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

Types of flow

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 (R i ) is used to predict when turbulence will occur at boundary layer in stratified water. R i = 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 Circulation

Langmuir Streaks Quake Lake, MT

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

Metalimnetic Tilting and Entrainment (or Erosion)

Seiches

Lake Erie water displacement 11/14/2003

Internal Progressive Waves

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, m 3 / sec W = width, m D = depth, m U = velocity, m / sec

The Hydrograph

USGS Real-Time Water Data

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 , , , , , , , , , ,

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 , , , , , , , , , , 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?

Water Movement in Streams and Rivers Network Channel Reach

Water Movement in Streams and Rivers Network

Network-scale controls on water movement Low-order: high gradient, low discharge, often geologically “constrained”.

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”.

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”.

Beads on a String

Channelized

How does mean velocity change moving downstream?

Water Movement in Streams and Rivers Network Channel

Erosion Entrainment Deposition Channel-scale variation in water velocity and direction

Erosion Entrainment Deposition Variation in substrate size

Variation in velocity  Variation in substrate size = Habitat diversity Lateral Longitudinal

Water Movement in Streams and Rivers Network Channel Reach

Water  Substrate = Reach Types RifflePool

Water  Substrate = Reach Types RifflePoolRunCascade Shallow High Moderate Turbulent Grav/Cob Deep Low Circulating Peb/Sand Shallow Very High High Very Turbulent Cob/Boulder /Bedrock Depth Velocity Gradient Flow Substrate Shallow Moderate Laminar Peb/Grav

Water  Substrate = Reach Types RifflePoolRunCascade

Water  Substrate = Reach Types RifflePoolRunCascade Shallow High Moderate Turbulent Grav/Cob Deep Low Circulating Peb/Sand Shallow Very High High Very Turbulent Cob/Boulder /Bedrock Depth Velocity Gradient Flow Substrate Shallow Moderate Laminar Peb/Grav

Patterns Resulting from Water  Substrate Interactions Boulder / Cobble Silt / Sand

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

Change in Velocity with Depth

Implications in streams

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