The Scottish Government

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Abstraction

• The drawing off of water from a river or reservoir for example.

Acoustic deterrent

• A device (sometimes referred to as a 'pinger') that generates sound waves to deter fish or other animals.

Algal bloom

• A relatively rapid increase in the population of (usually) phytoplankton algae in an aquatic system. Typically only one or a few species are involved and the bloom is recognized by discoloration of the water resulting from the high density of pigmented cells.

Aqueduct

• An artificial (man-made) channel that is constructed to convey water from one location to another.

Arctic Charr

• A native salmonid fish of Scotland where over 200 populations are known to exist. The species was probably the first fish to re-enter freshwater when the last ice-age ended. Local variants exist and in some instances two or more forms may inhabit the same loch. The species is now considered as threatened or declining in range due to climate change, land use changes and species introductions.

Autumn Parr

• A salmon parr that migrates (usually downstream) during the early autumn and winter months. The migration usually consists of a mixture of immature males and female parr, together with sexually mature ('precocious') males. Many autumn parr enter the sea as smolts in the following spring.

Compensation flow

• The flow which must be left in the river at the point of abstraction or diversion.

Compensation Flow Gauge

• A gauge that shows that compensation flows are being maintained.

Entrainment

• The process by which fish and debris are drawn into power station intakes.

Flood stage

• The elevation at which overflow of the natural banks of a stream or body of water begins in the reach or area in which the elevation is measured.

Freshet

• A rise or overflowing of a stream caused by the release of stored water, rainfall or melted snow.

Headwater(s)-

• (1) the source and upper reaches of a stream; also the upper reaches of a reservoir. (2) the water upstream from a structure or point on a stream. (3) the small streams that come together to form a river. Also may be thought of as any and all parts of a river basin except the main stream river and main tributaries.

• Takes advantage of the force of falling water. Large-scale facilities like the Hoover Dam and Grand Coulee Dam are examples of high-head hydro plants. Dams are built along major rivers to create reservoirs; the utility controls the flow of water through the dam in response to the demand for electricity.

Hydro

• A prefix meaning produced by or derived from water or the movement of water, as in hydroelectricity.

• Electrical power generated by the force of moving water. Hydroelectric power (H.E.P.) is normally associated with dams and reservoirs.

Hydropower

• See hydroelectric power.

Kilowatt (kW)

• One thousand watts

Megawatt (MW)

• One million watts

Needle valve

• A valve which allows fine control over the rate of liquid flowing through it. The valve contains a thin needle with a point that fits into a conical cup. When the valve is closed, the needle blocks an orifice in the bottom of the cup.

PIT tag(s)

• Passive Integrated Transponder tags, or PIT-tags, allow scientists and managers to monitor the movements and survival of fish moving through areas impacted by hydropower schemes. The staple-sized tags are implanted into the body cavity. Each tag is unique and identifies an individual fish. Detectors at dams can read the tags as the young fish move downstream and when the adult fish return to spawn, telling us how many fish survive as they move from one life stage to the next or from one location to the next.

Pumped-Storage Hydroelectric Power scheme

• A power generating facility that uses falling water from an elevated reservoir to generate electricity during high demand then pumps the water back to the reservoir during times of the day when demand is low.

Renewable energy resources

• An energy source that is more or less permanently available (such as sunshine) or can be easily replaced over a short timescale (such as wood).

Run of the river plant/scheme.

• Relies on the flow of the river to spin the turbines. Water is not stored. These plants produce relatively small amounts of electricity.

Smolt(s)

• Silvery coloured, migratory form of juvenile salmon or trout (at least one year old) that has adapted to the marine environment.

Smolt trap

• A permanent or temporary trap designed to intercept downstream migrating smolts.

Suspended sediment

• Very fine soil particles that remain in suspension in water for a considerable period of time without contact with the bottom. Such material remains in suspension due to the upward components of turbulence and currents and/or by suspension.

Tailrace

• The tailrace is the downstream part of a dam where the impounded water re-enters the river

Tributary

• A smaller river or stream that flows into a larger river or stream. Usually, a number of smaller tributaries merge to form a river.

VAKI Fish Counter

• A comparatively new fish counting system that is installed in fish ladders, pools, traps or similar places where fish have to pass. Fish pass through a scanner with a net of infra-red light beams, the resulting silhouette image is used to count and estimate the size of each fish. Each individual image is stored within a control unit so that the counting can be verified afterwards.

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