Rezatec

Key words and phrases

Abutment – Part of the valley side where a dam is constructed. An artificial abutment is sometimes constructed, as a concrete gravity section, to take the thrust of an arch dam where there is no suitable natural abutment. The left and right abutments of dams are defined with the observer viewing the dam looking in the downstream direction unless otherwise indicated.

Appurtenant structure—Supporting features of a dam e.g., outlets, spillways, powerplants, tunnels, etc.

Axis of dam– Vertical surface which coincides with the upstream face at the top of the dam.

Berm – A horizontal step in a sloping profile of an embankment used to break the continuity of the slope. This is usually constructed to reduce erosion or to increase the thickness of the embankment.

Breach – A dam opening is used to allow the draining of a reservoir. If constructed, this is more likely to be controlled in nature. This is usually associated with the partial or total failure of the dam.

Channel – An artificial or natural watercourse with a definitive bed and banks layout which confines and transports flowing water. 

Conduit – A type of closed channel which allows water to pass through, around or under a dam to a house or other conduits or pipes. This can consist of a concrete lined or a concrete/steel lined structure. 

Core wall – A structure, typically built from concrete, in the body of an embankment dam to prevent leakage. 

Crest gate/Spillway gate – Structure used to control the discharge or water level from a dam or reservoir. 

Crest length – The length of the dam measured along the centreline crest of the dam, at the top level of the main body of the dam, or the roadway surface on the crest.

Cross section – The elevated view of an object formed by passing a plane which is perpendicular to the object’s longest axis. 

Cut-off wall – A wall of the material located in the foundation beneath a dam, and which forms a barrier to reduce seepage beneath a dam.

Dam – Barrier across a watercourse to divert water. This should obstruct, direct, and store the flow of water. 

Dam Crest – The top surface of a particular dam or reservoir where water is prevented from flowing.

Dam Failure – A type of incident characterised by the sudden, rapid release of water or the likelihood of an uncontrollable release (see Low Hazard, Significant Hazard, and High Hazard for more information). 

• Low Hazard –Failure or misoperation which results in unlikely loss of human life and/or limited consequences economically or environmentally on the system. 
• Significant Hazard –Significant failure or misoperation which should result in no loss to human life but could have some consequences economically or environmentally on the system.
• High Hazard – Incident leading to huge consequences of failure and misoperation which will cause loss of human life.

Drain – System of pipe along the downstream part (or toe) of a dam used to collect seepage from the foundation or embankment. 

Drainage Area – An area which drains to a particular location on a river or stream. 

Drop Inlet – An uncontrollable location for flow to enter a spillway. This is achieved by flowing over a wall or other opening. 

Embankment Of Interest (EOI) – Specific location in which a customer requires information or data in and around the area of interest (AOI). This is usually in an area where a wall or bank of earth or stone has been built to prevent flooding.

Face – Exposed surface of dam materials such as earth or concrete upstream or downstream. 

Filter Zone – One or multiple layers of granular material which make up an embankment dam. Filter Zones can be graded naturally or by selection to allow seepage through or within the layers while preventing the movement of material from other areas. 

Flashboards – Temporary barriers (usually made of concrete, steel, or timber) connected to the crest of a spillway to increase storage in a reservoir.

Flood – A temporary rise in water level resulting in areas becoming affected by water that normally would not be in other normal circumstances. 

Foundation(s) – Materials such as soil and rock which help to support the structure of a dam or reservoir. 

Freeboard – Difference in elevation between the maximum water surface of a reservoir and the dam crest.

Gate – Structure for controlling the rate of flow into or from a canal or ditch.

Groin – The line of contact or area along the upstream or downstream face of a dam and the abutments. 

Heel of dam – Junction of the upstream face of a concrete gravity dam or arch dam with the ground surface. 

Hydraulic Height – Vertical difference between the lowest point in the original streambed at the centreline crest of the dam and the maximum controllable water surface. 

Intake – Establishes the drawdown level of the reservoir by the position of its openings to the outlet works. Usually placed at the beginning of a waterway (e.g., power conduit or water supply conduit). These intakes may be vertical or inclined towers, drop inlets, or box-shaped structures. 

Landslide – Movement of debris, mass, or earth down a slope. In dams/reservoir environments, this can lead to waves or displaced water which can overtop a dam. 

Leakage – Uncontrollable loss of water through a hole or crack in a structure. 

Length of dam – Distance along the top of the dam between abutments. This includes spillway, power plants, navigation lock, fish pass etc., where these form part of the length of the dam. 

Longitudinal – Lengthwise measurement of a structure. 

Monitoring Frequency – How often a dam(s) is/are monitored and recorded. 

Outlet – An opening through which water can be discharged from a reservoir to a river.

Outlet gate – A gate controlling the flow of water through a reservoir outlet. 

Phreatic Surface – The free surface of water seeping at atmospheric pressure through soil or rock.

Piping – The development of internal erosion caused by seepage.

Reservoir – Natural or artificial water body in which water can be managed, stored, or regulated. 

Reservoir surface area – Area covered by a reservoir when filled to a specific level.

Riprap – Layer of rocks, boulders, or sediment placed at random fashion on the upstream and downstream faces of any embankment or dam feature. This is achieved to protect these features from erosion caused typically by current, wind, or wave forces. 

Sand Boil – Seeping characterised by boiling at the surface surrounded by material from deposition of foundation or by embankment material carried by seepage. 

Seepage – Percolation of water through small cracks or pores without the formation of definitive channels. 

Slope Protection – See Riprap definition. The protection of a slope against erosion or wave activity. 

Spillway – A natural drainage channel or structure used as a passage for surplus water from a dam or reservoir. 

Spillway channel—An open channel or closed conduit allowing water to travel from the spillway inlet downstream. 

Spillway chute—A steeply sloping spillway channel set up to allow discharge at super-critical velocities. 

Spillway crest—The lowest level at which water can flow over or through a spillway. 

Storage—Retaining of water by planned operation or by a temporary filling of overflow areas.

Structural Height—The vertical distance between the top of the dam and the lowest point of the excavated foundation area, excluding narrow fault zones. 

Toe of the dam—The junction of a slope or face of a dam with the ground surface; also referred to as the heel. 

Transverse—Extension along the width of a structure and is perpendicular to the length of a structure. 

Trashrack—A structure (typically of metal or reinforced concrete) situated at the intake of a conduit, pipe or tunnel used to prevent debris over a certain size from entering. 

Valve—Device used to control the flow of water in a conduit, pipe, or tunnel that permanently obstructs a section of a waterway. 

Dam Types

Arch Dam – Usually constructed from concrete or masonry. This is curved upstream so that a major part of the water load is transported to the abutments and to keep the dam in compression.

Buttress Dam - Usually made from concrete or by masonry practices. They boast a watertight upstream side structure supported by triangular-shaped walls known as buttresses. These buttresses are positioned at intervals on the downstream side to resist the force of the reservoir water trying to push the dam over.

Concrete Dam – See definitions for an arch dam, buttress dam or gravity dam.

Embankment Dam - Usually constructed from excavated, natural materials. Embankment Dams are split into two main types called earthfill dams and rockfill dams. 

• Earthfill dams usually consist of compacted earth. 
• Rockfill dams are constructed from dumped and compacted rockfill. The materials are usually excavated or quarried from nearby sites, usually from within the reservoir basin if possible.

Gravity Dam –Usually constructed either by concrete, or masonry, or sometimes both. It is called a gravity dam as it relies on its weight and strength for stability.

Masonry Dam—Any dam constructed of stone, brick or concrete blocks jointed with mortar. 

Activities associated with Dams

Flood Control Dam - Water from snow and rainfall finds its way into stream and rivers and eventually into the sea. After severe storms, heavy snow, or rain over several days, the water level in rivers can rise dramatically. This can lead to water flowing over riverbanks or walls causing flooding of farmland, property, and in the worst cases, potential loss of life.

Hydroelectric power – Reservoirs are structures which can be used to store water used to power hydroelectric stations. Hydroelectric power is generated using energy from falling water to drive water turbines that, as a result, can power electric generators.

Irrigation Dam – Plants grow naturally on fertile soil which is given water provided by precipitation. However, in some regions of the world where the climate is very dry for some seasons throughout the year, some soils become too dry and, as a result, vegetation growth is restricted. A solution to this issue can be provided by irrigation, a man-made system for watering the land. Water from irrigation practices can be stored in reservoirs during rainy seasons which can be released from the reservoir and distributed over the land through a system of canals when seasons become much drier.

Water Supply Dam – Reservoir water can help supply our homes and factories with fresh water. Reservoirs are constructed to store falling precipitation during wetter periods of the year so that a continuous supply of water is still available for drier periods.

Dam Monitoring: Other approaches 

Annual audits/ground surveys – Typically conducted at designated points across a dam (using various tools), usually obtaining more in-depth information than visual inspections. Useful in determining structural issues and ground movement.

Direct and Inverted Pendulums – Used to measure rotations and translations of large structures such as concrete dams. 

• The direct pendulum usually measures the rotation of a structure. 
• The inverted pendulum detects horizontal movements (translation) of a structure considering deep points in the foundation rock.

Drones/Unmanned aerial vehicles (UAV’s) – Equipment which uses infra-red cameras and light construction to detect information such as movement, seepage, and cracks on dams.

Piezometer – Geotechnical sensors used to measure pore water pressure in the soil, earth/rock fills, foundations, and concrete structures.

Visual inspections – Physical ground truthing for cracks and issues by walk overs across the dam structure.