Lecture 11 - Hydroelectric Systems Flashcards
What are the effects of hydroelectric systems on aquatic ecosystems? (9)
Entrainment Fish passage issues Flows Gravel Large woody debris Nutrients Ramping rates Temperature TGP
Entrainment (4)
When fish are drawn into the penstocks or spillways due to:
- Attractant flows
- Concentrations of zooplankton
- Simply cannot avoid the high velocities near the penstock intakes
Tends to be a juvenile fish problem, since escape velocity is a function of fish size (larger fish can swim faster) (e.g. juvenile Kokanee = big problem)
How can we avoid entrainment issues? (3)
Change the timing of operation
- some fish species may be active at certain times of year
- eg. Annual maintenance
Screening or deflector
Use fish friendly turbines
Screening or deflectors (2)
Underground sound cannons, lights, bubbles, screens to keep fish from the main spillway
Removable spillway weirs provide a safe fish passage route (huge and very expensive but used on the Columbia)
Turbines (4)
Converts energy in the form of falling water into rotating shaft power
Run most efficiently at a particular speed, head, and flow combination
Design speed is determined by the head under which it operates (high, medium, or low head)
Can also be either impulse or reaction turbines
Reaction turbine (3)
Rotating element is fully immersed in water and is enclosed in a pressure casing
Blades are positioned so that pressure differences across them create lift forces (like an aircraft) which causes them to rotate
Eg. Francis turbine and Kaplan turbine
Francis turbine (2)
Type of reaction turbine
Variable fish mortality, depending on the head, turbine rotating speed, and opening/shape of wicket gates
Kaplan turbine (2)
Type of reaction turbine
Most fish friendly design
Impulse turbine (3)
Runner operates on air, driven by a jet of water
A nozzle converts pressurized low velocity water into a high speed jet
The rubber blades reflect the jet so as to maximize the change of momentum or the water and thus maximize the force on the blades
Eg. Pelton turbine
Pelton turbine (2)
Type of impulse turbine
Lethal to fish
How can we avoid fish passage issues? (2)
Remove the dam - especially at the end of its life (this is becoming increasingly more popular as water license renewals are becoming more expensive)
Provide fish passage using fish ladders, fish ways etc.
What things should be considered in fishway design? (10)
Lack of attraction flow False attraction flow Inconsistent jump signals No resting water Excessive turbulence High velocities Injury, mortality, predation Temperature effects/warming Loss of organic matter/gravel downstream Distracting, stressing fish
Flows (2)
Flow information is specific to species, life history, and time of year
Huge topic due to high value of water which can either be used to benefit ecosystems or for power generation
How can we avoid flow issues? (2)
Release more water into the river
Develop better fish-flow science - better understanding of flow needs for salmon, not only in terms of habitat suitability, but also in terms of food availability, predators, temperature etc. (better modelling)
Gravel (3)
Dams block the movement of gravel downstream
As a result, suitable spawning and rearing sized gravel decreases over time and contributes to loss of salmonid abundance (eventually extirpating salmon stocks)
Eg. John Hart Dam
How can we fix gravel recruitment issues? (3)
Replace the gravel downstream from a dam
Build spawning platforms
Build off-channel spawning channels that see protected from the extreme flow events
Large woody debris (3)
Dams block the movement of large woody debris downstream
As a result, the complexity of the channel and suitability for rearing salmonids declines, contributing to a depression of salmon stocks
Eg. Seymour River
How can we fix large woody debris recruitment issues? (2)
Replace the wood
Build off-channel rearing habitat protected from extreme flow events
Nutrients (3)
Dams trap nutrients upstream due to increased sedimentation and longer water retention times
Productivity of both the reservoir and rivers and lakes downstream decrease over time contributing to the long-term loss of productive capacity and decline in salmonid abundance
Eventually salmonid stocks and other species will become depressed as the stream is less productive
How can we fix nutrient loss issues? (2)
Stream fertilization
Lake and reservoir fertilization
Ramping rates (3)
The rate of change in output from a power plant - a maximum ramp rate is sometimes established to prevent undesirable effects due to rapid changes in discharge
Describes the speed at which the power output increases
Hydroelectric power plants have a very high ramp-up rate, which makes them particularly useful in peak load and emergency situations
Peaking plant (2)
Hydroelectric plants that are only used during periods of peak energy demand (ie. morning and evening periods)
The Wahleach Reservoir is a peaking plant - it is a small reservoir but has high head and is close to the huge energy demands of the Lower Mainland
What is the problem with ramping rates? (3)
Rapid fluctuations in discharge may cause:
Stranding: fish and inverts cannot respond quickly enough to stay in the water
Desiccation/freezing/heating/predation: can occur after stranding
Changes in community structure: net result of excessive ramping rates
What can be done to reduce the impacts of ramping rates? (5)
Negotiate maximum ramping rates -both ramping up and ramping down
Negotiate time of day for acceptable ramping (eg. Fish tend to experience increased stranding at night when flows are rapidly reduced as they cannot find escape routes)
Construct refuges that function as variable water levels
Conduct emergency fish salvages
Monitor the situation using adaptive management and develop improved ramping rate protocols
Temperature (3)
The water of a reservoir is usually warmer in the winter and cooler in the summer than it would be without a dam
As this water flows into its river, the altered temperature also affects range temperature of the river
This impacts the biota, often creating environments that are unnatural to the endemic species
What can be done to fix temperature differences in water released by dams? (3)
Design dams with a selective withdrawal structure so that you can select the top warmer water or the bottom cooler water at different times of year (eg. Top in summer, bottom in winter)
Stream fertilization - can compensate summer cold water to some degree by increasing productivity using stream fertilization (limited effectiveness because inverts are also growth limited by cold water)
Negotiate volumetric/time of year releases (not very practical)
Dissolved gas supersaturation/gas bubble trauma (3)
Potential threat to fish populations in B.C.
Individual atmospheric dissolved gases (oxygen, nitrogen, and trace argon and carbon dioxide) can be supersaturated without effects to aquatic organisms
However, when partial pressures of all gasses exceed atmospheric pressure, gas bubble trauma can occur
What are 3 physical effects of gas bubble trauma?
Bubble formation in the cardiovascular system causing blockage of blood flow and death
Overinflation and possible rupture of the swim bladder in smaller fish leading to dead or problems with over buoyancy
External bubbles in gills and mouth that can cause asphyxiation
What causes dissolved gas supersaturation? (3)
Entrainment of air in water released over dam sluice ways or low level ports or radial gates (causes white water at base of dam from elevated hydrostatic pressure)
Through turbo machinery associated with power generation (creates the same elevated hydrostatic pressure)
What can be done to avoid dissolved gas super saturation? (3)
Avoid spilling by better anticipating water levels in reservoirs
Better spillway design that avoid plunging pools or use baffle block spillways
Limit or restrict Synchronous Condense mode operations to specific facilities or times of year/day
