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Ditch |
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Generally, a long narrow excavation. |
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Diversion |
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A process which, having return flow and consumptive use elements, turns water from a given path. Removal of water from its natural channel for human use. |
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Diversion capacity |
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The flow which can be passed through the canal headworks at a dam under normal head. |
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Diversion channel |
Canal; Tunnel |
A waterway used to divert water from its natural course. The term is generally applied to a temporary arrangement, e.g., to bypass water around a damsite during construction. Channel is normally used instead of canal when the waterway is short. Occasionally the term is applied to a permanent arrangement (diversion canal, diversion tunnel, diversion aqueducts). |
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Diversion inlet |
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A conduit or tunnel upstream from an intake structure. Diversion inlet may be integral with the outlet works or be part of a separate conveyance structure that will only be used during construction. |
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Double curvature arch dam |
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An arch dam which is curved in plan and elevation, with undercutting of the heel and in most instances, a downstream overhang near the crest. An arch dam which is curved vertically as well as horizontally. |
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Downstream face |
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The inclined surface of a dam away from the reservoir. See face. |
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Drainage blanket |
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A layer of pervious material placed directly over the foundation material to facilitate drainage of the foundation and/or embankment. |
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Drainage layer |
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A layer of pervious material in an earthfill dam to relieve pore pressures or to facilitate drainage of the fill. |
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Drainage well |
Relief well |
Vertical wells or boreholes downstream of, or in downstream shoulder of, an embankment dam to collect and control seepage through or under the dam and so reduce water pressure. A line of such wells forms a drainage curtain. |
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Draw |
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A small valley or gully. |
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Drawdown |
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Lowering of a reservoir's water level; process of depleting a reservoir or groundwater storage. Vertical distance the free water surface elevation is lowered or the reduction of the pressure head due to the removal of free water. |
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Dredge |
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To dig under water. A machine that digs under water. |
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Drift |
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Food organisms, including algae, plankton, and even larval fish dislodged and moved by river current. A small, nearly horizontal tunnel. |
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Drop structure |
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A structure that conveys water to a lower elevation and dissipates the excess energy resulting from the drop. |
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Drum gate |
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A movable crest gate in the form of a sector of a cylinder hinged at the centerline. The arc face effects a seal with edge of a recess and the gate is operated by a reservoir pressure. Design permits overtopping. |
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Dry well |
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A deep hole, covered, and usually lined or filled with rocks, that holds drainage water until it soaks into the ground. |
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Dumped |
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A method of compacting soil by dumping the soil into place with no compactive effort. |
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Dynamic compaction |
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A method of compacting soil by dropping a heavy weight onto loose soil. |
