GEOL 101 Study Notes

GEOL 101: Key Concepts and Learning Objectives

Learning Objectives

• Communication Skills

  • Focus on Data Synthesis & Quantitative Skills

  • Reach out to CSI for successful application of geological principles.

Stream Generation and Geometries

• Key Concepts in Stream Generation:

  • Understand the concept of stream generation and its implications on drainage systems.

  • Friction Controls the velocity of water in streams.

• Geometries of Drainage Networks:

  • Different drainage network formations are influenced by site characteristics:

  • Dendritic: resembling a tree, formed in homogeneous materials.

  • Radial: emanates from a point, typically a hill or volcano.

  • Rectangular: characterized by right angles, follows joint control.

  • Trellis: resembles a garden trellis, often where different rock types exist.

  • Parallel: flows parallel to each other, common in steep areas.

Factors Controlling Drainage Network Formation

• Geological Influences:

  • Drainage networks are mainly influenced by the overlying geology.

  • The hardness and softness of rock types impact erosion and weathering, thereby affecting stream patterns.

  • Geologic Features: Certain features may promote specific drainage types.

Watersheds and Drainage Basins

• Definitions:

  • Watershed: Area that channels precipitation to outlets like rivers and oceans (NOAA, 2020).

  • Metaphor: Similar to a shower where all surfaces (bathtub, walls, etc.) direct water into the drain.

• Visual Explanation:

  • Drainage divides and watersheds denote particular drainage areas where water flows toward specific outflow points.

  • If water falls in different drainage basins, it reaches different drainage points (yellow star vs. red star).

Importance of Watershed Dynamics

• Environmental Sustainability:

  • Upstream land use profoundly affects downstream water resources.

  • Example: Chesapeake Bay Watershed is a 5-state region where precipitation drains into the Bay, carrying materials along with it.

  • The cumulative impact from numerous streams can lead to significant changes or catastrophes within the ecosystem.

Stream Flow Description

• Flow Characteristics:

  • Calculating Discharge: Formula $D = A^* v$

  • Where:

    • $D$ = Discharge (cubic length per time)

    • $A$ = Cross-sectional area of a stream (square length)

    • $v$ = Average velocity of stream (length per time)

• Velocity Profiles in Streams:

  • Discusses the variations in velocity along stream width and depth.

  • Friction: Major control on both horizontal and vertical velocity profiles; higher friction leads to lower velocity.

Example Calculations of Discharge

• Question 1: Given a rectangular stream cross-section with:

  • Height = 3 m, Base = 10 m, Average Velocity = 5 m/s.

  • Calculation of discharge:

  • $A = 10 m imes 3 m = 30 m^2$

  • $D = 30 m^2 imes 5 m/s = 150 m^3/s$.

• Question 2: Discharge = 54 m³/s, Cross-section Height = 2 m, Base = 9 m.

  • To find average velocity:

  • $A = 2 m imes 9 m = 18 m^2$

  • $D = 54 m^3/s$, hence $v = D/A = 54 m^3/s / 18 m^2 = 3 m/s$.

• Limitations: Velocity is not uniform across stream profiles; it varies due to numerous factors including friction and geometry.

Flooding Concepts

• Key Terminology:

  • Floodplain: The adjacent area to a river which floods during excursions of the water.

  • Flood Frequency:

  • Annual Probability: Likelihood of a flood of a certain magnitude occurring in a given year.

  • Related to recurrence interval concepts from previous units.

• Graph Analysis:

  • Understanding annual peaks in discharge gives insight into probabilities.

Flood Frequency Calculation

• 100-Year Flood: Describes the flood that has a 1% probability of occurring in a given year.

• Other Classifications:

  • 10-Year Flood: 10% chance in a year.

  • 500-Year Flood: 0.2% chance in a year.

• Real-World Application: Evaluation of individual property flood risks over time, extending to mortgage implications (e.g., 95% chance over 30 years for a 10-year flood).

Summary of Flood Concepts

• Recapitulation around floodplain definitions and frequency relationships, focused on understanding the environmental dynamics involved and implications for planning and sustainability.

• Visual representations enhance comprehension of varying scales of floods and their respective probabilities.

Overall, these concepts emphasize the intersection of geology, hydrology, and environmental science, and underline the importance of integrating these considerations into sustainable management practices.