The effect of climate and anthropogenic change on the spatial variability of turbidity maxima in the southwest delta of Bangladesh. by MORSHEDA BEGUM Erasmus Mundus Joint Master in Water and Coastal Management. WACOMA 9/28/2018 Research Supervisor Dr Alfredo Iquierdo González Research Co-Supervisor Dr. Hans Middelkoop Mentors: Mohammed Feroz Islam The author has been financially supported by Erasmus Mundus This Master Thesis was carried out in the Department of Applied Physics, Faculty of Marine and Environmental Sciences University of Cadiz, as part of the UNESCO/UNITWIN/WiCoP activities in Cádiz, Spain, and in Utrecht University. The work was part of the project “Living polders: dynamic polder management for sustainable livelihoods, applied to Bangladesh” financed by The Netherlands Organisation for Scientific Research (NOW) (W 07.69.201). The author was supported by an ERASMUS MUNDUS scholarship. STATEMENT I hear by declare that this work has been carried out by me and the thesis has been composed by me and has not been submitted for any other degree or professional qualification. This work is presented to obtain a masters’ degree in Water and Coastal Management (WACOMA). ----------------------------- MORSHEDA BEGUM D. Alfredo Izquierdo González, Profesor del Departamento de Fizică Aplicată de la Universidad de Cádiz y D. Hans Middelkoop, Profesor del Departamento de Departamento de Geografía Física de la Universidad de Utrecht, como sus directores HACEN CONSTAR: Que esta Memoria, titulada “(El efecto del cambio climático y antropogénico sobre la variabilidad espacial de los máximos de turbidez en el delta sudoeste de Bangladesh)”, presentada por D. Morsheda Begum, resume su trabajo de Tesis de Master y, considerando que reúne todos los requisitos legales, autorizan su presentación y defensa para optar al grado de Master Erasmus Mundus in Water and Coastal Management (WACOMA). Cádiz, (10/11/2018) ________________________________ ________________________________ Dr. Alfredo Izquierdo González Dr. Hans Middelkoop I dedicate this master thesis to …………………… ACKNOWLEDGEMENTS I thank my supervisor Prof Dr. Alfredo Izquierdo González, from the department of Applied Physics, University of Cadiz and my co-supervisor Prof. Dr. Hans Middelkoop, from the department of Physical Geography, University of Utrecht, for their valuable support and advice. ABSTRACT Outline of the thesis The southwest area of Bangladesh is a tide dominated delta and has a complex dynamics between sediment, season-dependent river discharge and tide. In this study, we apply 1D hydrodynamic model (MIKE 11) to investigate the fluvial dynamics with allowance for tidal influence in this region. An advection-dispersion model for cohesive sediment was applied and used to study the changes in suspended sediment concentration and sediment load. The results show the influence of seasonality and and interannual variability in the tidal range spatial pattern in the area of study. Tidal range shows maximum values in the western part (Sibsa and Arpangasia-Kobadak river) irrespective of seasons. During Monsoon, the area of tidal influence reduces shifting its boundary closer to sea. In our study area the sediment load is higher in the eastern part than the western part, as it is under the influence of the main sediment carrying channel, the Meghna river (lower). Regarding the sediment load along Gorai-Madhumati-Kocha-Baleswar river system, it is constant in Gorai river and then it reduces closer to the sea. The Arial khan and Meghna spills delivers sediment from the Meghna (lower) to the eastern part. We have also performed simulations to assess the impact of the climate change on the river hydrodynamics and the tidal influence in the delta system for years 2050 and 2080. Model results show that the expected changes fall within the natural interannual variability assessed from dry, flood and normal years. RESUMEN El area suroeste de Bangladesh es un estuario mareal que presenta unas interacciones muy complejas entre la dinámica sedimentaria, la fuertemente estacional descarga fluvial y la marea. En este estudio se aplica un modelo hidrodinámico unidimensional (MIKE 11) para investigar la dinámica fluvial teniendo en cuenta la influencia de la dinámica mareal en esta región. Además se aplica un modelo de advección-dispersión para sedimentos cohesivos para estudiar los cambios en la concentración de los sedimentos en suspensión y en la carga sedimentaria. Los resultados muestran la influencia de la estacionalidad y la variabilidad interanual en la distribución espacial del rango de marea en la región de estudio. El rango de marea presenta valores máximos en la zona occidental del delta (ríos Sibsa y Arpangasia-Kobadak) independientemente de la estación del año. Durante el monzón el área del delta sometido a la influencia de la marea se reduce, desplazando su límite hacia la costa. La carga sedimentaria es mayor en la zona oriental del delta que en la occidental, puesto que recibe los aportes del principal transportador de sedimentos, el río Meghna. La carga sedimentaria a lo largo del sistema fluvial Gorai-Madhumati-Kocha-Baleswar permanece constante a lo largo del río Gorai, y luego gradualmente se reduce hasta llegar al mar. Los ríos he Arial Khan y Meghna vierten sedimentos procedentes del Meghna a la parte oriental del delta. También se han realizado simulaciones para evaluar el impacto del cambio climático en la dinámica fluvial y la influencia de marea en el sistema deltaico en los años 2050 y 2080. Los resultados del modelo sugieren que los cambios esperados están dentro de la variabilidad interanual estimada a partir de años lluviosos, secos y el año promedio. Table of Contents CHAPTER 1: Introduction ..................................................................................................... 12 1.1 Background .................................................................................................................... 12 1.2 Climate ........................................................................................................................... 13 1.3 Study Area ...................................................................................................................... 14 1.4 Ecosystem of the Study Area ......................................................................................... 16 1.5 State of The Art .............................................................................................................. 16 1.6 Problem Statement ......................................................................................................... 16 1.7 Research Objective ......................................................................................................... 16 CHAPTER 2: Methodology .................................................................................................... 17 2.1 Flow Chart ...................................................................................................................... 17 2.2 Understanding the Nature of the Problem ...................................................................... 17 2.3 Data Collection ............................................................................................................... 17 2.4 Data Analysis ................................................................................................................. 17 2.5 Development of Cohesive Sediment Transport Model .................................................. 17 2.6 Development of Scenarios ............................................................................................. 17 2.7 Analyze and Compare the Result for Different Scenarios ............................................. 18 2.8 Investigate the Movement of Turbidity Maxima for Major South-western Rivers ....... 18 CHAPTER 3: Data Collection and Analysis .......................................................................... 19 3.1 Data Collection ............................................................................................................... 19 3.2 River Network ................................................................................................................ 19 3.3 The Geometry Data ........................................................................................................ 20 3.4 Water Level .................................................................................................................... 20 3.5 Discharge ........................................................................................................................ 24 3.6 Seasonal Variation.......................................................................................................... 24 3.7 Tidal Pattern ................................................................................................................... 25 3.1 Settling velocity.............................................................................................................. 25 CHAPTER 4: Development of Cohesive Sediment Transport Model ................................... 27 4.1 Hydrodynamic Model .................................................................................................... 27 4.1.1 Calibration............................................................................................................... 29 4.1.2 Validation ................................................................................................................ 32 4.1.3 Error Calculation ....................................................................................................