sediment discharge of the yellow river (china) and its effect on the sedimentation of the bohai and...

Continental Shelf-Research, Vol. 6, No. 6, pp. 785--810, 1986. 0278-4343186 $3.00 + 0.00 Printed in Great Britain. Pergamon Journals Ltd.

Sediment discharge of the Yellow River (China) and its effect on the sedimentation of the Bohai and the Yellow Sea

MEI-E REN* and YUN-LIANG SPa*

(Received 21 June 1985; accepted 8 April 1986)

Abstract--The Yellow River is noted for its small water discharge and huge sediment load, which amounts to about 11 x 108 tons every year, contributing 17% of the world's fluvial sediment discharge to the ocean. This has a profound effect on the sedimentation of the Bohai and the Yellow Sea. Changes of the outlet in the modern delta every 10 y result in frequent changes in the recession and progradation of the deltaic coastline both in space and time, and is the main reason why the Yellow River has not succeeded in building a bird-foot delta like the Mississippi. Owing to the huge sediment input from the Yellow River, the sedimentation rate of the Bohai is very high, about 0.6 m ka -1, but it is unlikely that the Bohai will be filled up in a few thousand years. In the late Quaternary period, the Yellow River extended its course across the Yellow Sea at least 4 times and probably discharged its heavy load into the Okinawa Trough during the last glacial maximum (15,000 B.P.).

I N T R O D U C T I O N

Im'ERACnON between major rivers and the sea forms one of the most interesting topics in sediment dynamics of oceans.

The Huang He, or Yellow River, is the cradle of the Chinese civilization and, to a certain degree, a symbol of the Chinese nation. In the world, the Yellow River is noted for its extremely heavy sediment load, contributing about 17% of the world's fluvial sediment discharge to the ocean from 21 major rivers (MILLIMAN et al., 1983).

F L U V I A L D I S C H A R G E A N D S E D I M E N T L O A D

The Yellow River is unique not only in China but also among major rivers of the world for its very small discharge and extremely heavy sediment load. As the Yellow River mainly flows through a semiarid region, with a mean annual precipitation of only 400 mm for the whole drainage' basin, its discharge is very small. The mean annual discharge at Lijin, on the apex of the delta, about 100 km upstream from the river mouth, is only about 0.7% of the Amazon and 4.5% of theYangtze, the largest river in China, but its annual sediment load is 118% of the Amazon and is more than twice that of the Yangtze. This is mainly due to the fact that, in its middle reaches, the Yellow River and its main tributaries drain the Loess Plateau (area about 500,000 km2), where soil erosion is very

* Nanjing University, Nanjing, People's Republic of China.

785

786 M.-E. REN and Y.-L. SHI

Table 1. Discharge and sediment load o f the Yellow River compared with the Amazon

Discharge Sediment load % of the Amazon Station (m3y ~ x l0 s) (tons y ~ x 10 ~) Discharge Sediment Year average

Yellow River Lijin 419.2 11).6 (1.7 118 1950-1983 Amazon* - - 63,000 9.0

* Data of the Amazon from M1LLIMAN et al. (1983).

Winter Summer

Fig. 1. Location map of the area, showing current systems: (1) Kuroshio, (2) Kuroshio Adverse Current, (3) Tsushima Warm Current, (4) Yellow Sea Warm Current, (5) Taiwan Warm Current, (6) Yellow Sea Longshore Current, (6a) Bohai Current, (7) East China Sea Longshore Current, (8) West Korea Longshore Current and (9) Liaotung Longshore Current. A = Bohai,

B = Yellow Sea, and Y = Yellow River.

ser ious . In fact , the Loess P l a t eau con t r ibu t e s a b o u t 90% of the huge s e d i m e n t load of

this r iver (Tab le 1, Figs 1 and 2). Owing to the s t rong m o n s o o n a l cha rac t e r o f the rainfal l and f r equen t heavy down-

pours ( s to rm ra infa l l ) , abou t 70% of the annua l s e d i m e n t d i scharge comes in J u l y - S e p t e m b e r and is c o n c e n t r a t e d in a few s t rong peaks . In a few e x t r e m e l y heavy s torms , 100 m m may fall in 1 h when f loods with a very high s e d i m e n t concen t r a t i on occur ; one - qua r t e r to one - th i rd of the annua l s e d i m e n t load can be p r o d u c e d in one single such f lood

Sediment discharge of the Yellow River (China) 787

T

7 E

1 5 0 0

3 O

113OO ~

' E

20

iQ.. 5 O O

I 0

0

,°

s $

s #

#

J

X

, ) I I I I . " ' " . . . . I ' I I " " J Q " " ~ " . :" "'4 .g' . . . . I I :' " '"" I ' " I : I I , I : ~ ' " I " I ~ I J I N G I J I I I "". I O I

i : :" , .:.<.. , . . . : ) , , , , V

"'t'.." . . . . . . i / ~ L....... ~, I " " . " ' "" ' " ' . . . , . " I %.. , - . . . . . . . . ~ . < \~ ,?... , . . . j ~ I I : "~ " " " ( " I ~ y / : . ..... I .!'i~'.. L [jin ,t ' ' f -

" " " " \ O : I " " :i -..... i . J 6 \ l I( : , , ~ - i ' , Xln in ,g i ~ \ \ I . . . . . : I k , , , l ~ / l _ l ~ k o ) . 3 . . . . " I k \ l i - ~ y l i l l l ! , ~ # ~ v

."~"":.i!,..... -' 7 / ~ l .U~t~o 'i , ] I I _.,)i \'"...I ~ ..........

.......... , .2o • " . . . . i .. . . . . . . . . . . . " l ' - l u o y u o n k o u

Fig. 2. Yellow River Basin, showing 30-y average (1950-1979) of water discharge and sediment concentration data for nine stations along the river. Note the abrupt increase of sediment concentration after the river flows through the Loess Plateau. Q = water discharge, and i~ =

sediment concentration.

Table 2. Maximum sediment concentration and total sediment load during high-concentration floods at Longmen (see Fig. 2)

Time

Maximum sediment Duration concentration

(h) (kg m -3) Total sediment load in the flood Tons x 10 s % of the year

18 July (09.00)- 20 July (19.00) 1966 58 933 4.53 26.5

2 August (00.00)- 4 August (24.00) 1970 72 826 4.97 35.3

(Table 2). In the Yellow River below Sanmenxia (Fig. 2), two floods of exceptionally high concentration in 1977 produced sediment discharges of 20.8 x 108 tons.

On account of the great variability of the rainfall of the drainage basin, the variability of the discharge and sediment load of the Yellow River is unusually great. At Lijin, according to 1949-1973 data, the annual discharge in the highest water year is 4.38 times that of the lowest water year, while the difference in the annual sediment load amounts to 5.25 times (Table 3).

At Shaanxian, where the hydrological record is longer, the variability of the annual sediment discharge is even more remarkable. Here, the largest annual sediment discharge is 39.1 x 108 tons (1933), in contrast to the smallest annual sediment discharge of 4.88 x 108 tons (1928).


Table 3. Variability of the annual discharge and sediment load at Lijin. 1949-1973

Annual discharge Annual sediment load Year ('m 3 × 1118) (tons x 10 ~)

1958 596.7 21.01) 1964 973.1 20.30 1972 222.8 4.08

I00

E ==

il~ 50

(a)

~' Longmen + Sanmenxia o Huayuankou

f

21 I I 1000 2000 30O0

Om (m-3 s-')

I0

~E

~cL~ 5

(b)

c~ Xunhua " Lonzhou / ' ~ c ~ + Toudaoguoi 7 / , / + 9 ~.

9

I I I000 2000

Om (m-3 s-~)

Fig. 3. (a) Correlation curves of mean monthly water discharge (Ore) and mean monthly sediment concentrat ion (/5,,) for Lijin, Huayuankou, Sanmenxia and Longmen (i.e. below Loess Plateau). (b) Correlation curves of Q,,, and P,, for Toudaoguai, Lanzhou and Xunhua (i.e. above

Loess Plateau).


Using 1950-1979 data, correlation curves of mean monthly water discharge and mean monthly sediment concentration have been drawn for representative stations. The curves are all clockwise (Fig. 3a and b), showing that the peak discharge and peak sediment load occur almost synchronously, which is different from the lower Yangtze where a different climatic regime and the presence of large lakes have resulted in curves of a counter- clockwise pattern (SHI et al., 1985).

The annual suspended-solid discharge of the Yellow River is given as 20.8 x 108 short tons by HOLEMAN (1968) or 17.5 X 108 metric tons (average 1933-1958, Shaanxian Station). This represents the suspended-solid discharge of the river when it just leaves the Loess Plateau. Although this is the actual largest sediment discharge value in the river, it is not the amount of sediment delivered to the sea. Below Sanmenxia, about one- quarter of the total suspended load is deposited on the river bed and does not reach Lijin; this is especially true for its coarse population (>0.050 mm) (which constitutes 60-80% of the total bed sediments in the main channel). For example, during July 1950-June 1960, a little over 17 x 108 metric tons of sediment was carried to the lower reaches per year, of which only 13.20 x 108 tons reached Lijin and more than 3.5 × 108 tons of sediment was deposited on the river bed between Shaanxian and Lijin, so that the stream bed is raised about 10 cm per year. Therefore, for the sediment discharge of the Yellow River to the sea, the data of Lijin, which is only 100 km from the mouth, instead of that of Shaanxian, about 700 km upstream from Lijin, should be taken.

The construction of the Sanmenxia Reservoir had a distinct influence on the sediment discharge of the Yellow River. The reservoir, with a capacity of 96 x 108 m 3, was completed in September 1960. From September 1960 to October 1964, 45.91 x 108 tons of sediment accumulated in the reservoir. Compared to the years before the construction of the reservoir, only 32% of the total sediment load was carried to the lower reaches.

From Table 4, it can be seen that owing to the construction of the Sanmenxia Reservoir, the sediment discharge at Lijin has been reduced by about one third between 1960 and 1964. It is only since measures for improvement of the reservoir have been installed that the sediment discharge has gradually returned to the normal (average about 11 × 108 tons), but it is still considerably smaller than before the building of the reservoir.

S U S P E N S I O N A N D B E D L O A D T R A N S P O R T S : E F F E C T S ON M A R I N E S E D I M E N T A T I O N

With its huge sediment discharge, the effect of the Yellow River on the sedimentation of the sea is profound both in time and space. In addition to the semi-enclosed sea of the Bohai, its sediment also exerts a considerable influence on the Yellow Sea and the Okinawa Trough.

Table 4. Fluctuations of annual sediment discharge at Lijin during different periods

1950-1959 1960-1964 1964-1973

Annual sediment discharge

(tons x l0 s) 14.63 9.81 11.63


Littoral spits

It is well-known that the Yellow River has frequently shifted its outlet to the sea during historical time, the most remarkable shift between 1128 and 1855, when its outlet was shifted to North Jiangsu and it flowed directly into the South Yellow Sea (Fig. 4). However, for most of the time, the Yellow River enters the Bohai. In the modern delta (formed since 1855), the river changes its outlet to the sea almost every 10 y. Two major recent changes of the outlet are: a shift to near Diaokou in 1964 and to Qingshuigou in 1976 (Fig. 5). Every time a new outlet enters the sea, coarse silts are rapidly deposited near the river mouth, forming spits which extend into the sea as bird-foot-like elongated sand bodies, at a rate of about 7-8 km y-~. For example, from February 1964 to April 1965, the river mouth spit near Diaokou extended nearly 10 km into the sea. Between 1964 and 1976, with the river mouth spits as the framework, a small bird-foot delta formed. However, since 1976, with the shift of the river outlet to Qingshuigou, the spits and coast near Diaokou were rapidly eroded and retreated. A study of satellite images shows that, from 1976 to 1981, the coast near Diaokou retreated about 6 km and the old spits have been cut and have almost disappeard. A field survey in July 1984 showed that miniature cheniers, in the form of shell beds, began to accumulate along this part of the coast, whereas, at the present river mouth at Qingshuigou, the coast has been rapidly prograding since 1976. In some localities it has extended as much as 12 km seaward between May 1976 and May 1977 (Fig. 6). As the tidal range and wave energy in the coastal zone of the Yellow River Delta are small and the sediment supplied by the river

Fig. 4. Changes of the outlet of the Yellow River between 1128 and 1855.


Bohai Bay

\ k .J ),/~"J - {

' I / I" - . I , / • \ \ . - , ; i ~ & ÷ ; f ~

Lij in

,,,'Z, 1964 - 1976

II'~ ~ t --% o~ . . . _ j * xx . / ~ : 1953 -1960 ~-

' ~/ ;5)" c.-t~

(

/ \

\~/... (" f . ¢--."

h'...., ( :2. t>z/

" \ F ~) >L. .... J

o, ,

Fig. 5.

- - Present river course . . . . Old river course

1854 coast l ine

. . . . . . . 1955 coast l ine

. . . . . . 1972 coost~.ine

Changes of the outlet of the Yellow River between 1855 and 1976 [after PANG (1979)].

great, it may be asked why a bird-foot delta like the Mississippi has not been formed. Evidently, the answer lies in the great frequency of movement of the river mouth.

Mud streams and mud-flats

The suspended sediment of the Yellow River at Lijin is rather fine, with an Ma of only 7 ~tm (Table 5).

It is estimated that, of the total suspended sediment at Lijin, 24% goes into the construction of a subaerial delta, 40% is deposited in the nearshore zone (which includes the shallow sea 20 km offshore from the tidal flat) and the remainder (36%) is transported and diffused to the sea beyond (PANG et al., 1980)•

In the coastal zone, the copious supply of suspended sediment, from the Yellow River is transported by currents to build wide mud-fiats along the Bohai.

Bohm Bay ,~ / .~":.\ / . ~ • .. .:~ /. ~, ,~

!.-:I /... ..Yc.>/. i

: ~ - - - . - . . . "-" : ' " " " #o:~ . -

. . ' l : ' " '.: "-,"

/ / ! /

/ / / /

/ / / /

/ / 0 5 IO km

I I, I

- - Present shorel ine ( 1982 )

- - - ShoreLine in 1964

T I d o l f L a t end sand sp i t

I

I

°° ,~

o• ~., b / Presen t Yet,(

L

. . o

° °

-~'%•

b "°°'•

- ¢

~. '"~ I"

o°j°° ::". " ; ."" 'Y

• • • ,

= ' . . •--" ~ ••'k:=,

. . . . • -

• ° ° . ~ . • . -

~ ~ 0 5 FO ~m I I I

- - - - Shore l ine before 1976 Present shore l ine (1982)

O ld i n t e r t i d a l f L o t ~ Present i n t e r t i d o l f r e t (1982) ( pre - 1976)

......... A p r o x i m a t e t~mit o f i n t e r t i d a l -fta±

Fig. 6. (a) Changes of the coastal zone near Diaokou in the modern Yellow River Delta due to shift of outlet of the Yellow River. 1964-1982 (modified after LANDSAT imagery). For explanation, see text. (b) Changes of coastal zone near Oingshuigou, in the modern Yellow River Delta due to shift of outlet of the Yellow River, 1964-1982 (modified after L A N D S A T imagery).

For explanation, see text.

Fig. 7. LANDSAT imagery (5 October !978), showing a distinct coastal mud stream from the present mouth of the Yellow River drifting southward to Laizhou Bay. Wind E (2 m s 1).

Fig. 8. NOAA-7 imagery (15 August 1983). Wind quiet, showing a turbidity front north of the present Yellow River mouth. Note also a distinct mud stream flowing southward from the present river mouth. Turbid water on the southern coast of Bohai Bay is due to a stronger wave action

(the coast facing NE, the prevailing and strongest wind direction of this region).

Fig.

19

. C

ore

sam

ple

from

the

out

er s

helf

of

the

Eas

t C

hina

Sea

at

31°4

5'N

, 12

7°15

'E (

sam

ple

from

230

-250

cm

bel

ow t

he s

ea f

loor

), s

how

ing

the

shel

l la

yer.

She

lls

are

mos

tly

coas

tal

and

estu

arin

e sp

ecie

s. W

ater

dep

th 1

29 m

. T

he s

hell

lay

er i

s ve

ry s

imil

ar t

o sh

ell

depo

sits

in

mod

ern

chen

iers

on

the

coas

t of

the

aba

ndon

ed Y

ello

w R

iver

Del

ta,

Jian

gsu

[fro

m R

EN (

1980

)].


Table 5. Grain size of the suspended sediment at Lijin*

Grain size (mm) 0.063-0.032 0.032-0.016 0.016-0.008 0.008-0.004 0.004 M,t

% of total 7.10 12.10 25.10 23.70 32.30 0.007

* Sample collected in July 1982. Grain-size analysis by TA II Coulter Counter [after ZHANG (1985)].

The changes of the outlet of the Yellow River have had a profound influence on the evolution of intertidal mud-flats. Before 1976, mud from the Yellow River drifted mainly towards the northwest and, consequently, a greater part of the mud-fiat along the Bohai Bay was prograding. Since 1976, with the shift of the river mouth to Qingshuigou, a major part of the fluvial mud drifted to the south instead of the northwest.

As can be vividly seen on the LANDSAT image of 5 October 1978, a distinct littoral mud stream is now flowing southward, reaching the head of Laizhou Bay (Fig. 7). Moreover, both oceanographical data (1983--1984) and NOAA-7 satellite images (14 July, 15 August, 14 September and 24 September 1983) prove that there exists a turbidity front north of the turbid water plume from the present Yellow River mouth (Fig. 8). These satellite images were taken under N, and E, NW and SW wind and quiet conditions, respectively. The turbidity front is located at 37°50'N, south of which the suspended sediment concentration is 300 mg 1-1 and salinity is 10%o, whereas north of the front it is 50 mg 1-1 and >20%~, The boundary between yellowish fresh water and clean, saline seawater can be clearly seen from a ship sailing along the front, the surface of the former being slightly higher than that of the latter. Computer analysis of LANDSAT tapes (CCTs) reveals that there are a series of clockwise eddies moving southward from the present Yellow River mouth, bringing sediment with them. Therefore, since 1976, the mud-flat south of the Qingshuigou has been prograding and a wide mud-fiat is formed, reaching more than 10 km in width, near the Guangli He mouth. However, north of the Qingshuigou, a greater part of the mud-flat, together with the coast, is now suffering from erosion and recession. Such rapid and marked changes in the coast within a man's lifetime is perhaps unique in deltas of major rivers of the world.

The wide mud-flat along the coast of North Jiangsu has been formed by sediments of the abandoned Yellow River which flowed into the South Yellow Sea for more than 700 y (1128-1855). Since the shift of the river into the Bohai, the coast of the delta of the abandoned Yellow River has experienced a rapid retreat and a line of low cheniers has formed. Outside the mouth of the abandoned Yellow River, a large subaqueous delta has formed in the South Yellow Sea. The outer edge of the subaqueous delta lies at about -25 m where it slopes with a steeper gradient to the 50-m isobath. The sediment of the subaqueous delta is distinguished by its high CaCO3 content, The 10% isopleth of CaCO3 makes a large lobe outside the mouth of the abandoned Yellow River (Fig. 9).

The radial submarine ridge field off the coast of North Jiangsu is one of the most distinct features on the continental shelf of China and, perhaps, also of the world. It is about 260 km long from north to south and 100 km wide from east to west, with a total area of more than 20,000 km 2. Its outer edge lies at 25 m. The morphology, sedimentation and evolution of this huge submarine ridge field will be discussed in another paper. It is sufficient to state here that material of the old Yellow River forms a considerable part of the substrate of this ridge field.

798 M.-E. RBN and Y.-L. SHI

liB* 120 ° 122 ° I~I ° 126"

Fig. 9.

I% ~ I-3°/o ~ 3-5"/o

i 1 ~ 5-10°/o ~ 100/.

CaCO 3 content in sea bottom sediments [after QIN (1983)].

Mineral composition

The suspended sediment of the Yellow River, derived mainly from loess, has a characteristic mineral assemblage and chemical composition. The surficiai sediment of Laizhou Bay and the southern part of Bohai Bay is distinguished by a high content of muscovite, carbonate minerals, plagioclase and hornblende, and by a low content of magnetite. These properties are essentially similar to the mineral assemblage of the lower Yellow River (Fig. 10a and b). However, the surficial sediment of those parts of the Bohai influenced by sediment discharged from the Liache and Luanhe has a very low content of muscovite, carbonate and hornblende (CHEN et al., 1980). This shows that suspended sediment of the Yellow River mainly diffuses to Laizhou Bay and the southern part of the Bohai Sea.

Changes in recent history

The distribution of the suspended-sediment concentration in the surficial water of the Bohai also clearly marks the area of diffusion of the Yellow River sediment. The suspended solid concentration of the surficial seawater was very high off the Yellow


llf I1~1 119o i~'u

4 1 o

4 0 •

3 9 °

3 8 °

Fig. 10.

3 7 °

(a) Distribution of muscovite in the Bohai Sea [after CHEN (1980)]. (b) Distribution of carbonate minerals in the Bohai Sea [after CHEN (1980)].

800 M.-E. REN and Y.-L. Sttl

River mouth (Fig. 11), in Bohai Bay and Laizhou Bay in July 1958 and 1962, reaching 100-150 mg 1 -i off the old Yellow River mouth (QIN et al., 1982). A survey in the summer of 1984 by the staff of Shandong College of Oceanography showed that, since the shift of the outlet of the Yellow River to Oingshuigou in 1976, the distribution of the concentration of suspended solids in the nearshore zone has changed markedly. The suspended-sediment concentration in the surficial seawater off the present river mouth is greater than 100 mg 1 -~, whereas off the former river mouth near Shunxianguo it is less than 50 mg I -j (Fig. 12).

Offshore transport

Finer particulates of the Yellow River are carried by the Bohai Current through the South Bohai Strait into the Yellow Sea, where they are transported by the Yellow Sea Longshore Current southward to near the Yangtze River mouth. During the summer, especially in the flood years of the Yangtze, they may join with the water plume of the Yangtze and reach the sea south of Cheju Island. From a study of clay mineralogy, it has been shown that the South Yellow Sea (about 34°N, 123°E) has received clay minerals supplied by the Yellow River as well as by the Yangtze (AoKI et al., 1983). During strong monsoon surges from mid-October to February, the wind velocity may reach 40 knots over the Central Yellow Sea when large waves with heights reaching 3-4 m are generated and fine sediments on the sea floor are resuspended. Highly turbid water is carried southward by the Laiotung Longshore Current in the coastal zone of the Liaotung Peninsula and by the West Korean Longshore Current in the coastal zone off the west coast of Korea: in the latter area, the volume of suspended sediment transported south has been estimated to be 25-250 x 10 ~ m 3 y-J, which is several orders of magnitude greater than the input from Korean rivers alone (WH.LS, 1984). It seems that a wide mud-flat along the west coast of Korea and the east coast of the Liaotung Feninsula is incompatible with a small sediment discharge from the Korean and Chinese rivers that

/ 7 - " - ~ ,#" i f / /

I I l l " " " " ' " ' ' ' ,1# , , , , . . i ] _ - ~ . . - - -

4 / ' # / ¢ "''. . . . . . " . - , "

~ " , ; " > , t : "- ~ z o -30

fj C: ::'/~<..f --., v/A~v-~v

I~O0-fSC

Fig. 11. Suspended sediment concentration (mg I ~) in surficial seawater of the Bohai Sea, July 1958 and 1962 [after Q1N (1982)[.


Fig. 12. Suspended sediment concentration (mg ! -t) in the upper 5 m of the water column off the modern Yellow River Delta, summer 1984 [isobaths in m (after Shandong College of

Oceanography)].

flow into this part of the Yellow Sea. [The average annual sediment discharge of the Yalu River is only 1.10 x 106 tons (average 1958-1980) and the suspended-sediment discharge of the Kum River, Korea, is 5.6 x 106 tons y-i (CHouGH et al . , 1981).] This suggests that muds may be also derived from the resuspension of old sediments from the bed of the Yellow Sea or from muds carried by the Yellow Sea Warm Current (a branch of the Kuroshio). It appears that the suspended solids in the coastal zone of Korea and the Liaotung Peninsula probably come from various sources and are highly mixed. There- fore, intertidal mud-flats in this area bear no clear indication of having been derived from the Yellow River.

It is well-known that the suspended sediments of the Yellow River, derived from loess, have a high carbonate and CaO content, and a distinct montmorillonite peak by which they may be distinguished from suspended sediments of the Yangtze, Yalu and other rivers (Table 6).

X-ray spectra (X-ray analyses were carried out on a Philips diffractometer by the Nanking Soils Institute, Academia Sinica) of separates (<2 Ixm) of intertidal flat sediments of Jiangsu Province show a distinct montmorillonite peak in sediments north of Jianggang (32°40'N), which is lacking in the sediments from further south. This fact clearly proves that, north of Jianggang, intertidal flat sediments are mainly derived from the abandoned Yellow River, whereas south of Jianggang it is greatly influenced by sediments from the Yangtze. The i.r. spectra of sediments north of Jianggang are characterized by a distinct calcite peak, but near the Yangtze mouth they are character-

802 M.-E. REN and Y.-L. SHJ

Table 6. Carbonate, CaO and char-mineral content in loess and bottom sediment ,~ff tile Yellow River mouth*

( 'aCO~ CaO Clay minerals t (%)

(%) (%) 1 M C K

Loess (generally) I1.6 Malan loess 7-,~ 68 9 12 11 Lishin loess 7-9 63-67 12-16 11 lO-I 1 Wucheng loess 7-2(I 60 19 11 III Bottom sediment

off the present Yellow River mouth 9.63 67 13 12

Bottom sediment in the Yangtze ¢ + K mouth 3.5-4.2 75-79 2-4 19-2 l

Yalu, 51) km from the mouth Trace 59 1 30 10

~' Data from Liu, Zheng and Zhang. Ages of loess (ky B.P.): Malan, 30-13; Lishin 12(IO-30: Wucheng, 2400-1200.

I I = illite, M = montmoril lonite, C = chlorite, and K = kaolinite.

ized by marked kaolinite peaks and an insignificant calcite peak. These results correspond well with data derived from drift bottles and oceanographic surveys in the coastal water of Jiangsu. Preliminary data from the sediments of the intertidal fiat at Konrun Shan, west of the Yalu River estuary, show that the Ca (0.58--0.65%) and CaCO3 (trace) contents are very low, and the X-ray spectra have no montmorillonite peak. These are very similar to sediments of the lower Yalu River but are entirely different from sediments of the Yellow River mouth. The clay-mineral assemblage of intertidal muds of the West Coast of Korea is illite (3):.chlorite (1):kaolinite (1) (WzLLS, 1983). Clay minerals from suspended particulate matter in water samples of the Yellow Sea off southwest Korea show a predominance of iilite (70%), with lesser amounts of kaolinite (10%) and chlorite (13%), but montmoriUonite is virtually absent (WELLS, 1984). Results of a clay-mineral study by CHOUOH et al. (1981) on the suspended sediment of the southeastern Yellow Sea, within 80 km of the Korean shore, also show a iilite-chlorite- kaolinite assemblage with montmorillonite occurring only in trace amounts. These authors suggested that kaolinite and chlorite seem to originate from the Korean, Kum and Yeongsan rivers. This evidently indicates that the influence of the present Yellow River sediment on this part of the Yellow Sea and Korean coast is insignificant.

N E T S E D I M E N T A T I O N . P R E S E N T . P A S T A N D F U T U R E

The rate of sediment accumulation in the western part of the northern Yellow Sea is high. Data from nearly 100 short gravity cores show that the thickest Holocene layer is 2.4 m thick and, therefore, the maximum average accumulation rate may be estimated as 0.22 m ka-t; this is higher than a greater part of the East China Sea, These data, together with the high CaCO3 content in bottom sediments in the shallow sea off the coast of Shandong, show that a considerable part of the Yellow River sediment has escaped the Bohai, as it is carried by the Bohai current through the Southern Bohai Strait into the Yellow Sea.


The present Yellow River is discharging into the Bohai Sea which is a shallow, semi- enclosed sea with an area of 77,000 km 2 and an average water depth of 18 m. With the annual sediment discharge of the Yellow River alone, the Bohai will be quickly silted up. In a core from the Bohai (38°59'27'~, 119°21'58"E, water depth 25.1 m), sediment from 5.4 m below the sea bottom has been dated at 9165 + 155 y B.P. (14C dating) (Ll, 1984). This core is located in deeper waters but is influenced by the present freshwater plume of the Yellow River. Therefore, it is considered that the accumulation rate in this core (about 0.6 m ka -1) may be taken as a rough estimate of the accumulation rate of the Bohai in the last 9000 y. Seismic profiling of the Bohai reveals that, below the sea bottom, the Holocene sediment is 5-10 m thick, overlying an uneven Pleistocene surface. Taking the average thickness of the Holocene sediment to be 7.5 m, the accumulation rate in the Holocene would also be about 0.6 m k a -1, which is only 12% of the figure calculated from the present sediment input of the Yellow River alone.

According to the experimental data and grain size of the Yellow River sediments (Wahan College of Hydraulic Engineering, Fluvial sediments, Vol. 1, pp. 13-17, 1981), one may allow 1.3 metric tons m 3 for uncompacted sediments and 2 tons m 3 for compacted sediments (McCAv~, 1985, written communication). Taking the volume of the Bohai to be 1386 × 109 m 3, the present influx, if all trapped, would fill in the Bohai Basin in about 2700 y, i.e. the sedimentation rate would be around 5 m ka -1.

There are a number of reasons for the obvious discrepancy between flux values and the rate of sediment accumulation of the past 9000 y.

(1) For more than 700 y (1128-1855), the Yellow River flowed into the Yellow Sea and did not enter the Bohai.

(2) Evidence from Chinese historical documents shows that, in prehistoric times and during several periods of historical time, the sediment flux of the Yellow River was considerably smaller than that at present (TAN, 1982).

(a) During the long prehistorical period before the eighth century B.C., the Loess Plateau was essentially a wooded steppe (natural vegetation), and, consequently, soil erosion and the sediment load of the Yellow River were much less than at present. YE et al. (1983) calculated that, between 6000 and 3000 y B.P., the sediment load of the lower Yellow River was only two-thirds of that between 1919 and 1980. TAN (1982), after a careful analysis of voluminous Chinese records, has shown conclusively that between 69 and 600, when the land use of a greater part of the Loess Plateau changed from farming to grassland, the Yellow River was "clear" (i.e. less muddy) and little flooding occurred in its lower reaches. (b) According to the geographical distribution of archaeological sites and historical records, it can be seen that, before the fourth century B.C., when the Yellow River began to be confined by dykes, the course of the lower Yellow River was extremely unstable. With frequent shifting of the river course, a large area of alluvial plain was frequently flooded, which explains why practically no Neolithic and historical sites are found in the Central North China Plain. It is evident that during the long period before the fourth century B.C., a great part of the Yellow River sediment was deposited on the North China Plain instead of entering the Bohai. Even after dykes came into being, breaching of them and flooding were frequent. For example, in 140 y during the ~tenth and eleventh centuries A.D., flooding occurred 95 times. It is only since the establish- ment of the People's Republic of China in 1949 that, with systematic strengthening of

804 M.-E. REN and Y.-L. SH!

dykes, no serious overflooding has occurred and the major part of the sediment load of the river has entered the Bohai. (c) From the fourth century B.C. to the eleventh century A.D. there existed many large rivers on both sides of the Yellow River, diverting water and silt from the latter. These rivers had significant water discharges and were used as important waterways for transportation. Through these latter rivers, the Yellow River was connected with the Huai River which entered the Yellow Sea (Fig. 13). As these rivers derived water from the Yellow River, they repeatedly silted up and were dredged for navigation. It is conceivable that, for about 1400 y in this period, a considerable part of the sediment had been diverted from the Yellow River. Taking these facts into consideration, it is evident that the present flux of the Yellow

River should not be used as a base to estimate the accumulation rate of the Bohai in the past 9000 y.

It may be interesting to speculate whether the present flux would remain unchanged in the near future. In view of major hydraulic works now under construction or being planned on the lower Yellow River, it can be foreseen that sediment discharge of the river to the Bohai will be considerably reduced in the next few decades. The construction

Fig. 13. River network connecting the Yellow River with the Huai River in the second and first centuries B.C. [after TAN (1982)].


of another large reservoir, Xiaolangdi (location 11, Fig. 14), below Sanmenxia, with a capacity of 127 × 108 m 3, will dam up a large amount of river sediment because, unlike other reservoirs on the Yellow River, the Xiaolangdi reservoir is intended primarily to produce a reduction in the sediment load of the lower Yellow River. The use of river water for irrigation and the city water supply has also rapidly increased. A large project to divert the Huanghe water for the water supply to the port city of Qingdao is scheduled to be completed in the next few years. These works will also take a considerable portion of suspended sediment from the river. For example, in 1980, 1.7 × l0 s tons of sediment was diverted from the river by irrigation works alone. Soil conservation measures, which have recently been taking place over large areas of the Loess Plateau, will also eventually reduce the amount of sediment discharge by the Yellow River to the sea. Geologically, the Bahai Basin is a centre of recent subsidence. According to repeated precise levelling in 1953-1972, a wide belt of the coastal plain west of the Bahai has subsided more than 20 mm in those 20 y (or >1 mm y-l) (Fig. 15) (THE GEODETIC SURVEY BRIGADE, 1977). Moreover, as mentioned above, a considerable part of the suspended sediment of the river has escaped the Bahai. In view of these facts, it seems very unlikely that the Bahai will be silted up in a few thousand years. For the accumulation rate of the Bahai, the present sediment flux of the Yellow River can neither be used as a scale to measure the past nor can it serve as a base to predict the future.

P A L A E O C E A N O G R A P H Y

As more than 90% of the sediment of the Yellow River comes from the Loess Plateau, it is interesting to note that recent Paleomagnetic studies show loess in China began to develop at about the Matayama-Gauss boundary about 2.40 million y (my) ago. However, the thickest loess layer (Lishin loess), which constitutes about 80% of the whole loess profile, began to accumulate about 1.20 my ago. Studies of the physiographic

(I) Longya ngxqa,(2) Liujiaxia ,(3)Yanguoxia,(4)Bo panx to,(5) Heishanxia ,(G) Qingtongxio ,(7) Sanshenggong~(8)Tianqiao, (9)Longmen~(lO)Sonmenxia,(ll)Xiootangdl,(12)R~s deGuxion,(13]R~s de Luhun,(14)Huayuankou,(15)Donobatou,(16) R(~s du LQC Dongping~(17)Taochengbu~ond (18)Zone de retenue des crues de Beijindi

.~ .~ ~ " r T T~ " r 1- n . n . n. .

Works already constructed }, - - - - Works planned ~ " 4 ~ - - - - . . . ~ " o g t o h Beijing ++++ Limi't o f drainage basin of "the f.~" ' 8 ~ J ¢rTionjin

Huanghe ~ I xJ ~ ~ ~Mel'~.~ /, ,~ ohOl :

,r-~ YellowLt~nchuan ~k,,~. ,1 ~.~,.~. 5 R i v e r ~ 7 6 -~t / ' ~ (~-~~,

"~ r ~' 12

Fig. 14. Main dams on the Yellow River.

806 M.-E. REN and Y.-L Sm

'~11111

C

20

: 2

/ ~o

/ : rn

. . . . Amoun t o f subsidence ( in ram)

I - - - A m o u n t of up l i f t

l - - - F ° O " ,o. so ,,OOk~

Fig. 15. Amount of subsidence of the coastal plain of the Bohai, 1953-1972 (based on repeated precise levelling, from Acta Geophysica Sinica, 1977).

history of the Yellow River show that the present course of the river, between Shanxi and Shaanxi Province (i.e. across the Loess Plateau) existed before the Pliocene and its large tributaries, the Jing He, Luo He and Wei He, which contribute a great amount of sediment to the main stream, had also established their present courses before the Pliocene. Therefore, it can be safely assumed that since about 1.20 my ago the Yellow River has consistently carried its heavy sediment load across the North China Plain to the Bohai and the Yellow Sea.

However, during periods of regression or glacial low sea level, when a large part of the continental shelf of East China was exposed, the Yellow River extended its course across the newly exposed plain, entering the sea further east from the present coast. Seismic profiling has identified a series of buried'channels on the middle and outer shelf, and, in or near these channels, fluvial deposits together with fresh water and estuarine fossils have been found (GENG, 1981; MILLIMAN et al., 1984). Between water depths of 50 and 75 m, coring has discovered four layers of paleosols and a number of peat beds (Fig. 16). In some paleosol layers, the old soil profile can still be clearly distinguished, its upper part rich in plant roots and detritus and its lower part containing carbonate concretions. These characteristics and chemical composition of paleosols on the shelf are similar to


Fig. 16.

• X

00

0 0 0 Q @ e

x F ~ • F~3Le~

X O

Late Quaternary paleosol and peat layers on the shelf of the Yellow Sea (after data from the First Institute of Oceanography, National Bureau of Oceanography).

paleosols in the loess of North China. The ages of the four paleosol layers are approximately 60-70, 42-55, 20-25 and 11-15 ka B.P., respectively (14C and palaeomag- netic dating), indicating four periods of regression in the last 70,000 y, when the shelf of the Yellow Sea was largely exposed. Near the present shelf break of the East China Sea, near the 150-m isobath, a series of cheniers, dated about 15,000 y B.P., was discovered, showing unmistakably the approximate position of the coastline 15,000 y B.P., when the Yellow Sea was entirely exposed (REN et al., 1980; EMERY et al., 1981; XtJ et al., 1982; PENG et al., 1984) (Figs 17-19). In sediments of these cheniers, Buccella frigida etc., various cold water species, were found below 0.8-1.0 m depth in core samples, indicating a cold climate at low sea levels, Moreover, these micro-fossils are severely abraded and broken, suggesting a strong wave action in the deposition of the sediments. However, the surface sediment (0-0.6 or 0.8 m) contains a large number of planktonic foraminifera with unbroken tests showing a deep-water environment, and give 14C dates of 7680 _+ 400 y B.P. Evidently, the surface sediments are quite different from sediments lower down and were deposited during the Holocene transgression (WANG et al., 1980). It is conceivable that, during the last glacial maximum, the Yellow River discharged its heavy load into the Okinawa Trough. A detailed study of the sedimentation of the Okinawa Trough would yield interesting results.

Acknowledgements--We thank I .N . McCave (University of Cambridge) for critical comments on the manuscript. He has also made several valuable suggestions and improved the English of the text. We are also


55

50

Yangtze

Shone

25~700 -I- 900 -112

k 20,550 +- IOOO

7 14,780 _+ 700 ~ f

-155

L I ~ t 120 125

Fig. 17. Submerged cheniers on the shelf of the East China Sea ]modified after WAN(; (1980) ] , showing three lines of cheniers. Figures are t4C dates (y B.P.) and water depths of samples

(m below sea level).

East Ch~no Sea

F=ne sand

Sand ~th shells

GraveLLy sand with shetLs

'%; .

• 0 . 1145 \ " ' : ~ " ~ Q ] \

OkLnOWO Trough

Fig. 18. Profile of a chenier deposit near the shelf break of the East China Sea (-150 m) (128°00'E, 31°30'N), based upon a core taken by the Second Institute of Oceanography.


grateful to K. F. Hou (Shandong College of Oceanography, China) for his assistance in acquiring data and LANDSAT imagery, and to M. B. Collins and the Department of Oceanography, University College, Swansea, for preparing the figures for publication. Data on the discharge and sediment of the Yellow River are from the Yellow River Conservancy Commission, and of other Chinese rivers from the Ministry of Water Conservancy, People's Republic of China.

R E F E R E N C E S

AOKI S. and K. QINEMA (1983) Clay mineral composition in surface sediment and the concentration of suspended matter of the East China Sea. In: Proceedings of the International Symposium on Sedimen- tation on the Continental Shelf. China Ocean Press, Beijing and Springer Verlag, Heidelberg, Vol. l, pp. 473-482.

CHENG L. R., Z. F. LUAN, T. M. ZHEN, W. Q. Xu and T. L. DONG (1980) Mineral assemblage and their distribution patterns in the sediments of the Gulf of Bohai Sea. Oceanologica et Limnologica Sinica, I1, 46-64.

CHOUGH S. K. and D. C. KIM (1981) Dispersal of fine-grained sediments in the southeastern Yellow Sea: a steady-state model. Journal of Sediment Petrology, 51,721-728.

EMERY K. O. and F. H. You (1981) Sea level changes in the western Pacific with emphasis on China. Oceanologica et Limnologica Sinica, 12, 297-310.

EISMA D. and D. W. VAN DER MAREL (1971) Marine mud along the Guyana Coast and their origin from the Amazon Basin. Contributions to Mineralogy and Petrology, 31,321-334.

GENG X. S. (1981) The geomorphological features and forming factors of submarine relief in the Pohai Sea and the Yellow Sea. Acta Geographica Sinica, 36, 423-434.

HOLEMAN J. N. (1968) The sediment yield of major rivers of the World. Water Resources Research, 4, 737-747. Ll C. X., H. C. SUN and P. I. LI (1984) Facies characteristics and physical and mechanical properties of

sedimentary strata in Bohai Gulf. Journal of Tonggi University, Shanghai, No. l, 115-123. LIu M. H. (1982) Fossil soil layer in Pleistocene sediment of the Huanghai Sea. In: Quaternary geology and

environment of China, T. S. LIU, editor, China Ocean Press, Beijing, pp. 143-146. LIU T. S. and Z. K. ZHANG (1962) Loess in China. Acta Geologica Sinica, 42, 1-14. L1u T. S. (1985) The loess-paleosol sequence in China and climatic history. Episodes, 8, 21-28. MILLIMAN J. D. and R. H. MEADE (1983) World-wide delivery of river sediment to the ocean. Journal of

Geology, 91, 1-22. MILLIMAN J. D. and Y. S. QIN (1984) Sediment dynamics in the East China Sea and Yellow Sea. Korea-U.S.

seminar and workshop on marine geology and physical processes of the Yellow Sea, pp. 75-76. PANG J. Z. and S. H. SI (1979) The estuary changes of Huanghe River. I. Changes in modern time.

Oceanologica et Limnologica Sinica, 10, 136-141. PANG J. Z. and S. H. SI (1980) Fluvial process of Huanghe River estuary. II. Hydrographical character and the

region of sediment silting. Oceanologica et Limnologica Sinica, 11,295-305. PENG F. N., L. R. SuI, J. T. LLANO and H. T. SHEN (1984) Data on the lowest sea level of the East China Sea in

late Pleistocene. Scientia Sinica, Series B, 27,865-876. QIN Y. S. and F. LI (1982) Study on the suspended matter of the seawater of the Bohai Gulf. Acta

Oceanologica Sinica, 4, 191-200. REN M. E. and ZSNG C. K. (1980) Late Quaternary continental shelf of East China. Acta Oceanologica Sinica,

2, 94-111. REN M. E., R. S. ZHANG and J. H. YANG (1983) Sedimentation on tidal mud flat of China--with special

reference to Wanggang Area, Jiangsu Province. In: Proceedings of the International Symposium on Sedimentation on the Continental Shelf. China Ocean Press, Beijing, Vol. 1, pp. 1-16.

SHI Y. L., W. YANG and M. E. REN (1985) Hydrological characteristics of the Changjing and its relation to sediment transport to the sea. Continental Shelf Research, 4, 5-15.

TAN C. X. (1962) On discussion of the reason why there was anion stable period of the Yellow River since Donghan Dynasty. Social Sciences Monthly, 2, 23-25.

TAN C. X., editor (1982) Historical geography of China. Science Press, pp. 18-34 and 38-85. THE GEODETIC SURVEY BRIGADE FOR EARTHQUAKES RESEARCH. NATIONAL SEISMOLOGICAL BUREAU (1977)

Ground surface deformation of the Haiching earthquakes of magnitude 7.3. Acta Geophysica Sinica, 20, 251-263.

WANG J. T. and P. S. WANG (1980) Relationship between sea-level changes and climatic fluctuations in East China since late Pleistocene. Acta Geographica Science, 20, 251-263.

WELLS J. T. (1983) Dynamics of coastal fluid muds in low-, moderate- and high-tide-range environments. Canadian Journal of Fisheries and Aquatic Science, 40, Suppl. 1, 130-142.

810 M.-E. REN and Y.-L. Stt~

WELt.S J. T. and O. K. HUH (1984) Fall-season patterns of turbidity and sediment transport in the Korea Strait and southeastern Yellow Sea. In: Ocean hydrodynamics of Japan and East China Sea. Elsevier, Amsterdam.

Xu J. S., J. X. GAO and F. Y. XIE (1982) The Huanghai Sea in the last glacial period. Sciemia Sinica, Series B, 25, 20(I-213.

YANG Z. K., Y. J. LI, Q. L. DING and C. HAO (1979) Some fundamental problems ,,f Ouaternary geology of eastern Hebei Plain. Acta Geologica Siniea, 26,3-279.

YE Q. C., K. JING, Y. F. YANG, Y. Z. CHEN and Y. F. ZHAN¢I (1983) Changes of the river course of the lowcr Yellow River with respect to erosion of Loess Plateau. In: Proceedings qf the Second International Symposium on Fluvial Sediments, pp. 597--607.

ZHANG Z. Z. (1985) Modern estuary sediment of some large rivers ill China. In: Modern sedimentation in the coastal and nearshore zone of China, M. E. REN, editor, China Ocean Press, Beijing, t52 pp.

ZHENG H. H. (1982) Paleoclimate events recorded in clay minerals in Loess of China. In: Quaternary geology and environment of China, T. S. LJu, editor, China Ocean Press, Belting, pp. 59-66.

sediment discharge of the yellow river (china) and its effect on the sedimentation of the bohai and...

Documents