TYPES OF TRANSPORT

arth.geol.ksu.eduUniversity of Aberdeen

Bedload- supported by inter-granular collisions

TYPES OF TRANSPORT

Suspended load- supported by turbulent fluctuations

Univ twente

LITTORAL TRANSPORT

Transport along the coast.

Can occur in both directions depending on wave climate

NET: sum of positive and negative drifts

GROSS: sum of positive and negative drift magnitudes.

How to measure???

No “miracle” longshore sediment transport meter exists!

LITTORAL TRANSPORT MEASURING TECHNIQUES

1) Current meters and optical or acoustic basckscatter sensors.

Product of 2 is estimate of instantaneous transport.

Difficulty, hard to image both signals over water column depth. Bedload problematic, bubbles deteriorate signal.

FOBS

LITTORAL TRANSPORT MEASURING TECHNIQUES

2) Streamer traps or other trapping mechanism

Integrated transport only

Komar, 1998

LSTF at ERDCSediment traps

Can get time dependent info

LITTORAL TRANSPORT MEASURING TECHNIQUES

3) Amount of required dredge material

http://bio.sbcc.net/tur/img/aircc.jpg

Dredge hole

LITTORAL TRANSPORT MEASURING TECHNIQUES

4) Tracer study: Use dyed or irradiated grains.

Geiger counter

LITTORAL TRANSPORT MEASURING TECHNIQUES

5) Continuity equation along with measured bathymetry differences

LITTORAL TRANSPORT CALCULATIONS

All essentially reduce to a form of the wave power

CPQ With units of volume per timeC is NOT dimensionless

Better:

bbgKECKPI cossin

bbgECP cossin

With units of immersed weight per timeK IS dimensionless

LITTORAL TRANSPORT CALCULATIONS

The coefficient, K, is normally given as about 0.77 if Hrms is used.

Note the scatter and log-log scale

Slope gives K

LITTORAL TRANSPORT APPLICATIONS

Preceding based on breaker information which we rarely have.

If we make some assumptions like straight and parallel contours, negligble energy losses from offshore and small incidence angles at breaking, we can use Energy conservation, Snell’s Law and shoaling to relate equation to offshore parameters only.

bps

TgKHQ

2.04.02.04.1

2.12.06.04.2

cos2)1)(1(8

sincos

S is ration of sediment to water density. If we assume breaker angle small than the cosine term in the denominator goes to one.

Still looks ugly

LITTORAL TRANSPORT APPLICATIONS

Littoral Drift Rose (LDR) can be used to shore variations in transport due to variations in shoreline orientation.

Drift roses are constructed using available data and longshore sediment transport equation.

D&D

LITTORAL TRANSPORT APPLICATIONS

LDR predicts accentuation of erosive feature

LDR predicts smoothing of erosive feature