Drainage Basins Study Notes

Drainage Basins

Chapter Overview

• Drainage Basins: Areas subdivided into watersheds and catchments that can vary in size. Most drainage basins are considered 'open'.

  • Sources: Bierman and Montgomery, 2020, Key Concepts in Geomorphology, 2nd Edition.

Types of Drainage Basins

Closed Drainage Basins

• Also known as Terminal or Endorheic basins.

• Characteristics:

  • No stream outlet present.

  • Water does not flow to an ocean or sea.

  • Water typically evaporates or infiltrates back into the ground.

• Ephemeral Lakes: After the water evaporates, what remains is referred to as ephemeral lakes.

  • Example Location: Deep Springs Valley, located just northwest of Death Valley National Park.

Continental Divide

• Definition: A geographical boundary that separates the flow of water to different oceans.

• Illustration:

  • Multiple oceans are referenced, including the Pacific Ocean, Arctic Ocean, Atlantic Ocean, and others along with examples of endorheic basins that do not drain to these oceans.

  • Mentioned Locations: Snow Dome and Triple Divide Peak exemplify continental divides.

Drainage Patterns

• Definition: Channel networks that show distinct characteristics in water and sediment transport.

• Factors Influencing Drainage Patterns: Controlled by earth materials, geological structure, tectonic setting, and the historical development of channels.

Basic Classifications of Drainage Patterns:

Dendritic Drainage Patterns

• Characteristics:

  • Resembles a tree structure; highly branched.

  • Formed on relatively horizontal rock or uniformly resistant crystalline rocks.

  • Observed in regions with a gentle slope and absence of major structural controls.

  • Formation Process: Developed primarily through random headward erosion.

  • Source: Bierman and Montgomery, 2020.

Parallel Drainage Patterns

• Description:

  • Found on moderate to steep slopes with elongate landforms, such as mountain ranges.

  • Streams maintain a swift and straight profile.

  • Not commonly observed and often limited in extent.

  • Example Location: Alpine slopes of the Chugach Range, Alaska.

Trellis Drainage Patterns

• Characteristics:

  • Dominated by geological structure involving dipping or folded rocks (e.g., the Appalachians).

  • Alternates between weak and resistant geological formations.

  • Small tributaries are nearly the same length on opposite sides of a main stream.

  • Source: Bierman and Montgomery, 2020.

Rectangular Drainage Patterns

• Definition:

  • Very regular pattern associated with jointed and horizontally aligned bedrock, often with faults.

  • Forms in low-relief topography and shows symmetry in drainage routes.

  • Common in areas of jointed sandstone and limestone.

  • Example Locations: Valley of Fire, Nevada; Gotel Mountains, Nigeria, and Cameroon.

Radial Drainage Patterns

• Characteristics:

  • Typically found on volcanoes or domes where the landform structure dictates the stream orientation.

  • Commonly seen in stratovolcanoes such as Mount Rainier.

  • Example Locations: Mount Fuji and Volcan Popo.

Annular Drainage Patterns

• Characteristics:

  • Occur around domes, basins, and small plutons.

Multibasinal Drainage Patterns

• Characteristics:

  • Formed by multiple mounds, hills, or knolls, usually in loose surficial deposits.

  • Examples: Sand dunes, kettle lakes (formed by melting ice), dolines (related to cave systems).

Contorted or Deranged Drainage Patterns

• Definition:

  • Lack coherent patterns; can emerge from the disruption of pre-existing drainage systems.

  • Often influenced by chaotic geologic structures such as dikes and veins in metamorphic rocks or thick glacial deposits.

Centripetal Drainage Patterns

• Characteristics:

  • Converge inward toward a central outlet, such as in craters or enclosed desert depressions (playas).

  • Example: Meteor Crater, Arizona.

Drainage Basin Characteristics

• Channel Position and Ranking:

  • Classification of streams by order:

  • 1st order streams - typically steep.

  • Largest order streams - relatively flat.

  • Stream order defines the geometry used in mapping and drainage basin assessments.

Sediment Budgets in Drainage Basins

• Definition:

  • Represent the balance of sediment sources and sinks.

  • Importance: Essential for understanding landscape evolution, dam filling dynamics, human impacts, and water quality.

Basin Denudation

• Definition:

  • General lowering of land surface due to erosion.

  • Uplift processes may counteract denudation, maintaining elevation (isostasy).

  • Measured based on stream sediment load at gaging stations or volume loss within reservoirs.

  • Rate expressed as $rac{ ext{depth of denudation}}{ ext{time}}$ (e.g., $ext{mm/1000 yr}$ ).

Sediment Yield

• Definition:

  • Measures geomorphic activity indicating soil loss from a basin.

• Factors Affecting Yield:

  • Climate, lithology, vegetation, relief, glaciation, and basin size.

• Higher sediment production correlates with increased relief and smaller basin sizes.

Global Sediment Yield

• Characteristics:

• Smaller drainage basins produce more sediment per square kilometer (due to steepness and mountainous terrain).

• Larger drainage basins transport more sediment overall due to greater flow capacity.

Impacts of Human Activity on Sediment Production

• Deforestation Effects:

  • Shifts in sediment delivery can alter basin dynamics through:

  • Stability, aggradation, incision, and widening processes.

Uplands to Lowlands

• Description:

  • Basins encompass a continuum that transitions from high elevation, diverse climates, and biota down to the lower elevations at the basin outlet.

  • Example: The Amazon basin from high frigid peaks to tropical lowlands presents predictions relating to geomorphology (uplands as sediment sources; lowlands as sinks).

Upstream vs. Downstream Dynamics

• Differences:

  • Upstream channels are typically narrow, and channel migration is confined.

  • Lowland floodplains tend to be wider, providing areas for sediment storage and enriching habitat complexity.

  • Active geomorphic processes vary downstream, leading to distinct landscape features.

Colluvial Valleys and Bedrock Valleys

1. Colluvial Valleys:

   • Characterized by unsorted, mobile hillslope materials moved by gravitational forces.

   • Headwaters represent upstream reaches; hollows are characterized by flow and sediment concentration.

2. Bedrock Valleys:

   • Notable for their lack of significant valley fill and narrow, V-shaped profiles.

   • Channel floors are typically made of a mix of alluvium and exposed bedrock.

Alluvial Valleys and Estuarine Valleys

1. Alluvial Valleys:

   • Comprise thick, unconsolidated deposits, resulting in low gradients with minimal bedrock exposure.

2. Estuarine Valleys:

   • Represent transitions between terrestrial and marine environments with wide, vegetated areas and fine sediment characteristics.

Longitudinal Profiles and Knickzones

• Longitudinal Profile:

  • A graphical representation plotting channel elevation against distance; exhibits a concave character from headwaters to base level.

• Knickzones:

  • Defined as discrete jumps in bed elevation due to geological features or faults.

Channel Confinement

• Description:

  • Upland channels are typically narrower and confined, while lowland channels are wider and provide sediment storage.

  • Human influences can significantly alter these natural characteristics.

Downstream Trends in Drainage Basins

• Observation: Bed load size typically decreases downstream, with larger boulders near headwaters giving way to gravel and eventually sand in lower reaches.

Terraces and Their Types

• Definition of Terraces: Flat-lying landforms situated above and parallel to stream channels.

  • Serve as a record of past fluvial behavior and sediment deposition.

• Types of Terraces:

  1. Erosional (Strath) Terraces:

  • Formed from incision processes indicating active uplift and energy in rivers capable of cutting through materials.

  1. Depositional (Fill) Terraces:

  • Created when sediment supply exceeds the river's transport capacity.

  • Paired terraces indicate similar elevation on both sides of a valley, while unpaired terraces result from varied erosion rates on one side.

Alluvial Fans and Fan Evolution

• Definition: Alluvial fans are predominant in arid to semi-arid conditions, characterized by a cone shape surrounding a dispersing channel.

• Fan Types:

  1. Type I Fans (Debris Flow Dominated):

  • Occur on steep slopes, with debris flow processes being prominent.

  1. Type II Fans (Fluvial-Dominated):

  • Characterized by fluvial flow and sheet floods, mainly occurring on lower gradients away from mountains.

• Fan Evolution: Influenced primarily by climate changes, determining whether a fan experiences aggradation or incision based on moisture availability and sediment delivery.

Bajada

• Description: A bajada is formed by the coalescence of multiple alluvial fans resulting in a broad, low-gradient area.

Conclusion

• The ecosystems and landforms influenced by drainage basins demonstrate a complex interaction of geological processes, climate, and human activities, shaping the landscape over time.