CN101533035A - Method for observing estuary seacoast near-bottom water and sediment under high turbidity environment - Google Patents

Abstract

The invention discloses a method for observing near-bottom water and sand in a high turbidity environment on the coast of an estuary. In the method, an observation system is firstly established. Composed of coupled mode Doppler acoustic velocity profiler (PC-ADP), Doppler point velocity meter (ADV-Ocean), optical backscatter turbidimeter (OBS) and tide meter (SBE-26), through instrument modulation Observation of water depth, significant wave height, near-bottom salinity and sediment concentration, and near-bottom flow velocity and flow direction of the near-bottom bed water-sediment process is completed through the steps of deployment of observation system, data collection, and data processing. The invention can effectively obtain the water and sand data near the bottom layer, and the obtained data has the characteristics of stability, continuity and high resolution; it is easy to operate, can realize automatic observation, automatic storage and can be applied to observation under extreme weather conditions.

Description

Observation method of near-bottom water and sediment in high turbidity environment in estuaries and coasts

technical field

The invention relates to the technical field of hydrological observation, in particular to an observation method for the process of water and sediment near the bottom bed under the environment of high turbidity water body in the estuary and coast.

Background technique

The water layer whose flow structure is significantly influenced by the bed is called the near-bottom boundary layer. As the level of direct interaction between the water body and the bottom bed, it is often accompanied by frequent exchange of particulate matter, chemicals and organisms between the two. As far as sediment is concerned, the processes of erosion, transport and deposition also mainly occur in the near-bottom boundary layer. These processes directly affect the stability of the bed surface, material transport and benthic fauna. Therefore, the near-bottom boundary layer of estuary coasts and continental shelves has always been the focus of oceanographers, coastal engineers and environmentalists.

The observation of the near-bottom boundary layer under natural conditions has always been a difficult point in research. Conventional hydrological observation methods generally use ship-borne Doppler current profilers to measure flow velocity. However, the signal interference of the Doppler current profiler is strong near the bottom bed, so it is difficult to obtain real near-bottom water flow data, and only sub-bottom data can be obtained; The accuracy requirements of the bottom vertical line; again, because the instrument carrier and the measuring ship will move with the current, the measured data are often not at the same location. Conventional hydrological observation methods generally use the "six-point method" to draw water, and indoor analysis methods to measure the sediment concentration. This method is cumbersome to operate and poor in continuity; secondly, because the lead fish is suspended at the bottom of the water fetcher, in fact the bottom water body taken by the water fetcher can only be the sub-bottom water body, and it is difficult to get the real bottom water body. In foreign studies, bottom anchoring systems have been designed to observe near-bottom water and sediment movement, but the observation environments are generally estuaries and continental shelf areas with relatively clear water. However, in a high turbidity environment, the measurement and processing of related instruments will encounter difficulties, and it is necessary to design observation devices and explore processing methods for high turbidity environments.

purpose of invention

The purpose of the present invention is to provide a method for observing water and sand near the bottom in a high turbidity environment on the coast of an estuary, which overcomes the difficulties in observing and obtaining data such as sediment content and current in the bottom water body, and provides The research on the near-bottom boundary layer of water flow, bed stability, and near-bottom sediment transport under natural water conditions provides new technical support.

The purpose of the present invention is achieved like this:

A method for observing near-bottom water and sand in a high turbidity environment on the coast of an estuary, comprising the following specific steps:

a. Build an observation system

The observation system includes: Doppler Acoustic Velocity Profiler (ADP), Pulse Coupled Mode Doppler Acoustic Velocity Profiler (PC-ADP), Doppler Point Velocity Instrument (ADV-Ocean), Optical Backscatter Nephelometer (OBS), wave meter (SBE-26) and bracket. The support is in the shape of a positive prism, with a total height of 2-3m. It is divided into three layers. The first layer has four sides with a length of 0.5-0.8m and rings on the four corners; the second layer is 1.5-2m from the bottom, and the four sides are 0.8-1.2m long. Plywood is erected on this layer and a lower steel pipe is fixed; the bottom layer is the base, with a side length of 2.5-3m, and the four corners of the base protrude downward and are made of cast iron, which is convenient for fixing on the river bed, and plywood with holes is laid between the corners; among them: Doppler acoustic flow velocity The profiler (ADP) is set on the second layer of plywood with the probe facing up to measure the high-resolution velocity field near the bottom; the pulse-coupled mode Doppler acoustic velocity profiler (PC-ADP) is set on the second layer of plywood And the probe is downward, used to measure the high-resolution flow velocity field near the bottom; the Doppler point velocity meter (ADV-Ocean) is set at the bottom of the second-layer downward steel pipe with the probe downward, used to measure the high-precision near-bottom The flow velocity process and turbulence process; the optical backscatter turbidity meter (OBS) is several and fixed on the side column of the bracket, which uses the principle of optical infrared backscattering to obtain the turbidity of suspended solids in the water body; the tide meter (SBE -26) Set at the bottom of the stand to measure wave and tide heights.

b. Instrument debugging settings

According to the observation location and characteristics, the instruments on the observation system are debugged and set, and all adopt the self-contained mode.

c. Deploy the observation system

A steel cable is fixed at one foot of the support, and one end of the steel cable is connected to a buoy. At the observation site, the support is hoisted by a crane on a ship and placed on the river bed stably.

d. Conduct observations and collect data

The instruments on the observation system are in working condition, recording and storing real-time observation data.

e. Observation system recovery

When recovering, first lift the buoy, and then drag the observation system.

f. Data processing

Stop the instrument and export the data; calibrate the turbidity value of the optical backscatter turbidimeter (OBS) by using the suspended sediment collected near the bottom on site. During the calibration, the sediment concentration is obtained by segmental calibration according to different sediment concentrations; The data of pulse-coupled mode Doppler acoustic current profiler (PC-ADP) is processed by the post-processing software developed for high velocity conditions, and the corresponding water depth velocity near the bottom is obtained; Doppler acoustic current profiler (ADP) is processed vertically. The current velocity at each depth on the line; the water depth and wave data processed by the tide meter (SBE-26).

The present invention adopts Doppler Acoustic Velocity Profiler (ADP), Pulse Coupling Mode Doppler Acoustic Velocity Profiler (PC-ADP), Doppler Point Velocimeter (ADV-Ocean) produced by SonTek Company, produced by D&A Company Optical backscatter turbidimeter (OBS) and SBE-26 tide meter produced by SEA-BIRD; ADP, PC-ADP, ADV-Ocean instruments are all based on the principle of acoustic Doppler, using the emission signal and particle reflection in water The phase difference between the signals is used to calculate the flow velocity, which can accurately measure the flow velocity without disturbing the water body. In recent years, it has been widely used at home and abroad. OBS uses the principle of optical infrared backscattering to obtain the turbidity of suspended solids in the water body, and then converts the turbidity into particle concentration through correlation analysis, which has the advantages of simple, fast, real-time, and continuous operation. The ADP is placed on the second layer of plywood, with the probe facing up, to measure the velocity field of the upper water body. PC-ADP is placed on the second layer of plywood, with the probe pointing down, to measure the high-resolution velocity field near the bottom. On the second layer, the downward steel pipe is fixed at the same time, and the ADV-Ocean with the probe downward is placed at the bottom of the steel pipe, which is used to measure the flow velocity process and turbulence process with high precision near the bottom. The OBS is fixed on the side columns of the four-corner frame, and generally 3 to 4 are placed. The SBE-26 tide meter is placed at the bottom to measure the height of waves and tides. Each instrument has its own battery and memory, and operates in self-capacitance mode. In the arrangement of instruments, in order to prevent the data from interference between instruments and the influence of the side columns of the support on the flow field, attention should be paid to the distance between the instruments and the distance from the side columns.

The present invention has the following characteristics:

(1) It can effectively obtain the water and sediment data near the bottom, and the obtained data has the characteristics of stability, continuity and high resolution.

(2), easy to operate. After the instrument is set and placed on the water surface, no manual operation is required, and it can realize automatic observation and automatic storage.

(3) It can be applied to observations under extreme weather conditions.

Description of drawings

Fig. 1 is the structural representation of observation system in the present invention

Fig. 2 is the observation results diagram of the water depth, significant wave height, salinity and sediment content of the four layers near the bottom, and the flow direction near the bottom of the embodiment of the present invention

Detailed ways

Now describe the present invention in detail by following examples:

Example

The implementation time is August 2007, and the location is the North Channel of the Yangtze Estuary, with coordinates of 31°14.007′W, 122°02.005′E. This implementation operates exactly as described above.

a. Build an observation system

Referring to Figure 1, the support is in the shape of a positive prism, with a total height of 2.3m, and is divided into 3 layers. The first layer has four sides with a length of 0.6m, and there are rings on the four corners, which are used for the deployment and recovery of the entire support; the distance from the second layer to the bottom is 1.8 m, the length of four sides is 1m, and the plywood is erected; the bottom layer is the base, the side length is 2.5m, the four corners of the base are made of cast iron, with downward protrusions, which are convenient for fixing on the river bed, and the plywood with holes is laid between the corners to increase the stability of the whole system on the river bed The upper stability prevents rollover. Four optical backscatter turbidimeters (OBS) were installed on the side columns of the support, and their heights from the bottom of the support were 30, 50, 75, and 120 cm from bottom to top; The height from the point to the bottom is 30cm; the pulse-coupled mode Doppler acoustic current profiler (PC-ADP) is 150cm from the bottom; the Doppler acoustic current profiler (ADP) is 180cm from the bottom; the tide meter (SBE-26 ) is set at the bottom of the bracket.

b. Instrument debugging settings

The Acoustic Doppler Velocity Profiler (ADP) sets the cell to 0.4m, the blind zone to 0.7m, and the sampling interval to 10 minutes; the Doppler Point Velocimeter (ADV-Ocean) adopts a multi-frequency coupling measurement mode, with a total of 3 frequencies, Frequency 1 is 0.5Hz, used for the measurement of average flow velocity, the sampling interval is 15 minutes, and the number of samples is 60; frequency 2 is 4Hz, used for the measurement of wave trajectory flow velocity, the sampling interval is 30 minutes, and the number of samples is 2048; It is 25Hz, used for the measurement of turbulent flow velocity, the sampling interval is 15 minutes, and the sampling number is 2500; the pulse-coupled mode Doppler acoustic velocity profiler (PC-ADP) sets the cell to 3.2cm, the dead zone is 10cm, and the sampling interval is 5 Minutes; optical backscatter nephelometer (OBS) set the sampling interval to 5 minutes; tide meter (SBE-26) set to measure the tide level every 10 minutes, and measure the wave every 1 hour.

c. Deploy the observation system

A steel cable is fixed at one foot of the support, and one end of the steel cable is connected to a buoy. At the observation site, the support is hoisted by a crane on a ship and placed on the river bed stably.

d. Conduct observations and collect data

The instruments on the observation system are in working condition, recording and storing real-time observation data.

e. Observation system recovery

When recovering, first lift the buoy, and then drag the observation system.

f. Data processing

The OBS turbidity value is calibrated by using the suspended sediment near the bottom on site. In the calibration, according to the different sediment concentrations, three calibration curves are obtained, and the turbidity value is converted into sediment concentration; PC-ADP adopts the method for high flow velocity The post-processing software developed by the situation is processed to obtain the corresponding water depth and flow velocity near the bottom; the ADP is processed to obtain the flow velocity at each depth on the vertical line; the tide meter data is separated from the wave and tide, and the water depth and wave data are processed.

Referring to Figure 2, the water depth, significant wave height, salinity and sediment content of the four layers near the bottom, and the flow direction of the near-bottom velocity are finally obtained. The flow direction of the flow velocity in the figure is the flow velocity at a height of 30cm from the bottom; 120cm in the figure means that the height from the bottom is 120cm.

Claims (1)

1, a kind of estuary seacoast near-bottom water and sediment under high turbidity environment observation procedure is characterized in that this method comprises following concrete steps:

A, establishment recording geometry

Recording geometry comprises: Doppler's acoustics fluid velocity profile instrument (ADP), pulse coupled mode Doppler acoustics fluid velocity profile instrument (PC-ADP), Doppler put current meter (ADV-Ocean), optics back scattering turbidimeter (OBS), tide instrument (SBE-26) and support, support is positive terrace with edge shape, height overall 2～3m, be divided into three layers, ground floor four length of sides 0.5～0.8m, four jiaos are provided with annulus; The second layer is apart from the end 1.5～2m, and four length of sides, 0.8～1.2m, this layer set up scale board and fix a downward steel pipe; Orlop is a base, the length of side 2.5～3m, and base four angle lower process are also cylinder iron made, and lay scale board with holes between the angle; Wherein: Doppler's acoustics fluid velocity profile instrument (ADP) is located on the second layer scale board and probe makes progress, pulse coupled mode Doppler acoustics fluid velocity profile instrument (PC-ADP) is located on the second layer scale board and pops one's head in downwards, Doppler puts current meter (ADV-Ocean) and is located at the bottom of the downward steel pipe of the second layer and pops one's head in downward, optics back scattering turbidimeter (OBS) is several and is fixed on the support side column that tide instrument (SBE-26) is arranged on frame bottom;

B, instrument testing setting

According to observation place and characteristics the instrument on the recording geometry is debugged and is provided with; All adopt from the molar formula;

C, lay recording geometry

At a pin fixing tightwire of support, cable wire one end links to each other with buoy, utilizes on the ship loop wheel machine that support is sling in the observation place, steadily is placed on the riverbed face;

D, observe, image data

Instrument on the recording geometry is in running order, record and storage real-time monitored data;

E, recording geometry reclaim

During recovery, the buoy of at first slinging has dragged recording geometry then;

F, data processing

Instrument is stopped, and data derive; The utilization scene is adopted suspension bed sediment of the nearly end optics back scattering turbidimeter (OBS) turbidity value is demarcated, and in demarcation, demarcates according to different sediment concentration segmentations, obtains silt content; The The data of pulse coupled mode Doppler acoustics fluid velocity profile instrument (PC-ADP) is handled at the poster processing soft of high flow condition exploitation, obtains corresponding depth flow velocity of the nearly end; Doppler's acoustics fluid velocity profile instrument (ADP) handle each degree of depth flow velocity on the vertical line; Tide instrument (SBE-26) handle the depth of water and wave data.

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