The Influences of Flow-Sediment Regulation Field Experiments on the Salinity in the

1 1 1 2 Xinyan Mao , Wensheng Jiang , Peng Zhao , Huiwang Gao 1 Physical Oceanography Laboratory, Ocean University of 2 College of Environmental Science and Engineering, Ocean University of China

Introduction The Bohai Sea consists of 5 parts: , Bay, , Bohai Strait, and central area. It is typically a shallow shelf sea, where the mean depth is only 18m, and the deepest place is at the Bohai Strait, not more than 80m. The variation of salinity in the Bohai Sea is influenced by freshwater flux, including runoff, evaporation, and precipitation. Besides, the exchange with North is also very important. In the last 20 years, the evaporation is more than annual-mean value (Lin, et al. 2001 ). It is reported by Wu that the mean salinity has increased from 28 to 30 in last 35 years before 2000, and North Yellow Sea water's strong intrusion often took place (Wu, et al. 2004). Generally speaking, Yellow River (YR) runoff is the key factor to the salinity in the Bohai Sea, especially in the . Because of the booming economy and other anthropogenic influences, the runoff into the sea was less and less these years. All of the factors lead to the increasing salinity. Since 2002, Yellow River Conservancy Commission (YRCC) has conducted a field experiment of flow-sediment regulation every year. The three schedules are, respectively, July 4th -15th, 2002; Sept. 6th -18th' 2003; June 19th - July 13th' 2004. The experiment's objective is to optimize the rebalance between flow and sediments released, transport the sediment into sea, and ultimately reduce lower reach's sedimentation. Referred to Communique on Water Resources of Yellow River, due to the regulation experiments, the runoff measured at the YR mouth in 2003 and 2004 is about 200 hundred million cubic meters, 4 times more than that in 2001 , 2002. Before the first experiment in 2002, runoff in non-flood season is less than 100 cubic meters per second. However, during the experiment, the flux could exceed 1000 cubic meters per second. In 2003, there was continuous precipitation from September to October, so the experiment was carried out then, and the maximum flux almost reached 2500 cubic meters per second. With the more runoff, how will the salinity adjust itself? Would it begin decreasing or keep increasing? The problem could be studied by use of model simulation.

Model Configuration and Results HAMSOM, Hamburg Shelf Ocean Model, is a three-dimension baroclinic model. The simulation range covers the Bohai Sea and part of North Yellow Sea. The open boundary is at the 122.5° E. In the simulation, we adopt the newest position of the YR mouth, at 37.8167° N, 119.2833 ° E. In HAMSOM, grid-C is used. The horizontal resolution is 1 minute. In the vertical, it's divided into 10 layers: 3m, 6m, 9m, 12m, 15m, 18m, 23m, 28m, 38m, and 65m. The simulation period covers 4 years from 2001 to 2004, with 360s time step. In the simulation, the atmospheric forcing data was downloaded from ECMWF

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salinit y y there. there.

fre s h h water water through through the the lower lower reach reach into into the the Laizhou Laizhou Bay , , and and contribute contribute a a lot lot to to decreasing decreasing the the

flow- s ediment ediment regulation regulation experiments experiments not not only only realize realize the the initial initial objectives , , but but also also bring bring more more

certain certain differences , , to to some some extent , , the the model model result result agrees agrees well well with with the the observation. observation. Fifthly , , the the

it s s variation variation lags lags one one to to three three months months compared compared with with the the YR YR mouth . . Fourthly , , although although there're there're

in in the the Laizhou Laizhou Bay Bay shows shows intra-annual intra-annual oscillation, oscillation, and and inter-annual inter-annual decreasing decreasing trend. trend. Furthermore , ,

water water from from YR YR flows flows out out of of Bohai Bohai Strait Strait along along the the south south bank bank of of Laizhou Laizhou Bay . . Thirdly, Thirdly, the the salinity salinity

Secondly , , the the salty salty water water of of central area area central flows flows to to Laizhou Laizhou Bay Bay along along south south ofBohai ofBohai Bay, Bay, and and fresh fresh

variation variation of of YR YR runoff runoff is is important important to to the the salinity salinity in in the the Bohai Bohai Sea , , especially especially in in the the Laizhou Laizhou Bay . .

However , , some some conclusions conclusions could could be be obtained obtained from from the the present present simulation simulation result . . Firstly , , the the

leads leads to to not not so so good good simulation simulation in in other other area . .

Moreover , , we we considered considered too too few few rivers rivers in in the the model , , only only Yellow Yellow River , , no no other other rivers , , which which

to to simulate simulate the the intrusion intrusion of of Yellow Yellow North Sea; Sea; also also it it is is difficult difficult to to assure assure the the simulation simulation accuracy. accuracy.

significant significant for for simulating simulating salinity. salinity. We We have have no no high-quality high-quality data data at at the the boundary, boundary, so so it's it's impossible impossible

the the salinity salinity less less that that real real value . . Besides , , it it is is known known that that the the open open boundary boundary condition condition is is very very

There There are are several several drawbacks drawbacks in in the the simulation. simulation. Lack Lack of of evaporation evaporation and and precipitation precipitation data data made made

Conclusions Conclusions

wasn't wasn't taken taken into into account account when when simulating . .

was was not not clear . . Maybe Maybe it's it's from from the the YR YR fresh fresh water , , or or from from the the Xiaoqinghe Xiaoqinghe River's River's runoff , , which which

it it could could be be seen seen clearly clearly that that there ' s s some some fresh fresh area area at at the the south south of of Laizhou Laizhou Bay. Bay. So So far , , the the source source

so so the the simulated simulated salinity salinity dido dido ' t t reach reach the the level level of of observation . . From From the the observation observation of of Sept. Sept. 2004 , ,

difference difference is is about about 2 2 psu. psu. It's It's probably probably related related to to not not employing employing the the evaporation evaporation data data in in the the model , ,

conducted conducted in in August August 2002 . . The The extending extending trend trend of of fresh fresh water water is is similar . . However , , the the value value

Figl Figl 7 7 and and Figl8 Figl8 are are two two comparisons comparisons between between observation observation and and model model results. results. The first first The one one was was

validates validates the the conclusion conclusion that that YR YR freshwater freshwater mainly mainly outflows outflows along along the the south south bank bank of of Laizhou Laizhou Bay. Bay.

is is a a time time lag lag of of the the occurrence occurrence of of minimum minimum SSS SSS between between these these two two points , , one one to to three three months. months. It It

salinity salinity at at A A and and B B shows shows intra-annual intra-annual oscillation oscillation and and inter-annual inter-annual decreasing decreasing trend . . Besides , , there there

Fig . 16 , , point point A A is is near near In In the the YR YR mouth , , and and point point B B is is in in the the Laizhou Laizhou Bay . . The The time time series series of of

Strait Strait

and and the the other other one one follows follows the the lower lower counterclockwise counterclockwise track , , at at last, last, outflow outflow along along south south of of Bohai Bohai

north north of of Bohai Bohai Strait , , and and then then divide divide into into two two branches . . One One follows follows the the upper upper clockwise clockwise track, track,

along along the the south south bank bank of of the the Laizhou Laizhou Bay . . This This is is related related to to the the Bohai Bohai circulation : : inflow inflow from from

bay , , and and has has too too little little influence influence on on the the other other part part in in the the Bohai Bohai Sea. Sea. flows flows out out of of the the Bohai Bohai Strait Strait It It

Besides , , the the freshwater freshwater from from YR YR mainly mainly extends extends to to south , , and and influences influences the the salinity salinity of of Laizhou Laizhou

than than before . . The The salty salty water water from from central central area area flows flows to to Laizhou Laizhou Bay Bay along along the the south south of of Bohai Bohai bay . .

Bohai Bohai Sea , , with with the the same same color color bar . . They They show show clearly clearly that that the the salinity salinity in in 2003 2003 and and 2004 2004 is is less less

Figures , , No. No. l l to to No . 15, 15, are are the the contours contours of of monthly monthly mean mean sea sea surface surface salinity salinity (SSS) (SSS) in in the the

Sediment Sediment of of China , , and and Communique Communique on on Water Water Resources Resources of of Yellow Yellow River . .

the the used used runoff runoff data data was was digitized digitized from from two two communiques: communiques: Communique Communique on on River River and and

The The data data is is 4 4 times times per per day , , respectively respectively at at 00 : 00 , , 06 : 00 , , 12:00, 12:00, and and 18:00. 18:00. Besides, Besides,

2m 2m air air temperature , , 2m 2m dewpoint dewpoint temperature, temperature, sea sea level level pressure pressure and and total total cloud cloud cover. cover.

(European (European Center Center for for Medium-range Medium-range Weather Weather Forecast) , , including including lOm lOm wind wind speed, speed, References Communique on River and Sediment of China 2001-2004 Communique on Water Resources of Yellow River 2001-2004 Lin Chuanlan, et al. Long-term variation of temperature and salinity of the Bohai Sea and their influence on its ecosystem Progress in Oceanography, 2001, 49 Wu Dexing, et al. Long-term variation characteristics of the salinity of the Bohai Sea and the probable leading factors Progress in Natural Science, 2004, 14(2)

Figures Fig.l-Fig.15 Contour of monthly mean SSS every three months from 2001.1to2004.7

200101 SSS Distribution In the Bohol Sea 200104 SSS Distribution In the Bohal Sea 200107 SSS Distribution In the Bohal Sea

200110 SSS Distribution In the Bohal Sea 200201 SSS Distribution in the Bohal Sea 200204 SSS Distribution In the Bohal Sea

200207 SSS Distribution In the Bohal Sea 200210 SSS Distribution In the Bohal Sea 200301 SSS Distribution In the Bohal SH

200304 SSS Distribution In the Bohal Sea 200307 SSS Distribution In the Bohal SH 20031 O SSS Oistrtbutlon In the Bo ha I Sea

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11 86 86 11 8 8 8 11 9 9 11 92 92 11 9 8 8 11 94 94 1 20 20 11 96 96 1 20 2 2 118 118 6 6 118 118 8 8 119 119 119 119 2 2 119 119 8 8 119 119 4 4 1 20 20 119 119 6 6 1202 1202

37 37 2 2 3 7 2 2 7

309 309

3 4 4 7 7 37 37 4 4

3 7 7 6 6

32 4 4

3 7 8 8 7

32 . 9 9

38 38

28 . 6 6

118

. 5 5

119 119

119 . 5 5

120

. 5 5

120 120 121 121

119 119 119 . 5 5

118

. 5 5 1 20 20 23 23 120 . 5 5 121 121 28 . 8 8

29 29 24 24

29 . 2 2

25 25

29 . 4 4

26 26

37 . 5 5

37 . 5 5 29 . 6 6

27 27

29 . 8 8

28 28 30 30

30 . 2 2 29 29

30 . 4 4

38 38

38 38 30 30

30.6 30.6

31 31

30 . 8 8

200208 200208 SSS SSS Dist~ibution Dist~ibution in in the the Laizhou Laizhou Bay Bay 200409 200409 SSS SSS Dist~ibution Dist~ibution in in the the Laizhou Laizhou Bay Bay

Fig.17 Fig.17 Comparison Comparison of2002 .8 .8 Fig . 18 18 Comparison Comparison of2004.9 of2004.9

time time

12/15/00 12/15/00 06/15/01 06/15/01 12115/01 12115/01 06/15/02 06/15/02 12115/02 12115/02 06/15/03 06/15/03 12115/03 12115/03 06/15/04 06/15/04 12115/04 12115/04

30 30 30 30

32 32 30 . 4 4

A A

B B

SSS SSS Time-Variation Time-Variation at at A A and and B B

Fig . 16 16 Time-series Time-series of of SSS SSS at at point point A A and and B B

200401 200401 SSS SSS Distribution Distribution In In the the 200404 200404 Bohal Bohal SSS SSS Sea Sea Distribution Distribution in in the the Boha l l Sea Sea 200407 200407 SSS SSS D istri bution bution In In the the Bohai Bohai Sea Sea