V o l. 53, N o. 3 M ay, 1998 A CTA GEO GRA PH ICA S IN ICA ) m 3 gs,

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1 A CTA GEO GRA PH ICA S IN ICA V o l. 53, N o. 3 M ay, 1998 (, 11201), 1,,,, [1, 2 ] m 3 gs, m 3 gs, [2 ],,, 2 A B ( 1a),,, 1a E F, E F, CN F ( 1b), 1a A CN F 1b A Cf, L, A C = x, l= Cf = L - x,, CM E, Ce,, ef S,,, :,,,,,,, : ; :

2 3 : 265 h f D arch2w eisbach : h f = Κ L R v 2 2g (221) Κ, R, v, g, L R : R = Ξ ς = 1 2 r2 (Υ- sinυ) Υ r = r (Υ- sinυ) 2Υ Ξ, (222) ς, r, Υ (0< Υ< Π) b : b = 2rsin Υ 2 (223) (221) : h f = Q ΚΥL (Υ- sinυ) 3 g b 5 (22) ( 1a A B ), W : A C CM E CN F [3 ] 1 a. b. F ig11 a. Changjiang river mouth b. Sim p le m odel of hydrodynam ical calculation W = Χ (H 1 - H x ) + Χ (H x - H 0) + ΧQ 3 (H x - H 0) = Χ (H 1 - H 0) (225) Χ, H 1 H x H 0 A C E F (E F, ) Q 3, = + Q 3 : h f = W = H 1 - H 0 = h f x + h f ΧQ L - x (226) 1 h f A B, h f x A C, CM E CN F h f L - x CM E ( 1b),, : h f = ΚΥx 2 (Υ- sinυ) 3 g 5 + ΚΥ (L - x ) 2 + S 2 2 (Υ- sinυ) 3 g 5 (227) h f x :

3 h f = 0, : h f = (Υ- ΚΥ sinυ) 3 g l = L - x = (L - x ) 2 5 (L - x ) 2 + S 2 S - 1 (228), h f, ΚΥ 2 S 2 h f = (Υ- sinυ) 3 g 5 [ (L - x ) 2 + S 2 ] g > 0, [ ], 1 1 (% ) Ξ Ta1 The percen tages of differen t f lows dur ing the r isig tide and the ebb tide in the Changj iang R iver mouth (% ) (% ) Ξ [ ] 1,,, (228), ( ) 5196 S 1b 3917 km (228) : l = L - x = = 8013 km , 77 km, : = 128%,,,,, [5 ],,,, (228),

4 3 : 267, > 215 = > = 1117 (% ),, 1117% 121% 1117%, (228),,,,,,,,,, 3,,, ( ) ( 2 [6, 7 ] ),,,,,, [2 ], ;,,,,,,,,,,,,,,,,,, [5 ],, ,,, F ig12 T he diagramm atic view of evo lutional p rocess,, of Changjiang delta in the past 7500 years

5 268 53,,,, ( ), ;,,,,,,,,, ( 2), ,, 500, 200 ( ),,,,,, (References) 1 Q iao Pengnian, Zhou Zh ide, Zhang H unan. A n introduction to the evo lution of river mouth in Ch ina. Beijing Sci2 ence P ress, ( In Ch inese) [,,.., ] 2 Q ian N ing, Zhang Ren, Zhou Zh ide. Science of river bed evo lution. Beijing Science P ress, , 309. ( In Ch i2 nese) [,,.., , 309. ] 3 Remo te sensing section, Geophysical airbrone p ro specting team, State Geo logical Bureau. A pho tograph album of Earth Resource Satellite. Beijing Geo logy P ress, ( In Ch inese) [.., ] Xu Sh iyuan, W ang J ingtai, L i P ing. O n the develop ing Phase of Changjiang riveṙ In P roceedings of the fo rce, mo r2 pho logy and sedim entary p rocess in coastal river mouth area. Beijing Science P ress, ( In Ch inese) [,,..., ] 5 Gao J in. T he confluence and division flow s in river channel. A cta Geog rap h ica S inica, 199, 9 (5), ( In Ch inese) [.., 199, 9 (5) ] 6 Xu Sh iyuan, W ang J ingtai, L i P ing. D evelop ing p rocess and sand body characteristics of the modern Changjiang river delta. In Yan Shangqin, Xu Sh iyuan eds. Sedim entary researches on the modern Changjiang river delta. Shanghai Publish ing House of N o rm al U niversity of East Ch ina, ( In Ch inese) [,,...., ] 7 D elta wo rk ing group, D ep ṫ of m arine geo logy, TongjiU niv. Fo rm ation and developm ent of the Ho locene delta. Ch i2 nese S cience B u lletin, 1982 (5) , 1982 (5) ] ( In Ch inese) [.,, 1939,, 1960,, 20

6 3 : 269 THE EVOL UT IONAL RUL E OF CHANGJ IANG R IVER MOUTH AND HYD RODY NAM ICE EFFECT Gao J in (X iang tan P oly technic U niversity, D ep artm ent of R esou rce E xp loration and M unicip al Construction, X iang tan 11201) Key words the evo lution of river mouth, Chao s, the p rincip le of the least resistance, Co rio lis fo rce, Environm ent p roblem Abstract T he key p roblem in discussing evo lutional rule of Changjiang river mouth is to study the de2 velop ing rule of river mouth sandbars in each period. In the past, scho lars studied the p roblem by geomopho logy and sedim eto logy m ethod, w hile the autho r inquires into the p roblem w ith hy2 drodynam ics m ethod. D evelop ing length and the arranged direction of sandbars can be calcu lat2 ed. In the paper, two questions are disscussed. 1. T he theo retical analysis of the develop ing length of sandbars T he theo retical fo rm ula of develop ing length Chongm ing island is as fo llow s: l = D ue to the irregular shape of Chongm ing island and the unsymm etrical character of the w a2 ter flow on bo th sides of the island, in o rder to simp lify the calculation, w e consider the south branch as one side of a right triangle and straighten the no rth branch as the hypo tenuse of the right triangle, the length of ano ther side is S. is ratio of flow fo r no rth branch to the to tal in ebb tide. S - 1 is the ratio of w idth betw een m ain channel and no rth branch. river channel is suppo sed to be arc. W hen S = 3917 km, = = 8013 km. T he theo retical value confo rm s to the p ractical length. and 2. T he evo lutional rule of Changjiang R iver mouth and its environm ent significance T he cro ss section of = 5196, w e can get l 2153 A n outstanding evo lutional rule of the p resent Changjiang R iver mouth is that the m ain channel is gradu lly deflected tow ards sou th and the river m ou th sandbars in differen t periods w ere arranged like w ild geese flying from no rthw est to southeast. T he effect of Co rio lis fo rce lies in that it contro lls the difference of initial conditions fo r the channels of division flow s, and this creates that the channels of division flow s evo lute tow ards different direction. branch is easily silted up and the south branch is develop ing further. T he no rth In the near future, Chong2 m ing island w ill be connected w ith the land on the no rth bank and the second Chongm ing island w ill be fo rm ed, w hich is compo sesed of Changxin and H engshan Island. south side, South H arbour w ill be mo re narrow in w idth. Pudong in shanghai w ill be eroded. T he channel on its T hese islands and the sea banks of T his is a po tential environm ental p roblem.