Modified Saint-Venant equations for flow simulation in tidal rivers

Flow in tidal rivers periodically propagates upstream or downstream under tidal influence. Hydrodynamic models based on the Saint-Venant equations （the SVN model） are extensively used to model tidal rivers. A force-corrected term expressed as the combination of flow velocity and the change rate of the tidal fevel was developed to represent tidal effects in the SVN model. A momentum equation incorporating with the corrected term was derived based on Newton＇s second law. By combing the modified momentum equation with the continuity equation, an improved SVN model for tidal rivers （the ISVN model） was constructed. The simulation of a tidal reach of the Qiantang River shows that the ISVN model performs better than the SVN model. It indicates that the corrected force derived for tidal effects is reasonable; the ISVN model provides an appropriate enhancement of the SVN model for flow simulation of tidal rivers.

DEVELOPMENT OF COUPLED 1D-2D MATHEMATICAL MODELS FOR TIDAL RIVERS

Some coupled 1D-2D hydrodynamic and water quality models depicting tidalwater bodies with complex topography were presented. For the coupled models, finite element methodwas used to solve the governing equations so as to study tidal rivers with complex topography. Sincethe 1D and 2D models were coupled, the principle of model coupling was proposed to accountappropriately for the factors of water level, flow and pollutant flux and the related dynamicalbehavior was simulated. Specifically the models were used to probe quantitative pollutioncontribution of receiving water from neighboring Jiangsu and Zhejiang Provinces to the pollution inthe Huangpu River passing through Shanghai City, Numerical examples indicated that the developedcoupled 1D-2D models are applicable in tidal river network region of Shanghai.

EXPERIMENTAL INVESTIGATIONS ON LONGITUDINAL DISPERSION CHARACTERISTICS OF TIDAL RIVERS

The longitudinal dispersion characteristics of tidal rivers areexperimentally investigated in a water channel. The longitudinal dispersion features and influentialfactors on pollutant in various stages of a tidal period in natural rivers are studied; the valueranges and variation trends of the longitudinal dispersion coefficient are obtained by means ofconcentration measurement. The results can provide important parameters for establishing the waterquality mathematical models in tidal rivers.

Hydrodynamic Characteristics and Sediment Transport of A Tidal River Under Influence of Wading Engineering Groups

By taking the Yong River for example in this paper, based on the multiple measured data during 1957 to 2009, the change process of runoff, tide feature, tidal wave, tidal influx and sediment transport are analyzed. Then a mathematical model is used to reveal the influence mechanism on hydrodynamic characteristics and sediment transport of the wading engineering groups such as a tide gate, a breakwater, reservoirs, bridges and wharves, which were built in different periods. The results showed the hydrodynamic characteristics and sediment transport of the Yong River changed obviously due to the wading engineering groups. The tide gate induced deformation of the tidal wave, obvious reduction of the tidal influx and weakness of the tidal dynamic, decrease of the sediment yield of flood and ebb tide and channel deposition. The breakwater blocked estuarine entrances, resulting in the change of the tidal current and the reduction of the tidal influx in the estuarine area. The large-scale reservoirs gradually made the decrease of the Yong River runoff. The bridge and wharf groups took up cross-section areas, the cumulative affection of which caused the increase of tidal level in the tidal river.

A combined numerical tidal model for the Hangzhou Bay and Qiantang River

-In order to avoid prescribing open boundary condition on the upstream side of the Hangzhou Bay, in numerical simulation of the tides and residual currents of the Bay, a 1-D model for the Qiantang River is connected to the 2-D model for the Hangzhou Bay. The harmonic constants of diurnal constituent [ (K1+O1)/2],semidiurnal constituent (M2) and shallow water constituent (M4) are obtained. The results produced by the combined model are in better agreement with the observed ones than those produced solely by the original 2-D model. The combined model gives much more reliable results for tide-induced residual water level and current.

Engineering application of submerged water jets for sediment removal in a tidal riverbed

Sediment deposition problems have attracted the interest of engineers and researchers.Several experimental studies have been conducted on scour depth using turbulent jets.However,field observation and monitoring have rarely been reported.This study aimed to eliminate sediments on a tidal riverbed using a prototype device,which consisted of a set of submerged vertical water nozzles and submerged horizontal air nozzles.The effectiveness of the water jet in sediment removal during spring and neap tides was evaluated.The quantitative relationships of dimen-sionless parameters,such as(1)the relative sediment scour volume versus the number of flows from the jet exit,(2)the relative sediment scour volume versus the relative scour depth,and(3)the relative scour size versus the relative jet intensity,were analyzed.The results showed that the freshwater flowing to the sea affected the sediment scour volume during the falling cycle of spring tides.In contrast,the rising cycle of spring tides retarded the freshwater flow,resulting in a decrease in the sediment scour volume.A steep water surface slope accelerated the river flow and further influenced the cross-flow current around the study area.As a result,a highly diffusive turbulent flow was produced,causing sus-pended sediments to be rapidly removed from the scour hole center.An increase in the number of flows from the jets led to intensified diffusion of turbulent energy into the flow.The rapidly varying water depth caused jet energy to be dissipated before approaching the riverbed,and it significantly affected the scour process during the spring-tide period.The proposed equations can be used to estimate the scour volume,scour size,and re-suspended sediments in tidal rivers within defined ranges of parameters.

Application of equivalent resistance to simplification of Sutong Bridge piers in tidal river section modeling

This paper describes some details and procedural steps in the equivalent resistance （E-R） method for simplifying the pier group of the Sutong Bridge, which is located on the tidal reach of the lower Yangtze River, in Jiangsu Province. Using a two-dimensional tidal current numerical model, three different models were established： the non-bridge pier model, original bridge pier model, and simplified bridge pier model. The difference in hydrodynamic parameters, including water level, velocity, and diversion ratio, as well as time efficiency between these three models is discussed in detail. The results show that simplifying the pier group using the E-R method influences the water level and velocity near the piers, but has no influence on the diversion ratio of each cross-section of the Xuliujing reach located in the lower Yangtze River. Furthermore, the simplified bridge pier model takes half the calculation time that the original bridge pier model needs. Thus, it is concluded that the E-R method can be use to simplify bridge piers in tidal river section modeling reasonably and efficiently.

Sedimentary facies of the Silurian tide-dominated paleo-estuary of the Tazhong area in the Tarim Basin

As the relative sea-level rose, a paleo-estuary was formed by the marine inundation of the braided river incised valley during the period of the lower sub-member of the upper member of the Kalpingtage. formation of the Silurian in the Tarim Basin, west China. Sandstone-mudstone rhythmite, tidal structures and bimodal cross-bedding are common in these deposits, indicating that tides played a significant role in generating the sedimentary structures and the estuary type was tide-dominated. Five depositional facies were grouped： tidal river, sandy and muddy subtidal flat, tidal flat, tidal bar, tidal channel on the basis of lithology, electric properties, rhythmicity, sedimentary structure, fossil and the contact relationship. The sediment distribution showing first fining seaward and subsequent coarsening seaward from head to mouth, implies the two sediment sources in the paleo-estuary. The paleo-estuary of the Tarim Basin is very different from other representative estuaries. The most important distinction is that there are two adjacent estuaries joined by tidal flat onshore and by sandy and muddy subtidal flat in the sea at the same time, while the others only architecture model for the tide-dominated estuary. have one, So the Tazhong paleo-estuary shows a good

Seasonal dynamics of meiofaunal distribution in the Dagu River Estuary, Jiaozhou Bay, China

Sediment samples were collected in the intertidal zone of the Dagu River Estuary, Jiaozhou Bay, China in April,July and October 2010 and February 2011 for examining seasonal dynamics of meiofaunal distribution and their relationship with environmental variables. A total of ten meiofaunal taxa were identified, including free-living marine nematodes, benthic copepods, polychaetes, oligochaetes, bivalves, ostracods, cnidarians, turbellarians,tardigrades and other animals. Free-living marine nematodes were the most dominant group in both abundance and biomass. The abundances of marine nematodes were higher in winter and spring than those in summer and autumn. Most of the meiofauna distributed in the 0–2 cm sediment layer. The abundance of meiofauna in hightidal zone was lower than those in low-tidal and mid-tidal zones. Results of correlation analysis showed that Chlorophyll a was the most important factor to influence the seasonal dynamics of the abundance, biomass of meiofauna and abundances of nematodes and copepods. CLUSTER analysis divided the meiofaunal assemblages into three groups and BIOENV results indicated that salinity, concentration of organic matter, sediment sorting coefficient and sediment median diameter were the main environmental factors influencing the meiofaunal assemblages.

Modelling of water quality of Minjiang estuary

In order to establish economic development region at Mawei districtwhich is nearby downstream of Minjiang river and to answer the question of impact of economic development on water quality of Minjiang estuary, the analyses of hydrologic and hydraulic characteristics of Mawei reach of Minjiang tidal river, a two-dimensional mathematical model has been established and simulation of water quality was studied. The results show that the flushing time of a conservative pollutant during dry and raining period are 12 and 7 days respectively from Mawei to Minjiang mouth, the decay rate constants of BOD and NH3-N are 0.1 to 0.4 and 0.18 to 0.45 d-1 respectively. The capacity of dilution and assimilation for pollutants is larger.

RESEARCH ON HYDRODYNAMIC AND WATER QUALITY MODEL FOR TIDAL RIVER NETWORKS

Hydrodynamic and water quality model for tidal river network is set up withMIKE11 modeling system, according to the features of tidal river networks in plain area. The modelwas calibrated using the hydrological and water quality data of 1999, and the results show that thesimulated values agree with the measured data very well. This model is used to numerically analyzethe effects of low flow augmentation on hydrodynamic and water quality conditions of Suzhou Creek.The simulation results show that the flow augmentation can increase net discharge of Suzhou Creekand improve its ability of re-aeration; and its concentration of dissolved oxygen in the rivernetworks can also increase correspondingly.

MATHEMATICAL MODEL FOR 2-D TIDAL FLOW AND WATER QUALITY WITH ORTHOGONAL CURVILINEAR COORDINATES

This paper presents a numerical method for simulating the 2-D tidal flow andwater quality with the orthogonal curvilinear coordinates. In order to overcome the computationaldifficulties in natural rivers, such as the complicated boundary figures, the great disparitybetween length and width of computational domain, etc. , orthogonal boundary-filled grid was used.The irregular domain in physical plane was transformed into a rectangular domain in a transformedplane, and the depth-averaged momentum equations and mass equation were given and discretized basedon the alternating direction implicit finite difference scheme in curvilinear coordinates. Theapplication of the presented method was illustrated by an example of analyzing the Yangtze River inthe vicinity of Nanjing city. A fair agreement between the measured data and computed resultsdemonstrates the validity of the developed method.

NUMERICAL SIMULATION OF 2-D TIDAL FLOW AND WATER QUALITY UNDER THE CURVILINEAR COORDINATES

This paper presents a numerical method to simulate the 2-D tidal flow and water quality under the curvilinear coordinates. In order to overcome the computational difficulties in natural rivers, such as the complicated boundary figures, the great disparity between length and width of computational domain, etc. , boundary-fitted grid is used, the irregular domain in physical plane is transformed into a rectangular domain in transformed plane, and the depth-averaged momentum equations and mass equation are rewritten and discretized based on the finite volume techniques in curvilinear coordinates. Practical application of the method is illustrated by an example for the Dachangzhen Section of the Yangtze River. A fair agreement between the values measured and computed demonstrates the validity of the method developed.

AN OPTIMIZATION METHOD OF AQUATIC ENVIRONMENTAL CAPACITY FOR TIDAL RIVER NETWORK

By using the high-efficiency of four-stage calculation method named ＂channel-junction-channel＂ and considering the influence of temporal and spatial variation of aquatic environmental capacity, an optimization method of aquatic environmental capacity for tidal river network was worked out. The method not only reflects characteristics of unsteady flow with variable directions, but also indicates that aquatic environmental capacity is influenced by boundary condition and water quality standard, etc. It has been applied to the regional program of Pudong area in Shanghai, and the computed results agree well with the practical data.

INVERSE PROBLEM METHOD FOR WATER ENVIRONMENT TOTAL CAPACITY CONTROL OF A TIDAL RIVER

In this paper, an improved method for water environment total capacity control of tidal rivers was presented. The maximal capacity of point pollution sources for the Huangpu River was computed by this method, and the result was compared with the practically observed data. The numerical result shows that the method is effective and efficient.

THREE-DIMENSIONAL NUMERICAL MODEL FOR WINDING TIDAL RIVER WITH BRANCHES

Natural rivers are usually winding with branches and shoals, which are difficult to be simulated with rectangular grids. A 3-D current numerical model was established based on the orthogonal curvilinear coordinate system and vertical o coordinate system. The equations were discretisized using a semi-implicit scheme. The ＂predictor＂ and ＂corrector＂ steps were applied for the horizontal momentum equations to meet the basic requirement that the depth-integrated currents obtained from the equations for 2-D and 3-D modes have identical values. And a modification of traditional method of dry/wet discriminance was proposed to determine accurately the boundary and ensure the continuity of variable boundary in the simulation. This model was verified with the data measured in a winding tidal river with branches in April, 2004. The simulated data of water levels and velocities agree well with the measured ones, and the computed results reveal well the practical flow characteristics, including the vertical secondary flow in a winding reach.

Numerical Analysis of the Mixing Zone for a Vertical Discharge into a Tidal River

This paper analyzes the mixing zone of a vertical discharge of sewage into a natural tidal river with strong tidal currents. The paper presents a numerical model, which combines 1 D and 2 D models to compute the mixing zone for the Sibao Segment of the Qiantang River. The simple 1 D model was used to model the flow for the entire river using field data as the boundary conditions. The complete depth averaged turbulence model was used for the 2 D computation. The calculated results agree well with the field observations. The analysis provides a practical method for the computation of mixing zones in tidal rivers.

AN ANALYSIS OF THE OXYGEN BALANCE IN AN ANOXIC TIDAL RIVER

A time-dependent, mixed-segment, slack tide oxygen balance model has been developed for the study of a heavily polluted tidal river discharging to a coastal bay.Deoxygenation and reaeration, BOD settling, benthal demand, freshwater flushing, and tidal mixing are the key processes modelled. Significant features of the model include the oxygen balance formulation under anoxic conditions and the tidal exchange condition at the seaward boundary. The simple model enables a clear and consistent interpretation of a set of dry season water quality data and an assessment of the assimilative capacity of the river is also made.

NUMERICAL MODELLING OF FLOW FIELD IN A TIDAL RIVER AND THE NEAR FIELD OF INTAKE FOR A NUCLEAR POWER PLANT

This Paper concerns with the numerical modelling of flow field in a tidal river and in the vicinity of intake of a nuclear power plant. The hybrid method of fractional steps presented in [1] was adopted in this modelling. In order to simulate the local flow field nearby the water intake meticulously, the technique of the match of the coarse and fine grids was used. The numerical results are in good agreement with the in-situ measurements of the main current. The detailed data of local flow field nearby the intake provides the assessment of the sediment transport characteristics in the vicinity of intake of the nuclear power plant.