COASTAL INUNDATION ALONG THE WEST COAST OF INDIA

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INTERACTION OF STORM TIDES WITH WIND WAVES:

COASTAL INUNDATION ALONG THE WEST COAST OF INDIA

JISMY POULOSE

CENTRE FOR ATMOSPHERIC SCIENCES INDIAN INSTITUTE OF TECHNOLOGY DELHI

MAY 2019

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©Indian Institute of Technology Delhi (IITD), New Delhi, 2019

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INTERACTION OF STORM TIDES WITH WIND WAVES:

COASTAL INUNDATION ALONG THE WEST COAST OF INDIA

by

JISMY POULOSE

Centre for Atmospheric Sciences

Submitted

in fulfilment of the requirements of the degree of DOCTOR OF PHILOSOPHY

to the

INDIAN INSTITUTE OF TECHNOLOGY DELHI

MAY 2019

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Dedicated to Appachan and Ammachi….

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Certificate

This is to certify that the thesis entitled "Interaction of storm tides with wind waves: coastal inundation along the west coast of India" being submitted by Ms. Jismy Poulose to the Indian Institute of Technology Delhi for the award of the degree of DOCTOR OF PHILOSOPHY is a record of original bonafide research carried out by her. Ms. Jismy has worked under my guidance and supervision and has fulfilled the requirements for the submission of this thesis.

The results contained in this thesis have not been submitted in part or full to any other University or Institute for the award of any degree or diploma.

(Dr. A. D. Rao) Professor,

Centre for Atmospheric Sciences

Indian Institute of Technology Delhi

New Delhi-110016, INDIA

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Acknowledgements

I would like to express my sincere gratitude to my guide, Prof. A. D. Rao, for his meticulous guidance, constructive criticism, invaluable suggestions and moral support throughout the tenure of the research work. He has been a continuous source of inspiration for me because of his dedication and a progressive outlook towards science. His personal attention and overall direction of this research work have been invaluable. Without his help, it would have been difficult for me to complete this venture successfully. Besides, I would like to thank Prof. S. K. Dube, who made my research life memorable in IIT. It was really a great experience to work with him.

I would like to thank Prof. Manju Mohan, Head, Centre for Atmospheric Sciences and all faculty members of the Centre for their support throughout the course of the research. I would like to thank Indian Institute of Technology, IIT Delhi, for the infrastructure and HPC facility as computational resource.

I would like to thank many of my friends who kept my life cheerful in IIT. The time I spent with my friends Rajeev, Sathyaseelan, DileepKunjai, Ragi, Vishnu, Malavika, Agnes, Pooja etc in IIT was always refreshing which helped to keep energy. I would like to thank my ocean lab mates for their support and help to carry out my research work. I also would like to thank NCMRWF friends Rajasree, Bushair and Karuna Sagar for their help in writing thesis.

I would like to acknowledge my brothers more like my friends, Jinto and Jis, who was always my well-wishers and always proud of their little sister. I would like to acknowledge Seemanth, my friend, now my husband, who always supported and encouraged me throughout my research career. He tolerated me in all my mood. It

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would have been difficult for me to complete my PhD without him. I can’t finish this without acknowledging Appachan and Ammachi, my father and mother, who always wished my success. My mother, whose unconditional love and kindness kept me contented throughout my career. My father, who have only primary education, taught me the value of education. He always tells me education is above to everything, rest will follow you. He made me an independent woman and sacrificed to pursue my education.

Jismy Poulose

New Delhi

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Abstract

The present thesis investigates non-linear interaction of storm surges, tides and wind waves and associated coastal inundation along the west coast of India. Storm surge is one of the most devastating components of a tropical cyclone, especially on the densely populated low-lying coast of India. The impact of tides and wind waves modifies the surges and the resultant water level is named as total water elevation (TWE). A state-of-art model, ADCIRC in a standalone mode and ADCIRC+SWAN in a coupled mode are used for the study. The role and dependence of continental shelf width and coastline geometry on the non-linear interaction mechanism among storm surges, tides, and wind-waves are analyzed. In this study, 13 idealized cyclone tracks are considered, separated by about 100 km each, which made landfall perpendicular to the coast. Simulations are performed for all these tracks by using idealized, as well as actual bathymetry of the west coast of India. The analysis shows that the surge gets amplified by about 10-12 cm for every 10 km increase in the shelf width from south to north. During different phases of the tide, surge-wave interaction modifies the water elevation and its occurrence as the tidal range significantly increases towards the north.

The maximum interaction of tides on surge-wave is observed at a low-tide, whilst it is minimal during a flood-tide. Non-linearity is computed for each track and tidal phase to estimate the modification in TWE during surge-tide-wave interaction. In general, the non- linear interaction is found to be 15-20% for any cyclone track or tidal phase. The study also highlights the effect of wind-wave on the total water elevation, which is incremental up to the shelf width of 100-120 km, beyond that the effect becomes marginal. Experiments related to the effect of local coastline shape and shallow bathymetry suggest that the coastal curvature and very shallow depths less than 5 m significantly contribute towards surge, tide and wave interaction.

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The number of extreme severe cyclonic events is increasing in the Arabian Sea in response to climate change. Impact of future climate change on tropical cyclones is studied in terms of Extreme Water Elevations (EWE) and associated coastal inundation for Gujarat and Maharashtra. Regions from Rann of Kutch to Gulf of Khambhat and the northern part of Maharashtra have broad low-lying topography and shallow near-shore bathymetry. In addition, the presence of high tidal range (11-12 m) inside the gulf region also enhances the EWE and associated coastal vulnerability. Coastal flooding may alter the shorelines and its impact can be diverse because the coastal flooding is tightly coupled to the morphological development of these coastal systems. Hence, a potential storm surge flooding maps for Gujarat and north Maharashtra coast are generated using climate change projections on the tropical cyclones. The inundation due to EWEs is computed using most probable synthetic cyclone tracks having a uniform pressure-drop of 66 hPa, which are generated based on historical cyclone tracks. Three different climate change scenarios are considered, which are No-climate change, moderate scenario (7% increases in wind speed) and extreme scenario (11% increases in wind speed). Highest EWEs ranging from 10-11 m are computed in the gulfs of Khambhat and Kutch and also along the coast of Navi Mumbai from these scenarios.

The lowest EWE of 4.5 m is computed along the coast from Porbandar to Diu from all scenarios. The maximum extent of inundation is noted in Rann of Kutch and adjoining areas of Gulf of Khambhat and Mumbai. The simulations show that the impact of climate change scenarios on the extent of inundation is comparatively less for the entire study region.

However, a noticeable increase of 5 m in the height of inundation is simulated near the Mumbai coast and gulfs of Kutch and Khambhat. The analysis concludes that the most vulnerable regions to EWE and cyclone induced inundation are Rann of Kutch and adjoining areas of the Gulf of Khambhat and Mumbai.

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A 3D model allows a more accurate representation of physics by including different boundary conditions. The 3D mode equations are important for modelling the stratified and wind-driven circulation in a semi-enclosed or enclosed region, in which the bottom and surface boundary layers encompass a significant part of the water column, or if the circulation is affected by the wave and current interaction. In such cases, it is required to solve the equations for the vertically varying profile of horizontal velocity. In the regions like gulfs of Khambhat and Kutch along the west coast of India, which represents the most complicated shallow coastal waters, very large amplitude of tides are observed resulting from strong tidal currents. Thus, a significant vertical current structure also could be evolved during this process. Hence, an analysis is made to compare 2D and 3D ADCIRC model simulations of tides, surges and its interactions, particularly in the gulf regions. The 3D model simulated the tides using various combination of vertical parameters, viz., bottom drag coefficient, eddy viscosity and bottom and surface roughness lengths. It is observed from the simulations that the 3D model results are sensitive to the vertical parameters. The smaller values of bottom drag coefficient, eddy viscosity, and bottom roughness length produce higher tides, whilst, large values of surface roughness length generate higher tides in the gulf regions. The analysis reveals that steep slope in the strong vertical velocity from bottom to surface modifies the bottom stress and modulate tides in the gulf regions. The vertical velocity is one order less and its slope is gentle along the straight-line coasts. The tides are better predicted with 3D in the Gulf of Khambhat and the RMSE at Bhavnagar are 0.05. Both the models have reproduced similar tidal heights along the straight-line coasts. It concludes that the 3D model computations are inevitable inside the gulf regions, whilst, the 2D model could be able to simulate tides accurately along the straight-line coasts. The simulations of surge-tide-wave interaction for the gulf regions emphasize that the TWE during the interaction is varied significantly with the 3D model in comparison to 2D.

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सारांश

वर्तमान थीसिसस भारर्त के पश्चि मी र्तट के साथ र्तूफानी लहरों, ज्वार और हवा की लहरों और संबद्ध र्तटीय बाढ़ की गैर-रैखि'क बार्तचीर्त की जांच करर्ती है। र्तूफान वृश्चिद्ध उष्णकटिटबंधीय चक्रवार्त के सबसे

टिवनाशकारी घटकों में से एक है, टिवशेष रूप से भारर्त के घनी आबादी वाले टिनचले र्तट पर। ज्वार और हवा

की लहरों का प्रभाव वृश्चिद्ध को संशोश्चिधर्त करर्ता है और परिरणामी जल स्र्तर को कुल जल उन्नयन (TWE) TWE) ) का

नाम टिदया गया है। एक अत्याधुटिनक मॉडल, एक स्टैंडअलोन मोड में ADCIRC और एक युखिNमर्त मोड में

ADCIRC + SWAN का उपयोग अध्ययन के खिलए टिकया जार्ता है। र्तूफानी लहरों, ज्वार, और हवा-लहरों के

बीच गैर-रे'ीय संपक र्तंत्र पर महाद्वीपीय शेल्फ चौड़ाई और र्तटीय रे'ा ज्याटिमश्चिर्त की भूटिमका और टिनभरर्ता

का टिवश्लेषण टिकया जार्ता है। इस अध्ययन में, 13 आदर्शिशर्त चक्रवार्त पटरिरयों को माना जार्ता है, जो लगभग 100 टिकमी अलग होर्ते हैं, सिजन्हें र्तट पर लंबवर्त बनाया जार्ता है। इन सभी पटरिरयों के खिलए आदश के साथ- साथ भारर्त के पश्चि मी र्तट के वास्र्तटिवक स्नानागार का अनुकरण टिकया जार्ता है। टिवश्लेषण से पर्ता चलर्ता है

टिक वृश्चिद्ध दश्चि`ण से उत्तर र्तक शेल्फ की चौड़ाई में प्रत्येक 10 टिकमी की वृश्चिद्ध के खिलए लगभग 10-12 सेमी

बढ़ जार्ती है। ज्वार के टिवभिभन्न चरणों के दौरान, सज-वेव इंटरैक्शन पानी की ऊंचाई और इसकी घटना को

संशोश्चिधर्त करर्ता है क्योंटिक ज्वार की सीमा उत्तर की ओर काफी बढ़ जार्ती है। सज -वेव पर ज्वार की

अश्चिधकर्तम सहभाटिगर्ता कम-ज्वार पर दे'ी जार्ती है, जबटिक बाढ़-ज्वार के दौरान यह न्यूनर्तम होर्ती है। गैर- रैखि'कर्ता की गणना प्रत्येक ट्रैक और ज्वारीय चरण के खिलए की जार्ती है, जो सज-टाइड-वेव इंटरैक्शन के

दौरान TWE) में संशोधन का अनुमान लगार्ता है। सामान्य र्तौर पर, टिकसी भी चक्रवार्त ट्रैक या ज्वार के चरण के खिलए गैर-रैखि'क बार्तचीर्त 15-20% र्तक पाई जार्ती है। अध्ययन में कुल जल ऊंचाई पर हवा-लहर के

प्रभाव पर भी प्रकाश डाला गया है, जो टिक 100-120 टिकमी की शेल्फ चौड़ाई र्तक वृश्चिद्धशील है, इसके

अलावा यह प्रभाव मामूली हो जार्ता है। स्थानीय र्तटरे'ा आकार और उथले स्नानागार के प्रभाव से संबंश्चिधर्त प्रयोगों से पर्ता चलर्ता है टिक र्तटीय वक्रर्ता और बहुर्त कम उथली गहराई 5 मीटर से कम की वृश्चिद्ध, ज्वार और लहर की बार्तचीर्त में योगदान करर्ती है।

जलवायु परिरवर्तन की प्रश्चिर्तटिक्रया में अरब सागर में अत्यश्चिधक गंभीर चक्रवार्ती घटनाओं की संख्या

बढ़ रही है। उष्णकटिटबंधीय चक्रवार्तों पर भटिवष्य के जलवायु परिरवर्तन के प्रभाव का अध्ययन एक्सट्रीम वाटर एलीवेशन (TWE) ईडब्ल्यूई) और गुजरार्त और महाराष्ट्र के खिलए र्तटीय र्तटीय बाढ़ के संदभ में टिकया जार्ता है। कच्छ के रण से लेकर 'ंभार्त की 'ाड़ी र्तक और महाराष्ट्र के उत्तरी भाग में व्यापक टिनम्न स्थलाकृश्चिर्त और उथले

र्तट के टिनकट स्नानागार हैं। इसके अलावा, 'ाड़ी `ेत्र के अंदर उच्च ज्वारीय रेंज (TWE) 11-12 मीटर) की

उपस्थिस्थश्चिर्त भी ईडब्ल्यूई और संबंश्चिधर्त र्तटीय भेद्यर्ता को बढ़ार्ती है। र्तटीय बाढ़ के कारण र्तटरे'ा बदल सकर्ती

है और इसका प्रभाव टिवटिवध हो सकर्ता है क्योंटिक र्तटीय बाढ़ इन र्तटीय प्रणाखिलयों के रूपात्मक टिवकास के

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खिलए कसकर युखिNमर्त है। इसखिलए, उष्णकटिटबंधीय चक्रवार्तों पर जलवायु परिरवर्तन के अनुमानों का उपयोग करके गुजरार्त और उत्तरी महाराष्ट्र र्तट के खिलए संभाटिवर्त र्तूफान से बाढ़ के नक्शे उत्पन्न होर्ते हैं। ईडब्ल्यूई के

कारण होने वाली बाढ़ की गणना सबसे संभाटिवर्त सिंसथेटिटक चक्रवार्त पटरिरयों का उपयोग करके की जार्ती है, सिजसमें 66 hPa की एक समान दबाव-बूंद होर्ती है, जो ऐश्चिर्तहासिसक चक्रवार्त पटरिरयों के आधार पर उत्पन्न होर्ती है। र्तीन अलग-अलग जलवायु परिरवर्तन परिरदृश्यों पर टिवचार टिकया जार्ता है, जो नो-क्लाइमेट चेंज हैं, मध्यम परिरदृश्य (TWE) हवा की गश्चिर्त में 7% वृश्चिद्ध) और चरम परिरदृश्य (TWE) हवा की गश्चिर्त में 11% वृश्चिद्ध) हैं। 10-11 मीटर की ऊंचाई वाले ईडब्ल्यूई की गणना 'ंभार्त और कच्छ की 'ाड़ी में की जार्ती है और इन परिरदृश्यों से

नवी मुंबई के र्तट पर भी। और, 4.5 m का टिनम्नर्तम ईडब्ल्यूई सभी परिरदृश्यों से पोरबंदर के दीव के र्तट के

साथ गणना की जार्ती है। कच्छ के रण में और 'ंभार्त और मुंबई की 'ाड़ी के आस-पास के `ेत्रों में बाढ़ की

अश्चिधकर्तम सीमा का उल्ले' टिकया गया है। सिसमुलेशन से पर्ता चलर्ता है टिक बाढ़ की हद र्तक जलवायु

परिरवर्तन परिरदृश्यों का प्रभाव पूरे अध्ययन `ेत्र के खिलए र्तुलनात्मक रूप से कम है। हालांटिक , मुंबई र्तट के

पास कच्छ और 'ंभार्त की 'ाड़ी में 5 मीटर की ऊंचाई पर एक उल्ले'नीय वृश्चिद्ध दे'ी जा सकर्ती है।

टिवश्लेषण का टिनष्कष है टिक ईडब्ल्यूई और चक्रवार्त प्रेरिरर्त बाढ़ के सबसे कमजोर `ेत्र 'ंभार्त और मुंबई की

'ाड़ी के कच्छ और आसपास के `ेत्रों के रण हैं।

एक 3 डी मॉडल टिवभिभन्न सीमा स्थिस्थश्चिर्तयों को शाटिमल करके भौश्चिर्तकी के अश्चिधक सटीक प्रश्चिर्तटिनश्चिधत्व की अनुमश्चिर्त देर्ता है। 3 डी मोड समीकरण अध-संलग्न या संलग्न `ेत्र में स्र्तरीकृर्त और हवा से

चलने वाले परिरसंचरण को मॉडलिंलग करने के खिलए महत्वपूण हैं, सिजसमें नीचे और सर्तह की सीमा परर्तें पानी

के स्र्तंभ का एक महत्वपूण टिहस्सा शाटिमल करर्ती हैं, या यटिद लहर द्वारा प्रभाटिवर्त होर्ता है। और वर्तमान बार्तचीर्त। ऐसे मामलों में, `ैश्चिर्तज वेग के लंबवर्त रूप से भिभन्न प्रोफ़ाइल के समीकरणों को हल करना आवश्यक है। भारर्त के पश्चि मी र्तट के साथ 'ंभार्त और कच्छ के 'ाड़ी जैसे `ेत्रों में, जो सबसे जटिटल उथले र्तटीय जल का प्रश्चिर्तटिनश्चिधत्व करर्ता है, ज्वार के बहुर्त बड़े आयाम मजबूर्त ज्वार की धाराओं के परिरणामस्वरूप दे'े

जार्ते हैं। इस प्रकार, एक महत्वपूण ऊध्वाधर वर्तमान संरचना भी इस प्रटिक्रया के दौरान टिवकसिसर्त की जा

सकर्ती है। इसखिलए, टिवशेष रूप से 'ाड़ी `ेत्रों में ज्वार , वृश्चिद्ध और इसके इंटरैक्शन के 2 डी और 3 डी

एडीसीआईआरसी मॉडल सिसमुलेशन की र्तुलना करने के खिलए एक टिवश्लेषण टिकया जार्ता है। 3 डी सिसम्युलेटेड ज्वार, ऊध्वाधर मापदंडों के टिवभिभन्न संयोजन का उपयोग करर्ते हुए , नीचे, नीचे 'ींचें गुणांक, एड़ी

श्चिचपश्चिचपाहट और नीचे और सर्तह 'ुरदरापन लंबाई। यह सिसमुलेशन से दे'ा गया है टिक 3 डी मॉडल परिरणाम ऊध्वाधर मापदंडों के प्रश्चिर्त संवेदनशील हैं। नीचे 'ींचें गुणांक, एड़ी श्चिचपश्चिचपापन, और नीचे 'ुरदरापन लंबाई के छोटे मूल्य उच्च ज्वार का उत्पादन करर्ते हैं, जबटिक सर्तह 'ुरदरापन लंबाई के बड़े मूल्य 'ाड़ी `ेत्रों में उच्च ज्वार उत्पन्न करर्ते हैं। टिवश्लेषण से पर्ता चलर्ता है टिक नीचे से सर्तह र्तक मजबूर्त ऊध्वाधर वेग में 'ड़ी ढलान

v

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नीचे र्तनाव को संशोश्चिधर्त करर्ती है और 'ाड़ी `ेत्रों में ज्वार को संशोश्चिधर्त करर्ती है। ऊध्वाधर वेग एक क्रम कम है और इसकी ढलान सीधी रे'ा के र्तटों के साथ कोमल है। ज्वार की 'ंभार्त की 'ाड़ी में 3 डी के

साथ बेहर्तर भटिवष्यवाणी की गई है और भावनगर में आरएमएसई 0.05 हैं। दोनों मॉडलों ने सीधी रे'ा के

र्तटों के साथ समान ज्वार की ऊँचाइयों को पुन: पेश टिकया है। यह टिनष्कष टिनकालर्ता है टिक 3 डी मॉडल अभिभकलन 'ाड़ी `ेत्रों के अंदर अपरिरहाय हैं, जबटिक, 2 डी मॉडल सीधी रे'ा के र्तटों के साथ सही ढंग से

ज्वार का अनुकरण करने में स`म हो सकर्ता है। 'ाड़ी `ेत्रों के खिलए वृश्चिद्ध -ज्वार-लहर बार्तचीर्त के

सिसमुलेशन पर जोर टिदया गया है टिक बार्तचीर्त के दौरान टीडब्ल्यूई 2 डी की र्तुलना में 3 डी मॉडल के साथ काफी भिभन्न है।

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vii

List of Figures

Fig. 1.1: Cross section of a Tropical Cyclone. 4

Fig. 1.2: Global Tropical Cyclone genesis areas with tracks during 1985-2005. 6 Fig. 1.3a: Severe cyclonic storms developed during pre-monsoon season (1990-

2017) in NIO.

8 Fig. 1.3b: Severe cyclonic storms developed during post-monsoon season (1990-

2017) in NIO.

8 Fig. 1.4: (a) Wind around the eye of a cyclone and associated vertical circulation

in deep ocean and (b) Wind around the eye of a cyclone and associated vertical circulation in shallow water.

11

Fig. 1.5: Bathymetry of eastern part of Arabian Sea and Topography of west coast of India.

24 Fig. 1.6: Change in seasonal mean tropical cyclone potential intensity for end of

the centuryRCP8.5 (2081–2100) minus Historical Control (1986–2005) in CMIP5 multi-model ensembles. (Top) August to October, 10°S to 40°N and (bottom) January to March,40°S to 10°N.

26

Fig. 2.1: Computational domain along with 1998 cyclone track. 45 Fig. 2.2: Comparison of modelled tide against the observed tide at Dahej and

Nirma tide gauge locations

47 Fig. 2.3: Comparison of modelled tide against the observed tide at Dahej and

Nirma tide gauge locations

48 Fig. 2.4: Comparison of surge and surge-wave residual during 1998 cyclone

against the observed surge residual at Vadinar tide gauge location.

50

Fig. 3.1: Idealized bathymetry for the analysis area. 53

Fig. 3.2: GEBCO bathymetry along with cyclone tracks (Domain 2). 54 Fig. 3.3: Idealized computational domain representing west coast of India along

with cyclone tracks (Domain 1).

56 Fig. 3.4: Temporal depiction of storm surges generated from the cyclone Tracks

1 to 13 a) Experiment 1, b) Experiment 2.

59 Fig. 3.5: (a) Peak surge values for Track2 to Track13, (b) Depth profile along the

Tracks up to shelf break, (c) Zoomed profile of (b) near the coast

59

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xi (Experiment 2).

Fig. 3.6: Composite depiction of the maximum current speed generated by the cyclone Tracks 1 to 13 (Experiment 1).

60 Fig. 3.7: Temporal depiction of maximum water levels of surge and surge-wave

for a) Track1, b) Track5 and c) Track13; and Temporal depiction of wave residual for d) Track1, e) Track5 and f) Track13 (Experiment 1).

62

Fig. 3.8: Temporal depiction of wave residual for Tracks 2, 4, 6, 8 10 and 13 computed from SW interaction (Experiment 2).

62 Fig. 3.9: Temporal depiction of current speed at the location of maximum

interaction of surge and surge-wave for a) Track1, b) Track5 and c) Track13; and Temporal depiction of wave residual for d) Track1, e) Track5 and f) Track13 (Experiment 1).

63

Fig. 3.10: a) Maximum radiation stress gradient across the coast associated with Track1, Track5 and Track13 (Experiment 1).

Maximum radiation stress gradient for Experiment 2 (b) across shelf for Tracks 2, 6 and 13, (c) along the shelf for Tracks 2, 6 and 13 (Experiment 2).

65

Fig. 3.11: Temporal depiction of total water elevation of surge, SW, pure tide, ST, STW at high tide, low tide, mid-flood tide and mid-ebb tide for Track1 (a-d), Track5 (e-h), Track9 (I-l) and Track13 (m-p) (Experiment 1).

69

Fig. 3.12: The temporal variation of wave residual computed from the total water elevation by considering without and with wave interaction at (a) high tide, (b) low tide, (c) mid-flood tide, (d) and mid-ebb tide for Track1, Track5, Track9 and Track13 (Experiment1).

70

Fig. 3.13: The composite picture of snapshot of depth averaged currents associated with SW (blue arrow) and STW for high tide (green arrow) and low tide (red arrow) at the time of maximum current where the peak surge occurred for (a) Track1 (b) Track13.

72

Fig. 3.14: Temporal depiction of total water elevation of surge and ST at high tide, low tide, mid-flood tide and mid-ebb tide for Tracks 2, 4, 6, 8 10 and 13 (Experiment 2).

74

Fig. 3.15: Temporal depiction of depth-averaged current for surge and tide at the location of peak surge for Track13 (Experiment 2).

74 Fig. 3.16: Temporal variation of wave residual computed from the TWE without

and with wave interaction at high tide, low tide, mid-flood tide, and mid-ebb tide for Tracks 2, 4, 6, 8 10 and 13 (Experiment 2).

75

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xii

Fig. 3.17: Temporal depiction of wave residual computed from the TWE of ST and STW interaction during different tide phases at 2 m, 5 m and 1 0m at P and Q locations for Track3 (Experiment 2).

76

Fig. 3.18: Composite picture of snapshot of depth-averaged currents associated with tide (blue arrow) and ST (red arrow) and STW (green arrow) at the time of peak surge for Track6 during (a) mid-flood tide (b) low tide phase (Experiment 2).

78

Fig. 3.19: Temporal depiction of wave residual computed from the TWE of ST and STW interaction during different tide phases at 2m, 5m and 10m of A, B, C and D locations for Track10 (Experiment 2).

79

Fig. 3.20: Composite picture of snapshot of depth-averaged currents associated with tide (blue arrow) and ST (red arrow) and STW (green arrow) at the time of peak surge around A, B, C and D for Track10 (left side of the figure). Four square boxes on the right side are zoomed ones around the region A, B, C and D (Experiment 2).

79

Fig. 3.21: Temporal variation of SW and linearly added pure tide at different phases with SW for (a) Track1, (b) Track5, (c) Track9, (d) Track13 (Experiment 1).

82

Fig. 3.22: The temporal variation of non-linear term for Track 1, Track5, Track9 and Track13 for (a) high tide, (b) low tide, (c) mid-flood tide, (d) mid- ebb tide (Experiment 1).

83

Fig. 3.23: Temporal variation of non-linear term (NLT) computed from STW and SW+T for Tracks2, 6, 10 and 13 at high tide, low tide, mid-flood tide and mid-ebb tide (Experiment 2).

84

Fig. 4.1: Analysis area for computation of coastal inundation along with synthetic cyclone tracks for Zone1, Zone2, Zone3, Zone4 and Zone5.

91 Fig. 4.2: (a) Schematic representation of total water elevation (TWE), maximum

extreme water elevation (MEWE) and height of inundated water level during a cyclone, (b) Synthetic cyclone tracks generated for the Zone3.

92

Fig. 4.3: Bathymetry (zoomed) of Zone1 derived from GEBCO and topography from SRTM.

94 Fig. 4.4: Time series of simulated tide at Mandvi, Kandla and Okha 95 Fig. 4.5: Composite depiction of maximum probable extreme water elevations

generated due to the cyclone tracks of Zone1 for (a) present scenario, (b) moderate scenario (c) extreme scenario and maximum probable associated inundation for (d) present scenario, (e) moderate scenario (f)

96

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xiii extreme scenario.

Fig. 4.6: Composite picture of additional water levels generated above the present scenario with (a) moderate scenario and (b) extreme scenario.

97 Fig. 4.7: Composite picture of maximum extent of coastal inundation for

different scenarios.

98 Fig. 4.8: Bathymetry (zoomed) of Zone2 derived from GEBCO and topography

from SRTM.

98 Fig. 4.9: Time series of simulated tide at Porbandar and Somnath. 99 Fig. 4.10: Composite depiction of maximum probable extreme water elevations

generated due to the cyclone tracks of Zone2 for (a) present scenario, (b) moderate scenario (c) extreme scenario and maximum probable associated inundation for (d) present scenario, (e) moderate scenario (f) extreme scenario.

100

from SRTM.

103 Fig. 4.14: Time series of simulated tide at Diu, Bhavnagar and Surat. 103 Fig. 4.15: Composite depiction of maximum probable extreme water elevations

104

from SRTM.

107 Fig. 4.19: Time series of simulated tide at Valsad and Dahanu. 107

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xiv

Fig. 4.20: Composite depiction of maximum probable extreme water elevations generated due to the cyclone tracks of Zone4 for (a) present scenario, (b) moderate scenario (c) extreme scenario and maximum probable associated inundation for (d) present scenario, (e) moderate scenario (f) extreme scenario.

108

Fig. 4.21: Composite picture of additional water levels generated above the

present scenario with (a) moderate scenario and (b) extreme scenario. 109 Fig. 4.22: Composite picture of maximum extent of coastal inundation for

from SRTM.

111 Fig. 4.24: Time series of simulated tide at Virar, Navi Mumbai and Dapoli. 111 Fig. 4.25: Composite depiction of maximum probable extreme water elevations

112

113 Fig. 5.1: Synthetic tracks used for the 3D model simulation and the locations of

analysis.

122 Fig. 5.2: Comparison of 2D and 3D model simulations on tides for different

bottom drag coefficient 𝐶_𝑓3𝑑 and 𝐶_𝑓2𝑑.

124 Fig. 5.3: Comparison of 2D and 3D model simulations for surface tidal currents

at different locations.

125 Fig. 5.4: Temporal depiction of vertical velocity for different vertical layers at

four coastal locations.

125 Fig. 5.5: Comparison of 2D and 3D model simulations on tides for different

values of eddy viscosity 𝐸_𝑣.

128 Fig. 5.6: Vertical velocity at 5 vertical layers for different values of eddy

viscosity 𝐸_𝑣.

128 Fig. 5.7: Comparison of 3D modelled tide for various values of bottom and 130

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xv

surface roughness length at four coastal locations.

Fig. 5.8: Comparison of surge and surge-wave residual (3D model) during 1998 cyclone against the observed surge residual at Vadinar tide gauge location.

131

Fig. 5.9: Comparison of 2D and 3D model simulated TWE associated with STW for Track1 at different locations.

133 Fig. 5.10: The composite picture of a snapshot of depth-averaged currents

associated with STW for Track1 using 2D (green arrow) and 3D (red arrow) models at the time of peak total water elevation.

133

Fig. 5.11: Comparison of 2D and 3D model simulated TWE associated with STW at Porbandar for Track2.

134 Fig. 5.12: The composite picture of a snapshot of depth-averaged currents

associated with STW for Track2 using 2D (green arrow) and 3D (red arrow) models at the time of peak total water elevation.

134

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xvi

List of Tables

Table 1.1: Classification of cyclonic disturbance by IMD. 5 Table 2.1: Correlation coefficient and RMSE at different tide gauge locations. 48 Table 5.1: Experiments with different combination of 3D model parameters. 118 Table 5.2: Correlation coefficient and RMSE at tide-gauge location ‘Nirma’. 131

COASTAL INUNDATION ALONG THE WEST COAST OF INDIA

INTERACTION OF STORM TIDES WITH WIND WAVES:

COASTAL INUNDATION ALONG THE WEST COAST OF INDIA

JISMY POULOSE

CENTRE FOR ATMOSPHERIC SCIENCES INDIAN INSTITUTE OF TECHNOLOGY DELHI

MAY 2019

©Indian Institute of Technology Delhi (IITD), New Delhi, 2019

INTERACTION OF STORM TIDES WITH WIND WAVES:

COASTAL INUNDATION ALONG THE WEST COAST OF INDIA

by

JISMY POULOSE

Centre for Atmospheric Sciences

Submitted

in fulfilment of the requirements of the degree of DOCTOR OF PHILOSOPHY

to the

INDIAN INSTITUTE OF TECHNOLOGY DELHI

MAY 2019

Dedicated to Appachan and Ammachi….

Certificate

The results contained in this thesis have not been submitted in part or full to any other University or Institute for the award of any degree or diploma.

(Dr. A. D. Rao) Professor,

Centre for Atmospheric Sciences

Indian Institute of Technology Delhi

New Delhi-110016, INDIA

Abstract

सारांश

Contents

List of Figures

List of Tables