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Fluvial Geography
Grade 12 Topic 2: Geomorphology
| Term | Definition |
|---|---|
| Confluence | Point where two rivers join |
| River mouth | The end of a river where it typically flows into the sea |
| Ground water | Water found underground, can feed springs and rivers as baseflow |
| Source | The starting point of a river |
| Interfluve | Ridges of high ground between individual channels |
| Water Table | The upper limit of the saturated zone |
| Aerated zone | Open-air spaces above the water table |
| Saturated zone | Water clogged zone below the water table |
| Watershed | High ground separating one drainage basin from the adjacent drainage basin |
| Drainage Basin | An area of land drained by a river system or stream network |
| Catchment Area | The area that collects water via rainfall and feeds it into a river system |
| Infiltration | The process by which water on the ground surface enters the soil |
| Tributary | A smaller river joining the main river |
| River System | The network of all the tributaries that join to form one main river that flows into the sea |
| Direct run-off | Water flowing over Earth in river/stream channels (also called discharge or stream flow) |
| Indirect run-off | Water entering a river from an indirect source such as a spring, surface or sub-surface run-off, baseflow |
| Surface Runoff | It is the portion of rainfall, which enters the stream immediately after the rainfall |
| Sub-Surface Runoff (Interflow) | The portion of rainfall which infiltrates into the soil and then moves laterally (without joining the water-table) to the streams, rivers or oceans |
| Base Flow | The portion of rainfall, which after falling on the ground surface, infiltrates into the soil and meets the water-table. It is delayed flow/runoff and the movement of water is very slow. |
| Total Runoff | Surface runoff (including sub-surface runoff) + Base flow |
| Permanent River | Flow all year round as the water table always lies above the bed of the river |
| Periodic River | Only flow during the rainy season, as during the dry seasons, the water table drops below the riverbed |
| Episodic River | flow after an episode of rain, they might flow for only a few hours as water rapidly infiltrates into the riverbed. |
| Exotic River | These rivers span two types of climatic regions. They usually begin in regions of high rainfall and flow into dry regions |
| Radial Pattern | Develops around a central elevated point, when rivers flow away from a high central point such as a dome |
| Trellis Pattern | Short tributary streams enter the main channel at nearly right angles as they run down sides of parallel ridges called anticlines |
| Rectangular Pattern | Found in regions that have undergone faulting. Streams follow the path of least resistance and thus are concentrated in places where exposed rock is the weakest |
| Centripetal Pattern | Streams flow toward a central depression |
| Dendritic Pattern | Looks like the branching pattern of tree roots. It develops in regions underlain by homogeneous material |
| Parallel Pattern | Tributary streams tend to stretch out in same direction as main channel, following the slope of the surface |
| Deranged Pattern | Typical of very flat areas that develop from the disruption of a pre-existing drainage pattern – has experienced glaciation |
| Drainage density | The total length of all the streams and rivers in a drainage basin divided by the total area of the drainage basin |
| First order streams | All the tiny streams that are at the start of the river system, closest to the highest point of the watershed |
| Discharge | The amount of water across the width of the river flowing past a point at a given time |
| Laminar Flow | Water moves as parallel sheets, found where water flows over a level and even riverbed. There is little friction, resulting in higher flow speeds (velocity). |
| Turbulent Flow | Water moves in a bubbling "rough" manner and continually changes levels. Occurs where the riverbed is uneven and steep |
| Longitudinal River Profile | Shows the change in altitude and gradient from the source to the mouth of a river |
| Permanent base level | The lowest level at which a river can erode |
| Temporary base level | Dams, rapids or a waterfall found across the course of an ungraded river |
| Transverse River Profile | A cross-section through a river valley at any given point along the long profile |
| Suspension | Fine, light material carried along a river |
| Solution | Minerals dissolved in water, chemical reaction has occurred. |
| Traction | Large boulders rolled along river bed, cause vertical erosion in a channel |
| Saltation | Small pebbles bounced along river bed, cause vertical erosion in a channel |
| Interlocking Spurs | Projecting ridges that extend alternately from the opposite sides of the wall of a young, V-shaped valley down which a river with a winding course flows |
| Waterfalls | Form when a river, after flowing over more resistant rock, flows over a band of less resistant rock over the edge of a plateau |
| Rapids | Form where a stream flows over a series of gently dipping bands of harder rock |
| Meanders | Form as a river erodes laterally creating bends and loops |
| Floodplain | Area of mostly flat land bordering a river subjected to periodic flooding |
| Levee | Natural embankment alongside a river channel, formed by deposition on a floodplain |
| Delta | Formed by layers of sediment deposited at the mouth of a river as rivers slow down |
| Oxbow lake | Abandoned meander |
| Ungraded profile | A longitudinal profile which has irregularities along its path – it is not smooth |
| Overgraded river | A fast flowing river that has a surplus of energy and is able to erode |
| Undergraded river | A slow flowing river that has so little energy that it deposits its load |
| Graded Profile | River has reached equilibrium between energy, discharge and channel processes |
| Rejuvenated River | Eroding the landscape in response to a lowering of its base level |
| Incised Meanders | Occur when a river’s base level has fallen giving the river a large amount of vertical erosion power around bends, allowing it to down-cut |
| River Terraces | Form when a rejuvenating river erodes vertically into the former flood plain |
| Knickpoint | A break in the slope of a river profile caused by a rejuvenated river. |
| River Capture / Stream Piracy | When a stream or river drainage system is diverted from its own bed and flows instead down the bed of a neighbouring stream |
| Abstraction | The lowering and shifting of a watershed through headward erosion |
| Captor Stream | The river which captured the waters of the other river |
| Captured Stream | The river whose waters were captured |
| Misfit Stream | The stream that has lost its water now flows in a valley that is too big for the stream |
| Elbow of Capture | The place where the stream piracy has taken place |
| Wind Gap | The dry river valley with river gravel between the elbow of capture and the misfit stream |
| Accordant Drainage | Drainage system or pattern correlates to the geology and relief of the landscape over which it flows |
| Discordant Drainage | Drainage system or pattern does not correlate to the topography and geology of the area |
| Antecedent Drainage Patterns | The river is older than the landscape and has cut through "newly" formed landforms and maintained the same path |
| Superimposed Drainage Patterns | The landscape is older than the river, stream inherited its course from younger overlying layer |
Created by:
MissBroadway29
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