12 Stream and Stream Sediments.pptx 1 (1)

The Origin and Evolution of the Marine Environment (MSCI*112)

Instructor Details

  • Instructor: Prof. Stewart

  • Phone: [Contact Not Provided]

  • Email: jstewar6@coastal.edu

  • Office Location: Science II 221

Streams and Stream Sediments

  • The study of streams and their interactions with sediment is crucial for understanding the geologic and hydrologic processes at play in the marine environment.

Geographic Locations and Types of Sedimentary Environments

  1. Continental Environments

    • 1. Lake

    • 2. Rivers

    • 3. Glacier

    • 4. Desert Lake

  2. Shoreline Environments

    • 5. Delta

    • 6. Beach

    • 7. Tidal Flat

  3. Marine Environments

    • 8. Deep Sea

    • 9. Continental Shelf

    1. Organic Reef

    1. Continental Margin/Slope

The Hydrologic Cycle

  • Definition: The hydrologic cycle refers to the continuous movement of water through the hydrosphere, atmosphere, biosphere, and lithosphere.

Components of the Hydrologic Cycle:

  • Evaporation:

    • Total water evaporated: 380,000 ext{ km}^3

    • Water evaporated from oceans: 284,000 ext{ km}^3

    • Water evaporated from land: 96,000 ext{ km}^3

    • Total precipitation: 320,000 ext{ km}^3

    • Runoff on land: 36,000 ext{ km}^3

    • Infiltration: decrease in water level making groundwater.

  • Definitions of Terms:

    • Runoff: Water that flows over land after rainfall.

    • Infiltration: Water that seeps into the ground to form groundwater.

    • Evapotranspiration: The sum of evaporation and transpiration processes returning water to the atmosphere.

Streams Formation and Characteristics

  • Formation of Streams:

    • Streams are formed when runoff gathers and flows down slopes in channels.

    • Streams can vary in size, being called brooks, creeks, or rivers based on width.

    • Example: Creek in South Dakota, Mississippi River in Louisiana, Waccamaw River in North Carolina.

  • Importance of Streams:

    • Streams are significant geological agents that erode landscapes, transport, and deposit sediments.

    • They are vital for transferring mass from land to ocean basins.

    • Notably, Earth is the only planet in the solar system currently known to have flowing water.

Anatomy of a Stream

  • Channel: A V-shaped path shaped by flowing water.

  • Riverbanks/Levees: The two sides of the channel that confine the stream.

  • Valley: A depression that houses the channel and is flanked by uplands.

  • Floodplain: A flat expanse in the valley beyond the channel.

Channel Types and Characteristics

  • Straight Channel: Consistent path, usually found in youth stage.

  • Meandering Channel: Sinusoidal path, typically formed in mature stages.

  • Oxbow Lake: The result of river divergence which leaves cut-off sections resembling lake formations.

Stream Flow Zones

  1. Zone 1: Headwaters

    • Characterized by fast-flowing water down steep slopes, creating deep V-shaped valleys with features like waterfalls and rapids.

  2. Zone 2: Transfer zone

    • Water flows down gentle slopes, where wider valleys begin to meander.

  3. Zone 3: Depositional zone

    • At low elevations, rivers meander across broad, nearly flat valleys and may transform into deltas as they flow into the ocean.

Stream Dynamics: Flow Velocity & Hydraulics

  • Flow Velocity: Defined as the speed of water flowing in a stream. Influences sediment transport and river morphology.

Key Points on Flow Velocity

  • Influencing factors include channel gradient, water volume, and channel shape.

  • Maximum flow velocity typically occurs in the center of straight channels.

  • In bended channels, the highest velocity shifts to the outside of bends; this is where the thalweg (deepest part of a stream) typically lies.

Stream Floodplains and Sediment Deposition

  • In Between Floods: Sediments accumulate primarily within the channel itself.

  • During Floods: Water spills over the floodplain, reducing speed, leading to sediment deposition along the channel borders, forming levees over time.

  • Post Flood Conditions: Levees can confine streams to their channels, even during high water.

Types of Stream Flow

  • Laminar Flow: Occurs at low velocities, shallow depths, and high viscosities.

  • Turbulent Flow: High velocities characterize it and is more chaotic.

Discharge of Streams

  • Definition: Discharge is the volume of water passing through a section of a stream per unit of time.

  • Formula: Q = A imes V

    • Where:

    • $Q$ = Discharge

    • $A$ = Cross-sectional area of the stream

    • $V$ = Velocity of the stream

  • Variability: Discharge changes seasonally based on precipitation and runoff levels.

Global Discharge Statistics of Major Rivers

Rank

River

Discharge (m³/sec)

% of Total

mm/yr entering oceans

Runoff Ratio

1

Amazon, Brazil

190,000

13.0

0.47

2

Congo, Zaire

42,000

2.9

0.25

3

Yangtse Kiang, China

35,000

2.4

0.50

4

Orinoco, Venezuela

29,000

2.0

0.46

…

(Other rivers listed as per original data).

Drainage Basins

  • Definition: Drainage basins are regions where runoff drains into a specific stream, also referred to as catchments or watersheds.

  • Separation: Adjacent drainage basins are separated by elevated land called drainage divides.

Patterns of Drainage Networks

  • Dendritic: Branching patterns resembling tree structures, commonly formed by uniform bedrock.

  • Radial: Streams diverge from a central uplift, such as plateaus or volcanoes.

  • Rectangular: Form rectangular networks, often influenced by jointed rock structures.

  • Trellis: Represents tributaries that are aligned parallel to ridges, often resulting from geological faulting or folding processes.

Stream Order and Discharge

  • Stream Order: A numerical system indicating the level of branching; Strahler order: a stream's order increases by 1 only where two streams of the same order converge.

Flood Management and Implications

Flood Dynamics

  • Definition: A flood occurs when the river discharge exceeds the channel's storage capacity, causing water to overflow.

  • Recurrence Interval: Refers to the expected time between successive floods of similar discharge; used to calculate flood risk probabilities.

  • Example: A flood maximum of 1800 ext{ m}^3/ ext{s} has a probability of occurrence at 10% over 12 years.

Climate Change Considerations

  • Increased global warming contributes to a greater moisture capacity in the atmosphere.

  • Such changes elevate the probabilities of extreme weather events leading to severe flooding.

Flood Control Measures

  • Flood management strategies often include the construction of dams, levees, and floodwalls; however, these can create downstream risks, leading to intensified flooding.

  • Proposals to establish floodways and reduce human occupancy in flood-prone areas can help mitigate extreme flood damage.

Deltas: The Mouths of Rivers

Delta Formation and Structure

  • Deltas are formed as rivers deposit sediment in a vast collection at river mouths, shaping unique ecological environments.

  • Components of Delta Structure:

    • Topset beds: Upper strata of accumulated sediments.

    • Foreset beds: Crystalline sand deposits facing the water flow direction.

    • Bottomset beds: Comprised of the finest clays and silts settled in calm waters.

Deltas of Notable Rivers

  • Example: The Mississippi River delta showcases a continuous relationship of sediment deposition and erosion influenced by various hydrological and geological phenomena.

Stream Behavior and Geosystems

  • Streams function as geosystems that undergo adjustments based on changes in hydrometric conditions over time, including floods, erosion, sediment transport, and deposition patterns.

  • The longitudinal profiles of streams illustrate how altitude varies significantly from headwaters to river mouths.

  • Factors like climate, slope, resistance of underlying geological material, and water volume play critical roles in shaping river ecosystems and landscapes.