Case Application at Yangshan Port

Field observation and survey at sea

From April 2010 to December 2011, East China Sea Forecast Center led and cooperated with East China Normal University and the Shanghai Estuary and Coasts Scientific Research Center which are implementing agencies of the offshore projects as well as the East China Sea Centre of Standard Metrology, SOA which is the field operation assistance unit to carry out the monitoring of sediment concentration and marine current at fixed-points and sections and two fixed points of subsurface buoy under extreme weather conditions at the time of spring tide and neap tide during four voyages in the wet season and dry season of 2010 and 2011, and obtained the data of sediment concentration and marine current at section at Yangshan Port area. The current field and sediment characteristics at Yangshan Port are then analyzed with the data.

The observation data obtained from the section survey and survey at fixed- points includes: 13 h continuous marine current monitoring data of sections with ADCP, about 26h monitoring data of the fixed-points at the time of spring tide and neap tide. Vertically six points corresponding to the surface. water depth of 0.2 H, 0.4 H, 0.6 H and 0.8 H and the bottom were adopted and the monitoring interval is one hour (half hour when the current velocity is large). The elements surveyed were the current velocity, current direction, water depth and sediment concentration. The data of subsurface buoy survey includes the data of ADCP monitoring of marine current and data of OBS monitoring of sediment concentration during two strong wind processes.

Survey basis

Contract for Sediment Transport Monitoring, Forecasting and Research of Storm Scouring, Silting at Yangshan Port

Plan of Implementing Sediment Transport Monitoring, Forecasting and Research of Storm Scouring, Silting at Yangshan Port

Specification for Oceanographic Survey (GB/T12763.2-2007)

Specification for Marine Monitoring (GB/T 17378.4-2007)

Survey method

Section survey

1) Survey time

A total of eight field surveys were carried out, with each survey conducted during the spring tide and neap in the dry season and wet season of 2010 and 2011 (namely, during December 2010 and December 2011, July 2010 and September 2011, respectively) (Table 8.1).

TABLE 8.1: Settings of Survey Method

No.

Item

Method

Reference standard

1

Moving monitoring of current of sections

ADCP method

7 'he Specification for Oceanographic Survey (GB/T 12763.2-2007)

2

Monitoring of current at fixed- points

Method of direct- reading current meter

The Specification for Oceanographic Survey (GB/T 12763.2-2007)

3

Sediment concentration of sections

Gravimetric

method

The Specification for Marine Monitoring (GB/T 17378.4-2007)

  • 2) Survey method
  • a) Hydrological elements

The monitoring of current velocity and current direction at fixed-points were carried out with direct-reading velocity meter. When the water depth is > 3, the current velocity and direction at surface, at the water depth of 0.2 H, 0.4 H, 0.6 H and 0.8 H and at the bottom were monitored. When the water depth is < 3, only the current velocity and direction at the water depth of 0.2 H and 0.6 H and at the bottom were monitored. The moving measurement of current was carried out with ADCP.

b) Sediment concentration

The sediment-containing water samples at six points were collected with horizontal water sampler during the spring tide and neap tide once every hour. Monitoring was carried out once every half hour during the tide change.

  • 3) Key technical indicators of the survey instrument
  • a) ADCP

Current velocity: Measurement range: ± 10 m/s 3-D current velocity;

Measurement accuracy: ±1%; ±0.5 cm/s;

Resolution: O.lcm/s;

Current direction: Measurement range: 0° to 360°;

Measurement accuracy: ±2°;

Resolution: 0.1°;

Sections measured: surface to depth of -5 m.

b) SCL-9 direct-reading current meter

Current velocity measurement range: 0.03-3.5 m/s, average measurement error ±2%;

Current direction measurement range: 0° to 360°, average measurement error ±10°.

4) Setting of the survey points

In order to comprehensively obtain the distribution of sediment concentration in Yangshan Port area, two sections at the wide door, narrow door and side door were set (Figure 8.1). The moving monitoring of current at sections A and C and fixed measurement and sampling of current and sediment concentration at points Al, A2, B, and C4 were carried out (Table 8.2).

Subsurface buoy monitoring

1) Survey time

Field survey during two strong wind processes from August to December 2011 (namely August 2011 and December 2011).

  • 2) Survey method
  • a) Marine current (velocity and direction)

The monitoring of current velocity and direction at fixed-points were carried out bottom-up with ADCP of Sontek and bottom-resting subsurface buoy. The spacing of monitoring layer is 1 m and the sampling interval is 20 minutes (Tables 8.3 through 8.5).

Settings of survey sections

FIGURE 8.1: Settings of survey sections

TABLE 8.2: Settings of survey points

Point

Latitude

Longitude

Water depth

Measuring element

Section A

9-10m

Marine current

Section C

26m

Marine current

A1

30°38'30"ЛГ

122°00'24"£

9.5m

Marine current Sediment concentration

A2

30°36'40"ЛГ

121°59'24"£

9.7m

Marine current Sediment concentration

В

30°35'40"ЛГ

122°00Т2"£

12m

Marine current Sediment concentration

C

30°35'59"ЛГ

122°05'45"£

26.9m

Marine current Sediment concentration

b) Sediment concentration

The sediment concentration is measured with OBS nephelometer imported from USA and the sampling interval is 20 minutes (which is consistent with that of ADCP monitoring).

3) Key technical indicators of the survey instrument a) ADCP

Current velocity: Measurement range: ± 10 m/s 3-D current velocity;

TABLE 8.3: Settings of survey methods

No.

Item

Method

Instrument

1

Marine current

Subsurface buoy method

ADCP

2

Sediment concentration

Subsurface buoy method

OBS

TABLE 8.4: Settings of original survey points

Point

Latitude

Longitude

Water depth

Measuring element

Qi

30°35.900'A

122°05.750"£

26.9m

Marine current Sediment concentration

Q2

30° 36.717'A

122°02.817'£

13m

Marine current Sediment concentration

TABLE 8.5: Settings of the subsurface buoy placement points after adjustment

Point

Latitude

Longitude

Water depth

Measuring element

Ql

30°35.87l'A

122°06.876'.E

20m

Marine current Sediment concentration

Q2

30°37.475'A

122°02.258'£

11m

Marine current Sediment concentration

Measurement accuracy: ±1%; ± 0.5 cm/s;

Resolution: 0.1 cm/s;

Current direction: Measurement range: 0° to 360°;

Measurement accuracy: ±2°;

Resolution: 0.1°;

Sections measured: surface to depth of 5 m. b) OBS

Measurement range: 0-4000 NTU;

Measurement accuracy: 0.25 NTU or 1% of reading;

Rated depth: 500 m.

4) Setting of the survey points

This survey project requires comprehensive^ obtaining the distribution of marine current and near-bottom sediment concentration in Yangshan Port area. Therefore, it is planned to set Ql and Q2 (Figure 8.2) at wide door and narrow door at Yangshan Port respectively to have continuous monitoring of the marine current and sediment concentration during the strong wind processes. In the survey process, the subsurface buoy placement points Ql and Q2 were re-adjusted (Figure 8.3): since the water at Ql is deep, the point in the surrounding area with appropriate water depth was re-selected to be the point Ql; the point Q2 was adjusted according to the existing seabed-based data to ensure that the observation data of point Q2 is consistent with the existing observation data.

Survey workload

1) Survey at fixed-points and of sections

Complete the 27 hours simultaneously continuous monitoring of current velocity, current direction, water depth and sediment concentration at four fixed-points and 13 hours monitoring of current velocity and current direction

Settings of the original subsurface buoy placement points

FIGURE 8.2: Settings of the original subsurface buoy placement points

Settings of the subsurface buoy points after adjustment

FIGURE 8.3: Settings of the subsurface buoy points after adjustment

of two sections at the time of spring tide and neap tide during eight voyages in two wet season and dry seasons.

2) Subsurface buoy survey

Complete the monitoring of marine current and sediment concentration at two subsurface buoy points during the two strong wind processes.

TABLE 8.6: Survey workload

Season

Field survey progress

Wet season

Complete the 27-hour simultaneously continuous monitoring of current velocity, current direction, water depth and sediment concentration at four fixed- points and 13-hour monitoring of current velocity and current direction of two sections at the time of spring tide and neap tide.

Dry season

Complete the 27-hour simultaneously continuous monitoring of current velocity, current direction, water depth and sediment concentration at four fixed- points and 13-hour monitoring of current velocity and current direction of two sections at the time of spring tide and neap tide.

Two strong wind processes

Complete the monitoring of marine current and sediment concentration at two subsurface buoy points during the strong wind processes.

Characteristics and engineering impact of hydrodynamics and sediment transport at Yangshan Port

Analysis of current field

Measured current state

1) Measured layered tidal current

The survey results show that the characteristics of the layered tidal current of the surveyed sea area are:

  • a) The tidal current has a large velocity which decreases gradually from the surface to the bottom;
  • b) The change of layered tidal current at each survey points is more consistent and the current flows generally southeast-northwestward, showing the characteristics of rectilinear current.
  • 2) Measured maximum current and the average current velocity of tidal section

The measured maximum current data indicates that the measured maximum current velocity at each survey point during the spring tide is generally greater than that during the neap tide; in general, the maximum current velocity at survey point A2 at the time of ebb tide is significantly larger than that at the time of flood tide, the ebb current occupies the significantly advantageous position; the maximum current velocity at survey points В and C at the time of flood tide is greater than that at the time of ebb tide, the flood current occupies the significantly advantageous position.

The average current velocity of tidal section can be obtained by taking the flood current data and ebb current data of each survey point over a tidal cycle for time averaging. The average current velocity of each survey point at the time of spring tide is generally greater than that at the time of neap tide. At the survey point A1 and A2, the average velocity of ebb current is greater than that of flood current; at the survey point В and C, the average velocity of flood current is greater than that of ebb current (Figure 8.4).

The maximum current data and average current velocity of tidal section at each survey point indicate that:

  • a) The velocity of tidal current in the sea area is large and the maximum current velocity at each survey point during the spring tide and neap tide is generally greater than 150.
  • b) At the survey points A1 and A2, the ebb current is the dominant current, the flood current is the dominant current at the survey points В and C.
  • c) The current velocity at the time of spring tide is significantly different from that at the time of neap tide. The measured maximum velocity of flood current and the average current velocity of tidal section at the time of spring tide are general^ greater than that at the time of neap tide.
  • d) The average current direction at the time of ebb tide is 83° to 135°, and that at the time of flood tide is 265° to 304°, relatively concentrated;
  • 3) Harmonic analysis of tidal current

The quasi-harmonic analysis indicates that the tidal current of the sea area is dominated by the regular semi-diurnal tidal current, and the semi-diurnal tidal constituent dominates, with the tidal constituent as the most dominant one.

Residual current

The characteristics of residual current at each survey point during spring tide and neap tide are (Figure 8.4):

  • 1) The average direction of residual current at each survey point is consistent with that of dominant current. The average residual current at the survey point A1 and A2 generally flows along the direction of ebb current while the average residual current at the survey point В and C generally flows along the direction of flood current.
  • 2) The average residual current direction is basically the same as that of surface residual current.
  • 3) The maximum residual current during the spring tide and neap tide appears on the surface and gradually decreases in the vertical direction.
Vector distribution of current at each survey point

FIGURE 8.4: Vector distribution of current at each survey point

 
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