Offshore to onshore transport across distinct landforms at Church Norton Spit
The aim of the project was to establish whether the orthogonal bars act as transport
pathways for pebbles across the intertidal.
SCOPAC contributed £4,000 to an undergraduate student project to investigate whether
the orthogonal bars are acting as sediment transport corridors. The project used
painted and tagged pebbles (using the RFID technology perfected in previous Eastern
Solent Coastal Partnership research www.escp.org.uk/beach-sediment-tracer-study)
during 3 deployments (17/18 February, 4/5 March and 18/19 April 2016). Pebbles previously
collected from the feature included two sizes (approximately 100g and 300g) and were
placed in rows parallel to the shore across the feature and left for two high tides
after which all pebbles found were collected again for the next test. Placement and
collection positions were collected with dGPS and an example of the layout and movements
of pebbles during the first deployment can be seen in Figure 2.
Figure 2: Example of pebble placement (yellow) and collection (red) positions from
the first deployment. Note that the aerial photography in the left hand panel is
from June 2013 (CCO) illustrating some of the shore parallel movement of the orthogonal
Wave conditions were different for all three events (Figure 3) with the first deployment
being the most energetic followed by deployment 2 and 3.
Those pebbles that moved, were transported almost exclusively landwards and obliquely
towards the north. The oblique movement is consistent with slow advance parallel
to the beach observed from survey data over the last few years and is a residual
of the general obliqueness of waves measured at Rustington to have come from ~250°during
The average distance travelled for all pebbles in deployment 1 was 7.77 m while the
average distance travelled during deployments 2 and 3 was 1.57 m and 0.96 m respectively.
This is consistent with wave energy over each of the deployments.
While smaller pebbles seemed to have travelled further than larger ones, there was
no statistical correlation between size and distance
The full report contains attempts to further analyse the data by position but the
sample seems to be too small to allow for any inferences.
1. Background and motivation
Church Norton Spit at Pagham Harbour, West Sussex has undergone cycles of accretion
and breaching since the harbour’s formation in 1910.
In the last 14 years, the spit has experienced excessive growth, although the source
of this material is unknown.
The material for this growth must therefore come from the sub-tidal as there is no
other input from land or alongshore. Some of the material will move as part of bedforms
(green circled in Figure 1) but some may move using bedforms as a transport path
(the orthogonal bar in the red circle). This latter process had been postulated by
Julian Orford in a few papers in the 1990s, but remained a general untested hypothesis.
University of Sussex (lead) £4,000
Minor Funds Contribution 2015-16
Figure 1: Aerial photography showing location of the more or less stationary orthogonal
bar (red) and other intertidal shingle features (green)
This project was instigated by Dr Uwe Dornbusch of the Environment Agency, Arun DC
and Chichester DC and was led by Dr Cherith Moses from the University of Sussex with
input from Professor David Sear from the University of Southampton.
The Eastern Solent Coastal Partnership provided the tracer study retrieval equipment.
Figure 3: Wave and tide conditions during deployments taken from Rustington wave
buoy and Littlehampton tide gauge.
The measurements on the orthogonal bar at Church Norton Spit show that pebbles move
along the bar even under comparatively low energy conditions and support the assumption
that these features act as transport corridors.
It is recommended that a future study deploy the tracers for more than one tidal
cycle to identify longer term fluctuations in transport. In addition, further work
on quantifying the volume of shingle moving along the orthogonal bars would be of
benefit to understand their significance as a transport mechanism in relation to
the wider sediment cell.
The project was carried out as part of an undergraduate thesis by Lucy White at the
University of Sussex. The thesis is available here (see right).