Option A: Freshwater

Drainage Basin

The area drained by a river and its tributaries

Freshwater

Freshwater includes rivers, lakes, wetlands, groundwater, glaciers and ice caps

Hydrological cycle

A conceptual model that describes the storage and movement of water between the bio/atmo/litho/hydrosphere

Watershed/Drainage divide

Imaginary line defining the boundary of a river/stream drainage basin separating it from adjacent basin(s)

Discharge

The volume of water passing a given a point over a set time

Physical water scarcity

Lack of water scarcity where water resource development is approaching/has exceeded unsustainable levels. Relating to availability to demand and implies that arid areas are not necessarily water scarce.

Economic water scarcity

lack of water where water is available locally, but not accessible for human, institutional or financial capital reasons

Storm hydrograph

A graph showing how a river changes over a short period, such as a day/couple of days

Flood

A discharge great enough to cause a body of water to overflow its channel and submerge surrounding land

drainage basin as an open system

Cycle has single input/ percipitation (PPT) and two major losses (output), evapotranspiration and run-off. A third output, leakage, may also occur from the deeper subsurface to other basins. The drainage basin system is an open system as it allows the movement of energy and matter across its boundaries.

Infiltration flows

the process bt which water soaks into or is absorbed by the soil.

Infiltration capacity

Maximum rate at which rain can be absorbed by a soil in a given condition

Overland flow

Water flows over the land’s surface

Overland flows occurs in 2 ways

1. When percipitations exceeds the infiltration rate

2. When the soil is saturated (all the pores spaces are filled with water)

Inputs

Percipitation ; forms of rainfall/snow/frost/hail/dew

Outputs

Corrasion/Abrasion

the wearing away of the bed and bank by the load carried by a river. 

Attrition

 is the wearing away of the load carried by a river. It creates

smaller, rounder particles.

Hydraulic action

Force of air and water on the sides of rivers and in cracks

Load

The heavier and sharper the load, the greater the potential for erosion

Velocity

The greater the velocity, the grater potential for erosion

Gradient

Increased gradient increases the rate of erosion

Geology

Soft, unconsolidated rocks such as a sand and gravel are easily eroded

pH

rates of solution are increased when the water is more acidic

Human impact

Deforestation, dams, and bridges interfere with the natural flow of a river and frequently end up increasing the rate of erosion.

Types of erosion

Attrition/abrasion/hydraulic action.

Corrasion

the mechanical impact produced by the debris eroding the bed and banks of the stream

Transport

The load is transported downstream in a number of ways

Types of transport

Suspended/saltated/tacted/flotation

suspended transport

small particles like silts and clays are carried in suspension

Saltated load

Larger particles like sand/gravels/veru small stones are transported in a series of “hops”

Tracted load

Pebbles are shunted along the bed

Causes of deposition

shallowing gradient → decreases velocity

Decrease in volume of water in channel

Increase in friction between water and channel

formation of typical river landforms

waterfalls

Waterfalls

Occur on horizontally bedded rocks.

Soft rock is undercut by hydraulic and abrasion.

Water weight + lack of support = waterfall to collapse and retreat

Main features of deposition

flood plains, meanders, levers, oxbow lakes and deltas

Flood plains

los relief formed by deposition when river floods

generally a mixture of sand and gravel, eroded on outside of meander & built up by channel deposition

Meanders

Normal behaviour of fluids and gases in motion.

• Occur on variety of materials, ice→ rock

• Develops when channel slope, discharge, and load combine create meander