influence of cross-shore sediment movement on long-term shoreline change simulation

Download Influence of cross-shore sediment movement on long-term shoreline change simulation

Post on 23-Jan-2016

27 views

Category:

Documents

0 download

Embed Size (px)

DESCRIPTION

Influence of cross-shore sediment movement on long-term shoreline change simulation. by H. Kang, H. Tanaka Dept. of Civil Eng. Tohoku Univ. Japan. Data2. Data3. EOF method. Shoreline evolution : caused by LST caused by CST. Data1. Calibration of sediment transport coefficient. - PowerPoint PPT Presentation

TRANSCRIPT

  • Influence of cross-shore sediment movement on long-term shoreline change simulation

    by H. Kang, H. TanakaDept. of Civil Eng. Tohoku Univ. Japan

  • Numerical simulation of shoreline change by one-line model

    Introduction

    Study area Measured data Empirical Orthogonal Function

    One-line model

    Comparison of calibration K (sediment transport coefficient) Summary Outline of this presentation Measured data including both influence of LST and CST * Longshore Sediment Transport, Cross-shore Sediment Transport

  • Introduction * Longshore Sediment Transport, Cross-shore Sediment Transport Objective of this presentation To calibrate K (Sediment transport coefficient)in one-line model. To compare K based on measured data and separated data by EOF method.

  • Length : about 12km Bounded by Sendai Port and Natori River mouth Study area the jettiesthe breakwaterBreakwaters

  • Breakwaters Nanakita Riverthe jetties at the Natori River mouththe breakwater at Sendai PortSt.13Measured data

  • Breakwaters Nanakita Riverthe jetties at the Natori River mouththe breakwater at Sendai PortSt.8Measured data

  • Length : about 12km Bounded by solid boundaries (Sendai Port & Natori River mouth) Breakwaters Nanakita Riverthe jetties at the Natori River mouththe breakwater at Sendai PortSt.4Measured data

  • E.O.F Empirical Orthogonal Function It assume that shoreline position combines temporal function with spatial function. 1/2EOF method separated data of a complex topography change on the coast into parts of data that have the same characteristic of topography change on the coast as simple data.(1)

  • 2nd E.O.F. component2/2* Longshore Sediment Transport

  • One-line model Governing equation: Shoreline position of on-offshore: The Longshore Sediment Transport Rate: The closure depthOne-line(shoreline) model, beach evolution is represented by the shoreline change, is a numerical prediction model based on the sediment continuity equation and an equation for the longshore sediment transport rate. 1-line modelDefinition sketch for shoreline change calculationq : Cross-shore sediment transport rate

  • Long shore sediment transport rate :wave energy: wave group speed : angle of breaking waves to the local shoreline : sediment transport coefficient(3)b wave breaking condition(CERC equation)* Longshore Sediment Transport

  • Conditions for calculation

    Bathymetry dataIn 1980 from Geographical Survey InstituteInitial shoreline positionAerial photo on Nov. 1996Wave conditionsT0 : 8.55(s), H0 : 0.75(m), : 121.86Wave transformationWave ray methodWave breaking (Goda, 1973 )Sediment transport coefficient (K)from 0.01 to 0.09

  • Data 1: separated data that shoreline change caused by longshore sediment transport, C2e2 ( )Data setCalibration of K (sediment transport coefficient) is carried out using three data set to examine influence of cross-shore sediment transport.

  • Error is calculated in three case to decide value of K.Case 1 : To calculate error between obtained shoreline position by 1-line model and data1 Case 2 : To calculate error between obtained shoreline position by 1-line model and data2 Case 3 : To calculate error between obtained shoreline position by 1-line model and data3 Comparison of calibration K ycal : shoreline position calculated by 1-line modelydata1 : shoreline position based on separated dataydata2 : shoreline position based on measured data ydata3 : shoreline position based on measured data once a yearT: the number of survey times from Nov. 1996 to Aug. 2003N: the number of station, from 1 to 13 K is calibrated based on three data set in order to examine influence of cross-shore sediment movement on calibration of K. Error calculate between calculated shoreline position and measured data(4)

  • Relationship between error and K

  • Summary Case1 : using separated data, the error is smaller in whole area than that of the other cases. Because separated data is shoreline evolution cased by longshore sediment transport.

    Case2 : the optimum value of K is same value as that obtained by separated data because survey is carried out in a relative short-term period. However, the error is bigger than that based on separated data because data2 include influence of shoreline change due to cross-shore sediment transport.

    Case3 : using survey data in once a year, the optimum value of K is bigger than that in case 1 and 2. it includes an error due to cross-shore change.

    According to these results, shoreline evolution due to cross-shore sediment transport has effect on calibration of K value. Therefore, it is important that raw survey data are separated into a part of data caused by longshore sediment transport and cross-shore sediment transport, when value of K is calibrated in one-line model.

  • Nanakita River Characteristic of shoreline change on study area Advance of Shoreline : St. 10, St. 11 and St. 4

  • 1st EOF componentSimultaneous erosion and accretion occur along the coast. rate of change of the first temporal eigenfunctionE.O.F.ErosionAccretion The 1st temporal eigenfunction The 1st spatial eigenfunction

  • (mori and tanaka 1998) Prediction of first temporal eigenfunction continuity of time is low. C1 is predicted in the other term and verified.

  • 2nd E.O.F. component2/2(2) : Wave direction at breaking point.b : breaking pointH : wave heightCg : group celerity : density of seawater : gravitational acceleration 2nd temporal eigenfuncion and Energy flux of longshore direction* Longshore Sediment Transport

  • Beach evolution is classified into two types according to direction; one is cross-shore change occurred in short term and the other is longshore change occurred in long-term. It is difficult to analyzes a complicated evolution of shoreline using measured data, because it is containing both influence of longshore and cross-shore sediment movement.If measured data are separated into shoreline change caused by longshore and cross-shore sediment transport, a shoreline behavior will be clearly analyzed and understood.2/2

    Good morning everyone, my name is Kang and I belong to department of civil engineering Tohoku university in JapanI would like to took about Influence of cross-shore sediment movement on long-term shoreline change simulation. Out line of this presentation Introduction,Took characteristic of study area Appling EOF method, we separate measured data into shoreline evolution caused by LST and caused by CST We expected shoreline change using one-line model. Using three set data, we calibrated sediment transport coefficient and compared these.

    At first, Introduction.Erosion is continually progressing on Sendai Coast caused by sediment is interrupted by coastal structure, sediment supply from river is rapidly reduced and sediment is keep moving northward.End of northern part of study area, middle of study area and End of southern part of study area Survey has been being carried out twice a month since 1996 to examine topography change.It is difficult to analyzes a complicated evolution of shoreline using measured data, because it is containing both influence of LST and CST.The complex topography change is separated into topography change due to LST and CST by EOF method in order that characteristic of topography change can be more clarified and easily understood.

    Object of presentationTo calibrate K (Sediment transport coefficient)in one-line model. To compare K based on measured data and separated data by EOF method. I would like to show study areaIt is located north-east in Japan and length about 12kmStudy area is bounded Sendai port and Natori River mouth.And there is breakwaters in the middle of study area and Nanakita River located about 2km from Sadai Port.Incident wave direction is East South East and South East, so that longshore sediment transport move from south to north.Breakwater and Nanakita River interrupt longshore sediment transport, Accumulation occurs on the southern port of Breakwater and Nanakita River.

    EOF method separated data of a complex topography change on the coast into parts of data that have the same characteristic of topography change on the coast.It assume that shoreline position combines temporal and spatial function.Using correlation matrix, shoreline position is separated into temporal and spatial.In this presentation, we focus on second component. We examined second temporal eigenfunction and Energy flux of longshore direction.

    Despite the assumption of constancy of beach profile shape alongshore, the shoreline change numerical model has proved to be robust in predictions and provides a general solution of the equation governing shoreline change. Because the profile shape is assumed to remain constant, in principle, landward and seaward movement of any contour could be used in the modeling to represent beach position change.

    , .

    because data2 is obtained by survey in relatively shore-term. data 2 is including shoreline change due to cross-shore sediment transport Caused data3 is including shoreline change due to cross-shore sediment transportWe calculated rate of shoreline change every station to examine shoreline evolution in long-term change.And this figure shows rate of shoreline change along the coast.We can find that shoreline advance offshore-ward on station 10, 11 and 4.Incident wave comes from east-south-east and south-ears in study area so that longshore sediment transport moves northward from right hand side to left hand side.And longshore sediment transport is interrupt by breakwater and nanakita riv

Recommended

View more >