River Notes

Drainage Basin

  • An area where water from precipitation is transferred to oceans, lakes, or streams.

  • Divided by watersheds (drainage divides).

    • Watershed: Imaginary lines separating adjacent basins, similar to a sloping roof's edges.

Bradshaw Model

  • Illustrates river characteristics (width, depth, speed) as they flow downstream.

  • Considers factors affecting rivers:

    • Geology: Soft rocks = faster erosion, wider channels; hard rocks = narrower channels.

    • Climate: Rainfall volume impacts river size.

    • Vegetation: Shapes rivers and reduces erosion.

    • Human Activities: Urbanization & agriculture increase runoff; dams alter flow.

    • Topography: Steeper land increases river speed and erosion.

Hydrological Cycle

  • Movement of water between biosphere, atmosphere, lithosphere, and hydrosphere.

  • Local drainage basin has one input (precipitation) and two major outputs (evapotranspiration, runoff).

  • Water stores: vegetation, surface, soil moisture, groundwater, water channels.

Precipitation

  • Main input into drainage basin; includes rain, snow, frost, hail, dew.

  • Key characteristics affecting local hydrology:

    • Total amount, intensity, type, geographic distribution, variability.

Evapotranspiration

  • Combination of evaporation and transpiration; water vapor escapes surfaces into the atmosphere.

Order of Streams

  • First-order streams have no tributaries; they connect to form higher-order streams.

  • Stream gradient: Elevation drop over distance affecting stream energy.

Erosion Types

  1. Hydraulic Action: Water enters rock cracks, causing splits.

  2. Abrasion: Water carrying particles smooths rocks.

  3. Attrition: Rocks smash into each other.

  4. Bed Load: Rolling rocks erode as they move downstream.

  5. Solution/Corrosion: Chemical erosion, e.g., acidic water dissolving limestone.

Factors Affecting Erosion

  • Load weight/sharpness

  • Water velocity

  • Slope gradient

  • Geology

  • pH levels

  • Human impacts

Meanders

  • Curves or bends in rivers formed by water flow hitting obstacles.

  • Erosion on outer banks; deposition on inner banks over time.

V-Shaped Valleys

  • Formed by water erosion, especially in mountainous areas.

  • Hydraulic action and freeze-thaw weathering contribute to valley shaping.

Oxbow Lakes

  • U-shaped lakes formed when meanders are cut off.

River Processes

  • Formation:

    1. Pools and Riffles: Changes in depth affect flow speed.

    2. Helicoidal Flow: Curved river flow due to pools and riffles.

    3. Outer Bend Erosion: Erosion on outer bends, deposition on inner bends.

  • Deposition: Occurs when flow slows and sediment settles, influenced by gradient and flow velocity.

Types of Landforms

  1. Alluvial Fan: Fan-shaped deposit where water exits a canyon.

  2. Floodplain: Land adjacent to rivers that floods during high discharge.

  3. Levee: Embankments to prevent flooding.

  4. Deltas: Formed where rivers enter a larger body of water, slowing and dropping sediment.

Transport and Hjulstrom Curve

  • Types of Transportation: Bedload, suspended load, dissolved load.

  • Hjulstrom Curve: Shows particle erosion and deposition thresholds based on size and velocity.

Hydrographs

  • Measure how river discharge responds to rainfall.

  • Key Components: Rising limb, peak discharge, lag time, base flow, recessional limb.

    • Urban hydrographs differ due to more impermeable surfaces.

Waterfalls Formation

  1. Differential erosion creates a waterfall due to soft rock being undercut.

  2. Overhang collapses, creating a plunge pool below.

  3. Waterfall retreats over time, forming a gorge.

Lower Course vs. Upper Course

  • Lower Course: Wide, deep, fast flow; useful for industry.

  • Upper Course: Near source, slow flow, characterized by V-shaped valleys.

Distributaries

  • Streams that split from a river, do not return to the mainstream.

Equations

  • Discharge: v (velocity) x A (area)

  • Cumecs: Cubic meters per second.

  • Aquifer: Water storage in permeable rock.

  • Water Budget Formula: P = R + E + ΔS (P = precipitation, R = runoff, E = evapotranspiration, ΔS = storage change).

V-shaped valleys are formed primarily through water erosion, especially in mountainous areas. The process involves:

  • Hydraulic Action: Water exerts pressure on rock cracks, causing them to break apart.

  • Freeze-thaw weathering occurs when water seeps into rock fissures, freezes, expands, and eventually fractures the rock.

  • Erosion: Over time, the constant flow of water down the slope erodes the landscape, creating a V shape as the valley deepens and widens.

  • These valleys are characterized by steep sides and a narrow floor, reflecting the intense erosion process in areas where the river flows swiftly.