Geomorphology The Changing Landscape

Water Supply Water is one of the most powerful earth-carving forces there is Water is one of the most powerful earth-carving forces there is Run off = precipitation – [surface retention + infiltration + evaporation + evapo-transpiration + interception ] Run off = precipitation – [surface retention + infiltration + evaporation + evapo-transpiration + interception ]

Sheet/laminar Flow

Turbulent flow _p62_bot.jpg

Factors producing decreased run-off Gradient Gradient Vegetation Vegetation Rock type Rock type Soil type Soil type Soil moisture Soil moisture Evaporation rate Evaporation rate Amount of rainfall Amount of rainfall Type of rainfall Type of rainfall Gentle Dense Permeable Porous, Sandy Dry High Little Soft soaking rain

Factors producing increased run-off Gradient Gradient Vegetation Vegetation Rock type Rock type Soil type Soil type Soil moisture Soil moisture Evaporation rate Evaporation rate Amount of rainfall Amount of rainfall Type of rainfall Type of rainfall Steep Sparse Impermeable Not porous Wet soils Low e.g. overcast Lots Thunderstorms

Drainage Basin

Watershed

Other Important Definitions Interfluve Interfluve Water-table Water-table Permeable rock Permeable rock Impermeable rock Impermeable rock Base flow Base flow Through flow Through flow Aquifer Aquifer Artesian basin Artesian basin Confluence Tributaries Distributaries River rises River mouth

Interfluve a minor watershed. a minor watershed. a watershed within a drainage basin. a watershed within a drainage basin.

Confluence Where two rivers join

Tributaries A smaller stream that joins a bigger stream

Distributaries A large river that flows into a number of smaller rivers e.g. at a delta

River Source Where a river rises or begins

River Mouth Where a river enters the sea

Types of Rivers Permanent Permanent Periodic Periodic Episodic Episodic Exoti c Exoti c

Permanent Rivers Always has base flow as even the dry season water table is above the river bed Always has base flow as even the dry season water table is above the river bed Found on the south and east coasts of South Africa Found on the south and east coasts of South Africa

Periodic Rivers Flow only in rainy season Flow only in rainy season Dry season water table is below the river bed Dry season water table is below the river bed Found on plateau of South Africa Found on plateau of South Africa

Episodic Rivers Flow only after a heavy rainfall Flow only after a heavy rainfall Wet season water table is also below the river bed Wet season water table is also below the river bed River never enjoys base flow River never enjoys base flow Found in dry western parts of South Africa Found in dry western parts of South Africa

Exotic Rivers Exotic Rivers Rise in a high rainfall area where there is plentiful run off and base flow Rise in a high rainfall area where there is plentiful run off and base flow Travel through dry areas where there is very little run off and no base flow Travel through dry areas where there is very little run off and no base flow Orange and Nile Orange and Nile

Activity 1 p71 Focus

Drainage Density/Texture

Drainage Density This is the ratio between the total length of streams and the area drained by them

Run-off determines Texture Factors determining run-off 1. Evaporation rates 2. Precipitation rates 3. Infiltration rates – type of rock – im/permeable 4. Resistance of rocks – channels form in softer rock easier therefore higher density 5. Vegetation – sparse – higher run-off – high density

Activity 2 p72 Focus

Drainage Patterns determined by underlying geology

Drainage Pattern? Photo: Mrs B Fleming Photo: Mrs B Fleming

Drainage Pattern?

Drainage pattern?

Drainage Pattern?

Drainage Patterns not determined by underlying geology 1. Superimposed drainage

Vredefort Dome

Drainage Patterns not determined by underlying geology 2. Antecedent Drainage

Drainage Patterns not determined by underlying geology 2. Antecedent drainage

Drainage Patterns not determined by underlying geology 2. Antecedent Drainage

Drainage Patterns not determined by underlying geology 2. Antecedent drainage

The Mbashe River winds its way through the Transkei region of the Eastern Cape.

The Grand Canyon

See Skywalk Pics

What do you think? In which drainage pattern is the river younger than the present landscape, antecedent or superimposed drainage? In which drainage pattern is the river younger than the present landscape, antecedent or superimposed drainage? Superimposed Superimposed

Stream Ordering

Does this make sense?

Example Stream Order# Segments Characteristics 1139Steep, short, many Gentle, long, few

Stream Order to Drainage Basin Size

Activity 4 p 75 Focus

Discharge

Discharge

Construction And Analysis of Hydrographs ©Microsoft Word clipart Ollie Bray – Knox Academy, East Lothian

Hydrograph Record of River Discharge over a period of time River Discharge = cross sectional area rivers mean (average) velocity X (at a particular point in its course) Storm Hydrographs Show the change in discharge caused by a period of rainfall

Why Construct & Analyse Hydrographs ? To find out discharge patterns of a particular drainage basin Help predict flooding events, therefore influence implementation of flood prevention measures ©Microsoft Word clipart

Construction Of Storm (flood) Hydrographs ©Microsoft Word clipart

Hours from start of rain storm Discharge (m 3 /s) Base flow Through flow Overland flow Rising limb Recession limb Basin lag time mm Peak flow Flood Hydrograph

Hours from start of rain storm Discharge (m 3 /s)

Hours from start of rain storm Discharge (m 3 /s) mm Rainfall shown in mm, as a bar graph

Hours from start of rain storm Discharge (m 3 /s) mm Discharge in m 3 /s, as a line graph

Hours from start of rain storm Discharge (m 3 /s) Rising limb mm Rising limb The rising flood water in the river

Hours from start of rain storm Discharge (m 3 /s) Rising limb mm Peak flow Maximum discharge in the river

Hours from start of rain storm Discharge (m 3 /s) Rising limb Recession limb mm Peak flow Recession limb Falling flood water in the river

Hours from start of rain storm Discharge (m 3 /s) Rising limb Recession limb Basin lag time mm Peak flow Basin lag time Time difference between the peak of the rain storm and the peak flow of the river

Hours from start of rain storm Discharge (m 3 /s) Base flow Rising limb Recession limb Basin lag time mm Peak flow Base flow Normal discharge of the river

Hours from start of rain storm Discharge (m 3 /s) Base flow Through flow Overland flow Rising limb Recession limb Basin lag time mm Peak flow Overland flow Through flow + = Storm Flow

Volume of water reaching the river from surface run off Overland flowThrough flow Volume of water reaching the river through the soil and underlying rock layers

Analysis ©Microsoft Word clipart

Factors influencing Storm Hydrographs Area Shape Slope Rock Type Soil Land Use Drainage Density Precipitation / Temp Tidal Conditions ©Microsoft Word clipart

Interpretation of Storm Hydrographs Rainfall Intensity Rising Limb Recession Limb Lag time Peak flow compared to Base flow Recovery rate, back to Base flow You need to refer to: Basin lag time Hours from start of rain storm Discharge (m 3 /s) Base flow Through flow Overland flow Rising limb Recession limb mm Peak flow

When interpreting hydrographs all factors must be considered together ! Here are some theoretical interpretations of influencing factors BUT…… ©Microsoft Word clipart

Area Large basins receive more precipitation than small therefore have larger runoff Larger size means longer lag time as water has a longer distance to travel to reach the trunk river AreaRock TypeDrainage Density ShapeSoilPrecipitation / Temp SlopeLand UseTidal Conditions

Shape Elongated basin will produce a lower peak flow and longer lag time than a circular one of the same size AreaRock TypeDrainage Density ShapeSoilPrecipitation / Temp SlopeLand UseTidal Conditions

Slope Channel flow can be faster down a steep slope therefore steeper rising limb and shorter lag time AreaRock TypeDrainage Density ShapeSoilPrecipitation / Temp SlopeLand UseTidal Conditions

Rock Type Permeable rocks mean rapid infiltration and little overland flow therefore shallow rising limb AreaRock TypeDrainage Density ShapeSoilPrecipitation / Temp SlopeLand UseTidal Conditions

Soil Infiltration is generally greater on thick soil, although less porous soils eg. clay act as impermeable layers The more infiltration occurs the longer the lag time and shallower the rising limb AreaRock TypeDrainage Density ShapeSoilPrecipitation / Temp SlopeLand UseTidal Conditions

Land Use Urbanisation - concrete and tarmac form impermeable surfaces, creating a steep rising limb and shortening the time lag Afforestation - intercepts the precipitation, creating a shallow rising limb and lengthening the time lag AreaRock TypeDrainage Density ShapeSoilPrecipitation / Temp SlopeLand UseTidal Conditions

Drainage Density A higher density will allow rapid overland flow AreaRock TypeDrainage Density ShapeSoilPrecipitation / Temp SlopeLand UseTidal Conditions

Precipitation & Temperature Short intense rainstorms can produce rapid overland flow and steep rising limb If there have been extreme temperatures, the ground can be hard (either baked or frozen) causing rapid surface run off Snow on the ground can act as a store producing a long lag time and shallow rising limb. Once a thaw sets in the rising limb will become steep AreaRock TypeDrainage Density ShapeSoilPrecipitation / Temp SlopeLand UseTidal Conditions

Tidal Conditions High spring tides can block the normal exit for the water, therefore extending the length of time the river basin takes to return to base flow AreaRock TypeDrainage Density ShapeSoilPrecipitation / Temp SlopeLand UseTidal Conditions

Remember! These influencing factors will: Influence each other Change throughout the rivers course ©Microsoft Word clipart

Volume of water reaching the river from surface run off Overland flowThrough flow Volume of water reaching the river through the soil and underlying rock layers

Discharge of a River

Comparing Urban/Rural Discharge

Value of Flow Hydrographs Agricultural land management Agricultural land management Urban water management e.g. storm water Urban water management e.g. storm water Domestic / industrial use Domestic / industrial use Flood precautions e.g. settlement planning Flood precautions e.g. settlement planning Water resources protection Water resources protection Water infrastructure Water infrastructure Sewerage farms Sewerage farms

Value of Flow Hydrographs Public use of dams and rivers e.g. Hartebeespoort dam Public use of dams and rivers e.g. Hartebeespoort dam Water quality management Water quality management Groundwater levels Groundwater levels Impact of exotic flora on water levels e.g. Jacaranda trees Impact of exotic flora on water levels e.g. Jacaranda trees Protect environmentally sensitive areas e.g. Sterkfontein caves Protect environmentally sensitive areas e.g. Sterkfontein caves Tourism e.g. crocodile ramble Tourism e.g. crocodile ramble

Shape of Drainage Basins and Discharge

Flooding Once river reaches bankful stage Once river reaches bankful stage well/goodies/elearning/module12swf.s wf well/goodies/elearning/module12swf.s wf

Abstraction

Abstraction Definition: one drainage basin expands at the expense of another Definition: one drainage basin expands at the expense of another Causes: Causes: - Steeper gradient - More run-off - Softer rock

Stream Capture Stream capture is the process where the upper portion of a river basin is diverted, by natural erosion, to flow to a different river basin. Stream capture is the process where the upper portion of a river basin is diverted, by natural erosion, to flow to a different river basin. You need to be able to identify; You need to be able to identify;

Process of Stream Capture A first order stream flowing on a lower level A first order stream flowing on a lower level Recedes upslope through headward erosion Recedes upslope through headward erosion Cutting through the watershed Cutting through the watershed Intercepting a stream flowing on a higher level Intercepting a stream flowing on a higher level Diverting the headwaters of the captured stream Diverting the headwaters of the captured stream Into the captor stream Into the captor stream Which becomes rejuvenated Which becomes rejuvenated

Headward Erosion Headward erosion is demonstrated in this photo taken in Marin County, California. Groundwater sapping is causing this gully to lengthen up the slope. Headward erosion is demonstrated in this photo taken in Marin County, California. Groundwater sapping is causing this gully to lengthen up the slope.Marin County, California Groundwater sappingMarin County, California Groundwater sapping g/wiki/Headward_er osion g/wiki/Headward_er osion

River Capture

Do you really understand?

Stream Capture The Scioto River flows out of the screen to the left. The Teays River flowed in the opposite direction, which is into the screen. The patchwork appearance of the Teays River valley reflects the presence of many farms. The Scioto River flows out of the screen to the left. The Teays River flowed in the opposite direction, which is into the screen. The patchwork appearance of the Teays River valley reflects the presence of many farms. wiki/Teays_River wiki/Teays_River

Stream Piracy

Activity

Longitudinal Profile of a River

Graded Profile

Grade vs. Gradient Grade – State of balance where there is no active deposition or erosion occurring. The full energy of the river is being used to transport the river load. Signs of a graded river are: Grade – State of balance where there is no active deposition or erosion occurring. The full energy of the river is being used to transport the river load. Signs of a graded river are: -No recently collapsed river banks - No deposition on river channel floor - Gradient – the slope of the river bed

Types of Graded Streams Overgraded – erosion is dominant Overgraded – erosion is dominant Undergraded – deposition is dominant Undergraded – deposition is dominant Graded – erosion and deposition is balanced Graded – erosion and deposition is balanced

Base Levels of Erosion The lowest level to which the river can erode The lowest level to which the river can erode Temporary: a lake Temporary: a lake Permanent: the sea Permanent: the sea

Stream Channel Patterns

1. Braided

2. Meandering

The Mbashe River winds its way through the Transkei region of the Eastern Cape.

3. Rock Controlled ( rock on the bottom and both sides) Can indicate rectangular drainage

Rock Controlled

Revision Questions Define the terms; drainage basin, watershed, and drainage texture Define the terms; drainage basin, watershed, and drainage texture Differentiate between the following terms: Differentiate between the following terms: - Drainage pattern and stream pattern - Antecedent and superimposed drainage - Abstraction and headward erosion - Grade and gradient - Temporary and permanent base levels of erosion

Answers Drainage basin: the area drained by a river and all its tributaries Drainage basin: the area drained by a river and all its tributaries Watershed: The highlying area separating drainage basins Watershed: The highlying area separating drainage basins Drainage density/texture: This is the ratio between the total length of streams and the area drained by them Drainage density/texture: This is the ratio between the total length of streams and the area drained by them

Answers Drainage pattern: the shape of the stream network in a drainage basin Drainage pattern: the shape of the stream network in a drainage basin Stream pattern: the shape of an individual stream segment within a stream network

Answers Antecedent drainage: when a river has maintained its original direction of flow across later tectonic topography Antecedent drainage: when a river has maintained its original direction of flow across later tectonic topography Superimposed drainage: Drainage pattern contrary to structure, created by erosion of layers originally above hard rock strata.

Answers Abstraction: Where drainage basin A expands at the expense of drainage basin B, because A has one or more of the following characteristics; a steeper slope, more runoff or softer rock Headward erosion: the process whereby a stream lengthens its course upstream. This reluts in abstraction.

Answers Grade: State of balance where there is no deposition or erosion occurring. The full energy of the river is being used to transport the river load. Signs of a graded river are: Grade: State of balance where there is no deposition or erosion occurring. The full energy of the river is being used to transport the river load. Signs of a graded river are: -No recently collapsed river banks - No deposition on river channel floor Gradient: the slope of the river bed

Answers The lowest level to which the river can erode The lowest level to which the river can erode Temporary: a lake Temporary: a lake Permanent: the sea Permanent: the sea