Term | Description |
---|---|
Interventions | |
Bypass | A structure that collects fish upstream and deposits fish downstream of the facility. Typically used for juveniles. Several bypass types, but surface and turbine bypasses are most common |
Dam | Structure for impounding water. Dam height generates head pressure for the turbines |
Draft tube | A column (structure) from the turbine outlet to the tailrace that water flows through |
Exclusionary device | Structure(s) to prevent or divert fish entrance/passage. Often used to divert fish from turbines into bypasses. Common structures include various screens |
General infrastructure | Category used to capture studies that evaluated entrainment or impingement through > 1 components of a hydroelectric facility. Within the meta-analysis, this category encompassed lab studies that simulate conditions fish may experience (e.g., shear forces) through various infrastructure |
Louver | A structure of set angled bars or slats that can be used to divert/guide fish towards bypasses or sluices. These structures do not exclude fish like screens, rather alter hydraulic flow patterns and/or streamflow to guide fish |
Outlet works | A combination of structures designed to control reservoir water levels and/or water release for hydropower facility operations. Structures can include intake towers, outlet tunnels and/or conduits, control gates, and discharge channels. Intake structures can have trash racks or other purposefully designed fish intakes |
Penstock | An intake structure (channel, pipe) that leads into the turbines |
Screen | An exclusionary device to prevent fish from entering a structure (e.g., turbine) or divert fish towards a bypass |
Spillway | An outlet or channel in a dam or reservoir that discharges surplus water downstream of a dam. Spillways can vary by design (e.g., channel type, height) |
Sluiceways | A surface channel extending from the forebay to the tailrace designed to allow ice and debris to pass |
Surface bypasses | Structures that spill minimal amounts of water to facilitate passage over a dam. Several types exist (see [23]). Fish are collected and pass through a series channels that discharges downstream of the facility into the tailrace. Typically used for juvenile salmonids, taking advantage of their surface-oriented swimming behaviour |
Trash rack | A type of exclusionary device designed to keep debris out of turbine intakes, but can be used to guide fish to “safer” passage routes such as bypasses and sluices |
Turbine (hydraulic) | A structure that converts the energy of flowing water into mechanical energy. There are several turbine types with different configurations, the most common are Francis and Kaplan (see definitions below) |
Kaplan turbine | An “axial”, vertical, propeller-like turbine used for lower pressure heads (less than 100 m). Smaller in overall size (relative to Francis), typically has 4 to 8 adjustable blades and a specific running speed ranging 250 to 850 rpm |
Francis turbine | A “radial” turbine used for higher pressure heads (100 to 500 m). Larger in overall size (relative to Kaplan), typically has 16 to 24 fixed blades and a specific running speed of 50 to 250 rpm |
Turbine bypass | A structure that fish can enter from the gatewell, bypasses the turbines and powerhouse through a series of channels, and discharges downstream into the tailrace. Typically used for juvenile salmonids |
Fish injuries/impacts | |
Abrasion | Damage to skin and/or scales |
Blade strike | Turbine blade striking a fish. Can result in injuries/mortality from grinding (depending on blade spacing, small fish more prone to this), bruising, and cuts of varying severity (superficial, mortal wounding) |
Barotrauma | Damage caused from exposure to rapid changes in barometric pressure, typically during turbine passage. The most common injuries/mortalities are related to swim bladder ruptures. In the presence of high total dissolved gasses, rapid pressure changes can cause gas embolisms in tissues/organs and other symptoms of gas bubble disease |
Descaling | Scale loss. Often expressed as a percentage of the scale loss on the whole fish (e.g., 20% scale loss) |
Entrainment | When fish (non-) volitionally pass through hydropower infrastructure |
Hemorrhage | Bleeding, blood loss |
Impingement | When a fish becomes pinned/trapped against an infrastructure |
Cavitation | Formation of gas bubbles in water, which when collapsed generate a pressure wave that can cause ill effects for fish in close proximity |
Mechanical effects | Damage (injury/mortality) caused from fish physically interacting with structures (e.g., blade strike) |
Pressure effects | Rapid changes in pressure (perpendicular to surface, dorsoventral) during passage that can cause fish damage |
Shear effects | Rapid changes in pressure (parallel to surface, anteroposterior) during passage that can cause fish damage |
Turbulence effects | Damage (injury/mortality) to fish caused by turbulent water (irregular movement of water) |
General terms | |
Forebay | Impoundment area directly above a hydropower facility |
Head | Difference in elevation between two water levels (e.g., reservoir water level and tailrace). There are various operational head definitions (see [34]) |
Passive Integrated Transponder (PIT) tag | A small tag implanted into a fish that transmits a unique code when activated. Can be used to track fish passage and survival through specific routes and river systems |
Tailrace | A channel downstream of turbine outlets discharged water flows away from the facility |
Telemetry | A system for tracking fish movements through specific routes at a facility as well as along watercourses. Common methods are acoustic, radio, and passive integrated transponder (PIT) tag telemetry |