Watershed assessment

Question 1

What were some of the findings from Ah’ ta’ ape creek?

Answer 1

• channel aggradation
• avulsions
• infilling
• widening of channel
• subsurface flow in lower reaches
• movement of some log jam complexes
• loss of spawning and rearing habitat

Question 2

What overarching controls influence channel equilibrium

Answer 2

• local geology (bedrock control)
• geomorphic/glacial history
• climate, riparian vegetation and land use
• geology

Question 3

watershed

Answer 3

-topographic high points where all same water will collect

Question 4

To understand channels you need to look at?

Answer 4

• land use
• disturbances
• sediment
• slope and grain size

Question 5

What characteristics influence the amount and rate at which excess rainfall or snowmelt will be delivered to a channel?

Answer 5

topographic and physiographic characteristics

Question 6

small watershed

Answer 6

<250 km2
dominant land phase and overland flow
highly sensitive to high intensity short rainfalls

Question 7

large water shed

Answer 7

> 2500km2
well developed channel networks and phases, channel storage
less sensitive to high intensity short rainfalls

Question 8

what does the gradient say about the channel

Answer 8

-steeper, higher bed load, vertical erosion
-less steep, medium to one bed load, lateral erosion wider channel
lower slope more meanders

Question 9

What is hydraulic geometry?

Answer 9

rivers always trying to achieve equilibrium- all of the water and some/all of the sediment
Q=wxdxv
sediment supply=sediment transport

Question 10

What will rivers adjust to get sediment supply and transport at equilibrium?

Answer 10

• width
• depth
• slope
• grain size

Question 11

Why is it important to understand sediment in river channels?

Answer 11

• power of stream (greater slope, greater grain size)

- variability of habitat (greater variability the better)

Question 12

If sediment caliber (grain size- silt to boulders) increases what happens with channel stability and the channel gradient?

Answer 12

the channel stability will decrease and the

channel gradient will increase

Question 13

what happens to channel stability when sediment supply increases?

Answer 13

channel stability decreases with sediment supply

Question 14

What does the number of channels say about the stability?

Answer 14

the higher number of channels the more unstable it is

Question 15

list a few multiple channels

Answer 15

• wandering
• anastomosed
• braided

Question 16

list a couple single channels

Answer 16

• straight

- meandering

Question 17

Channel morphology is based on

Answer 17

• slope
• sediment supply
• stability

Question 18

In a single channel stability increases with?

Answer 18

sinuosity

Question 19

what happens when sediment supply is higher than transport

Answer 19

too high for streams capacity
unpredictable
river is laterally active
bank erosion occurs during blowout events (floods)
avulsion occurs

Question 20

What is more stable a straight or meandering channel?

Answer 20

meander because higher sinuosity=high stability

Question 21

What happens when sediment supply increases but water discharge is the same?

Answer 21

aggradation, widening of the channel and higher instability

Question 22

what happens when sediment supply stays the same but water discharge increases?

Answer 22

narrowing and down cutting of the channel

Question 23

what happens when sediment supply stays the same but water discharge decreases?

Answer 23

aggradation, narrower channel, instability

Question 24

What components can we look at to determine the stability of a channel

Answer 24

• w:d:slope
• sediment supply
• local geology
• geomorphic history
• climate, riparian zone, land use
• number of channels
• sinuousity