Re: Scouring/deposition of inter-tidal mud


"N Cook" <diverse@xxxxxxxxx> skrev i en meddelelse
news:dm6h0g$dc0$1@xxxxxxxxxxxxxxxxxx
> There is a local site of historic interest that consists of the
> remnants of wood piles in intertidal mud of a local river.
> Recently, viewing the site, there was nothing to be seen but previous
> occassions the stumps are exposed by as much as a foot each.
> Could someone tell me what the mechanism is and whether the
> scouring/deposition is related to springs/neap tides, time of year,
> upstream
> rainfall, temperature, wind, worm activity or what ?

I have difficulties visioning your setting, but you obviously have a site at
the 'end of a river'. One thing that primarily comes to mind is the question
of the magnitude of the tidal cycle, the wave/wind-climate of the coast, the
hinterland and the shelf, but it may not alter some basic characteristics.
One characteristic scouring is related to low-tide: at high tide the total
area covered by water may act as a conduite for the flow of water. When the
area is reduced, the flow to and from is confined to smaller and smaller
areas that consequently suffers scouring. - this may evolve into a dendritic
drainage-pattern. Sedimentation happens at high tide and covers large areas,
so the scour and the sedimentation differs. The characteristics of the tidal
sediments may be the heterolithic mix of small pockets of sand draped by a
fine clay that binds the sand and gives it less resistance (smooth surface)
to erosion by subsequent return-flow.
The tidal flow happens in response to a changing gradient of the
sea-surface - if a large shelf is inundated, this gradient makes in and
out-flow different: the out-flow has to pass a volume of water under a lower
surface-height, than the inflow. This is why an 'inland' drainage-pattern
may be prolonged to cover the shelf outside the tidal zone.
I cannot tell weather your setting is so that enhanced runoff in rainy
periods makes for a fluvial (stream) sedimentation on the premises of the
river - and that the principles of this deposits later interfer with the
coastal/tidal sedimentation. The alternative is, that the river-mouth
naturally displace barres over time - which, I believe, you already have
considered, as well as weather the covering of the stumps has been related
to storm-events? The slushing to and fro of tidal waters potentially makes
it a dynamic place for moving sediments around.
I see that you write from uk, so I wonder weather your river faces an east
or a west coast. There is a large differens in tidal magnitude and
wind/wave-climate between the two.

Carsten


.

Relevant Pages

  • Re: Dove Pier Incident Report
    ... of the tide the ebb runs fast along the river wall to The Terrace, ... encouraging this secondary flow pattern. ... water to bottom water and accept that this can cause a spiralling effect ... The difference between the regimes causing scour or sedimentation lies ...
    (rec.sport.rowing)
  • Re: Dove Pier Incident Report
    ... of the tide the ebb runs fast along the river wall to The Terrace, ... encouraging this secondary flow pattern. ... I can see that there must be a flow rate gradient from surface water to bottom water and accept that this can cause a spiralling effect on the ebb as you describe. ... The difference between the regimes causing scour or sedimentation lies largely in the flow velocity close to the surface & to the degree of turbulence. ...
    (rec.sport.rowing)
  • Identification of Mutagenic Particles in River bed of Yamuna" : By Vagish Sharma
    ... A report on "Identification of Mutagenic Particles in River bed of ... Yamuna": By Vagish Sharma ... This report focuses on the water pollution in Yamuna and addresses the ...
    (talk.environment)
  • Bangladesh in Peril - Another Farrukha in Offing
    ... When completed in 1970 by India, the Farakka Barrage, around 18 ... as the entire south-western region of Bangladesh was affected due to ... the dearth of water. ... Indo-Bangladesh joint river commission in 1972. ...
    (soc.culture.pakistan)
  • Dhaka Reeking Of Toxic Stink ..... ..... Re: Mandia Bedi - Ugly indian hindoo woman with p
    ... Casting a grim look at the black and stinky liquid waste flow in the ... narrow Devdholai river, Afazuddin Mia, a resident of Nasirabad village ... the water is so toxic that even a snake would not dare to cross it. ...
    (soc.culture.bangladesh)
Quantcast