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Hyperpycnal flows at the Mouth of Huanghe (Yellow River): Past, Present and FutureH oujie W A NG 1, 2, Naishuang B I 1, 2, Z uosheng Y A NG 1, 2, Y oshiki SA I T O 3
1 C ollege of M ar ine G eosciences, Ocean Univer sity of C hina, 238 Songling R d., Qingdao 266100, C hina2 K ey L abor ator y of Submar ine Science and Pr ospecting T echniques, Ocean Univer sity of C hina, Qingdao 266100, C hina
3 A I ST , G eological Sur vey of J apan, I G G , C entr al 7, H igashi 1-1-1, T sukuba 305-8567, J apan
A G U C hapman C onfer enceJ an. 24-27, 2011 Oxnar d, USAPoster Number : T 4
Suppor ted by M OST , C hina (2010C B 951202) and NSF C (40876019)
R apid incr ease in the H uanghe (Y ellow R iver ) sediment yield fr om the L oess Plateau at 3000 yr B P was caused by the human inter ventions. A s a r esult, the sediment load deliver ed to the sea incr eased to appr oximately ten folds of the pr istine level (100 M T /yr ) with suspended sediment concentr ation (SSC ) high up to 25 kg/m3 at the r iver mouth that is favor able for the for mation of hyper pycnal flows in the coastal envir onment. Obser vations fr om cr uises in the 1980s and 1995 suggest that hyper pycnal flows off the H uanghe mouth ar e maintained by high concentr ation of r iver sediment and modulated by tides. T he hyper pycnal flows star t at the slack befor e high water , and dur ing the developing stage the bottom suspended sediment concentr ation incr eases r apidly while the salinity dr astically decr eases and the median gr ain size of suspended par ticles within the hyper pycnal layer incr eases, cr eating a sediment-str atified water column due to the str aining effect fr om tides. B ecause of the momentum dissipation, they begin attenuating at the slack befor e low water while the str atification of the water column becomes collapsed owing to the enhanced tidal mixing. A s a r esult, both the sediment concentr ation and median gr ain size of suspended par ticles within bottom layer decr eases. A s coar ser sediment par ticles ar e dumped on the seafloor , the hyper pycnal flows ar e no longer maintained because of density loss. Near ly 90% of the r iver -laden sediment is deliver ed to the sea dur ing the per iod when the hyper pycnal flows ar e pr ominent. G iven the extr emely high SSC at the r iver mouth dur ing the past thousands of year s, hyper pycnal flows have been a dominant patter n for the ter r estr ial sediment disper sal in the coastal ocean. H owever , constr uction of lar ge r eser voir s and soil-conser vation pr actices within the r iver basin dur ing the past sever al decades have r educed the sediment flux to the sea by ~90% and incr eased the gr ain size of suspended sediment deliver ed to the sea (30 um now ver sus 18 um befor e in median gr ain size). Scour ing of the channel in the lower r eaches has added a new sediment sour ce to those der ived fr om the loess r egion of the middle r eaches. T hose conditions ar e unfavor able for the for mation of hyper pycnal flows at the r iver mouth. Obser vations fr om cr uises after the oper ations of the X iaolangdi R eser voir , suggest that buoyant hypopycnal plumes, r ather than hyper pycnal plumes, have occur r ed at the r iver mouth since the dr amatic changes in concentr ation and gr ain size of suspended sediment dischar ged to the sea. C limate change (E NSO events impacted r egional pr ecipitation) and human activities in the r iver basin have alter ed the
'Sour ce-to-Sink' patter n of the H uanghe sediment as indicated by the infr equency of hyper pycnal flows at the r iver mouth. T he H uanghe has becoming an ar tificially r egulated r iver , and the delta, similar to the example of the Nile, will be star ved. A s a r esult, the delta er osion by monsoon activities will pr obably be a dominant sour ce for sediment expor ting to the distal mud deposition on the continental shelf. T he per tur bations fr om climate change and human activities pr opagate thr oughout the sediment disper sal system fr om sour ce to sink.
A B ST R A C T :
95o 97o 99o 101o 103o 105o 107o 109o 111o 113o 115o 117o 119o32o
34o
36o
38o
40o
42o
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
GC
ASH LJTNH LYX
LJX
LZH
TDG
SMX
XLD HYKLM
TG
Loess PlateauQinghai-Tibet Plateau
Bohai Sea
MaowusuDesert
Longitude
Latit
ude
Gauging StationTNH: Tangnaihai; LZH: Lanzhou; TDG:Toudaoguai; LM: Longmen; TG: Tongguan; HYK: Huayuankou;GC: Gaocun; ASH: Aishan; LJ: Lijin
ReservoirLYX: Longyangxia; LJX: Liujiaxia; SMX: Sanmenxia; XLD: Xiaolangdi
elevation (m)
Lanzhou Toudaoguai Huayuankou Lijin0
10
20
30
40
50
0.0
0.5
1.0
1.5
2.0Water dischargeSediment load
Wat
er d
isch
arge
(km
3 /yr
)
Sedi
men
t loa
d (1
09 t)
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 20100
4
8
12
16
20
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 20100
0.2
0.4
0.6
0.8
1
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 20100
20
40
60
80
100
Wat
er d
isch
arge
(km
3 )Se
dim
ent l
oad
(109
t)SS
C (k
g/m
3 )
(A)
(B)
(C)
Year
Monthly water discharge (A), sediment load (B) and suspended sediment concentration (C) at Station Lijin from 1950-2009
Before Xiaolangdi Reservoir
TNH LZH TDG LM TG SMX XLD HYK GC ASH LJ
0
200
400
600
800
1000
1200
Ann
ual s
edim
ent l
oad
(Mt/y
r)
Sediment source
A
TNH LZH TDG LM TG SMX XLD HYK GC ASH LJ
0
5
10
15
20
25
30
35
Med
ian
grai
n si
ze (µ
m)
B
TNH LZH TDG LM TG SMX XLD HYK GC ASH LJ
0
5
10
15
20
25
30
35
Med
ian
grai
n si
ze (µ
m)
B
TNH LZH TDG LM TG SMX XLD HYK GC ASH LJ
0
200
400
600
800
1000
1200
Ann
ual s
edim
ent l
oad
(Mt/y
r)
Sediment source
A
0
20
40
60
80
100
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0
20
40
60
80
100M
onth
ly S
SC
(kg/
m3 )
Cum
ulat
ive
ratio
of s
edim
ent l
oad
at s
tatio
n Li
jin (%
)
1950-1999
35 kg/m3
C
0
20
40
60
80
100
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0
20
40
60
80
100
Mon
thly
SS
C (k
g/m
3 )
Cum
ulat
ive
ratio
of s
edim
ent l
oad
at s
tatio
n Li
jin (%
)
2000-2006
Month
C
35 kg/m3
After Xiaolangdi Reservoir
Operation of Xiaolangdi Reservoir
11:00 16:00 21:00 02:00 07:00 12:00 17:00 22:00 03:00 08:00 13:00Jun. 21, 2005 Jun. 22 Jun. 23
Time
Wat
er d
epth
(m)
-5.0
-4.0
-3.0
-2.0
-1.0
0.0
0.00.51.01.52.02.53.03.54.04.5
Interrupted by storm
D SSC (kg/m3)
10:00 15:00 20:00 01:00 06:00
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
020406080100120140160180
Sept. 18, 1995 Sept. 19
Wat
er d
epth
(m)
Hyperpycnal event Hyperpycnal eventHyperpycnalevent
<3 PSU
<3 PSU
>24 PSU
SSC (kg/m3)D
Time
Figure caption: Annual sediment load at stations along the main stream 1950-1999 (A); Annual median grain size at stations along the mainstreas 1950-1999 (B); Monthly SSC at station Lijin 1950-1999 (C) and hyperpycnal plumes observed at the river mouth in September 1995 (D)
Figure caption: Annual sediment load at stations along the main stream 2000-2006 (A); Annual median grain size at stations along the mainstreas 2000-2006 (B); Monthly SSC at station Lijin 2000-2006 (C) and hypopycnal plumes observed at the river mouth in July 2005 (D)
Before high intervention from human activities on the river system, nearly 90% of the Huanghe-laden sediment is delivered to the sea during the period when the hyperpycnal flows are prominent. Since the middle Holocene, high-SSC drevied hyperpycnal flow at the river mouth has been a dominant pattern for the terrestrial sediment dispersal in the coastal ocean, and has acted as a driving force for the rapid accretion of the mega-delta. Intensive human activities during the past several decades including dam-orientated flow regulation, sediment entrappment and soil-conservation works have altered the river system. The SSC decreased drastically and sediment became much coarser than ever. Those are unfavorable for the formation of hyperpycnal flows at the river mouth. Significant changes have happened for the delta morphology. Sediment transfer within the framework of Source to Sink has been controlled by the different behaviors of human activities, such as the high sediment yeild due to agriculture since the middle Holocene and rapidly decreasing sediment load to the sea due to dam operation during the past several decades. In the future, delta erosion will be a dominant pattern instead of the rapid accretion due to insufficient sediment supply. The delta will be more vulnerable than ever to the sea-level rise and attack from storm surges, as well as to the natural and accelerated subsidence.
Average of 1950s
Huanghe (Yellow River) catchment
Figure caption:
Correspondance to H.Wang: [email protected]
(A)
(B)