渤海流場(chǎng)的數(shù)學(xué)模擬和應(yīng)用

1、渤海流場(chǎng)的數(shù)學(xué)模擬和應(yīng)用王萬(wàn)戰(zhàn) 余欣 楊明（黃河水利科學(xué)研究院， 鄭州 450003）摘要 利用渤海實(shí)測(cè)資料率定了渤海平面二維潮流模型，模擬了渤海潮流場(chǎng)。進(jìn)行了水流參數(shù)靈敏度分析，發(fā)現(xiàn)渦粘系數(shù)變化對(duì)水位和流速影響不大，而糙率影響較大。數(shù)學(xué)模擬的成果表明，與河流水流相比，渤海潮流場(chǎng)的基本特點(diǎn)是，水流不僅存在“水向低處流”的過(guò)程、而且還存在“水向高處流”的過(guò)程，兩個(gè)過(guò)程相互轉(zhuǎn)化，其實(shí)質(zhì)是動(dòng)能和勢(shì)能“此漲彼消”、相互轉(zhuǎn)換的過(guò)程。與相對(duì)狹長(zhǎng)海峽內(nèi)的潮波、潮流比，渤海流場(chǎng)的特點(diǎn)是，渤海潮波、潮流是旋轉(zhuǎn)型，而不是前進(jìn)波型。這些特點(diǎn)也是黃河口實(shí)體模型水流控制技術(shù)的難點(diǎn)。把此數(shù)學(xué)模型應(yīng)用于黃河口濱海區(qū)地形測(cè)驗(yàn)

2、中，發(fā)現(xiàn)如果使用數(shù)學(xué)模型給出各測(cè)點(diǎn)逐時(shí)水位，可減少誤差±0.5m, 消除用常規(guī)方法造成的不合實(shí)際的“深海淤積現(xiàn)象”。水動(dòng)力模擬成果表明，用把黃河口導(dǎo)向深海、或加大黃河口入海流量，都不能解決入海泥沙淤積口門附近的問(wèn)題。黃河口治理的出路是，在于控制適當(dāng)?shù)娜牒Ｋ硹l件和用較大的容沙體積換取較長(zhǎng)的行河時(shí)間。關(guān)鍵詞 渤海；流場(chǎng)；M2分潮；二維潮流數(shù)學(xué)模型黃河口濱海區(qū)及渤海深海流場(chǎng)特性是影響黃河口水沙運(yùn)動(dòng)的基礎(chǔ)。本文利用平面二維模型的水動(dòng)力模塊模擬渤海流場(chǎng)水位、流速大小和方向的動(dòng)態(tài)變化；在此基礎(chǔ)上，分析了黃河口實(shí)體模型的水流控制的難點(diǎn)所在，分析了黃河口濱海地形測(cè)驗(yàn)資料整編傳統(tǒng)方法的缺點(diǎn)關(guān)鍵技術(shù)，

3、初步分析了用向深海延伸黃河口、治理黃河口的方法是否可行。1 基本方程基于水動(dòng)力學(xué)和泥沙運(yùn)動(dòng)力學(xué)的河口模型能夠計(jì)算在河流來(lái)水來(lái)沙、風(fēng)、浪、潮汐、鹽度、溫度等因素共同作用下河口海域的水沙運(yùn)動(dòng)和地形演變。其基本方程為水流連續(xù)方程和動(dòng)量方程。 X方向動(dòng)量方程：Y方向動(dòng)量方程：式中，為水位(m)，d為河底高程(m)，h為水深（d）（m），p、q 分別為 x,y方向的單寬流量(m3/s/m)，即p=hu,q=vh,u、v分別為流速在x、y方向的分量，C(x，y)謝才系數(shù)(m1/2/s)，與曼寧系數(shù)的關(guān)系為 c=n-1h1/6,g為重力加速度(m/s2)，f(v)為風(fēng)摩擦系數(shù)，V、Vx、Vy 分別為風(fēng)速及其

4、在x,y方向的分量(m/s)， 科氏力系數(shù)s-1， pa 為 大氣壓力(kg/m/s2),w水的密度(kg/m3),x，y為距離(m),t 為時(shí)間(s)，E為水流紊動(dòng)粘滯系數(shù)，由Smagorinsky公式計(jì)算，由于本研究重點(diǎn)在于分析渤海潮流場(chǎng)的基本特性，所以暫時(shí)不考慮潮汐以外的其他因素如風(fēng)、浪、溫度、鹽度和河流入?yún)R的影響。2 模擬的基本條件和率定本研究模擬范圍為黃河口以外、渤海海峽以西的整個(gè)渤海。黃河口附近海域地形采用黃河水利委員觀測(cè)的1980年、1981年的濱海區(qū)地形，其他海域地形采用黃河水利委員設(shè)計(jì)院測(cè)繪總隊(duì)和中國(guó)人民解放軍4210工廠在1998年共同編匯的1：1百萬(wàn)的渤海地形圖。計(jì)算網(wǎng)格

5、為邊長(zhǎng)5000m的正方型網(wǎng)格。邊界條件：利用渤海海峽的北長(zhǎng)山、北隍城、羊頭洼三站潮汐調(diào)和常數(shù)，用調(diào)和分析模型預(yù)報(bào)出三站的潮汐過(guò)程，做空間線性內(nèi)差作為模型的邊界條件。模擬周期為1981年7月1日8月22日，模擬時(shí)間步長(zhǎng)為30秒。模型的率定：需要率定的參數(shù)主要為Smagorinsky公式子渦擴(kuò)散系數(shù)（Cs）和反映河床糙率的曼寧系數(shù)（n）。率定的結(jié)果為，曼寧系數(shù)為0.0125s/m1/3、Smagorinsky系數(shù)為0.5時(shí)，模擬結(jié)果，如M2分潮無(wú)潮點(diǎn)位置、渤海M2分潮潮差空間分布（圖1）、渤海灣附近海域潮流逆時(shí)針?lè)较蛐D(zhuǎn)、K1、O1、S2等分潮潮差遠(yuǎn)小于M2分潮潮差等指標(biāo)與實(shí)測(cè)資料相符。（a）模型

6、計(jì)算的M2分潮潮差(b)基于實(shí)測(cè)資料的M2分潮潮差圖1 實(shí)測(cè)和計(jì)算的渤海M2分潮潮差分布3 模型參數(shù)的靈敏度分析進(jìn)行模型參數(shù)靈敏度分析的目的是研究每個(gè)參數(shù)對(duì)水流的影響程度，本文的可調(diào)參數(shù)為子渦擴(kuò)散系數(shù)（Cs）和河床糙率。由圖2可知，在曼寧系數(shù)不變的情況下，隨著Cs增大，潮位、流速降低，但是變幅很小。由圖3可知，在渦粘系數(shù)一定時(shí)，隨著曼寧系數(shù)的增加，潮差和流速振幅明顯變小。圖2 曼寧系數(shù)為0.0125s/m3、不同Cs條件下的水位圖3 Cs=0.5、不同曼寧系數(shù)(n)條件下的水位、流速過(guò)程4渤海流場(chǎng)特征4.1 水既向低水位處流、也向高水位處流常見(jiàn)的河流水流特征是水向低水位處流，而在潮汐影響的水域

7、，水流既可向低水位處流，也可向高水位處流，簡(jiǎn)述如下。圖4表示渤海灣中部某處的流速（流速方向以北向?yàn)榛€，順時(shí)針為正，單位為弧度），圖5各圖中等值線上的數(shù)字表示水位，箭頭方向表示流向，箭頭長(zhǎng)短表示流速大小。圖4 計(jì)算渤海灣中部某處的水位、流速、方向9：00時(shí)渤海灣處于較高水位（圖4），由圖5可知，此時(shí)渤海海峽水位較低，從渤海灣到渤海海峽水面比降向東，水向東流，呈現(xiàn)水向低水位處流的特征， 而此時(shí)萊州灣水流卻是向高水位處流。其后，由于水流流出渤海灣，渤海灣水位逐漸降低、流速變大，與此同時(shí)，渤海海峽附近由于水流流入，潮位逐漸升高、流速變小。(a)(b)(c)(d）圖5（a）(b) (c) (d) 計(jì)算

8、的渤海水位和流速12：20時(shí)渤海灣水位接近低潮位、但水流繼續(xù)東流，呈現(xiàn)水向高處流的特征，流速接近最大，此時(shí)渤海海峽附近水位接近高潮位，流速接近于零；其后至至14：20，渤海灣水位繼續(xù)降低、流速開(kāi)始降低，及至14：20時(shí)渤海灣水流流速接近于零，渤海海峽附近水位較高，水向低水位處流（即向西流）；15：20時(shí)，渤海灣水位由低逐漸升高、水流向西，呈現(xiàn)水向低水位處流的特征。與渤海灣水流相似，萊州灣、遼東灣水流也具有水向低水位處流和水向高水位處流兩種相互轉(zhuǎn)化的過(guò)程。這是典型的水流動(dòng)能和勢(shì)能相互轉(zhuǎn)化的過(guò)程。此特征表明，在某一時(shí)段內(nèi)，渤海水面比降是水流的主動(dòng)驅(qū)動(dòng)力，而在其他時(shí)段，其是水流的阻力此特征是一般河道

9、水流所沒(méi)有的。這是黃河口實(shí)體模型試驗(yàn)水流不同于其他單向重力流的特征之一。42 旋轉(zhuǎn)流和往復(fù)流圖4最大流速出現(xiàn)在半潮位時(shí)刻，而最小流速則出現(xiàn)在高、低潮位附近，表明渤海潮波為旋轉(zhuǎn)型。不同的地點(diǎn)流速矢量旋轉(zhuǎn)的方向不同（順時(shí)針、或逆時(shí)針）例如，在渤海灣為逆時(shí)針旋轉(zhuǎn)。越近岸邊，潮流橢圓長(zhǎng)軸相對(duì)較長(zhǎng)，且平行于海岸線，表現(xiàn)為越為明顯的往復(fù)流。5應(yīng)用5.1 黃河口實(shí)體模型水流控制的難點(diǎn)渤海水流既朝低水位處流，也朝高水位處流，同時(shí)，渤海水流為旋轉(zhuǎn)流，神仙溝口外存在M2無(wú)潮點(diǎn)等，都是黃河口實(shí)體模型水流控制的難點(diǎn)所在。5.2 黃河口濱海地形測(cè)驗(yàn)中潮位的確定測(cè)驗(yàn)斷面某點(diǎn)的高程Hb，是通過(guò)水位Z和該點(diǎn)瞬時(shí)實(shí)測(cè)水深（h）

10、得到的，即Hb=Z-h (圖6)。瞬時(shí)水位 Z 海底高程 Hb h高程基面 圖6 海底高程的求法問(wèn)題是，如何求出水位？傳統(tǒng)的方法是，假定任意測(cè)點(diǎn)水位等于附近岸邊測(cè)點(diǎn)水位。然而，這個(gè)假定常常造成黃河口濱海區(qū)深水區(qū)出現(xiàn)嚴(yán)重的淤積顯然不符合實(shí)際。用數(shù)學(xué)模型檢查這樣的假定。先看黃河口外濱海測(cè)驗(yàn)常用的35個(gè)斷面中的第12斷面（圖7）。點(diǎn)繪第12斷面兩端點(diǎn)瞬時(shí)水位，計(jì)算兩端點(diǎn)水位差，如圖8所示，可見(jiàn)測(cè)驗(yàn)斷面兩端點(diǎn)水位差不是像假定那樣為零，而是-0.4m 到 +0.6m。圖7渤海灣濱海區(qū)地形測(cè)驗(yàn)斷面分布圖8 第12斷面兩端點(diǎn)處水位差同理，可計(jì)算處其他34斷面兩端點(diǎn)的水位差（圖9），可見(jiàn)35個(gè)斷面兩端點(diǎn)水位差

11、約為-0.4m - +0.5m. 由上述可見(jiàn)，有必要使用數(shù)學(xué)模型為黃河口濱海區(qū)地形資料整編提供所需的水位。圖9 黃河口濱海區(qū)每個(gè)斷面兩端點(diǎn)水位差5.3 篩選黃河口治理戰(zhàn)略和方案如何治理黃河口一直是大家關(guān)心的大事之一，不同的專家提出了各種不同的觀點(diǎn)。數(shù)學(xué)模型是篩選治理方案的經(jīng)濟(jì)手段之一。 黃河口治理觀點(diǎn)1研究：黃河口向深海延伸有專家提出，盡量向深海延伸黃河口，希冀突出的沙嘴造成的流速增大能夠把泥沙輸送更遠(yuǎn)。下面用數(shù)學(xué)模型來(lái)論證此觀點(diǎn)是否可行?？紤]兩種情形：黃河口向東延伸、以及黃河口向西延伸。首先看黃河口向東延伸的情形。用數(shù)學(xué)模型計(jì)算出當(dāng)黃河口延伸0 km、10km、20km、30km、40km、

12、50km、60km、70km、80km、和90km時(shí)各點(diǎn)的流速，取流速最大值，然后用延伸后的流速最大值減去延伸前的流速最大值。圖10為當(dāng)黃河口延伸30 km時(shí)的流速最大值減去延伸20 km時(shí)流速最大值所得的差值分布圖?？梢?jiàn)，黃河口延伸的確可以增加沙嘴附近的流速，但是流速明顯增加的區(qū)域面積較小。. 這些結(jié)果表明，即使黃河口延伸造成口門局部流場(chǎng)增強(qiáng)，輸送到黃河口的泥沙的較粗沙仍不會(huì)被水流帶到較遠(yuǎn)的地方，仍將淤積在口門附近。模擬結(jié)果初步否定了此種治河觀點(diǎn)。圖10 黃河口延伸30 km、20km時(shí)流速最大值差值幾十年來(lái)黃河口研究表明，盡管專家們對(duì)黃河口淤積延伸對(duì)黃河下游河道演變影響有不同的認(rèn)識(shí)，但是對(duì)

13、黃河口淤積延伸必然反饋抬高其上游河道的看法還是一致的。因此，用把黃河口延伸到深海、希冀借助突出沙嘴造成流速增大把泥沙帶向深海的方法是既不可行、如果實(shí)施此方法，會(huì)加快黃河口上游河道河床抬升的速率。黃河口治理觀點(diǎn)2研究：加大入海流量，希望大流量把泥沙帶到深海有專家提出，黃河口治理可以通過(guò)加大入海流量，希冀大流量把泥沙帶到深海。用數(shù)學(xué)模型模擬了清水溝口門大流量（5000 m3/s）、 出流方向?yàn)?度(N)、45度(NE)、90度(E)、135度(SE)、180度(S)時(shí)黃河口口外的流場(chǎng)。這些流場(chǎng)與清水溝口門流量（0 m3/s）時(shí)的流場(chǎng)相比較，可看出當(dāng)清水溝口門大流量時(shí)的影響范圍（圖11），其大致為口

14、門附近40km (南北向)×30km(向東)。這個(gè)范圍還是比較小的，無(wú)法把泥沙輸送更遠(yuǎn)。 黃河口治理的根本出路：用堆沙空間換行河時(shí)間黃河口來(lái)沙多時(shí)，河口延伸長(zhǎng)，反之，來(lái)沙少時(shí)則短釣口河1976年后停止行河后，釣口河附近海岸大量蝕退。這些事實(shí)表明，入海沙量是決定黃河口地貌演變的關(guān)鍵因素，因此，如何控制黃河口入海水沙應(yīng)是黃河口治理的關(guān)鍵。 圖11 黃河口流路向東時(shí)不同出流角度對(duì)向東西向流速的影響 (河口流量5000 m3/s)從理想的角度，適量（既不太多、也不太少）的泥沙既能防止黃河口河道萎縮、也能使河口海岸處于沖淤平衡。但是，實(shí)現(xiàn)起來(lái)可能不太容易：需要為黃河口建立一個(gè)或多個(gè)分水分沙系統(tǒng)

15、,還需要?jiǎng)討B(tài)調(diào)度黃河口水沙過(guò)程。黃河口治理的出路是，在盡量控制黃河口來(lái)沙量的基礎(chǔ)上，先相對(duì)穩(wěn)定地使用一入海流路，然后有計(jì)劃地?cái)[動(dòng)到另一流路，由海洋動(dòng)力蝕退非行河流路海岸，待蝕推達(dá)到一定程度后，伺機(jī)再使用。即用有限的容沙體積換取黃河口流路的行河時(shí)間。至于何時(shí)實(shí)施人工流路擺動(dòng)等，需要大量的數(shù)學(xué)模擬工作。6結(jié)論（1）平面二維數(shù)學(xué)模型能夠再現(xiàn)渤海流場(chǎng)的基本特性。（2）在平面二維潮流參數(shù)中，子渦擴(kuò)散系數(shù)的變化引起的水流變化較小，而糙率的變化引起的水流變化較大。（3） 渤海流場(chǎng)的基本特性是：渤海潮波、潮流是旋轉(zhuǎn)型的，水流既可由高水位向低水位流，也可由低水位向高水位流。這些特點(diǎn)決定了黃河口實(shí)體模型水流控制的

16、難點(diǎn)所在。（4）黃河口濱海區(qū)水位不是水平的，岸邊與深海處水位相差約-0.4m-+0.5 m；至今黃河口瀕海區(qū)地形整編時(shí)使用的假定（深水區(qū)水位等于岸邊水位）造成深水區(qū)出現(xiàn)虛假的淤積現(xiàn)象，可由數(shù)學(xué)模型提供動(dòng)態(tài)的水位加以消除。（5）渤海水動(dòng)力數(shù)學(xué)模型模擬表明，藉把黃河口牽引到深水區(qū)或增加黃河口入海流量的方法都只能增加口門附近局部的流場(chǎng)強(qiáng)度，對(duì)此小范圍之外的流場(chǎng)影響不大，因此，這些方法無(wú)法把黃河口入海泥沙的較粗部分輸沙到深海。（6）黃河口治理的根本出路是，在控制黃河口的水沙量的基礎(chǔ)上，同時(shí)（b）給黃河口流路留以擺動(dòng)的空間，用大范圍的容沙空間換取相對(duì)較長(zhǎng)的行河時(shí)間。 Numerical Modeling

17、 of the Flow in Bo Sea and its ApplicationsWang Wan Zhan Yu Xin Yang Ming（ Yellow River Institute of Hydraulic Research, Zhengzhou, 450003,Abstract: With a 2D depth-integrated hydrodynamic model, we did parameters analysis and simulation of the flow in the Bo Sea. On the basis we have found some app

18、lications in defining what the challenging problems in the physical modeling, compiling nearshore bathymetric data , and exploring feasibility of each of the strategies for training the Yellow River estuary. Keywords:Bo Sea; Flow Field; M2 tidal constituent; 2D numerical model Hydrodymics is fundame

19、ntal in affecting flow and sediment transport in estuaries and rivers as well. Simulation of the flow in the Bo Sea has been done with a 2D depth-integrated numerical model，to have a more in-depth understanding of the interactions between water level, speed, and flow direction there. With the modeli

20、ng, we could deduce its implications to the physical modeling for the Yellow River estuary, compiling of nearshore bathymetry, and feasibility of the scenarios for the various training strategies. 1 Governing EquationsThe 2D depth integrated numerical hydrodynamic model we used is a numerical modeli

21、ng tool for modeling of the flow field in estuaries and open seas due to river feedings, wind, tides, waves, salinity, temperature and other factors. The fundamental equations are given as follows.Continuity equation: Momentum equation in X direction: Momentum equation in Y direction:Where is flow l

22、evel (m)，d bed elevation(m)，h flow depth（d）（m），p and q flow rates per unit width in X and directions respectively(m3/s/m)，where p=hu, q=vh, u and v velocity components in X and Y directions respectively, C(x，y) Chezy Coefficient(m1/2/s)，bearing the relationship with Manning Coefficient as c=n-1h1/6,

23、 g gravitational acceleration(m/s2)，f(v) wind friction coefficient，V、Vx、and Vy wind speed and its components in X and Y directions respectively (m/s)， Corilis Force factor s-1， pa air pressure(kg/m/s2), w water density (kg/m3), x and y distance in X and Y direction(m),t time(s)，E eddy viscosity，whic

24、h is calculated with Smagorinsky Formula:In order to investigate the basic flow features in the Bo Sea, weinclude only tides in the modeling without considering the other factors for the time being.2 Conditions specification and model parameters calibrationThe simulated area covers the whole Bo Sea

25、west of the Bo Sea Strait, excluding the rivers flowing in. The bathymetrical data for the initial bed topography is composed of two parts: one is the data set of the measurements in the nearshore area bordering the Yellow River Delta, which was made in 1980 and 1981. The other part the sea chart of

26、 a scale of 1:1,000,000. The modeling domain is cut into squares, each side 5000 m long.Water level hydrographs at the Bo Sea Strait are taken as boundary conditions.Simulation period starts from July 1,1981 to Aug.22 1981 with the time step 30s.The parameters to be calibrated are (Cs) in the Smagor

27、insky formula and Manning Coefficient (n). When Manning Coefficient is 0.0125s/m1/3 and Smagorinsky Coefficient is 0.5, the model results are found in a nice agreement with the measured ones in terms of the tidal constituent (M2) (Fig.1). Details of the calibration and verification are omitted for c

28、oncise purpose.（a） calculated tidal ranges of constituent M2(b) Measured tidal ranges of the constituent M2 Fig.1 (a)(b) calculated and measured tidal ranges of the constituent M23Sensitivity analysis of model parametersSensitivity analysis is done to evaluate how the parameters (Cs and n) affect th

29、e flow in the Bo Sea. It is found that the increase in Cs, given a constant Manning coefficient, leads to the decrease in flow level and velocity with, however, a small margin (Fig.2). In contrast, it is found that for a constant value of Cs given, amplitudes of tidal level and velocity are lowered

30、by a larger margin each with Manning coefficient increasing (Fig.3)Fig.2 Water level hydrographs for various Cs values and n of 0.0125 s/m3Fig.3 flow level and velocity hydrographs for various n and Cs of 0.54Flow features4.1 Tidal current going from low to high level and from high to low level Rive

31、r flow usually goes from high to low elevation while water in the tides-affected estuary is found able to run from high to low at one moment and run from low to high at another moment, which is described in a little more details as follows. Fig.4 shows the level, speed and direction of the flow at a

32、 site in the center of the Bo Sea Bay, where the flow direction is measured clockwise with respect to the north. Fig.5 shows flow level marked on the contour lines and velocity vectors.Fig.4 Flow level, speed and direction near the center of Bo Sea Bay.At nine oclock the site in Bo Sea Bay is at a h

33、igh water (Fig.4) while water level at the Bo Sea Strait is much lower (Fig.5), consequently forming a surface gradient in the eastern direction, much the same as the flow direction. Meanwhile, flow in the Laizhou Bay goes from low to high level.Later on, water flowing out of the Bo Sea Bay graduall

34、y results in the flow level decreasing and current speed increasing while the water level at the Bo Sea Strait is seen rising and the current speed decreasing. Around 12:20, the Bo Sea Bay is at a low water, and the water is continuously flowing east, which means the flow, which goes from low to hig

35、h level, is approaching the maximum. Meanwhile, the water at the Strait is approaching the high water with flow speed close to zero. Later on, the flow level in the Bo Sea Bay is continuously going lower and lower with flow speed turning into a decreasing process, which is going on until 14:20 when

36、the east-going flow in the Bo Sea Bay is approaching to zero and the water at the strait flows westwards from the high level at the strait to the low level in the bay. After 15:20 the flow in the Bo Sea Bay turns into a rising process in water level, going westwards from high to low level.In a word,

37、 the flow in the Bo Sea have the moments when the water flows from high to low and the moments when flows goes from low to high. The processes are the ones when kinetic energy and potential energy are transferred between each other. It means that the water surface slope/gradient is a force to accele

38、rate the flow in a certain period while it is a force to slow down the flow for another period. This is one of the major differences from the unidirectional river. The feature poses more challenging requirements for the techniques and equipments for flow control for the physical model for the Yellow

39、 River Estuary.(a) (b)(c)(d）Fig.5（a）, (b), (c) and (d) Calculated current velocity and water level4.2 Rotary flow featuring the flow in Bo SeaWhen Tidal waves come into the Bo Sea, it is characterized by maximum velocity occurring usually at halfway from high waters and low waters, and the high wate

40、rs occurring usually at current-slack moment (Fig.4). The features indicate the nature of rotary waves in the Bo Sea.The tidal waves rotate clockwise in the Bo Sea bay while it does counterclockwise in the Laizhou Bay. Closer to the shore, the tidal current demonstrates more of to-and fro current th

41、an the rotary current. 5. Applications of numerical modeling 5.1 to define nutshells in controlling the flow in the physical model for the estuary The flow features as mentioned above are, in fact, the nutshells in control the flow in the physical model for the estuary.5.2 to prediction water level

42、for nearshore bathymetric data compiling The elevation (Hb) of any site in the nearshore area bordering the Yellow River Delta is obtained by subtracting the value of the water depth (h) from the value of the water level (Z) (i.e., Hb=Z-h) while Z is assumed the same as that measured at the shore (F

43、ig.6). The easy principle, unfortunately, doesnt lead to satisfactory results, which often shows heavy sedimentation in the deep water, opposite to the truth.Sea bed , Hb Water level Z ele. DatumhFig.6 Relationship of elevation of seabed, water depth, and water levelLets find out the reasons for the

44、 false sedimentation. With the modeling results, we have found the differences between the values of water levels at the two ends of the cross shore profile No.12 (Fig.7) varying between -0.4 m-+0.6 m. In the same way, we have found the water level differences at the two ends of all the 35 profiles

45、(Fig.7) varying between -0.4 m and +0.5 m (Fig.8).In a word, it is necessary to use the hydrodynamic model to give the water levels at any sites when compiling the bathymetrical data for accurate results. Fig.7 35 cross shore profiles in the nearshore around the Yellow River DeltaFig.8 water level d

46、ifferences at the both ends of CS 12Fig.9 Maximum differences of water levels at the two ends of the each cross shore profile5.3: to investigate feasibility of proposals for the estuary trainingHow to train the Yellow River estuarine course has been a hot issue in China so far. Experts made various

47、proposals, which could be cost-efficiently evaluated by numerical modeling. Study on Proposal 1One of the proposals for the training is by extending the course seawards as long as long as possible as to make the best of the velocity increased at the river mouth to carry as much sediment load to the

48、deeper waters offshore as possible. Lets check whether or not it is justifiable by modeling the scenarios where the river mouth extends eastwards and northwards, respectively.Fig.10 shows the differences between the maximum velocity values at the river mouth when it extending eastwards 30 km and 20

49、km. It is found that the river mouth extending can increase the maximum velocity near the river mouth as expected, which, unfortunately, covers quite a small area, unexpectedly. Similar results have been found when the river mouth extends northwards. The results above mean sediment delivered out of

50、the river mouth will not be transported very far, therefore, deposition of coarse sediment fraction can be expected to remain around the river mouth.In addition, considering previous research results to the effect that long extension of the river mouth leads to the rising of the river bed upstream o

51、f the river mouth although there are great differences between the understandings of the effect in terms of the length affected, we, therefore, are confident to make the conclusion that the proposal for training the Yellow River estuarine course by extending seawards far enough so as to deliver more

52、 the sediment load into deep water is not feasible. Fig.10 Differences in maximum current speed values when river mouth extends (note: positive values in the figures means the increasing of maximum velocity values while negative values the decreasing). Study on proposal 2Another proposal for the tra

53、ining by other experts is by increasing the flow rate released out of the river mouth so large as to carry more sediment with it into the farther water. Lets resort to the model to simulate the flow field when the flow out of the river mouth maintains as large as 5000 m3/s with various injection ang

54、les ranging from 0, 45, 90, 135, 180 degrees from the north clockwise, respectively. It is found from the modeling results (Fig.11) that the injected flow rate, can increase the local velocity as expected, around the river mouth, which, however, covers a small area, 40 km×30km, unexpectedly. Th

55、e result isnt a good supporter for the training proposal. Fig.11 Area affected by the Flow released out of the Yellow River Mouth 5.3.3 A practical way out: through vast space for the estuarine course to run for long term Lets consider the facts that the Yellow River mouth always extends seawar

56、ds longer when a larger sediment load coming to the estuary, and that the shore near the river mouth is found under significant erosion when less sediment load coming, say, since the Dikouhe River was abandoned in 1976. With these facts in mind, we could deduce that sediment load is one of the signi

57、ficant factors affecting the estuarine morphology. So how to control the incoming flow and sediment load will be key factor in making strategies for training the estuary.Ideally, a certain magnitude of sediment coming to the estuary, not too much or not too less, can prevent the estuarine channel from withering in channel geometry and flood conveyance, and can lead to less effect of the deltaic shore extension. To realize the proposal, however, will demand one large hydraulic complex, or even more, to regulate water and sediment