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- To present the external and internal physical processes that determine how water moves in lakes and streams.
- To discuss some of the important consequences of water movement for other aspects of physical habitat in lakes and streams, and for species that inhabit these systems.

- Laminar: layered and orderly
- Turbulent: disordered

Laminar → Turbulent Transition

- The greater the difference in fluid velocity, the greater the probability of turbulence.
- The greater the differences in density, the greater the difference in velocity needed to get turbulence.

Laminar → Turbulent Transition

- The Richardson Number (Ri) is used to predict when turbulence will occur at boundary layer in stratified water.
- Ri = f(difference in density, velocity)
- Ri > 0.25 = Stable flow
- Ri <0.25 = Turbulent flow

- At surface
- At metalimnion

Types of Water Movement in Lakes

- Langmuir circulation
- Metalimnetic tilting and entrainment
- Seiches
- Internal progressive waves

Quake Lake, MT

- Lake Erie water displacement
- 11/14/2003

Water Movement Streams and Rivers

- Discharge (Q) → How much water is moving at a particular time?
- The Hydrograph → How does Q change over time?
- Floods → Extreme Q-events!

- Q = WDU
- Q = discharge, m3 / sec
- W = width, m
- D = depth, m
- U = velocity, m / sec

http://nwis.waterdata.usgs.gov/mt/nwis/rt

Floods – Extreme Discharge Events

- Flood frequency (e.g., 50-yr, 100-yr)
- What does it really mean?

- Probability of occurrence does not depend on the past.

Recurrence Interval – DESCRIPTIVE

- Time (e.g., years) between past occurrences of a random event.
- T = (n + 1) / m
- n = years of record
- m = rank magnitude of flood, where 1 is highest, 2 is next highest, etc.

Year Discharge rank (m) recurrence interval (n+1)/m

1976 57,406 10 1.1

1972 75,806 9 1.2

1970 81,806 8 1.4

1977 95,106 7 1.6

1974 99,706 6 1.83

1973 112,006 5 2.2

1979 112,006 4 2.8

1975 114,006 3 3.7

1971 123,006 2 5.5

1978 147,006 1 11

- Relies on the mathematics of probability
- Flood probability (P) = Likelihood than an annual maximum flow will equal or exceed the value of a flood event of a given recurrence interval.
- P = 1 / Recurrence interval (T)

Year Discharge rank (m) recurrence interval (n+1)/m

1976 57,406 10 1.1

1972 75,806 9 1.2

1970 81,806 8 1.4

1977 95,106 7 1.6

1974 99,706 6 1.83

1973 112,006 5 2.2

1979 112,006 4 2.8

1975 114,006 3 3.7

1971 123,006 2 5.5

1978 147,006 1 11

P = 1 / T = 0.55

- Discharge has exceeded that value on average once every 100 years in the past.
- What is the minimum number of years of record needed to identify a 100-yr flood?
- What is the probability of such a flood occurring next year?
- If it occurs next year, how about the year after that?
- What is the probability of a 100-yr flood occurring in the next 100 years?

Network-scale controls on water movement

- Low-order: high gradient, low discharge, often geologically “constrained”.

Network-scale controls on water movement

- Low-order: high gradient, low discharge, often geologically “constrained”.
- Mid-order: intermediate gradient, intermediate discharge, “beads on a string”.
- High-order: low gradient, high discharge, often “unconstrained”.

Network-scale controls on water movement

- Low-order: high gradient, low discharge, often geologically “constrained”.
- Mid-order: intermediate gradient, intermediate discharge, “beads on a string”.
- High-order: low gradient, high discharge, often “unconstrained”.

Depth

Shallow

Shallow

Low

Moderate

High

Velocity

Low

Moderate

Gradient

Moderate

Circulating

Flow

Turbulent

Laminar

Peb/Sand

Substrate

Peb/Grav

Grav/Cob

Water Substrate = Reach Types

Cascade

Riffle

Run

Pool

Shallow

Very High

High

Very Turbulent

Cob/Boulder/Bedrock

Depth

Shallow

Shallow

Low

Moderate

High

Velocity

Low

Moderate

Gradient

Moderate

Circulating

Flow

Turbulent

Laminar

Peb/Sand

Substrate

Peb/Grav

Grav/Cob

Water Substrate = Reach Types

Cascade

Riffle

Run

Pool

Shallow

Very High

High

Very Turbulent

Cob/Boulder/Bedrock

Fine-scale patterns of flow in streams and rivers

- What is the boundary layer?
- Implications in streams
- Implications in lakes
- Implications for respiration

- Adds “effective” mass
- Clogs filters
- Impedes movement of small organisms

- Fish, amphibians, and insects rely on diffusion of oxygen from environment
- Need oxygen gradient from outside (high) to inside (low)
- Can deplete oxygen in boundary layer → diffusion stops
- Need to increase water flow (i.e., ↓ boundary layer):
- > Select parts of the stream with high flow
- > Move – whole animal or just gills:
- - Flaring gills in fish
- - Waving gills in insects
- - Push-ups in insects and salamanders

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