Remote Sensing study for environmental and engineering geology in Lianyungang

Remote Sensing study for environmental and engineering geology in Lianyungang

Cai Zejian, Yan Gang
Remote Sensing Station, Geology of Jiangsu, Nanjing, China

Abstract
Lianyungang lies on the bank of the Yellow Sea. It is one of the most important harbor cities, which are open to outsides in the East China. With the development of economic construction in the region. the environmental and engineering problems become more urgent and serious ones. Based on the MSS and TM image data provided by Landsat 2.5 of USA and its combined analysis with aerial photos and geophysical and drilling data, it is stated that not one coastal current flowing from North to South commonly known before but two coastal currents flowing North to South alternatively exit. It is possible that the harbor is silted up after it is sealed off in one side. It is advocated that the dam across the sea must be built in ' open ' state to allow the currents to flow through. The disadvantage engineering geological factors such as active faults, distribution of soft mud layers, landslides

Image feature of coastal currents and its movement in Lianyungang.
Lianyungang lies in the middle of the bank of the Yellow Sea. It has coastal line of about 120 km. Many rivers enter into the Yellow Sea at the plot, where coastal geomorphology develop well. There are three types of coasts, ie: depositive, erosive and steady cost (Fig.1). Based on analysis of the shifting of main channels of sea-entering rivers and the dynamic features of coastal geomorphology, it is stated that two coastal currents exist, flowing from N to S alternatively, By comparative analysis of photos of three periods ( 1954, 1964, 1983), it is discovered that the 'claw' sand mouth in Longwanhe river mouth in Haizhou Bay stretched out about 600 m from N to S in 30 years, at the average rate of abut 20 m per year. The stretching as more clear at 'claw-head' (Fig.2). With no exception, the claw sand mouth in sea-entering river mounts is Haizhou Bay stretch out from North to South at different rate. It depicts that materials brought by inner rivers, effected by a coastal current from N To S at river mounts, is forced to deposits in the sought of rivers in Hai hou Bay. Opposed to the drifting tendency of sand mounthes in Haizhou Bay, main channel of Liezhihe river mouth, originally flowing towards SN< deviated 30!c westward in 30 years from 1954 to 1983. Deviation rate was about 10 per year. Generally main channels in Liezhihe-Guanhe deviate from E to W. Shell sand dams develop will in wide region in the east of Lianyungang. All of waving axes of the well developed sand dams arrange in oblique from NW to ES (Fig 3). All of these show that the formation of the shell sand dams are restrained strictly by the coastal current flowing form S to N. The satellite images show in a larger range that there exist two coastal currents flowing form N To S alternatively (Photo 1 Landsat2 MSS4). The coastal current form the South, carrying the large amount of mud and sand from abandoned Huanghe river mouth, flows northward. Combined with the coastal current from North haizhou Bay at the east of the harbor, it stretches out and diverse towards sea. The amount of mud and sand brought by the coastal current from the South and its moving rate seems to be the one brought by the current from the North and its moving rate. From the intepretation results of remote sensing data stated above, it can be drawn definitely that not only the coasttal current flowing from S to N, but also the one from N to S exist and act on in the near bank. The discovery will bring about great effect on back-forth, deposition-erosion of the coastal line and series of engineering construction along sea bank. It is significant that researches of directions, patterns and effects of coastal currents are carried out.

The tendency of sand and mud movement and its effect on the harbor
In order to enlarge the handling capacity of Lianyungang harbour, it is suggested that a dam connecting inland and East-West Liandao island be built. The length of the dam would be 67 km. The project is going to be carried out (Fig 4). Based on dynamic analysis and researches so aerial photos of differential periods of times in Lainyungang, the general deposition erosion tendency in past 30 years can be stated as follows:

The west of Haizhou Bay has been under deposition for a long period of. The east has been under erosion since the Yellow river changed its channel and flowed into the sea at Shantong in 1855. The middle part of the harbour belongs to steady coast of rock. According to the real hydraulic data, the harbour has been under deposition-erosion balance for a long time. Maintaining of the state is related closely to not only back and forth currents formed by the flowing of two coastal currents form S to N alternately in two sides of the harbour in the bay, but also the 'wave-shaped back-forth current produced by tide. The two coastal currents can be seen on TM2 image flowing through the bay, carrying sand and mud (Photo 2 Landsat 5 TM2). The problems are: Nowadays the currents can flow through the bay. As the dam constructed, the bay will come semiislandshaped' cape, the Photo 2 Landsat 2 TM2 Two coastal currents flowing through from S to N alternatively harbour 'bag-shaped' cape bay. Curvature of Haizhou Bay will beenlarged in the west. Simultaneougly, the original water-power condition will not exist. North coastal current will bend to flow outside the island. The direct effects brought about on the harbour is stated as follows.

Sand and mud brought by coastal current may deposit at three deifferent paces. Haizhou Bay, East Liandao island and harbour.
The deposition may be increased in Haizhou Bay. It will endanger the function of the outside of the dam.
Sand mouth may be formed in the east of Laindao island, which may bring disadvantage to the safty of the main channel.
After detouring to outer part of Liandao island, the coastal current, flowing from N To S, forms a circling current in the east. The coast current flowing from S to N flows directly through relatively narrow cape-shaped 'bag' and into the wide harbour, which will increase the deposition in the harbour and reduce the function of the harbour.
After the dam is built, the harbour will be in 'semi-sealed' state' which will increase the contamination in the harbour.

After all, with the construction of the sea-cross dam carried out, more attention must be paid to two coastal currents as well as the effect brought by the change of hydraulic condition. Whether semisealed or open dam is built, further consideration must be taken. It is believed that the open dam may preserve the original waterpower condition, natural movement of back and forth currents and originally good hydraulic engineering geology environment.

Fault movement, underslide rock and landslide
Because of the neotectonic movement and crosscutting of faults, the Yuntaishan mountain, consisting of a series of Precambrian stratum, stretches NW as fault block mountain and stand on the wide paralos plain. Also the step-like hills in the west and odd isolated hills in the east stretch NE for the same reasons. More than 150 hidden or bare faults of different scopes, directions, properties and periods are interpreted. Dozens of underslide rocks and several landlides are located. The main activities of faults and the distribution of underslide rocks and landslides in the economical development region are stated as follows.

The Feature of Neotetonic Movement of Faults in East Lianyungang

More than 10 linar structures are interpreated from the downtown to the harbou in, which mainly stretch NNE, NE, NNW, NW. The principal ones are Haizhou-Shiyang (F1), Houzui-Nanchen (F2), Paidanhe fault (F4), Hushan-Zhongun fault (F5) and the fault in the east of Yuntaishan mountain (F3) (Fig5). The neotectonic movement of F3, F4, F5 is more apparent. F3 strikes N 45-50 E. It appears to be linar image veins is TM and MSS images, stetching out along the east of Yuntaishan mountain. The most vestiges of the belt are hidden in the marine deposition plain. Its bare part can be seen only in Shanzhongdao island and Pingshandao island, appearing to be a group of compresso-shear faults doznes of meters wide. The feature of neotectonic movement of compresso-shear, left sheared belt is stated as follows:
1. The quarty dikes well developed in Precambrian metamorphic rock get compressed, rubed and kneaded as the results of the movement of the belt. Also the belt appears to be geosynclinal concave in Quaternary shallow statum after it stretches out to se (*1). It shows that the fault belt inherented from the Quaternay fault movement.
2. Being boundary active faults, they arise of differential up-down movement apparently. Yuntaishan mountain rise up rapidly since Quaternary period. Sea caves can be seen at the height of more than 400 m above sea level. The vast area of marine deposition plain in the esat descends significantly. To a great extent, the differential extent of up-down movement can be up to about 1000 m (*2).
3. No distribution of Neogene system can be discovered in Yuntaisan. Planation surfaces develop at the height of 400-500 m above sea level. It can be compared with the planation surfaces formed by Neotectonic movement of Tangxain period in Zhaitang of Hebri province. It can be inferred that Yuntaishan mountain, under the controlling of active boundary faults, rises up rapidly since Neogene period (*3).
F4, F5 belong to another group of active boundary faults, which made Yuntaishan mountain rise up rapidly. Ancient bay was formed at two sides of Zhongyuntai mountain, while thick soft and sand layers developed. Although there are no clear evidence for the crosscutting Quaternary System of faults, there are reflections of neotectonic movement of two groups of faults mentioned above. In order to predict the geological disaster, the location, scale, and activities of faults must be surveyed definitely.
Underslide of Rock and Landslides
1. Underslide of rock Based on aerial photos, many underslide of rocks develop in harbour-economical development region in Lianyungang. They are isolated rock blocks and distribute at the different height of mountains. Roughly morethan 20 underslides of rocks are interpreted. The underslides of rocks then are formed. Presently these rocks are under balance relatively because of the gravity. If the balance of forces gets changed, the rocks will fall and roll down. The dynamic geological disasters will occur. It can be seem form the state of underslides of rocks, most of them remain steady. But some of them have rolled down for some distance. They stop rolling just because of 'being stranded' by other rocks. On the other hand, it can be seen clearly in the images that relatively larger sharp cliffs, structural fissures develope well in the North of the back of Yuntaishan mountain where the harbour relys on.
  
  The key to the problems is: Crowds of buildings stand around Yuntaishan mountain. In order to avoid the falling of underslides and ebouleument of rocks, it is suggested that except the prohibition of using explosives and rock mining in the underslide rock region mentioned above, further administration and management should be adopted in order to eliminate the hidden dangers.
2. Landslide: Recently, landslides occur occasionally in Yuntaishan mountatin in Lainyungang, such as the ones in the west of Liandao island, Souchen and Zhongyuntaishan mountatin. Although the extent and destruction are not so serious, more attentions should be paid to how and why they occur. Mostly the landslides direct reason for the forming of landslies is the manual destruction at the foot of the mountain. Based on inteptetations of aerial photos, about 100 rock mining plots of different scopes are around the Yuntaishan mountain. The whole length of plots reaches to about 24000m, taking the proportion of 13.2% of circumference of the mountain. They destroy not only the balance of mountain blocks, but also the tourist scenes of Lianyungang. Because of the destruction of the mountain foot, the previlain-talus layers originally being at the state of natural balance rise steeply. Under the effect of soaking of rain and fissure water, or earthquake, or using explosive, in rock mining, the geological disasters such as landslide and mud flow occur easily.

Distribution of mud layer and its effect on engineering construction
Lianyungang lies in the ancient bay. Hillocks are to the west, NE' strip shaped low mountains are to east of Lianyungang. The most of the region is marine plain. Lianyungang has the complicated engineering geological conditions (Fig 5). Ancient coastal lines of the bay of two periods can be seen clearly in images. The lines appear 'Since-are'. The lines 'Since-are'. The Geomorphogical features of the isolated ancient bay provides with a good site for the development of mud layer. From falsecolor image of combination MSS 7,5, 4, TM 2, 5, TM3, 4, 5, and MSS images processed in S101 processing system, the ancient bay has clearer color anomaly than nearby has. Generally it appears dark gray tone. Color contrast in not apparent and fissure is tiny. Specific geometric boundarys can be seen in no places other than in specific structure plots.

All of these mentioned above shows that there is the vast area of distribution of mud layer in the ancient bay. Assistant proofs are provided with the drilling data. Analysed from the known data, it can be stated that the mud layer distributes from W to E, relatively from thin to thick. The depth of the mud layer is 5-10 m n the west and 10-15 m in the east. Generally the layer consists of mud and muddy subcaly. Notely, being the economical development region, the north of Xigou-Zhonyuntaishan belongs to the ancient bay. According to drilling and geophysical data, the region is the thickest part of the mud layer (Fig 6).

The average depth of the mud and sand layers is 15-20 m. In some area it may reach to 30 m, where engineering geological conditions are poor. Because of lack of clear understanding of the existence of the mud-sand layer, Lianyungang alkali factory, one of the biggest alkali factory in China, was sleeted to be built at the thick part of the mud-sand layer. It results in the construction of essential engineering being at the bases of fluid-state material. The pile drillings must reach to bedrock and cost much. The site of Huaihai university, being selected at the tuck part of the mud-sad layer originally, has to be changed in order that construction can be implemented. At present, some sites of big key projects are selected or are going to be selected at the belt. it is suggested that the key projects must be carried out in the south of Bianfushan-Hushan mountain, Cheboygan, and Dachum in order to avoid the mentioned above cases. From the images, it can be seen that these areas have wide alluvial-pluvial plains and slope belts in front of mountains, which provide good engineering geology environment.