Fluvial Processes Fluvial Processes and Landformsand Landforms

Stream systems

Streams Streams

Flowing water exerts great influence in shaping landforms.

Water is more effective than any other gradational process

Running water modified existing landforms through erosion and deposition.

Water flows overland surface or in confined channels.

Stream SystemStream System

Streams are bodies of water that flow in well defined channels. In Earth Sciences the Term Stream means water flowing in natural channel of any size.

ProcessesProcesses

Processes associated with work of streams.These are known as Fluvial Processes.From Latin means Fluvius, river.

Sources of waterSources of water

Three main sources◦Precipitation◦melted water from ice and snow◦ground water from springs

Each of these contribute to the flow of water on land surface called Runoff.

Rills Rills

For short distance runoff may occur in sheets [as sheet wash ]

Or un concentrated flow Or it may from tiny channels

called Rills . Tributaries are smaller streams that feed into a larger one.

Stream System Stream System

three major sub systems◦Catchments system ◦Transport system◦Depositional or dispersal system

Drainage basin are surface areas that feed runoff into a stream and exist for every channel.

Inter fluve Inter fluve

From Latin , inter----between, fluvius----river

Higher land between two tributary valleys of a drainage basin is referred as an interfluves.

An imaginary line that separates two drainage basins called Divide.

Infiltration Infiltration

Process of water seeping into surface is called Infiltration.

Ability of a ground surface to hold water is called Infiltration Capacity.

In times of high flow streams over flow their banks ,flat low lands on either sides known as Flood plains.

Stream Discharge Stream Discharge

The volume of water flowing in a section of channel in a given unit of time.

Stream Hydro graph is a record of changes in discharge of stream over time.

These hydro graphs indicate high and fast water levels due to precipitation.

Hydro Graph Hydro Graph

Discharge of a stream is recorded by a gagging station in form of a hydro graph curve.

Hydro graph curve plotted on a graph which represents ◦The rising limb◦Peak flow or flood crest ◦The receding limb

Erosion by StreamErosion by Stream

Force of gravity affect stream water in two ways◦Gravitational force causes water to flow down slope.◦Gravity causes water to exert pressure on the

stream bed.

Causes of ErosionCauses of Erosion

When volume of flow in a stream increase ,the amount of energy to shape the land also increases.

Ability of a stream to pick material determined by the volume of water, its depth, its friction with stream bed, strength and size of rocks over which it flows, and degree of stream turbulance.

Types of erosionTypes of erosion

There are three types of erosion.◦Hydraulic action◦Stream abrasion◦Solution [or dissolution]

Hydraulic ActionHydraulic Action

Hydraulic action occurs as◦As turbulent river currents wedge under rock

slabs on the bed◦Pound away at river banks ◦Below water fallsHydraulic action displaces loose particles from

stream bed or channel walls .Sediments range in size from clay to silt ,sand ,

pebbles, cobbles .Gravel ,a general term for rock particles larger than sand.

Stream AbrasionStream Abrasion

Rock particles bounce, scrape , and drag along bottom and side of channels and break off additional fragments is stream abrasion.

This process make round depressions in the rock of the stream bed is called pot holes.

Solution or DissolutionSolution or Dissolution

Chemically dissolving the bed rock is a process of solution.

Limited effect on rocks but may be significant in limestone area.

Rock particles gradually reduce in size and shape changes from angular to rounded is called attrition .[ wear and tear on sediments as they tumble and bounce against one another and against stream channel.

Stream TransportationStream Transportation

A greater proportion of sediments eroded by surface run off .

The material transported by fluvial processes are called Stream load.

Stream transport its load in several waySolution

SuspensionTraction

Saltation

Solution Solution

Some materials dissolved in water and carried in solution like;

lime , calcium, and ions of sodium and other minerals.

Suspension are finest solid particles which carried in suspension .

Such particles remain suspended as long as the force of upward turbulence is stronger than downward settling tendency of particles.

Traction Traction

“Sliding or rolling of particles along with river bed” is traction.

Traction breaks down pebbles into gravels, sand size. Saltation is a combination of suspension and traction.

When large particles hop and bounce along the channel bottom is called saltation.

Stream load Stream load

Three types of stream loadSuspended Load the material carried in

suspension. The largest portion of sediments load is suspended load.

Bed Load the particles that roll or saltate along the stream bed.

Dissolved Load is held in solution.

Stream transport Stream transport

Two terms used to convey relation ship of load and transportation

Stream Capacity refers how much load a stream can carry.

Stream Competence is determined by the diameter of the largest particles it can transport as bed load.

Both increase in response of velocity, discharge, and gradient increase.

Stream Deposition Stream Deposition

A reduction in velocity and discharge will cause a stream to reduce its load through deposition.

Aggradations [deposition] occurs where velocity is slow such as inside of bends in channels, on floods plains, at river mouths [deltas] ,and where stream gradient abruptly flattens.

Alluvium is a general name of fluvial deposits .

Land Forms made by StreamsLand Forms made by Streams

As the study of river course from its headwaters to its mouth , three stages are to be observed;◦Upper◦Middle◦Lower

Erosion tends to be significant in upper stage, while deposition in lower course .

Features of upper courseFeatures of upper course

Steep sided valleys , a gorge, a ravine created by erosion when stream channel in the bottom of valley cuts deeply into the land.

Steep sided valleys encourage mass movement of rock material directly into the flowing stream.

Many streams spills from lake to lake in upper course .

Features of upper courseFeatures of upper course

V shaped valleys valleys dominated by down cutting

activity of the streams , called v shaped valleys because of their shape.

Features of middle courseFeatures of middle courseWhen a stream reduces its gradient ,

smoothed out its channel bed and begins to approach its base level , vertical erosion becomes less significant and lateral erosion of channel sides assumes a more important role.

It produces a narrow flood plain along the banks.

Vertical erosion is minimized because the stream is flowing over a gentle gradient

Features of Middles FeaturesFeatures of Middles Features

Vertical erosion become less significant and lateral erosion assumes more important role.

Produces a valley floor with a smoother stream gradient.

Produces a narrow flood plain along the banks.

Verticals erosion is minimized.River valley contains a floodplain but

maintain definite valley walls.The stream course is meandering , loops

oxbow lakes ,and flood plains.

Features of lower courseFeatures of lower course

Dominated by depositional land forms.Sediment – laden water deposits alluvium

on valley floor called alluvial plains.Oxbow lakesNatural leaves

Base Level Base Level

The level below which a stream can not erode its bed , is base level.

Three types of base level.◦Absolute base level◦Local base level◦Temporary base level

Absolute base levelAbsolute base level

When the capacity to erode ends, near the ocean, is absolute level

Stream slows downDeposits its sedimentary loadErosion is terminated

Local base levelLocal base level

A stream that flows into a lake does not relate the global sea level, the lake becomes local base level.

Some times a stream erodes downward, reaches a resistant rock barrier, that keeps the river from developing a smooth profile.

It creates a temporary base level.