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# Lecture Goals - PowerPoint PPT Presentation

Lecture Goals. 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.

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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

• Langmuir circulation

• Metalimnetic tilting and entrainment

• Seiches

• Internal progressive waves

Quake Lake, MT

Just because you saw it, doesn’t make it real…

Langmuir Streaks

Bigfoot

• Lake Erie water displacement

• 11/14/2003

• 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

• Flood frequency (e.g., 50-yr, 100-yr)

• What does it really mean?

• Probability of occurrence does not depend on the past.

• 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

Channel

Reach

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

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

• High-order: low gradient, high discharge, often “unconstrained”.

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

• High-order: low gradient, high discharge, often “unconstrained”.

Network

Channel

Erosion

Entrainment

Deposition

Erosion

Entrainment

Deposition

Variation in velocity  Variation in substrate size = Habitat diversity

Longitudinal

Lateral

Network

Channel

Reach

Water  Substrate = Reach Types

Riffle

Pool

Depth

Shallow

Shallow

Low

Moderate

High

Velocity

Low

Moderate

Moderate

Circulating

Flow

Turbulent

Laminar

Peb/Sand

Substrate

Peb/Grav

Grav/Cob

Water  Substrate = Reach Types

Riffle

Run

Pool

Shallow

Very High

High

Very Turbulent

Cob/Boulder/Bedrock

Water  Substrate = Reach Types

Riffle

Run

Pool

Depth

Shallow

Shallow

Low

Moderate

High

Velocity

Low

Moderate

Moderate

Circulating

Flow

Turbulent

Laminar

Peb/Sand

Substrate

Peb/Grav

Grav/Cob

Water  Substrate = Reach Types

Riffle

Run

Pool

Shallow

Very High

High

Very Turbulent

Cob/Boulder/Bedrock

Patterns Resulting from Water  Substrate Interactions

Silt / Sand

Boulder / Cobble

Network

Channel

Reach

Microhabitat

• What is the boundary layer?

• Implications in streams

• Implications in lakes

• Implications for respiration

• 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