SKM_75824101608580.pdf - Geography Notes PDF

# Topic 3: Geomorphology ## Chapter 1: Drainage systems in South Africa ### Unit 1: Important Concepts - Drainage systems refer to river systems. - A river is a body of water flowing in a defined channel from a source to a mouth. - The area drained by a river system or stream network is called th...

# Topic 3: Geomorphology ## Chapter 1: Drainage systems in South Africa ### Unit 1: Important Concepts - Drainage systems refer to river systems. - A river is a body of water flowing in a defined channel from a source to a mouth. - The area drained by a river system or stream network is called the drainage basin. - The catchment area is the drainage area that supplies water to a river. - Water in a drainage basin comes from surface runoff and groundwater. - The high ground separating one drainage basin from the adjacent drainage basin is called the watershed. - Individual river channels forming the stream network are called tributaries. - The confluence is the point where one river in the network joins another. - Spurs are the ridges of high ground between individual channels. - The source is the place where a river begins. - The mouth is where the river flows into a sea or lake. - Overland flow - rainwater flowing over the surface. - Channel flow - water flowing in a river channel. - Throughflow - water flowing through the soil. - Permeable rocks - rocks that allow water to seep in. - Groundwater - underground water - Groundwater flow - water flowing through underground rocks. - Water table - upper surface of the groundwater. - Baseflow - groundwater that seeps into a river. - Drainage density - total length of streams per unit area of a drainage basin. ### Unit 2: Types of Rivers - Rivers can be classified according to whether or not groundwater flows into the river. #### Types of Rivers * **Permanent rivers** receive groundwater all year. * **Periodic rivers** receive groundwater only in the rainy season. * **Episodic rivers** are never supplied with underground water. * **Exotic rivers** flow all year round but only receive water from the source region. ### Unit 3: Drainage Patterns - Drainage patterns refer to the way in which the rivers within a river system or network are arranged. - Most patterns depend either on the geology and topography of the area or develop independently from those factors. #### Patterns Depending on Geology and Topography * **Radial** - streams flow outwards from a dome. * **Trellis** - occurs on inclined strata that are unequally resistant to erosion, or in areas where there are parallel fold mountains. * **Rectangular** - develops when streams follow cracks or joints within a rock layer. * **Centripetal** - streams flow into a central pan or low-lying area. #### Patterns that Develop Independently of Rock Structure and Gradient * **Dendritic** - has a tree-like appearance; forms on rocks of similar hardness in an area with a similar gradient. * **Parallel** - develops on a surface that slopes uniformly but is fairly steep; the river and its tributaries flow downslope nearly parallel to one another. * **Deranged** - no apparent drainage pattern. ### Unit 4: Drainage Density and Texture - Drainage density refers to the total length of streams per unit area of a drainage basin. - Drainage density can be described as low, medium, high or very high. - Drainage density is influenced by factors such as evaporation rates, rainfall, infiltration, and the hardness of rocks. ### Unit 5: Use of Topographic Maps to Identify Stream Order and Drainage Density - Topographic maps can be used to identify stream order and drainage density. #### Stream Order - First-order streams are the lowest category, and are those channels with no streams feeding them. - Where two streams of the same order in a network join, a stream of a higher order is formed. ### Unit 6: Discharge of a River - Laminar and Turbulent Flow - Discharge is the amount of water flowing in a river channel past a point at a given time. - Discharge is measured in cubic metres per second (cumecs). - Laminar flow describes water flowing over a smooth surface - flow speeds can be great. - Turbulent flow describes water flowing in a bubbling motion - creates internal friction which reduces speed. ### Unit 7: River Profiles - Transverse Profiles and Longitudinal Profiles, and their Relationship to Different Stages of a River - **Longitudinal profile** - a visual representation of the gradient down which the river flows. - The upper course is the steeper upstream (towards the source) section of the profile near the source of the river. - The middle course is downstream (towards the mouth) of the upper course, where the river has left the mountains and the gradient is more gentle. - The lower course is the flatter, final stage of the river as it gets closer to sea level. - **Transverse profile** - a section drawn transversely across the valley at right angles to the river. - The cross-profile of a river in the upper course will have a deep, narrow V-shape, - The cross-profile of a river in the middle course will have a more open V-shape, - The cross-profile of a river in the lower course will have a wide, open V-shape. ### Unit 8: Identification and Description of Fluvial Landforms - Fluvial landforms are landforms created by a river. #### Landforms from the Upper Course of a River * **Rapids** * **Waterfalls** #### Landforms from the Middle Course of a River * **Meanders** * **Alluvial Fans** #### Landforms from the Lower Course of a River * **Levees** * **Braided Streams** * **Oxbow Lakes** * **Flood Plains** * **Deltas** ### Unit 9: River Grading - The energy of a river is dependent on the velocity (speed) of the water. - A graded river is one where a balance has been achieved between its gradient, volume and channel shape, so that it has just sufficient energy to flow, with erosion rates in balance with the deposition rates. - Overgraded rivers have excess energy and erode their channels. - Undergraded rivers do not have enough energy to flow and deposit their load. ### Unit 10: Rejuvenation of Rivers - Reasons and Resultant Features - Rejuvenation occurs when the energy level of a river increases due to factors such as isostatic uplift or a drop in sea level, increased runoff, or the addition of water from another river. - **Knickpoints** occur at the sharp changes in gradient. - **River terraces** mark the original level of the valley floor. - **Valley within a valley** is created when a rejuvenated river erodes a new valley within an old one. - **Entrenched meanders** are formed when a rejuvenated river maintains its meandering course and vertical erosion leads to the formation of meanders between steep valley sides. - **Ingrown meanders** are meanders that cut sideways into the bank so that there is a slight overhang above the stream. ### Unit 11: River Capture - Concepts of Abstraction and River Capture; Features Associated with River Capture - River capture is the process of a more energetic river capturing the water of a less energetic river. - This occurs through headward erosion, and often results in the formation of distinctive landforms. - **Captor stream** - the more energetic river - **Captive stream** - the less energetic river - **Misfit or beheaded stream** - the part of the river that has lost its headwaters. - **Elbow of capture** - the point where capture occurred. - **Wind gap** - the part of the original river valley between the elbow and misfit. - **Knickpoint waterfall** - the sharp change in gradient where the higher-lying captive flows into the captor, which is flowing on a lower level. - **Abstraction** is the process whereby the watershed becomes lower and its position shifts. ### Unit 12: Superimposed and Antecedent Rivers - Superimposed rivers develop a patter that bears no relation to the geology and relief of the landscape. - Antecedent rivers develop their course before the high-lying area was formed and then maintain their pattern as the area is uplifted. ### Unit 13: Importance of Managing Drainage Basins and Catchment Areas - Drainage basins are essential for collecting and storing precipitation and providing fresh, clean water for people and the environment. - Wetlands are important because they trap and store water, regulate stream flow, and filter and purify the water that flows through them. ### Unit 14: Impact of People on Drainage Basins and Catchment Areas - People impact all parts of a drainage basin, including: - the volume and flow of water in the river channel - land surfaces over which the river flows - the quality of water ### Unit 15: Case Study of One Catchment Management Strategy in South Africa - Catchment and drainage basin management is essential to ensure healthy drainage basins, hydrology, catchment areas, rivers and wetlands. - Important aspects of catchment and drainage basin management include: - legislation to control the use and pollution of water sources - legislation to control what is discharged into rivers - maintaining vegetation in the riparian zone - carrying out thorough investigations before building dams - clearing vegetation and planting alien trees - controlling construction and settlement on the flood plain - taking greater care when altering river channels - educating farmers about sustainable farming practice - making the public aware of the need to conserve water resources ### Unit 16: Impact of People on Drainage Basins and Catchment Areas - Different human activities can affect drainage basins, including: - deforestation - agriculture - urbanization - mining - pollution - dam construction - recreation ### Unit 17: Understanding the Importance of Managing Catchment Areas and Drainage Basins - The Marico River is an example of a threatened river system. - Mining in the catchment area could have detrimental impacts on the river, its ecosystem, and the people and communities that rely on it.