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MONITORING REPORT No. 9

DREDGING AND RECLAMATION PROGRAMME IN KINGSTON HARBOUR

 

May 31, 2002

 

 

 

 

 

 

Prepared for:

The Port Authority of Jamaica

 

 

 

 

 

 

 

 

 

Prepared by:


1.0    BACKGROUND

 

 

The dredging Programme was suspended by NEPA on Friday 4th May and resumed on 11th May.  This was due to problems of excessive sedimentation beyond the weir at R1.  Dredging resumed when separate licences were subsequently granted for various aspects of the program.  The licence for continuation of activities at R1 was withheld pending advice to NEPA the National Works Agency on the hydraulics of the Jew Gully outfall.

 

In keeping with increased intensity of monitoring operations, as required by NEPA, water quality sampling fieldwork was carried out on May 13th and 17th  2002.  Sampling scheduled for Monday May 27th had to be postponed due to inclement weather as flood rains affected the island.

 

The sampling exercise carried out on  May 13th  was intended to provide measurement of TSS (total suspended solids)/turbidity in the vicinity of the bund being established in the R2.reclamation area, west of Gordon Cay   On May 17th, sampling was done at the temporary disposal site at two stations to investigate how effective the screen is in minimizing the amount of suspended solids reaching the reef.  However, high currents tore sections of the northern part of the screen.  Therefore, sampling was confined to southern section of the screen which was secure.

 

Monitoring flights took place on May 13th and 28th and a selection of the photographs taken is attached.

 

Inspections of the silt screen at West Middle shoal took place on May 17, shortly after it was installed.  The sea was very rough and the installation of the screen proved to be quite challenging for the divers.  As mentioned above, the northern end of the screen was torn shortly after installation.  Efforts were made to patch the screen when currents subsided.  Another dive to inspect the screen, scheduled for the 26th  May, was postponed due to inclement weather.

 

 

2.0    WATER QUALITY MONITIORING

 

The objectives were:

May 13: To obtain data on TSS (total suspended solids)/turbidity in the vicinity of the bund being established in R2 just  south east of the causeway.

May 17: To obtain measurements of TSS/Turbidity in the vicinity of west middle shoal during dredging.

 

 

Field Work

 

On both occasions sites were established for the collection of water samples and field measurements at multiple depths. Sub-surface samples were taken using a Model No. 12.25 Eijkelkamp peristaltic pump provided by Jan De Nul, as well as a Van Dorn water sampler.  Samples were denoted T (surface), M (middle depth), and B (bottom depth). Sampling was carried out between 1020 and 1208 hours.

May 13

Six sites were monitored, five of them starting in the vicinity of the screen at R2 and heading south toward the channel (these were identified as KTP 1-5 (Figure 1). A sample was also taken in the shallow area just offshore the bund. All sites were assigned a GPS location (Table 1). 

 

Table 1: Dredging And Reclamation In Kingston Harbour

Water Quality Sampling Sites - May 13, 2002

 

STATION NO

DESCRIPTION

N COORD.

W COORD

1

Just Outside Screen at R2

18o 00.214'

76o 46.196'

2

South of Screen

17o 58.617'

76o 50.344'

3

South of 2

17o 58.562'

76o 50.278'

4

South of 3

17o 58.422'

76o 50.153'

5

Channel

17o 58.166'

76o 49.857'

 

 

 

 

 

 

 

May 17  

Four sets of samples were collected at two sites – at the dredge site west of West Middle Shoal, and outside the southern section of the screen protecting the shoal. (Figure 2).  Shallow depth prevented the collection of samples inside the screen.

 

Table 2: Dredging And Reclamation In Kingston Harbour

Water Quality Sampling Sites – May 17, 2002

 

STATION NO

DESCRIPTION

N COORD.

W COORD.

1

Dredge Site - West Middle Shoal

17o 55.415'

76o 51.216'

2

At Screen (outside)

17o 55.376'

76o 51.000'

3

Dredge Site - Resampled

17o 55.450'

76o 51.288'

4

At Screen - Resampled

17o 55.343'

76o 51.017'

 

 

 

 



Sample Analysis

 

Samples were analysed by the Geological Survey Division laboratory. Samples were analysed to determine TSS and turbidity.  Analyses were conducted in accordance with Standard Methods for the Analysis of Water and Waste Water.

 

TSS was determined by filtration of a known sample volume through a dried, pre- weighed filter. After filtration, the filter was dried and re-weighed. TSS in mg/l is obtained through a determination of the weight difference of the filter before and after filtration.

 

Turbidity was performed using the colorimetric method and reported in FAU (formazin attenuated units). FAU includes a correction for colour and is approximately equivalent to TSS mg/l.

 

Observation and Results

May 13, 2002

 

During this sampling exercise heavy-duty equipment was observed assisting in the establishment of the bund at R2. Though progress was obvious, there was significant slippage of material as well as the emergence of small mud waves which created a shallow area extending about 15 M southward from the bund  (Appendix - Plate 1).  The silt screen was in place though it appeared to be overwhelmed by the choppy seas (Appendix - Plate 2). The screen extended from the southern shore of Gordon Cay but was discontinuous in front of the southern side of the bund closer to the Causeway. This was reported immediately on observation and corrected. On May 14th the bund lineation was adjusted to run closer to Gordon Cay, this to limit the emergence of mud waves.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Results of laboratory and field analyses are presented in Table 3 along with sampling depth and time of sample collection. 

 

Table 3:  Dredge Monitoring - R2 Bund near Causeway – May 13, 2002

 

STATION NO

TIME

DEPTH (M)

LAB. RESULTS

FIELD DATA*

T (FAU)*

TSS (mg/l)

TSS (mg/l)

1T

1020

 

21

12.00

50

1Ta

 

 

28

17.00

 

1M

 

2.0

31

20.00

200

1Ma

 

 

28

18.00

 

1B

 

4.0

2835

2117.00

200

1Ba

 

 

4933

23420.00

 

2T

1117

 

18

12.00

50

2Ta

 

 

27

25.00

 

2B

 

4.0

23

14.00

50

2Ba

 

 

30

41.00

 

3T

1125

 

19

2.00

50

3Ta

 

 

20

3.00

 

3B

 

5.0

<14

4.00

350

3Ba

 

 

38

32.00

 

4T

1200

 

<14

2

50

4B

 

6

<14

24

50

5T

1210

 

<14

<1

50

5B

 

7.0

<14

13.00

50

KTP R2 Bund

 

0.5

82

55.00

 

T - Surface sample

B - Depth sample

(a) - duplicate/replicate samples

TSS mg/l - Total Suspended Solids

T (FAU) - Turbidity in Formazin Attenuated Units

 

 

Laboratory results indicate TSS values ranging from <1 - 23,420 mg/l (Figure 3). The highest values, 2117 and 23420mg/l were reported for the bottom samples taken in the vicinity of the screen (KTP 1B, and KTP1Ba respectively). All other samples analysed had a TSS range of <1 – 55mg/l. The highest value in this range was determined for the sample collected at the bund (behind the screen) where depth was around 1M. For samples taken just outside the screen, TSS was determined to be around 15mg/l in surface water. In general TSS in surface water decreased steadily moving from the Bund (R2) towards the channel (Figure 4).