4% by states, <br />and the rest by the federal govenunent and public utilities <br />Manmade dams are classified according to the type of construction material used, the <br />methods used in construction, the slope orcross-section of the dam, the way the dam <br />resists the forces of water pressure, the means used for controlling seepage and, <br />occasionally, according to the purpose of the dam, <br />The materials used for' construction of dams include earth, rock, tailings from mining or <br />milling, concrete, masonry, steel, timber, miscellaneous materials (such as plastic or <br />rubber) and any combination of these materials.. Embankment dams, the most common <br />type of dam, are usually constructed ofnatural soil or rock or waste materials obtained <br />from mining or milling operations, An embankment dam is termed an "earthfill" or <br />"rockfill" dam depending on whether it is comprised of compacted earth or mostly <br />compacted rock. The ability of an embankment dam to resist water pressure is primarily a <br />result of the mass, weight, type and strength of the materials from which the dam is <br />made. <br />Overtopping of an embankment dam is very undesirable since embanlanent materials <br />may be eroded away. Water normally passes through the main spillway or outlet works; it <br />should pass over an auxiliary spillway only during periods of high reservoir levels and <br />high water inflow, All embankment and most concrete dams have some seepage; <br />however, it is important to conhol the seepage to prevent internal erosion and instability. <br />Proper dam construction, maintenance, and monitoring of seepage provide this control. <br />Intentional release of water is confined to water releases through outlet works and <br />spillways, A dam typically has a principal or mechanical spillway and a drawdown <br />facility, Additionally, some dams are equipped with auxiliary spillways to manage <br />extreme floods.. Spillways ensure that the reservoir does not overtop the dam. Outlet <br />works maybe provided so that water can be drawn continuously, or as needed, from the <br />reservoir. Outlets also provide a way to draw down the reservoir for repair or safety <br />concerns.. Water withdrawn may be discharged into the river below the dam, run through <br />generators to provide hydroelectric power, or used for irrigation. Dam outlets usually <br />consist of pipes, box culverts or tunnels with intake inverts near minimum reservoir level.. <br />Such outlets are provided with gates or valves to regulate the flow rate,. <br />Dazz: Classificatiozzs <br />Dams are classified in one of three categories: <br />Dam Hazard Classification <br />Hazard Description of Quantitative <br />Classification Potential Damage Guidelines <br />16 <br />