SCOTTISH SEA FARMS LTD HORSE ISLAND HYDROGRAPHIC REPORT
Transcript of SCOTTISH SEA FARMS LTD HORSE ISLAND HYDROGRAPHIC REPORT
SCOTTISH SEA FARMS LTD
HORSE ISLAND
HYDROGRAPHIC REPORT
Report To: Scottish Environment Protection Agency
Report No: H0817- 01
Our Ref: RS
Status: V1
Date: 08 August 2017
Scottish Sea Farms Ltd
South Shian
Connel
PA37 1SB
Tel:
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1. Introduction
A hydrographic survey was carried out by Scottish Sea Farms on the site of an existing shellfish lease located
on the east side of Horse Island, Summer Isles. The survey location is approximately 5.5 km southeast of the
existing SSF fish farm sites of Tanera and Fada. This data has been collected with a view to creating a new
marine cage fish farm on the site of the shellfish lease.
Current speed and direction, depth and meteorological data were collected as part of this survey for use
with SEPA’ s consenting model AutoDEPOMOD to assess this site’ s suitability for development.
2. Site Location
The survey location is at the southeastern end of Horse Island in Horse Sound. The site is sheltered from
west to north with the greatest exposure to the wind from southerly directions. Admiralty charts indicate
that the bathymetry follows the general contour of the island with areas of deeper water to the east.
Figure 1: Locational map showing Horse Island Hydrographic Survey location
3. Methods
A 600 kHz RDI Workhorse ADCP was deployed on 03/ 08/ 2012 and recovered on 09/ 09/ 2012, all of which is
presented in this report. A 15 day subset will be used for AutoDepomod modelling purposes ( 17/ 08/ 2012 –
01/ 09/ 2012). Concurrent weather data was obtained from the station at Aultbea along with a bathymetric
survey of the site.
3.1 Current data
The ADCP was deployed at 57 58.884 N 05 20.281 W (202733, 904007). The meter was mounted in a
fiberglass Seaspider frame and deployed in a u-shaped mooring with ground rope running to weights
attached to surface buoys.
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Current flow and direction were recorded at throughout the water column using 0.75 m bins with an
averaging period of 20 minutes.
Deployment configuration:
Broadband 614.4 kHz
Pings/ Ens 350
Time/ Ping 00:03.42
First Ensemble Date 03/ 08/ 2012
First Ensemble Time 10:36:39:66
Ensemble Interval (s) 1200
1st Bin Range ( m) 1.87
Bin Size ( m) 0.75
Table 1: ADCP configuration for Horse Island Hydrographic Survey
3.2 Bathymetric data
Spot depths were obtained at the survey site using a Hawkeye Digital Sonar hand-held depth sounder. All
depths were later converted to chart datum using predicted tidal heights for Tanera Mor obtained from
Admiralty Total Tide.
3.3 GPS
Position fixes were obtained using a Garmin GPSmap 76S in WGS84. The GPS position accuracy was
compared against a known location and checked for consistency at the end of the survey.
3.4 Weather
Weather data for the survey period was obtained from the station at Aultbea 21 km to the south west.
3. Data processing
3.1 Processing
All bathymetric data collected was corrected to chart datum using tidal heights taken for Admiralty TotalTide
from the Tanera Mor station.
Three depth cells were selected as outlined in Appendix 8 of SEPA’ s Fish Farm manual.
Bins 1, 28 and 38 were selected to represent seabed, cage bottom and sub-surface conditions. Several
ensembles were removed at both the start and end of the recorded to remove data recorded during
deployment and retrieval. Each bin was then checked for missing or erroneous data then analysed using the
SEPA tool HGdata_ analysis_ v7. The summaries for each bin can be found in section 4.3.
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3.2 QC
The RDI Workhorse carries out a series of internal checks on each ping as a measure of quality control. If any
of the returning pings fail the QC criteria ( correlation, echo intensity and error velocity) they are rejected and
not included in the averaged ensemble. Rejected pings have an impact on the expected standard deviation
of the dataset however this can be calculated by using the percentage of good pings.
Depth and Current
Pressure records indicate that the mean depth during the deployment including the height of the frame was
37.7 m, removing the influence of tide gives a depth of 34.3 mCD. This corresponds well with the recorded
depth of 37.3 m (34.4 mCD).
The recorded pressure was also compared with the predicted tidal heights taken from the station at Tanera
Mor (TotalTide). Both range and low water and high water are consistent with those predicted.
Current direction is consistent with local bathymetry and the speeds recorded are within expected range and
are consistent with other sites in the Summer Isles region.
The residual currents at the subsurface, mid and bed bins are 43%, 21% and 19% of the mean current speed
respectively, while the direction appears consistent with that of a weak residual current.
Meter position
Pitch and roll data are somewhat unsettled during the deployment ( figure 2) however heading remains fairly
consistent with no large spikes to indicate a significant disturbance of the meter. These fluctuations remain
within an overall pitch or roll of +/- 5° well within the machine tolerance of 15°. 15 day datasets will be
selected to minimize these fluctuations where possible.
Meter position was recorded during deployment and recovery showing that the position of the meter had
not changed during the survey.
Figure 2: Time series showing pitch, roll, pressure record and heading vs days deployed at Horse Island.
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4. Results
4.1 Bathymetric data
Figure 3: Admiralty chart extract showing location of recorded depths
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STATION ACTUAL WGS84 SOUNDING
DEPTH ( M)
TIDAL HEIGHT
M)
DEPTH
MCD)
A1 57° 59.054' 5° 20.373' 7.5 3.3 4.2
A2 57° 59.001' 5° 20.412' 16.3 3.318 12.982
A3 57° 58.951' 5° 20.450' 19.2 3.336 15.864
A4 57° 58.903' 5° 20.517' 18.2 3.354 14.846
A5 57° 58.856' 5° 20.570' 18.7 3.372 15.328
A6 57° 58.854' 5° 20.571' 29 3.39 25.61
B1 57° 58.805' 5° 20.594' 35.6 3.408 32.192
B2 57° 58.787' 5° 20.516' 28.9 3.426 25.474
B3 57° 58.846' 5° 20.499' 24.2 3.444 20.756
B4 57° 58.942' 5° 20.415' 24.5 3.462 21.038
B5 57° 58.989' 5° 20.355' 26.8 3.48 23.32
B6 57° 59.034' 5° 20.301' 27.9 3.498 24.402
B7 57° 59.077' 5° 20.255' 22.4 3.516 18.884
B8 57° 59.129' 5° 20.203' 28.2 3.534 24.666
C1 57° 59.177' 5° 20.110' 53.5 3.552 49.948
C2 57° 59.128' 5° 20.150' 33.2 3.588 29.612
C3 57° 59.076' 5° 20.190' 35 3.606 31.394
C4 57° 59.026' 5° 20.230' 43 3.624 39.376
C5 57° 58.976' 5° 20.279' 38.8 3.642 35.158
C6 57° 58.932' 5° 20.329' 32.7 3.66 29.04
C7 57° 58.884' 5° 20.377' 29.1 3.678 25.422
C8 57° 58.838' 5° 20.441' 34.1 3.696 30.404
C9 57° 58.786' 5° 20.480' 36.4 3.714 32.686
C10 57° 58.741' 5° 20.498' 30.5 3.57 26.93
D1 57° 58.760' 5° 20.406' 28.6 3.732 24.868
D2 57° 58.813' 5° 20.356' 37.3 3.75 33.55
D3 57° 58.863' 5° 20.335' 35 3.768 31.232
D4 57° 58.917' 5° 20.292' 36.4 3.786 32.614
D5 57° 58.963' 5° 20.247' 44.1 3.804 40.296
D6 57° 58.010' 5° 20.195' 50.8 3.822 46.978
D7 57° 59.042' 5° 20.136' 54.6 3.84 50.76
E1 57° 59.085' 5° 20.015' 47.1 3.858 43.242
E2 57° 59.031' 5° 20.058' 58.2 3.876 54.324
E3 57° 58.997' 5° 20.141' 56 3.894 52.106
E4 57° 58.948' 5° 20.200' 50.7 3.912 46.788
E5 57° 58.903' 5° 20.248' 41.2 3.93 37.27
E6 57° 58.854' 5° 20.311' 37.6 3.948 33.652
E7 57° 58.795' 5° 20.360' 35.6 3.966 31.634
E8 57° 58.744' 5° 20.335' 26.7 3.984 22.716
F1 57° 58.729' 5° 20.253' 34.5 4.002 30.498
F2 57° 58.783' 5° 20.226' 34.1 4.02 30.08
F3 57° 58.835' 5° 20.191' 37.1 4.038 33.062
F4 57° 58.881' 5° 20.138' 52 4.056 47.944
F5 57° 58.927' 5° 20.087' 58 4.074 53.926
Table 2: Depths recorded during Horse Island Hydrographic Survey
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4.2 Meteorological data
Hourly wind speed and direction were obtained from the weather station at Aultbea approximately 21 km
south west of the survey location. As can be seen from the figures below at no point did the wind exceed 10
m/ s for a period of three days. The predominant wind direction during this period was westerly.
Figure 4: Wind rose of wind speed and direction recorded at Aultbea during survey period.
Figure 5: Mean wind speed recorded at Aultbea Weather Station 01/08/ 2012 – 10/ 09/2012
0
20
40
60
80
100N
NNE
NE
ENE
E
ESE
SE
SSE
S
SSW
SW
WSW
W
WNW
NW
NNW
Aultbea Wind Rose
0 m/ s
1 m/ s
2 m/ s
3 m/ s
4 m/ s
5 m/ s
5 m/ s
0
2
4
6
8
10
12
14
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01/ 08/ 2012 00: 00 11/ 08/ 2012 00: 00 21/ 08/ 2012 00: 00 31/ 08/ 2012 00: 00 10/ 09/ 2012 00:00WindSpeed (m/s)
Date and Time Aultbea Wind Speed 01/ 08/ 2012 -
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4.3 Current data
Bed Cage bottom Subsurface
Bin number 1 28 38
Bin depth ( m) 2.7 22.9 30.4
Mean velocity (m/ s) 0.021 0.039 0.046
Min velocity (m/ s) 0.000 0.000 0.001
Max velocity (m/ s) 0.134 0.197 0.204
Ranked percentage of mean velocity 60 59 58
Ranked percentage of 3 cm/ s 82 46 35
Ranked percentage of 9.5 cm/ s 94 96 93
Residual velocity (m/ s) 0.004 0.009 0.019
Residual direction (°G) 18.4 14 3.6
Major axis 25 35 25
Residual parallel (m/ s) 0.004 0.008 0.017
Residual normal (m/ s) 0.000 - 0.003 - 0.007
Amplitude parallel (m/ s) 0.031 0.058 0.064
Amplitude normal (m/ s) 0.018 0.031 0.035
Longitudinal amplitude anisotropy 8.66 2.57 2.56
Latitudinal amplitude anisotropy 1.71 1.88 1.81
Table 3: Current data statistics of each of the 3 bins
The current speeds and directions recorded at each of the 3 bins are in general agreement with each other
with current speed decreasing with depth as would be would be expected. Current speeds are relatively low
and typical other sites in the region. Maximum current speed recorded during the deployment was 0.204
ms¯¹. Currents at all depths were weakly directional and changes in current speed correspond with the
flooding and ebbing of the tide as indicated by the pressure record although there is some evidence of wind
driven events corresponding to periods of peak wind speed. Summaries from the SEPA tool HG_ Analysis for
the whole survey period are displayed in the figures below:
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Figure 6: HG_Analysis summary page Horse Island 2012 – subsurface
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Figure 7: HG_Analysis summary page Horse Island 2012 – cage bottom
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Figure 6: HG_ Analysis summary page Horse Island 2012 – bed