Lecture 11 - Hydroelectric Systems

Question 1

What are the effects of hydroelectric systems on aquatic ecosystems? (9)

Answer 1

Entrainment 
Fish passage issues 
Flows 
Gravel
Large woody debris 
Nutrients 
Ramping rates 
Temperature 
TGP

Question 2

Entrainment (4)

Answer 2

When fish are drawn into the penstocks or spillways due to:

1. Attractant flows
2. Concentrations of zooplankton
3. 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)

Question 3

How can we avoid entrainment issues? (3)

Answer 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

Question 4

Screening or deflectors (2)

Answer 4

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)

Question 5

Turbines (4)

Answer 5

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

Question 6

Reaction turbine (3)

Answer 6

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

Question 7

Francis turbine (2)

Answer 7

Type of reaction turbine

Variable fish mortality, depending on the head, turbine rotating speed, and opening/shape of wicket gates

Question 8

Kaplan turbine (2)

Answer 8

Type of reaction turbine

Most fish friendly design

Question 9

Impulse turbine (3)

Answer 9

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

Question 10

Pelton turbine (2)

Answer 10

Type of impulse turbine

Lethal to fish

Question 11

How can we avoid fish passage issues? (2)

Answer 11

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.

Question 12

What things should be considered in fishway design? (10)

Answer 12

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

Question 13

Flows (2)

Answer 13

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

Question 14

How can we avoid flow issues? (2)

Answer 14

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)

Question 15

Gravel (3)

Answer 15

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

Question 16

How can we fix gravel recruitment issues? (3)

Answer 16

Replace the gravel downstream from a dam

Build spawning platforms

Build off-channel spawning channels that see protected from the extreme flow events

Question 17

Large woody debris (3)

Answer 17

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

Question 18

How can we fix large woody debris recruitment issues? (2)

Answer 18

Replace the wood

Build off-channel rearing habitat protected from extreme flow events

Question 19

Nutrients (3)

Answer 19

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

Question 20

How can we fix nutrient loss issues? (2)

Answer 20

Stream fertilization

Lake and reservoir fertilization

Question 21

Ramping rates (3)

Answer 21

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

Question 22

Peaking plant (2)

Answer 22

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

Question 23

What is the problem with ramping rates? (3)

Answer 23

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

Question 24

What can be done to reduce the impacts of ramping rates? (5)

Answer 24

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

Question 25

Temperature (3)

Answer 25

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

Question 26

What can be done to fix temperature differences in water released by dams? (3)

Answer 26

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)

Question 27

Dissolved gas supersaturation/gas bubble trauma (3)

Answer 27

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

Question 28

What are 3 physical effects of gas bubble trauma?

Answer 28

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

Question 29

What causes dissolved gas supersaturation? (3)

Answer 29

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)

Question 30

What can be done to avoid dissolved gas super saturation? (3)

Answer 30

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