River Basin Dynamics and Hydrology

Posted on Nov 30, 2024 in Geology

River Basin Types

There are three types of river basins:

  • Exoreic: Drains water into the sea or ocean. Example: Rimac River.
  • Endorheic: Flows into lakes, lagoons, and salt flats with no outlet to the sea.
  • Arreic: Water evaporates or seeps into the ground before reaching a drainage system. Example: Streams and canyons of the central Patagonian plateau.

Functions of a River Basin

Hydrologic Function

  1. Collects water from various sources, including precipitation runoff, springs, rivers, and streams.
  2. Stores water in different forms and durations.
  3. Discharges water as runoff.

Ecological Function

  1. Provides habitat for flora and fauna, supporting ecosystem interactions between physical and biological water characteristics.

Environmental Function

  1. Acts as a CO2 sink.
  2. Serves as a gene bank.
  3. Regulates water recharge and biogeochemical cycles.
  4. Conserves biodiversity.
  5. Maintains soil integrity and diversity.

Socio-Economic Role

  1. Provides resources for productive activities supporting the population.
  2. Offers a space for social and cultural development.

Surface Water, Rivers, and Floods

Hydrograph: A record of river flow over time, used for:

  • Studying water inputs (runoff and groundwater components)
  • Relating rainfall to flow
  • Determining maximum and minimum flows

Capacity: Measurement of flow in a river.

Methods for Surface Hydrology Studies

Direct Measurement

  • Windlasses: Small mills (typically Archimedes screw type) rotated by submersion in a stream. Speed is determined by rotations per minute (RPM).
  • Tracer Gauging: Introducing a tracer (uranine, rhodamine, H3, etc.) and measuring its downstream concentration to deduce flow.
  • Float Gauging: Measuring surface velocity (Vs) by dividing the distance traveled by a floating object by the time taken.

Indirect Measurement

  • Water Level Recorder: Measures water level and tracks flow.

Study of Flow in a River

Conducted to understand:

  • Average water volume carried by a river.
  • Potential water volume during a flood.

Runoff Coefficient: Proportion of total rainfall that becomes runoff.

Floods

Floods are natural disasters with inevitable human and economic losses.

Flood Protection Measures

  • Zoning and land use planning
  • Retention ponds and diversion channels
  • Canalization, dams, and reservoirs

Channeling: Altering the channel section (deepening and/or widening) or route (removing meanders, straightening the channel) to increase water velocity.

Dams: Raising riverbanks.

  • Effects: Effective upstream protection but potential downstream issues.
  • Risks: Dam failure can cause greater and longer-lasting damage.

Sediment Transport

  • Bottom Trawl:
    • Mass: Movement of bottom material en masse.
    • Saltation: Particles move by rolling, sliding, and jumping.
  • Suspension Transport: Balance between sedimentation and turbulence.

Definitions

  • Load: Total amount of entrained solids.
  • Capacity: Amount of sediment that can be transported.
  • Competence: Size of sediment that can be moved.

Inland Waters

Inland waters are located on continents and have lost salinity through evaporation. This natural purification process results in freshwater, suitable for drinking.

Rivers

Rivers are streams flowing from highlands to lowlands, shaped primarily by relief. The basin, the area enclosed by mountains or hills, captures water to feed the streams. The highest point, the watershed, divides rainwater flow between different rivers. Relief influences basin size and shape, determining water volume (flow). Flow speed and strength vary along the river’s center, known as discharge, calculated by dividing water volume by the length of the river stretch. Water flows fastest in the center and slowest along the bottom and banks. Discharge affects the amount of solid material carried and the river’s potential for electricity generation. River flow fluctuates throughout the year. Minimal flow is the dry season, preceding the rainy season. In arid or semi-arid areas, rivers may dry up intermittently, posing risks to crops, livestock, and even altering river channels and international boundaries. Relief determines river age, reflected in current strength. Young rivers in steep mountainous areas carve deep canyons, suitable for electricity generation but not navigation. Mature rivers in gentler relief have wider, deeper channels, slower flow, and arable valleys, suitable for navigation. Old rivers in flat areas have high volume, low speed, meandering channels, and are ideal for navigation and agriculture. A river’s longitudinal profile, the curve depicting average elevation and base level (the lowest point), helps determine its age and characteristics.