Surface Water and Groundwater: A Comprehensive Overview

Posted on Aug 23, 2024 in Geology

SURFACE WATER:

Water Movement:

Over 97% of the water on Earth is found in oceans. After reaching land, rainwater has three possible paths:

  • Some becomes groundwater through the process of infiltration.
  • Some evaporates and returns to the atmosphere.
  • The remainder stays on the surface, forming surface water, which includes:
    • Surface runoff
    • Rivers and torrents
    • Lakes

SURFACE RUNOFF:

Forms because the terrain becomes saturated and the water begins to flow along the surface. This type of surface water is called runoff because it isn’t flowing in a valley or riverbed, it simply moves as a layer of water over the terrain. It has great erosive power. As this water moves to lower regions, it can pull lots of material with it and erode rock.

WHAT DETERMINES IT:

  • Climate: Influences how much rain will fall, how quickly it will fall and how much of it will evaporate.
  • Type of terrain: For example, in a region with sandy soil, erosion happens more easily than in regions with solid rock like granite.
  • The gradient of the terrain: This influences how quickly the water will flow. The steeper the gradient, the faster the water will flow; this causes the erosion to be more severe.
  • Vegetation: Plants influence in two ways: Firstly, they decrease the velocity of water and their roots help hold on to the soil and other materials, increasing the terrain’s resistance to erosion.

LANDFORMS CREATED:

  • Fairy chimneys: Are formed when the terrain is made of two materials that respond differently to the same erosive force.
  • Rills: As overland flow moves along the surface of the terrain, it erodes material and creates small paths.

TORRENTS:

A torrent is a short, fast-flowing stream that has a fixed course, but varies in flow rate. Flow rate is the volume of water that is moved by the river in a particular amount of time. They have three parts:

  • Catch basin: Is the upper course of the torrent. Normally are funnel-shaped. The majority of erosion happens here.
  • Main channel: Water from the catch basin moves into it, carrying the material that it has eroded from above. Transport is the main geological process, but erosion does continue. This makes the valley wider.
  • Alluvial fan: Is the fan-shaped formation that results from the deposition of the eroded material. Deposition is the main geological process.

RIVERS:

A river is a fixed path of flowing water, like a torrent, but with a longer route, a gentler gradient and a more consistent flow rate.

FLUVIAL EROSION:

As water flows in a river, it gradually erodes the riverbed and causes the river to become wider and deeper. The erosion depends on:

  • The flow rate: The greater the volume of water that a river transports in a given time, the greater its potential for erosion.
  • Gradient: The steeper the river, the faster the water will flow, increasing its erosive force.

RIVER’S LOAD:

Is what we call all of the material transported by the river. They can move in:

  • In solution: Soluble materials, salts, move in this way.
  • As solids: Small particles are carried by suspension, medium-sized by saltation and large particles by attraction.

WHAT CAUSES RIVER’S DEPOSITION:

  • Its flow rate: Any decrease in the flow rate means the river is only able to carry a smaller load.
  • The gradient of the terrain: When a river moves from a region with a steep gradient to one that is gentler, the water moves more slowly.
  • The type of material: Larger particles will be deposited first. Smaller particles stay suspended longer and can even stay in suspension when the river is flowing very slowly. Once deposited the material is called sediment.

THE ORIGIN OF FLUVIAL LANDFORMS:

Are classified according to the processes that have shaped them:

  • Erosional landforms: Such as V-shaped valleys and waterfalls.
  • Middle course landforms: Such as meanders and fluvial terraces, which are the result of both erosion and deposition.
  • Depositional landforms: Such as flood plains, alluvial fans and river deltas, which are formed near the mouths of some rivers.

GROUNDWATER:

Rainwater, surface water and water from melting ice infiltrates the ground through pores and cracks. The water continues to move into the ground until it becomes blocked by impermeable rock. The permeability of a rock or soil is the measure of how easy it is for water to pass through it.

AQUIFERS:

Refer to the porous subsoil that retains water and allows it to flow.

DIFFERENCES BETWEEN THE MOVEMENT:

  • The velocity of subsurface water is much slower.
  • The course of groundwater is influenced by the presence of permeable rocks that prevent flowing in certain places.
  • Their extension: Surface waters are usually confined and channeled within a riverbed or a lake.

FACTORS THAT INFLUENCE VOLUME:

  • The permeability of the terrain: A land relief with more pores and cracks will allow more water to infiltrate.
  • The gradient: If the terrain has a steep gradient, surface water will move more quickly.
  • The density of vegetation: The leaves and stems of plants slow down the surface water, increasing the amount of infiltration.
  • The climate: Greater total rainfall and lower evaporation rates both lead to greater degrees of infiltration.

AQUIFERS:

Aquifers are refilled by water infiltration. They are emptied as water runs off into other areas or it’s extracted for human use through wells. To overuse an aquifer means that the volume of water being extracted is greater than the volume of water the aquifer receives when it is recharged.