Sediment Transport and Deposition 2.2

What is material in water moved by

Traction- large heavy material dragged along sea floor

Saltation- smaller material lifted by water bounces along river bed

Suspension/ solution- lighter material carried within river flow

Long shore drift- influencing sediment transport

Main process of deposition and transportation along coast

As wave breaks, swash carries material up beach at angle

As swash dies, backwash carries material down beach at 90°

Process repeats, transporting material along beach in zig zag movement

What is long shire drift influenced by

Prevailing wind causes waves approaching beach at angle

Current- influencing sediment transport

Current is flow of water in certain direction, transporting sediment

Tidal current

They’re associated with rising and falling tides

Greater the tidal range, greater the strength of current

Rip currents

Underwater currents occurring near coastline

Transport sediment few metres out to sea

What causes tides and what’s tidal range

Gravitational pull of sun and moon

Difference between high and low tide

What do larger tidal ranges do

Produce stronger tidal currents which transports more sediment

Why do waves loose energy causing deposition

• Wind slows or changes direction

• Wave experiences friction

High energy coastlines deposit large rocks but maintain enough energy to carry smaller sediment particles- create rocky beaches

Low energy coastlines deposit smaller sediment due to low wage velocity, creste sandy beaches

Where do depositional landforms occur

At low energy coastlines when waves don’t have enough negate to carry large sediment

Most common depositional landform is a beach

Beaches can be drift aligned or swash aligned- what are these

Drift aligned- form where longshore drift moves sediment along beach as waves approach at an angle

Swash aligned- energy us low, waves are parallel to shore so little horizontal movement of sediment

What are spits

Extended stretch of sand going to to sea from shore

How are spits formed

• sediment transported by waves along coast

• When coastline changes direction, waves don’t have energy to carry sediment and its deposited

• Build up of deposited sediment out to sea is a spit.

What are tombolo and bars formed from

When spits forms across an estuary or around a headland- sediment meets an island or opposite side of headland

They are formed in the same way- through long shire drift and deposition

Lagoon

A small body of water cut off from sea

Form behind a bar or tombolo

Tombolo

Formed when a spit joins the mainland to an island

Off shore bars

a ridge of sand running parallel to coast

Formed when destructive waves pick sediment from beach and carry it offshore

Sediment is deposited offshore, creating raised area under sea

Double spit

2 spits extend out in opposite directions of bay to middle

Form when long shire drift happens in different directions, opposite sides of bay.

Hooked/ recurved spit

Spit which end is curved landward

Due to change in prevailing wind bending end of spit

Cuspate forelands and how are they formed

Low lying triangular shaped headlands, extending from shoreline

Formed through deposition of sediment by longshoreman drift from 2 directions.

Salt marshes

Behind spits/barrier beaches, area is sheltered from tidal currents leading to deposition, forming salt marshes

What is a sediment cell

Linked system of sources, transfers and sinks of sediment along section of coastline

Sediment cell being a closed system

It’s a closed system with no inputs or outputs of sediment from cell

Inside of the sediment system, can be divided into sub cells where there’s inputs (sources), transfers and outputs (sinks)

Inputs (sources) of a sediment cell

Where sediment is generated- e.g. cliff erosion, river transport

Transfers of sediment cell

How sediment moves e.g. longshoreman drift, tidal currents

Outputs (sinks) of sediment cells

Sinks are located where sediment is deposited e.g. beaches, spits

How many sediment cells are in the uk

11 around the Uk coastline

Dynamic equilibrium- sediment cells

Sediment cell is in dynamic equilibrium when inputs= outputs even though sediment is constantly shifting

Landforms in transfer zone stay same size but source and sink features change

Dynamic equilibrium can be disrupted (storms) but restores through negative feedback

Negative feedback- sediment cell system

Acts to counteract change to reduce impact and restored equilibrium

E.g. cliff collapse- erosion causes part of cliff to fall, fallen material gathers at base, acting as a barrier to protect cliff from further erosion

Positive feedback- sediment cell system

It amplifies original change leading to greater imbalance in system

E..g dune erosion- storm eroded part of dune, removing vegetation. Without stabilisation from vegetation, even light winds blow sand, increasing erosion