REPORT OF SURVEY
Strategic Regional Coastal Monitoring Programme
TSW4 - Lands End to Bude
Baseline Survey
7A2-7 Hayle Estuary to Godrevy Point
Job No:
Date of Survey:
16/03 - 21/03/2007
TSW4
7A2-7 Hayle Estuary to Godrevy Point
Baseline Survey
To:
Plymouth Coastal Observatory
Reynolds Building
University of Plymouth
Drake Circus
Plymouth
PL4 8AA
From:
Land & Sea Survey Company
Higher Filleigh
Lapford
Devon
EX17 6NA
Company Ref:
TSW4_7A2-7
Date of Survey:
16/03 - 21/03/2007
TSW4 7A2-7 Hayle Estuary to Godrevy Point – Baseline Survey
Date: 16/03 - 21/03/2007
Contents
1.0
Scope
2.0
Survey Control
3.0
Topography
4.0
Survey Diary
5.0
Comments
TSW4 7A2-7 Hayle Estuary to Godrevy Point – Baseline Survey
Date: 16/03 - 21/03/2007
TSW4
7A2-7 Hayle Estuary to Godrevy Point
Baseline Survey
Report of Survey
Date of Survey:
1.0
16/03 - 21/03/2007
Scope
1.1
Baseline Survey of Management Unit 7A2-7 Hayle Estuary to Godrevy
Point, to include:
Accessible frontage profile lines 7a00818 to 7a00928 inclusive.
2.0
3.0
Survey Control
2.1
Survey control points used: Gwithian2 (RTK base); Gwithian1 and
Porth_Kidney2 (RTK check)
2.2
Details of the permanent survey control stations are described in the
station description sheets and are appended separately.
2.3
No Start Point Markers were installed in this Management Unit
2.4
Final co-ordinates are given as either ETRS89/WGS84 or transformed
to OSGB36 and Ordnance Datum using OSTN02/OSGM02.
Topography
3.1
The topography has been surveyed using 4 x Leica 1230GX (1 x Trailer
mounted antennae) 1 x Leica SR530 RTK GPS receivers and 1 x Leica
TPS 1205 Smart Station, processed using LGOv5 and Terramodel
v10.2.
3.2
The precision of heights on hard surfaces may be taken, to a 95%
confidence level, to be within ±20mm relative to the control station
height.
3.3
All profile lines 7a00818 to 7a00928 inclusive were surveyed.
TSW4 7A2-7 Hayle Estuary to Godrevy Point – Baseline Survey
Date: 16/03 - 21/03/2007
4.0
Survey Diary
4.1
The survey of the dunes commenced on 16/03/2007 and was
conducted by C. Fanshawe, A. Russell and A. Garbe
4.1
The survey of the beach was conducted by C. Gaskell, A. Russell, C.
Fanshawe and A. Garbe between 07:30 and 17:00 on 17/03/2007 to
19/03/2007; C. Gaskell and A. Garbe only on 20/03/2007 and
C.Gaskell, A.Garbe and A.Russell on 21/03/2007.
4.2
The following control points were checked using RTK GPS:
16/03/2007
17/03/2007
TSW4 7A2-7 Hayle Estuary to Godrevy Point – Baseline Survey
Date: 16/03 - 21/03/2007
18/03/2007
19/03/2007
19/03/2007
TSW4 7A2-7 Hayle Estuary to Godrevy Point – Baseline Survey
Date: 16/03 - 21/03/2007
20/03/2007
21/03/2007
TSW4 7A2-7 Hayle Estuary to Godrevy Point – Baseline Survey
Date: 16/03 - 21/03/2007
4.3
4.4
5.0
Low Waters were predicted to occur as follows:
Date
LW Ht (CD)
Time (GMT)
16/03/2007
1.4
09:29
17/03/2007
1.0
10:14
18/03/2007
0.5
10:55
19/03/2007
0.2
11:34
20/03/2007
0.1
12:15
21/03/2007
0.2
12:57
Wind: N-NW 6-8 during 15-19 March veering NE 5-6 on 20-21 March
2007; Sea state: Very rough, waves 2.5-3m decreasing 1.5-2m.
Comments
5.1
Gwithian and Godrevy beach is bounded to the north by cliffs at
Godrevy Point and to the south by Management Unit 7A2-6 Hayle
Estuary. Mexico Towans, Upton Towans and Gwithian Towans make
up the inhabited and vegetated sand dunes and cliffs of the landward
barrier.
5.2
The survey was conducted during a period of particularly poor weather
conditions with the beach experiencing northerly and northwesterly
gales which proceeded to cut into the dune toe between profile lines
7a00829 and 7a00871, reducing the level at the top of the beach by up
to
two
metres
over
the
5
days.
Photograph
7a00850_20070320_Dune_1_up.jpg shows part of the wave-cut dune
edge. Extra baseline and profile data were collected here to ensure a
smooth transition between the two areas which were mobile during the
evening high waters. Much of the beach up to the high water mark
between 7a00855 and 7a00900 was covered with approximately 50100mm of standing water throughout the survey, being held up the
prevailing winds.
5.3
The beach is generally very flat compacted fine sand with occasional
areas of deeply scoured pockmarks caused by wind and wave action
and further areas containing very soft, almost muddy sand. This was
particularly noticeable mid-beach between 7a00820 and 7a00829 and
also 7a00899 and 7a00903. Small gaps in survey data occurred on line
7a00903 and approximately +/-35m alongshore and +/- 15m up and
down the beach from E 158077 N 42370 due to very deep water-filled
TSW4 7A2-7 Hayle Estuary to Godrevy Point – Baseline Survey
Date: 16/03 - 21/03/2007
scour holes and liquid sand which caused both quad-bike and
surveyors on foot to sink. Further scour holes were evident in the
region of E 158077 N 42370 on profile line 7a00915. Both areas were
assessed by the survey team and care was taken not top compromise
the safety of personnel and equipment.
5.4
Towards the north end of the beach rocky outcrops appear with the
dune backing diminishing to leave the remains of old saltings works.
Red River flows onto the beach between the saltings and Gwithian
Towans over a bed of pebbles and small cobbles which have been
coded as gravel. North of the river, the beach topography undulates
around further rocky outcrops with a deep water channel running along
the beach
5.5
During the daily assessment of work completed, several small areas of
sandy beach were found to require extra data particularly approx
1800sqm near line 7a00887 chainage 590 centred on E 157630 N
41200 and measuring approx 41m x 45m. This and other smaller
areas were surveyed on 20/03/2007. Data was logged in the field but
on downloading was found to be unreadable. Calls were made to
Leica Geosystems to find out if the data was likely to be recoverable
and since the response was favourable the survey team continued with
data collection in other areas. The data was sent to Leica and then
further passed on to the database developers in Switzerland for
analysis and finally on 08/05/2007 it was found that the data would not
be recoverable. Beach topography in this area consists of very flat or
gently sloping sand and whilst profile data exists through the centre of
the gap it is considered that the loss of data will not significantly affect
the overall DTM formation:
Data Gap
Rocks
TSW4 7A2-7 Hayle Estuary to Godrevy Point – Baseline Survey
Date: 16/03 - 21/03/2007
5.6
A similar logging problem occurred at Management Unit 7A2-5 Carbis
Bay – see report Topo_report_7A2-5_20070322.pdf. Following the two
incidents the instruments and data cards were re-formatted and project
data re-loaded. No further data recording problems have occurred
during the beach surveys.
5.7
All RTK GPS checks from Gwithian2 show Gwithian1 and
Porth_Kidney Sands2 station appearing to be located approximately
30mm to the northwest of the given coordinates whilst the height
difference is generally greater than 25mm. For Gwithian1, the most
likely reason for such large height differences is the close proximity of
the lifeguard hut to the survey marker. Signals received at the GPS
antenna are likely to be affected by reflections from the wall and roof
structure which will also create an interruption in the signal path from
the north-east around to south-east. The checks at Porth_Kidney
Sands show a very poor correlation in both position and height
between two separate survey days.
5.8
There are no structures in this Management Unit.
5.9
The survey as a whole has been quality checked by C Gaskell
TSW4 7A2-7 Hayle Estuary to Godrevy Point – Baseline Survey
Date: 16/03 - 21/03/2007
View of Hayle Estuary to Godrevy Point
TSW4 7A2-7 Hayle Estuary to Godrevy Point – Baseline Survey
Date: 16/03 - 21/03/2007