Analysis of the Change of Tidal Flat Area in Jiangsu in the Past 20

Years Using Hydrodynamic Model and Landsat Data

Kaizheng Wang

, HuanLi

, Zeyu Han

, Jin Wang

and Weibo Lin

College of Harbour, Coastal and Offshore Engineering, Hohai University, Nanjing, China

Tidal Flat Research Center of Jiangsu Province, Nanjing, China

Keywords: Landsat, Delft3D, Coastline Change, Tidal Flat Area.

Abstract: Based on the Landsat series data, this paper interprets the remote sensing images of the coastal areas of Jiangsu

in 2001, 2011, and 2021, cooperates with the hydrodynamic model and the measured slope, calculates the

average spring tide line, and defines the area between the coastline and the average spring low tide line as a

tidal flat. Area, and analyze the changes in the Jiangsu coastline and tidal flat area in the past 20 years. The

results show that from 2001 to 2021, the coastline of Jiangsu has increased by nearly 17%, with an average

annual growth rate of 6 km/a, and the tidal flat area has decreased by nearly 10%, with an average annual

decrease rate of 17.31 km

/a.

1 INTRODUCTION

In recent years, with the rapid development of the

global economy, coastal cities have made

unprecedented efforts to develop and utilize coastal

areas. Especially in the context of global climate

change and rising sea levels, coastlines have

undergone drastic changes. More than half of the

world's coastlines have been eroded and retreated(Dar

& Dar, 2009). It has an enormous impact on ecology,

the environment, and the economy of society. For the

coast of China, due to tidal tides, storm surges, and

super-intensive reclamation, the position of the

coastline is constantly changing, and the tidal flat area

is reduced(Murray, 2014; Wu, Hou, & Xu, 2014; Y.

et al., 2022). Therefore, the monitoring and protection

of coastal zones are becoming more and more

important, which has important practical significance

for ecological protection and national development.

There are generally two methods for obtaining

information on coastal areas: field measurement and

remote sensing technology monitoring. The

traditional field survey is to use various instruments

and means to directly obtain tidal flat information

through the field survey(Allen & Duffy, 1998;

Lawler, 2006; R. et al., 2002). Remote sensing

technology can obtain information quickly and in a

large area, and it has an advantage that cannot be

underestimated for the difficulty of obtaining

information in the complex and changeable coastal

zone(Liu, Li, Zhou, Yang, & Mao, 2013; Lohani,

1999; Mason, Davenport, Robinson, Flather, &

McCartney, 1995; Ryu et al., 2008; Samuel, Huan,

Ebenezer, Temitope, & Zheng, 2022; Weiqi et al.,

2021; Xuhui et al., 2021). Previous studies on tidal

flat area changes only used low-tide images to extract

tidal flat areas. Due to differences in tidal levels, there

is no unified benchmark for tidal flat extraction, and

it is difficult to compare.

This paper intends to use a combination of field

measurement, remote sensing technology, numerical

simulation, and GIS technology to visually interpret

the remote sensing images of the coastal areas of

Jiangsu in 2001, 2011, and 2021, and extract the

Jiangsu coastline and instantaneous water edge in

each time phase. By establishing the Jiangsu coastal

hydrodynamic model to obtain the instantaneous tidal

level value of the waterside line, and synergistically

with the slope prediction analysis method, the average

spring tide low tide line is calculated. The area

between the coastline and the average spring and low

tide line is defined as the tidal flat area, and we

162

Wang, K., Li, H., Han, Z., Wang, J. and Lin, W.

Analysis of the Change of Tidal Flat Area in Jiangsu in the Past 20 Years Using Hydrodynamic Model and Landsat Data.

DOI: 10.5220/0011952300003536

In Proceedings of the 3rd International Symposium on Water, Ecology and Environment (ISWEE 2022), pages 162-168

ISBN: 978-989-758-639-2; ISSN: 2975-9439

 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

analyze the changes in the Jiangsu coastline and tidal

flat area in the past 20 years.

2 MATERIALS AND METHODS

2.1 Study Area

This paper selects the coastal flat of Jiangsu as the

study area. The coast of Jiangsu starts from the mouth

of Xiuzhen River in the north and reaches Lianxing

Port in the east of Qidong in the south. For the

convenience of statistics, according to the

characteristics of the coastline of Jiangsu Province,

the coastline of Jiangsu Province is divided into three

sections: the northern section (Xiaozhen River

Estuary - Biandan River Estuary), the middle section

(Biandan River Estuary - Tuanjie Port), and the

southern section (Tuanjie Port - Lianxing Port).

Figure 1: Location of the study area.

2.2 Data Acquisition and Processing

The remote sensing data selected Landsat-7 ETM+

and Landsat-8 OLI images with low cloud content and

high definition in 2001, 2011, and 2021, a total of 9

images, and performed geometric correction and

image enhancement preprocessing on the remote

sensing images. The measured section data adopts the

topographic data of 22 sections along the coast of

Jiangsu Province obtained in April and September

2021 (Figure 1).

Table 1: Remote sensing image information

Region Sensor Year

North Landsat 7 ETM+ 2001、2011

North Landsat 8 OLI 2021

Middle Landsat 8 OLI 2021

Middle Landsat 7 ETM+ 2001、2011

South Landsat 7 ETM+ 2001、2011

South Landsat 8 OLI 2021

Analysis of the Change of Tidal Flat Area in Jiangsu in the Past 20 Years Using Hydrodynamic Model and Landsat Data

163

2.3 Methods

2.3.1 Shoreline Extraction

The artificial coastline is subject to seawall, and the

natural coastline is discussed in the following

situations.

Bedrock shoreline: A bedrock shoreline refers to a

coastline composed of exposed bedrock. The location

of the bedrock shoreline is defined as the trace line of

the sea-land boundary or the base of the cliff at the

average spring tide level for many years; Sandy

shoreline: Sandy shoreline refers to the shoreline

composed of sandy and gravelly sandstone. The

sandy shoreline is generally relatively straight, and

the upper part of the beach is often piled up into

ridged sandy sediment parallel to the shore, called a

beach ridge. The coastline is generally defined on the

seaward side of the top of the beach ridge; Muddy

shoreline: the muddy coast is mainly a low and flat

coast shaped by tidal action, and the intertidal width

is wide and gentle. The coastline should be defined

according to the comprehensive analysis of the trace

line of the sea-land boundary at the average high tide

level of the spring tide for many years, as well as the

trace line of the distribution of coastal vegetation,

plant debris, shell fragments, etc. Estuary shoreline:

The tidal gate (dam) outer boundary line or the first

bridge is used as the estuary shoreline. If the tidal

sluice (dam) or the first bridge is too deep inland, the

prominent point where the estuary suddenly widens is

selected as the estuary shoreline.

2.3.2 Hydrodynamic Model Establishment

To obtain the tidal level values of discrete points in a

typical area, a hydrodynamic model is established.

This time, Delft3D software was used for

hydrodynamic simulation. The tidal level data of

Lianyungang and Sheshan stations were collected for

model verification, and the root mean square errors

(RMSE) of tidal levels were 0.32m and 0.29m

respectively. The distribution of the stations is shown

in Figure 1, and the model verification results are

shown in Figure 2.

(a) Lianyungang

(b)Sheshan

Figure 2: Tide level verification result.

2.3.3 Average Spring Tide and Low Tide

Line Projection

(1) Instantaneous Waterline Discretization

The water's edge is the boundary between the water

body and the tidal flat at the time of remote sensing

image imaging. The low tide remote sensing image is

selected, and the visual interpretation method is used

to extract the instantaneous waterline. Due to the large

spatial range covered by the image, different locations

on the waterline at the same time have different tide

levels, so it is necessary to divide the instantaneous

waterline for assignment. In this paper, we first use

the ArcGIS buffer tool to draw a baseline of 800m

from the water's edge to the seaside and then use the

DASA tool to draw a vertical line every 500 meters

on the baseline as split lines. There is a total of 707

split lines in Jiangsu Province, and the intersection of

the waterline and the split lines, discrete points, is

extracted through ArcGIS.

(2) Tide Level Assignment and Slope

Calculation

Based on the established hydrodynamic model, the

tide level is extracted at the time of image imaging,

and then the tide level is assigned to the

corresponding discrete points.

ISWEE 2022 - International Symposium on Water, Ecology and Environment

164

The slope calculation of discrete points is to

calculate the slope by selecting the measured data of

22 sections along the coast of Jiangsu Province. The

data includes the measured points' longitude, latitude,

and elevation information. The formula is as follows

( 𝑖: Average slope; 𝐿: The distance between two

adjacent measuring points; 𝑧 : Elevation of two

adjacent measuring points;𝑥, : Coordinates of two

adjacent measuring points)

Through the above formula, the slope of each

section is calculated. According to the geographical

location, sections 1-8 are classified as the northern

area, sections 9-18 are classified as the central area,

and sections 19-22 are classified as the southern area.

The average value of the slopes of all sections in the

region is taken as the slope of the region, and finally,

the slopes of the northern, middle and southern

regions are 6.20‰, 1.42%, and 8.73‰, respectively.

(3) Average Spring Tide and Low Tide Line

Projection

The average spring tide low tide line is calculated

based on the tide level assignment results and the

slope calculation results. The calculation formula is as

follows:

In the formula: 𝛼



、𝛼



are the projected angles

of the slope in the longitude and latitude directions,

𝛼 is the slope assigned by discrete points, （𝑎



，𝑏



）（𝑎



，𝑏



）are the longitude and latitude coordinates

of the two points on the dividing line, 𝑥,𝑦 are the

longitude and latitude coordinates of the discrete

points on the average spring tide and low tide line, and

ℎ



，ℎ



are the tidal heights and the average spring

tide and low tide levels at the discrete points.

Figure 3: Calculation of discrete points of Multi-year

average low tide line

According to the results of the hydrodynamic

model, the low tide level of the spring tide is extracted

in each discrete point area. According to the above

formula, the latitude and longitude coordinates of the

discrete points of the average low tide level of the

spring tide are calculated, and the calculated discrete

points are connected in sequence to form a line, that

is, the average low tide line of the spring tide is

obtained.

3 RESULTS AND ANALYSIS

3.1 Coastline Change

The coastlines are classified into artificial coastlines,

natural coastlines, and estuary coastlines.

The results show that (Table 2), from 2001 to

2021, the coastline of Jiangsu Province as a whole

was mainly advancing to the sea, and the length of the

coastline increased from 728.69km to 849.67km.

Among them, the natural coastline decreased from

526.51km to 301.03km. It has increased from

197.92km to 542.40km, and the estuary line has

increased from 4.25km to 6.23km.

𝑖

𝑖



𝑖



⋯𝑖



𝑖



𝑛

(1)

𝑖





𝑧



𝑧



𝐿



𝑗 1,2,⋯,𝑛



(2)

𝐿







𝑥



𝑥







𝑦



𝑦







(3)

𝑡𝑎𝑛𝛼



𝑡𝑎𝑛𝛼



𝑎



𝑎







𝑏



𝑏







𝑎



𝑎



(4)

𝑡𝑎𝑛𝛼



𝑡𝑎𝑛𝛼





𝑎



𝑎











𝑏



𝑏







𝑏



𝑏



(5)

𝑥𝑎





ℎ



ℎ



𝑡𝑎𝑛𝛼



(6)

𝑦𝑏





ℎ



ℎ



𝑡𝑎𝑛𝛼



(7)

Analysis of the Change of Tidal Flat Area in Jiangsu in the Past 20 Years Using Hydrodynamic Model and Landsat Data

165

Table 2: Coastline length in Jiangsu Province in 2001, 2011,

and 2021 (km).

Region Year Natural Artificial Estuary All

North

2001 83.79 122.02 2.00 207.81

2011 82.41 127.62 2.23 212.26

2021 81.41 176.89 2.33 260.64

Middle

2001 219.69 42.47 1.97 264.13

2011 204.96 63.27 2.54 270.76

2021 148.54 167.73 2.62 318.88

South

2001 223.03 33.43 0.29 256.75

2011 131.57 143.12 0.86 275.55

2021 71.09 197.78 1.56 270.43

All

2001 526.51 197.92 4.25 728.69

2011 418.93 334.28 5.37 758.58

2021 301.03 542.40 6.23 849.67

Figure 4: Coastline of Jiangsu Province in 2001, 2011 and

2021.

The northern coastline increased from 207.81km to

260.64km from 2001 to 2021, of which the natural

coastline decreased from 83.79km to 81.41km, the

artificial coastline increased from 122.02km to

176.89km, and the river port line increased from 2km

to 2.33km.

Figure 5: Variation of coastline length in Jiangsu Province.

During 2001-2021, the central coastline increased

from 264.13km to 318.88km, of which the natural

coastline decreased from 219.69km to 148.54km, the

artificial coastline increased from 42.47km to

167.73km, and the river port line increased from

1.97km to 2.62km.

The southern coastline increased from 256.75km

to 270.43km during 2001-2021, of which the natural

coastline decreased from 223.03km to 71.09km, the

artificial coastline increased from 33.43km to

197.78km, and the river port coastline increased from

0.29km to 1.56km.

3.2 Changes in the Area of Tidal Flats

The upper boundary of the tidal flat is the coastline,

and the lower boundary is on the calculated average

spring and low tide line. The final calculation of the

tidal flat area along the Jiangsu coast in 2001 is

3447.22 km

, and the tidal flat area along the Jiangsu

coast in 2021 is 3100.94 km

Figure 6: Tidal flats in Jiangsu Province in 2001 and 2021.

ISWEE 2022 - International Symposium on Water, Ecology and Environment

166

The area of tidal flats in Jiangsu Province has

decreased by nearly 10% from 2001 to 2021, with an

average annual decrease rate of 17.31 km

/a.

Figure 7: Overlay map of tidal flats in Jiangsu Province in

2001 and 2021.

4 CONCLUSIONS

Based on multi-temporal remote sensing image data

and topographic survey data, combined with

numerical simulation technology, the evolution

characteristics of the coastline in Jiangsu Province

and the distribution of monitoring tidal flat resources

are analyzed. The main conclusions are as follows:

(1) From 2001 to 2021, the length of the coastline

shows an overall increasing trend, in which the

artificial coastline has increased significantly and the

natural coastline has decreased.

(2) From 2001 to 2021, the area of coastal tidal flats

in Jiangsu Province has decreased significantly, and

active measures should be taken to maintain the

stability of tidal flat resources.

ACKNOWLEDGEMENTS

National Natural Science Foundation of China

(NSFC, grant no. 41976156）

This work was supported in part by the Marine

Science and Technology Innovation Project of

Jiangsu Province under Grant JSZRHYKJ202214, in

part by the Carbon Peak Carbon Neutral Science and

Technology Innovation Projects of Jiangsu Province

under Grant BK20220020, and in part by the National

Natural Science Foundation of China under Grant

41401371.

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