Ardyne, Loch Striven – site and hydrographic survey report

Ardyne, Loch Striven – site and hydrographic
survey report
October 2014
The Scottish Salmon Company
8 Melville Crescent
Edinburgh
EH3 7JA
Report No: 001
Issued By: Mathew Laughton
Checked By: Mark Edmonds
Status: FINAL
Date: 07/10/2014
Contents _______________________________________________________________
1
2
3
Introduction
Site description
Survey programme
3.1
Current meter set up
3.2
Weather station set up
3.4
Mooring system
4 Bathymetry and site survey
5 Data processing
5.1
Valeport data
5.2
Magnetic heading corrections
5.3
Summary statistics
5.4
Meterological results
6 Discussion
3
3
4
4
4
4
5
6
6
8
8
9
10
Appendices
11-13
2
The Scottish Salmon Company November 2011
1 Introduction
This report describes the methods used to acquire current speed and direction data
and spot depths at a site in Loch Striven and presents the outcomes of the survey
exercise.
This deployment was carried out by an independent contractor; AMSL Ltd, using a
Valeport BFM105D rotary meters.
Analyses were carried out in accordance with SEPA guidelines (Regulation and
monitoring of marine cage fish farming in Scotland - a procedures manual.
Attachment VIII Site and Hydrographic Survey Requirements. Version 2.7, 31st
October 2008).
2 Site description
The site is located south of Loch Striven and east of the East Kyle of Bute, Firth of
Clyde. Within the survey area, the seabed slopes to the west, to water depths >50m.
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3 Survey programme
3.1 Current meter set up
The deployment position was (WGS84) 55º 52.789’N 005° 03.052’W (NS 09259
69394).
The survey period comprised a half-lunar 15-day period; from 10th June 2013 to 25th
June 2013. Positioning for the survey was provided by a permanently installed
Trimble AgGPS differential GPS receiver, using public broadcast MF beacons.
Previous calibration indicates that the single fix accuracy of this instrument is
consistently <5m. Between 6 and 9 satellites were visible during the site survey.
Detailed bathymetric data (collected in 2007), in excess of that required by the SEPA
guidelines is included.
Depth at the mooring location was recorded using a Furuno CV108 colour
echosounder (resolution 0.1m), with both GPS and sounder logging directly to PC.
Recorded depth was corrected to chart datum using tidal height predictions for
Rothesay Bay (WXTide). Positions were converted from WGS84 to OSGB36 datum
using DatumPro v1.1 software.
3.2 Weather station set up
Weather data was obtained from
http://www.tutiempo.net/en/Climate/United_Kingdom/GB.html. The nearest recording
station was found to be at Glasgow International Airport.
3.3 Mooring system
Meters were moored from a single J-mooring in a nominal water depth of 42m, at
specified depths of:
 Sub-surface – from a depth 5m below the lowest predicted spring tide during
the deployment period.
 Cage-bottom – at a depth corresponding to the bottom of the cages at mean
sea level ±1m
 Near-bottom – as close to the bed as practicable
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4 Bathymetry and Site Survey
A full bathymetric survey was carried out by AMSL Ltd in 2007.
RDCP
Figure 2: Bathymetric plot.
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RCM position and spot depth information is tabulated below:
Label
Time
Predicted
tidal height
(m)
UTC
Depth (m)
Position
Sounding
Chart
Datum
WGS84
NGR
55º 52.789’ N
05º 3.052’ W
55º 52.778’ N
05º 2.730’ W
55º 52.795’ N
05º 2.851’ W
55º 52.969’ N
05º 2.964’ W
55º 52.901’ N
05º 2.950’ W
55º 52.605’ N
05º 3.082’ W
55º 52.657’ N
05º 3.040’ W
55º 52.828’ N
05º 3.305’ W
55º 52.802’ N
05º 3.104’ W
55º 52.863’ N
05º 2.994’ W
55º 52.857’ N
05º 2.915’ W
55º 52.749’ N
05º 3.038’ W
55º 52.744’ N
05º 2.962’ W
209259
669394
209598
669364
209473
669401
209370
669728
209379
669602
209217
669059
209265
669153
209003
669483
209210
669425
209330
669533
209412
669518
209275
669324
209353
669311
RCM
10:35
3.0
45.0
42.0
E spot 1
11:43
1.93
25.5
23.5
E spot 2
11:43
1.93
35.3
33.3
N spot 1
10:55
1.46
33.9
32.5
N spot 2
10:58
1.49
36.4
34.9
S spot 1
11:31
1.82
44.3
42.5
S spot 2
11:29
1.8
42.8
41
W spot 1
11:11
1.62
47.2
45.6
W spot 2
11:12
1.63
41.2
39.5
NW cage
corner
NE cage
corner
SW cage
corner
SE cage
corner
09:53
0.85
39.2
38.4
09:55
0.86
38.9
38
09:58
0.89
42.7
41.8
10:01
0.92
41.9
41
No. of
Satellites
Fixed
Duration
(seconds)
8
60
7
1
7
1
7
1
7
1
7
1
7
1
7
1
7
1
8
60
8
60
8
60
8
60
5 Data Processing
5.1 Valeport BFM105D data
Hydrographic data were collected using a string of three Valeport BFM105D current
meters, each meter having a sampling period of 60s and averaging period of 20min.
Meter specifications are shown below:
Data was extracted from the Valeport BFM105D to Microsoft Notepad and later
Excel.
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SEPA specify that data should be presented for specified depths so the data was
selected against these requirements:
• Sub-surface – from a depth 5m below the lowest predicted spring tide during the
deployment period
• Cage-bottom – at a depth corresponding to the bottom of the cages at mean sea
level
±1m
• Near-bottom – as close to the bed as practicable
Mean tidal height recorded by the RCM during the deployment (MSL) was 43.9m,
and minimum tidal height for the deployment was 38.3m. Cage depth was assumed
to be 10m.
As such near-bottom depth was taken at 2m, cage-bottom at 29.6m and sub-surface
at 35.6m.All figures are distance from bed.
Specified and deployed depths of data retrieval are compared below:
Measured depth at
deployment
Predicted tidal height at
deployment (from
Admiralty tide tables)
Corrected depth at
deployment (CD)
Lowest
predicted
tide
during deployment
Charted mean sea level
(range)
Average tidal ht
Mean sea level height
above bed
Assumed cage depth
42.0m
3.0m
39.0m
0.0m
3.7m
1.9 m
40.9m
10m
Height above bed
- Bed cell
- Mid cell
- Surface cell
2.0m
29.6m
35.6m
Depth below MSL
- Bed cell
- Mid cell
- Surface cell
4.0m
10.0m
6.4m
Hydrographic data were analysed using the SEPA tool HGdata_analysis_v7, running
in Excel.
Pre and post-deployment values were rejected from the dataset, restricting the full
data records to 1081 records.
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5.2 Magnetic heading corrections
A Grid Magnetic Angle of 1.32º W (from
http://www.geomag.bgs.ac.uk/data_service/models_compass/gma_calc.html ) was
applied and grid convergence (from HGdata_analysis_v7) was 2.54º W to give
overall declination of –3.86º.
Date
10/06/13
Lat
55°52.7
89N
Long
NGR_X
005°03 209259
.052W
NGR_Y
669394
mag. dec
3.86W
Notes:
 grid magnetic angle = magnetic declination – grid convergence
5.3 Summary statistics:
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grid conv. GMA
2.54W
1.32W
5.4 Meterological results
The data obtained from
http://www.tutiempo.net/en/Climate/United_Kingdom/GB.html were analysed using
the SEPA tool HGdata_analysis_v7. The data shows the 24hr average did not
exceed 10m/sec over the survey period.
The data from the weather station exhibits 24h rolling averages between 1.6 and 6.2
m/s, with no wind speeds recorded in excess of 10m/s. The data obtained is a record
of daily average, which does not meet the SEPA requirement for 3 hourly interval
data. However, on the basis that maximum daily average was 6.17 m/s, this is well
below the threshold of 10 m/s and the requirements are for a minimum of 3
consecutive days to be below 10 m/s. 50% of the daily records were below 4m/s.
Over this period the addition of more frequent hourly records would not alter the
validity of the current data over the survey period.
Mean wind speed over the whole deployment was 3.8m/s. The deployment period
therefore met the requirement with mean daily wind speed <10m/s.
Graph:
Graph of wind speed from Glasgow Airport weather station, 10th – 25th June 2013
taken from http://www.tutiempo.net.
e4
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6.0 Discussion
Observed depth data were shown to be consistent with charted depths. Chart
bathymetry is considered suitable for use in modelling.
The tidal height range and time series are consistent with predicted tidal heights. In
general, the site was characterised by moderately high tidal energy. There were
considerable differences between current velocity and direction at all depths,
indicating substantial current shear. Current major axis was observed to be North
direction at seabed and South for Mid and Surface depths. Velocities were
moderate, with a maximum recorded velocity of 0.303m/s at sub surface, and the resuspension threshold of 9.5cm/s was exceeded 15% of the time for the net depth
data. The site is therefore likely to result in low to moderate export of released solids
in AutoDepomod modelling. Velocity and direction showed clear 12.5h periodicity at
all depths and velocity showed clear spring neap variation.
Overall, the recorded data are indicative of a moderately flushed site, typical of an
open loch location and is considered suitable for development in terms of
hydrography and bathymetry. This dataset is considered to provide a good basis for
AutoDepomod modelling.
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