Video 3 C2: Dangers of low-head dams

Question 1

once dams are left untouched once they are no linger useful, they can become _______

Answer 1

dangerous

Question 2

contrary to popular belief, the ______ dams are usually the most dangerous

Answer 2

smallest

Question 3

In the US, dam safety regulations focus primarily on the possibility of a dam ______

Answer 3

breaching

Question 4

though they pose little danger in the event of a breach, low head dams create a public safety issue that has caused more ______ in the US than all ____ _______

Answer 4

fatalities; dam failures

Question 5

any location with fast moving water and high turbulence can be dangerous to _____ or _____

Answer 5

swimmers; kayakers

Question 6

the depth of the flow downstream of a dam is called _____

Answer 6

the tailwater

Question 7

the tailwater controls…

Answer 7

the location of the hydraulic jump

Question 8

when the tailwater is low, the hydraulic jump forms ____ from the dam. good or bad thing?

Answer 8

away; good- although the swimmer may experience turbulence, it isn’t too troubling

Question 9

as the tailwater rises, the jump moves ____ to the dam

Answer 9

closer

Question 10

what is the condition called when the hydraulic jump meets the dam? (2 options)

Answer 10

submerged or drowned jump

Question 11

why is it called the drowned jump?

Answer 11

because it creates an area of recirculation immediately downstream of the dam, meaning the person would keep falling under water and couldn’t get up- drowning

Question 12

what is the area of recirculation immediately downstream of the dam called sometimes?

Answer 12

a keeper

Question 13

what are someother bad things about the “keeper” area?

Answer 13

• not only could you drown, but this area also traps large debris in the motions, which could also pose danger to yourself
• water is often cold = increased chance of hypothermia/further disorientation
• the turbulence of the jumps reduces the buoyancy of a swimmer
• dams often span the entire width of the river, meaning there is no still water nearby for the swimmer to escape to

Question 14

what’re the best ways to mitigate these issues of drowned jump/submerged jump? (3)

Answer 14

1. keep people away: exclusion zones, signage, buoys
2. modify the structure: retrofits
3. remove these dams entirely

Question 15

removing dams help restore _____

Answer 15

ecosystems