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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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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.


Types of flow

  • 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


Water Movement in Lakes

  • At surface

  • At metalimnion


Types of Water Movement in Lakes

  • Langmuir circulation

  • Metalimnetic tilting and entrainment

  • Seiches

  • Internal progressive waves



Langmuir Streaks

Quake Lake, MT


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

Langmuir Streaks

Bigfoot





Seiches

  • 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!


Discharge

  • Q = WDU

  • Q = discharge, m3 / sec

  • W = width, m

  • D = depth, m

  • U = velocity, m / sec



USGS Real-Time Water Data

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?


Floods are RANDOM

  • 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.



Recurrence Interval

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


Flood Forecasting

  • 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)


Recurrence Interval

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


100-yr Flood

  • 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”.







Variation in substrate size

Erosion

Entrainment

Deposition


Variation in velocity  Variation in substrate size = Habitat diversity

Longitudinal

Lateral



Water  Substrate = Reach Types

Riffle

Pool


Deep

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


Water  Substrate = Reach Types

Cascade

Riffle

Run

Pool


Deep

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


Patterns Resulting from Water  Substrate Interactions

Silt / Sand

Boulder / Cobble


Water Movement in Streams and Rivers

Network

Channel

Reach

Microhabitat


Fine-scale patterns of flow in streams and rivers

  • What is the boundary layer?

  • Implications in streams

  • Implications in lakes

  • Implications for respiration




Implications in lakes

  • Adds “effective” mass

  • Clogs filters

  • Impedes movement of small organisms


Implications for respiration

  • 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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