Drainage Basin Hydrology and Geomorphology

• drainage basin

  • Definition: Areas where precipitation drains into bodies of water (rivers, lakes, wetlands, oceans).
  • System Type: Open systems with inputs, transfers, and outputs.
• key features of a drainage basin

  • Watershed: Boundary separating drainage basins.
  • Source: Origin point of the river.
  • Tributary: Smaller streams feeding into the main river.
  • Confluence: Meeting point of two rivers.
  • Floodplain: Flat area prone to flooding adjacent to a river.
  • Mouth: Endpoint where the river meets another body of water.
• Hydrological Cycle INPUTS

  • Primarily precipitation (rain, snow, hail)
• hydrological cycle FLOWS

  • Infiltration: Absorption of water into the soil.
  • Surface Runoff: Water flowing over the ground when saturation occurs.
  • Throughflow: Water movement through soil.
  • Base Flow: Groundwater feeding into rivers.
• hydrological cycle STORES

  • Vegetation: Interception of water on leaves.
  • Soil Moisture: Water retained in soil.
  • Aquifers: Underground water reserves that recharge slowly.
• Groundwater Recharge

  • Types:
  • Infiltration: Water entering from precipitation.
  • Seepage: Water moving from water bodies.
  • Artificially: Through irrigation or reservoirs.
• Cryosphere

  • Comprises snow and ice, containing up to 66% of Earth's freshwater.
• Outputs

  • Evaporation: Transformation of water into vapor, influenced by climate.
  • Transpiration: Water vapor released by plants; combined with evaporation to form evapotranspiration (ET).
• Water Budget

  • Annual balance of inputs (precipitation) and outputs (evapotranspiration).
  • Factors affecting the water budget include rock permeability, vegetation, drainage basin characteristics, seasonality, and climate.

  
• River Discharge

  • Definition: Volume of water passing a specific point in a river over time.
  • Change Downstream: Discharge generally increases downstream due to contributions from tributaries.
• Bradshaw Model


  Illustrates changes in river characteristics as they move downstream, highlighting various physical parameters.

  
• How does discharge change as you move downstream in a river?


  Discharge increases downstream.
• What happens to the occupied channel width as tributaries add water?

  Occupied channel width increases as tributaries add water.
• How does channel depth generally change downstream?


  Channel depth generally increases downstream.
• Why does average velocity increase downstream?

  Average velocity increases due to greater discharge and steeper gradients.
• What happens to load quantity as materials are eroded into smaller particles?


  Load quantity increases.
• How does load particle size change as erosion occurs?


  Load particle size decreases as erosion reduces size.
• What effect does channel bed roughness have as you move downstream?

  Channel bed roughness decreases downstream as finer sediments accumulate.
• How does slope angle change as you move downstream?


  Slope angle decreases downstream.
• What is the hydraulic radius and how is it calculated?


  The hydraulic radius is the cross-sectional area divided by the wetted perimeter; it indicates channel efficiency.
• Measuring River Discharge

  Steps:

  1. Depth: Measure depth at multiple points; calculate mean depth.
  2. Cross-Sectional Area: Width × Mean Depth.
  3. Velocity: Measure time for a float to travel a distance; calculate average speed.
  4. Discharge Calculation: Discharge = Cross-Sectional Area × Velocity.
• What is hydraulics the study of?


  Water flow influenced by gravity and friction
• What characterizes turbulent flow?


  It is characterized by eddies and supports particle suspension
• How does channel shape affect turbulence?


  Channel shape and velocity affect the occurrence of turbulence
• What is laminar flow?


  Smooth, layered flow typical in low-velocity conditions
• In what conditions is laminar flow often seen?


  It is often seen in groundwater
• Where is the velocity of stream flow fastest?


  In the center of the stream
• Where is the velocity of stream flow slowest?


  Near the banks and bed
• How does channel shape influence stream efficiency?


  It is measured by hydraulic radius
• What is the relationship between hydraulic radius and stream efficiency?


  A higher hydraulic radius indicates greater efficiency and less friction
• What factors contribute to channel roughness?


  Bed irregularities, vegetation, and bank contact
• How does channel roughness affect stream flow?


  It introduces friction into the flow
• River Erosion

  • Definition: The wearing away of land as water flows past the riverbed and banks, contributing material that is transported downstream.
• Types of Erosion

  • Vertical Erosion: Deepens the channel by cutting down into the riverbed.
  • Lateral Erosion: Widens the channel by cutting into the banks.
• Methods of River Erosion

  
• Factors Affecting Erosion Rates

  • river velocity, discharge, sediment load, and bank material.
• Processes of Transportation

  • Suspension: Small particles carried within the water.
  • Saltation: Larger particles are bounced along the riverbed.
  • Traction: Heavy particles roll or slide along the bottom.
  • Solution: Dissolved minerals carried in the water.
  • Floatation: Light materials, like debris, float on the surface.
• Stream Capacity

  • Maximum amount of debris a river can carry.
• Competence


  Diameter of the largest particle a river can transport.
• Critical Erosion Velocity

  • Minimum velocity required to move specific grain sizes.