Luận văn reliabilty analysis of the red river dike system in vietnam

In fact, the flood defences in the Red River Delta have been established for hundreds of years and the safety standard has increased from a design water level of 1/5 years in the Imperia

RELIABILITY ANALYSIS

OF THE RED RIVER DIE SYSTEM IN VIET NAM

Procfschrift

ter verkrijging van de graad van doctor aun de Technische Universileil Delf,

op gezag van de Rector Magnificus prof ir K.C A.M Luyben,

vooyzitter van het College voor Promotes, inthet openbaar te verdedigen op woensda 8 oktober 2014 om 1230 uur

door Pham Quanc TU civiel ingenivur geboren te Ia Nam, Viet Nam

Dit proefschrift is goedgekeurd door de promotoren:

Prof, drs ir J.K Viijling

Prof dr ir PH.A.J.M van Gelder

Samenstelling promotiecommissie:

Prof drs ir JK Vrijling, Technische Universiteit Delft, promotor

Prof, dr ir 2 H.A.J.M van Gelder, Technische Universiteit Delft, promotor

Prof dr 7 M, Thu, Water Resources University of Viet Nam

Prof dr ir M Kok, ‘Technische Universiteit Delft

Dr.ir K J Bakker, ‘Technische Universiteit Delft

Dị W Kanning Colorado School of Mines/Deltares

Prof dr.C.Jommi, ‘Technische Universiteit Delft, reservelid

Keywords: Geotechnical reliability, flood defence, Red River dike, piping, uplift

geotechnical engineering, hydraulic engineering Printed by: Ridderprint B.V., Ridderkerk, the Netherlands

Front & Back: Red River Dike on the right bank in Ha Noi, by Pham Anh Tuan (2010) Cover layout by: Pham Anh Tuan

Copyright © 2014 by Pham Quang Tu

ISBN 978-90-5335-887-0

An electronic version of this dissertation is available at

http://repository-tudelft n1/.

RELIABILITY ANALYSIS OF THE Rep Riven Dike system

1N VIET NAM

by Pham Quang Tu

1, Red River Dike safety is lower than cxpected, even in some so far undoubted locations (in this thesis)

2, Ground conditions contribute greatly to uncertainty in the assessment of dikes,

Along durstion flood mightthreaten the Red River dikes in the future when seservoirs are compleled fin this Uncsisi

4, The highest failure prahahility of a dike occurs in the next few hours after the flood peak tin this thesis)

The reduction of seepage length can he used to predict the piping process during repeated and long duration floods (in this thesis)

6 inlegration of Hydraulic Engineering and Geuwchnical buginecring is an extremely important and fertile research area

Reliability based analysis in Geotechnical Enginvering is applicable in de veloping countries

‘The particular climatological conditions and the geography of lakes and es- tuaries contribute (o Le success ul the flood risk uranagementin the Netlier- lands

4J, Flooding has been the issue of mast concern since antiquity in the society

of Viet Nam, us shown by the clussieal warning “thty, hoa, dao, tic” (dhe

Vietnamese proverb):"flooding, firing, robbing, and invading"

10, The challenge of a PhD’s life is the same as that of learning a new sporc but suore interesting wid beneficial,

‘These propositions are regarded as opposable aud defendable, and have been approved

as such by the supervisors prof dis ir, J.K Vrijing and prof dr i RL A IM van Gelder,

Stellingen hehorende bij het proefachrift

RELIABILITY ANALYSIS OF THE RED River Dike sysTEM

IN VIET NAM

door Pham Quang Tu

1 De veiligheid van de Rude Rivier Dijkis lager dun verwachl, zells in suinenige jotmu toc onbetwijfelde locatics (dit procfschrift

2, De grondgesteldheid draagt in grote mate bij (ol onzekesheid bij de bevor- deling van dijken

3, Hen langdurige hoogwatergolf zal in de toekomst, wanneer reservoirs zijn vollugid, cen bedrviging vormen voor de Rade Rivier Dijk (dil pruefichrif),

6, Integratic van Waterbonwkuade en Geotcchnick kan tot con uiterst belang ijk en vruchtbaer onderzoeksterrein leiden,

Deop hetrouwhaarheid gebaseerde analysein de Geotechnick is tnepashaat

in ontwikkelingslanden,

8, De hijzondere klimatalogische omstandigheden an de gengrafie van meran

en riviermondingen dragen hij aan het succes van het heheer van overstra-

mingsrisicos In Nederland,

3 Sinds de oudheid zijn overstromingen het grootste probleem geweest in de

Vietnamese samenieving, betgeen blijkt uil de klussicke waarschuwing “thủy,

héa, dao, tc" (Vietvamees spreekwwoord): " overstroming, brand, beroving

en invasie"

10, Deuitdaging van het leven van cen PhD is dezetfde als dic van het leren van

een nieuwe sport, maar inferessanter en heilzamer

Deze stellingen worden opponeerbaa en verdediabaar peacht en jn als zodanig goed- gekeurd door de promotoren prof drs ix JK Viijling en prof dr.it.BUL.A.J M van Gelder

‘This dissertation synthesises the application of a probabilistic-based framework in geotech- nical and hydraulic engineering, for the assessment of the Red River dikes in Viet Nam The study area promotes the probabilistic-based approach because of its typical natural condi- tions Lack of understanding of soil and water behaviours may lead to failures of engineer- ing design, as is proven from practice This study is intended to fill part of these gaps

Dikes along rivers often spread over the deltaic environment and its earthen structures are parts of a long civilian history, from hundreds to thousands of years, Uncertainties of soil properties of the dike embankment and its foundation, and contribute to the probabil- ity of failure under a given water level To carry out an assessment of the safety of the flood defences, both a conventional approach and a reliability analysis may be applied The for- mer relies on the factors of safety while the latter takes uncertainties of both water level (load) and soil properties (resistance) more explicitly into account The reliability-based framework proved its benefits in important projects and in dealing with large uncertainties

in design This is demonstrated through the chapters in this thesis

Firstly, the background information of the natural conditions, the socio-economic is- sues and the flood defences in the Red River Delta are presented in Chapter 2 The topo- graphic conditions and meteorological characteristics play an important role in the flood defence management of the Red River Delta Around 50% of the delta area is lower than 2m (above mean sea level) and the delta is partly surrounded by high mountains Conse- quently, under extreme weather conditions such as typhoons, fronts, and tropical depres- sions, flooding will affect the lowlands area On the other hand, the socio-economic issues indicate a fast growing economy of Viet Nam Hence, new requirements of higher safety standards for the flood defences seem advisable In fact, the flood defences in the Red River Delta have been established for hundreds of years and the safety standard has increased from a design water level of 1/5 years (in the Imperial period ~ the 1890s) to 1/500 years (at the present) The current design water level is 13.4 m (above mean sea level) at the gauging station of Ha Noi, which will be routed to the dike stretches in the whole delta area

Secondly, the analyses of the hydraulic boundary conditions are performed in Chapter

4 with a detailed description of the Red River system and an evaluation of the hydraulic pa- rameters for the reliability analysis The Red River is formed by three tributaries (the Da,

‘Thao, and Lo River), and the maximum observed discharge was 37,800 mls in August 1971

at Son Tay in the area of Ha Noi The reservoirs systems in the Da and Lo River significantly reduce the peak flood discharge in the delta area by a storage capacity of 8.5 billion cubic metres; as for instance in the flood with frequency of 1/500 years, the peak discharge will

decrease approximately 40%, from 48,500 nr'/s to 30,000 m*/s By doing so, the dike sys-

tem may be severely loaded during a long duration flood of around 120 hours but the water level is lower than the original Another issue is the increasing trend of the water level at the same river discharge, which is due to the over expansion of residents in the flood plain, therefore the resulting probability of overflow will become higher in future if there are no measures to control such developments

‘Thirdly, the probabilistic-based analysis framework and its application are treated in

v

vi SUMMARY

Chapter + and 5, including classification of ground conditions, model uncertainties, and spatial variability of soil parameters Currently, the calculation level 1 (semi-probabilistic) has been embedded in the design codes while the calculation level 2 (e.g FORM) and3 (e.g Monte Carlo simulation) are used for important projects or the calibration of the level 1 de- sign codes Soils properties and ground conditions are analysed by different approaches, cither by classical statistics or by a probabilistic-based framework It is hoped to increase the engineer's understanding about the use of probabilistic-based methods in practice, To take examples, uplift and ground coefficient are analysed by using the model factor The former presents a physical-based model of uplift which was calibrated for the study area by field tests The latter discusses a new model of ground uncertainties (the ground coefficient

- a) that represents the cumulative effects of the internal erosion process in both flood and dry season Moreover, an illustration of spatial estimation was performed on two data series

of the top-layer thickness (with the distance of sampling of around 30 m and 200 m) The calculation results indicate a correlation between the scales of fluctuation and the distance

of sampling, It is expected that the mentioned theories and applications will be incorpo- rated in Geotechnical Engineering and Flood Defences assessment, especially in Viet Nam Fourthly, the theory of reliability analysis of a river dike and its application in the Red River Dikes are discussed in Chapters 6 and 7, where piping, overflow, and instability are considered under a long duration flood Probabilities of overflow are predicted to be high

in the dike stretches of the Ha Tay area due to a lower design water level in the past There- fore, dike crests should be heightened to meet the same safety standards as that in the Ha Noi area To evaluate piping during a long duration flood, a model of seepage length reduc- tion of piping with respect to time is developed from a basic principle: the internal erosion process depending on seepage gradient and ground conditions The proposed model, after calibrating by a historical dike failure in the study area, predicts an increase of the erosion length from 3% to 20% (the seepage length shortening from 100% to 97% or 80% respec- tively) in one typical flood wave, which leads to the cumulative effects of piping and inter- nal erosion under the dike embankment On the other hand, the geotechnical instability is proven to be less affected during a long flood wave However, only homogeneous models

of embankments are mentioned in this study It is suggested that in future research more attention should be given to the heterogeneity of dike embankments with regard to perme- ability Finally, by taking the length-effect into account, the probability of failure of dike stretches in the study area may significantly increase depending on its stretch length and the spatial variation of soil parameters, as for instance the total probability of failure of the dike system will jump from 21%-25% to 38%-47% (by without or/and with taking length- effect into account respectively),

‘The findings of this research hope to contribute to a new understanding of Red River Dike safety in Viet Nam They also open up several research directions in the combined field of hydraulic engineering and geotechnical engineering, and widen the applications of probabilistic-based approaches in Viet Nam and developing countries,

In deze dissertatie wordt een synthese uitgevoerd van de toepassing van een ap proba- bilisdsche methoden gebaseerd kader in de geotechniek en de waterbouwkunde, ten be- hoeve van de beoordeling van de betrouwbaarheid van dijken langs de Rode Rivier (in Viet-

namees: Song Hong) in Viet Nam De toepassing van een probabilistische benadering is

hier met name opportuun vanwege de typisch natuurlijke omstandigheden in dit onder- zoeksgebied Een gebrekkig begrip van grond- en watercondities zou namelijk, zoals uit de praktijk gebleken is, tot mislukkingen in technische ontwerpen kunnen leiden Deze studie

is bedoeld om een deel van deze lacunes te vullen

Dijken langs rivieren strekken zich uit over de delta en dergelijke grondconstructies zijn deel van een lange civiele geschiedenis, van honderden tot duizenden jaren De onzeker- heden in de grondeigenschappen van dijklichaam en fundering dragen bij aan de faalkans bij een bepaalde waterstand Om een inschatting te kunnen maken van de veiligheid van waterkeringen, worden vaak zowel een conventionele analyse als een betrouwbaarheids- analyse toegepast De eerste, conventionele benadering verlaat zich op veiligheidsfactoren, terwijl de tweede methode onzekerheden in waterstanden (belasting) en grondeigenschap- pen (sterkte) in acht neemt Het op betrouwbaarheid gebaseerde toetsingskader heeft zijn nut al bewezen in belangrijke projecten en bij grote ontwerponzekerheden Deze benade- ring wordt in de hoofdstukken van deze dissertatie gedemonstreerd

De achtergrondinformatie over de natuurlijke omstandigheden, de soeiaaleconomische situatie en de waterkeringen in de regio wordt in hoofdstuk 2 gepresenteerd De topogra- fische condities en de meteorologische omstandigheden spelen een belangrijke rol in de hoogwaterbescherming van de Rode Rivier Delta Ongeveer 50% van de delta ligt lager dan

2 meter (boven gemiddeld zeeniveau) en is gedeeltelijk omringd door hoge bergen Der- halve, onder extreme weersomstandigheden, zoals tyfoons, fronten en tropische depres- sies, zal het laaggelegen land door overstromingen getroffen worden Omdat de huidige sociaaleconomische situatie van Viet Nam echter op een snel groeiende economie duidt, lijken nieuwe eisen voor hogere veiligheidsnormen voor de hoofwaterbescherming daarom raadzaam In feite, in de honderden jaren van het bestaan van waterkeringen in de Rode Ri- vier Delta zijn de veiligheidsnormen al toegenomen van een ontwerpwaterhoogte van 1/5 jaar (in de imperiale periode ~1890s) tot 1/500 jaar (2014) De huidige ontwerpwaterhoogte

is 13.4 m (boven gemiddeld zeeniveau) bij het meetstation van Ha Noi, en wordt vervolgens naar alle dijken in de gehele delta doorberekend

In hoofdstuk 3 worden de hydraulische randvoorwaarden bepaald door een gedetail- leerde beschrijving van het Rode Rivier systeem en een evaluatie van đe hydraulische pa- rameters voor de betrouwbaarheidsanalyse De Rode Rivier wordt gevormd door drie zi vieren, de Da, de Thao en de Lo rivier, die samenkomen bij Son Tay in de omgeving van Ha Noi, waar in augustus 1971 een maximum debiet van 37,800 m'/s werd geobserveerd De reservoirs in de Da en de Lo rivier hebben door een opslagcapaciteit van 8.5 miljard kubieke meter een reductie van de piekwaterafvoer in de delta tot gevolg, zoals bijvoorbeeld met be- trekking tot de overstromingsfrequentie van 1/500 jaar, zal de piekafvoer verminderen met

40%, van 48,500 m*/s tot 30,000 m*/s Het gevolg hiervan kan zijn, dat het dijksysteem ern-

vii

viii SAMENVATTING

stig belast kan worden gedurende een langdurige hoogwaterstand van ongeveer 120 uur, Een ander aspect is een toenemend waterniveau bij gelikblijvende afvoer, als gevolg van bewoning in de hoogwaterbedding, welke, indien geen maatregelen worden getroffen, kan resulteren in een hogere waarschijnlijkheid van overstromen in de toekomst

De beschrijving en toepassing van het op probabilistiek gebaseerde kader van analyse, inclusief de classificatie van grondcondities, modelonzekerheden en ruimtelijke variatie van grondparameters, wordt in hoofdstuk 4 en 5 behandeld Momenteel is het niveau 1 be- rekeningsmodel ingebed in de ontwerpnormen, terwijl berekeningsniveau 2 en 3 gebruikt worden voor grote projecten of voor de kalibratie van de niveau 1 ontwerpnormen, Grond- eigenschappen en bodemcondities worden op verschillende manieren geanalyseerd, na- melijk met de klassieke statistische benadering, of met een probabilistisch gebaseerd ka- der, Het is de hoopvolle verwachting dat er meer kennis zal ontstaan onder ingenieurs voor de toepassing van een probabilistische methode in het veld, Als voorbeeld worden het opdrijven van de afdekkende laag aan de binnenzijde van de dijk en de grondcoéfficiént geanalyseerd met gebruikmaking van een modelfactor Het eerste voorbeeld behelst een fysisch gebaseerd model van opwaartse druk welke in het studiegebied werd gekalibreerd door veldonderzoek Laatstgenoemd voorbeeld beschrijft een nieuw model van grondon- zekerheid (grondcoéfficiént - a), dat de cumulatieve effecten van het interne erosieproces

in zowel het regen- als het droge seizoen vertegenwoordigt Bovendien werd een illustratie van ruimtelijke inschatting gemaakt voor twee dataseries van de boventaagdikte (met een steekproefafstand van ca 30m en 200m) De berekeningen geven een correlatie aan tussen

de schaal van fluctuatie en de afstand tussen de metingen Het wordt verwacht dat de the- orieén en hun toepassingen in de geotechniek en toetsing van waterkeringen, in met name Vietnam, geincorporeerd zullen worden

In hoofdstuk 6 en 7 wordt de theorie van de betrouwbaarheidsanalyse van een rivier- dijk en de toepassing daarvan op de dijken van de Rode Rivier besproken; overstromen, instabiliteit en “piping” worden bekeken onder een langdurige hoogwaterstand De kans

op overstromen wordt naar verwachting hoog in de dijkvakken in de omgeving van Ha Tay ten gevolge van een lagere ontwerpwaterstand in het verleden De kruinhoogte zou daarom verhoogd moeten worden om dezelfde veiligheidsstandaard als in het gebied rond Ha Noite realiseren Om “piping” (zandvoerende wel) gedurende een langdurige hoogwaterstand te evalueren, wordt een model van kwellengtereductie als functie van de tijd ontwikkeld van- uit een basisprincipe: namelijk het interne erosieproces dat afhangt van de kwelgradiént en grondeigenschappen Na de kalibratie van het falen van een dijk in het onderzoeksgebied voorspelt het voorgestelde model een toename in de lengte van erosie van 3% tot 20% (de lengte van de kwel respectievelijk verminder van 100% tot 97% of 80%) gedurende een ty- pische vloedgolf Dit leidt tot een opeenstapeling van de effecten van “piping” en interne erosie onder de dijk Anderzijds wordt bewezen dat de geotechnische instabiliteit minder wordt bedreigd tijdens een langdurige alvoergolt In dit onderzoek zijn echter slechts ho- mogene modellen van dijken bestudeerd De suggestie is dan ook dat in toekomstig onder- zoek meer aandacht wordt geschonken aan de heterogeniteit van dijken met betrekking tot hun waterdoorlatendheid Tot slot, door het lengte-effect in acht te nemen, kan de waar- schijnlijkheid van een dijkbreuk in het studiegebied aanzienlijk hoger biijken te zijn dan was aangenomen, afhankelijk van de lengte en de ruimtelijke variatie in grondparameters, zodat bijvoorbeeld de totale faalkans van het dijksysteem zal toenemen van 21%-25% (zon- der lengte-effect) tot 38%-47% (met lengte-effect)

De resultaten van dit onderzoek zullen hopelijk bijdragen tot een nieuw begrip van vei-

perspectieven in het interdisciplinaire veld van waterbouwkunde en geotechniek en ver men de toepassingsmogelijkheden van probabilistische methoden in Viet Nam en ontwik- kelende landen

Acknowledgement: Mariette van Tilburg and Mark Z Voorendt are acknowledged for their translation this summary into the Dutch language

TOM TAT

dng hợp ứng dụng của phương pháp tính toán dựa trên lý thuyết

stic-based) trong địa kỹ thuật và thủy công để đánh giá hệ thống

đê sông Hỏng ở Việt Nam Vùng nghiên cứu khuyến khích việc áp dụng phương pháp tính toán dựa trên lý thuyết xác suất do những đặc thù riêng của vùng Những hiểu biết không đầy đủ về tương tác giữa đất và nước có thể dân tối sai xót trong tính

toán thiết kế công trình, điều này đã được chứng, minh trong thực tế Nghiên cứu

này nhăm phân nào khắc phục những hạn chế vừa nêu,

'Đê sông thường trải dài trên vùng đồng bằng và nên đắp (thân đê) được hình

thành trong lịch sử dài hàng trầm đến hàng nghìn năm Những bắt định tiêm ẩn

trong thân để hoặc dưới nên đê có thể ảnh hưởng đến an toàn đê dưới tác động

của nước lũ Để tiên hành đánh giá an toàn cho đê, cả phương pháp tiếp cận truyền

thong (tat dinh - deterministic) va phương pháp độ tin cậy (teliability- based) thường,

được áp dụng Phương pháp truyền thông chủ yếu dựa vào hệ số an toàn trong khi

phương pháp độ tin cậy xét đến sự bắt định (uncertainties) của mực nước sông (tai

à chỉ tiêu cơ lý của dat nén (sức chồng đỡ) Phương pháp độ tin cậy khang

tả trong các dự án lớn, quan trọng hoặc các thiết kế có sai số lớn trong

các tham số đầu vào, Những nội dung này sẽ được thể hiện qua các chương trong

toàn bộ nội dung luận án

Một, điều kiện tự nhiên, các vẫn đẻ kinh tế xã hội và hệ thống công trình phòng

lũ được trình bày ở Chương 2 Đặc điểm địa hình và điều kiện khí tượng thủy văn

đồng vai trò quan trong trong kiểm soát và vận hành hệ thống công trình phòng lũ

ở đồng bằng sông Hồng Khoảng 50% diện tích toàn đông bằng sông Hồng có cao

độ dưới +2.0m (so với mực nước biển) và bao quanh đồng bằng là đồi và núi Do

đó, dưới ảnh hưởng của mưa lớn (do bão, áp thấp nhiệt đói, front ) lũ lụt có thể đe

dọa những vùng có cao độ thấp, Mặt khác, kinh tế Việt Nam đã và đang tăng trưởng nhanh, do đó một tiêu chuẩn phòng lũ cao hơn cho hệ thống đê là điều cần thiết

Trên thực tế, ,hệ thống đê sông Hồng được xây dựng từ hàng trăm năm trước với mực

nước thiết kế tương ng trận lũ có tân suất 1/5 năm (giai đoạn phong kiên ~ 18905) tới mực nước tương ứng trận lũ có tân suất 1/500 năm (giai đoạn hiện tại) Mực nước thiết kế là 13.4m tại trạm thủy văn Hà Nội và được truyền dẫn đi tới từng đoạn đê

trên toàn đồng bằng

Hai, những phân tích về điều kiện biên thủy lực được trình bày trong Chương 3 với phân mô tả chỉ tiết hệ thong song Hong va phan tính toán các tham số thủy lực

để dùng trong phân tích cho các chương sau Sông Hồng gồm có ba phụ lưu (sông

Đà, sông Thao và sông Lô) và lưu lượng lớn nhất quan trắc được là 37,800 m3/s vào

thang 8 năm 1971 tại Sơn Tây, Hà Nội Hệ thống hỏ chứa trên sông Da va sông Lô giảm đáng kể đỉnh lũ ở vùng đồng bằng với khả năng cắt lũ tổng cộng khoảng 8.5 tỷ m3, ví dụ như ở trận lũ tản suất 1/500 năm, đỉnh lũ sẽ giảm khoảng 40% từ 48,500 m3/s xuỏng còn khoảng 30,000 m3/s Bằng cách điều tiết đó, hệ thông đê sẽ phải

chịu mực nước lũ cao kéo đài khoảng 120 giờ (ở cao độ +13.0m) Một vấn đề khác là

sự gia tăng mực nước ở cùng mức lưu lượng do sự gia tăng dân cư sinh sống dọc các

pháp xử lý nào được tiền hành

Ba, phương pháp phân tích dựa vào lý thuyết xác suất (probabilistic-based) và

các ứng dụng được trình bày trong chương 4 và 5, bao gồm phân loại điều kiện nên,

hệ số mô hình, ước lượng tham só của chỉ tiêu cơ lý của đất Hiện nay, tính toán theo

lý thuyết xác suất với mức 1 (hay còn gọi là bán xác suất) đã được sử dụng trong các

tiêu chuẩn thiết kế trong khi các tính toàn với mức 2 (ví dụ: FORM) và 3 (ví dụ: Monte

Carlo simulation) thường được áp dụng cho các dự án quan trọng hoặc đểhiệu chỉnh

các tiêu chuẩn thiết kế tính toán theo mức 1 Chỉ tiêu cơ lý và đặc điểm đắt nền được

phân tích với nhiễu phương pháp khác nhau: phương pháp thống kê truyền thống,

hoặc phương pháp tính toán dựa trên lý thuyết xác suất (probabilistic-based), Điều

này được kỳ Vọng sẽ nâng, cao hiểu biết của ky sư để sử dụng các phương ¡pháp tính

toán dựa trên xác suất trong thực tế thiết kế Vi dụ như hiện tượng đẩy trỏi và hệ số

nền trong phân tích bằng hệ số mô hình Phần phân tích hiện tượng đẩy tri trình

bày mô hình dựa trên cơ chế vật lý của hiện tượng có kết hợp hiệu chính bằng thí

) trường Phan phan tich hé s6 nén xem xét các sai số dưới nền đê (đặc

số ø), hệ số này cũng có thể dùng để diễn tả hiện tượng tích lũy xói ngầm

do ảnh hưởng của đồng thấm vào mùa lũ và mùa kiệt Ngoài ra, mot vi du minh hoa phần ước lượng trong không gian với hai chuỗi số liệu vẻ bê day tang phủ (với khoảng

cách mẫu là 30m va 200m) cũng được trình bày trong chương 5 Kết quả tính toán

;g minh sự phụ thuộc của tỷ lệ biến đổi (sacle offluctuation) và khoảng cách lầy mẫu, Những phương pháp tính toán nêu trên kỳ vọng sẽ được áp dụng trong phân

tích ổn định đê, đặc biệt là ở Việt Nam

Bồn, lý thuyết phân tích ổn định đệ và ứng dụng cho đẻ sông Hồng được trình bày trong chương 6 va 7, trong dé x6i ngằm, tràn dé và mắt dn định được xem xét dưới

điều kiện lũ kéo dài Xác suất tràn đê được dự báo là cao ở các đoạn đê của Hà Tây

cũ do mực nước thiết kế cũ thấp hơn (so với mực nước thiết kế của đề thuộc Hà Nội

cũ) Do đó, đỉnh dé cân được nâng cao để đạt cùng tiêu chuẩn an toàn với hệ thon

đê trên toàn Hà Nội mới Để đánh giá an toàn hệ thông đê trong điều kiệ

mô hình đường thâm giảm dẫn theo thời gian được đề xuất dựa trên các nguyên tắc

cơ bản: xói ngắm phụ thuộc vào gradient thậm, điều kiện đắt nên và chiều đài đường,

thắm ban đảu Mô hình chiều dài đường thắm giảm dân theo thời gian, sau khi hiệ

chỉnh 1 bang một trường hợp vờ đê ở vùng nghiên cứu, dự báo chiều dai xói ngắm

có thể phát triển từ 3% đên 20% (tương ứng chiều đài đường | thấm giảm từ 1009

lũy các nguy cơ tiêm ẩn dưới nên đê do xói m

định nên đề chứng minh hệ số an toàn ít bị ảnh trông: do mực nước sông đâng cao,

nhưng chỉ có phân tích cho thân đê đồng nhất được tiễn hành Trong tương lai, can

đánh giá sự ảnh hưởng này trong trường hợp thân đê không đồng nhất, đặc biệt à về tính thám Cuối cùng, bằng việc xét đến sự ảnh hưởng theo chiều dài (length-efect), xác suất phá hủy của từng đoạn và toàn hệ thong dé tang lên đáng kể, do ảnh hưởng

của chiều dài mỗi đoạn đề và sự biến đổi chỉ tiêu cơ lý của đắt nền trong không gian

Chang han, xác suất phá hủy của toàn hệ thông đê tăng từ:21%-25% khi chưa xét đến length-effect tăng lên 38%-47% khi xét dén length- effect

Những phát hiện trong nghiên cứu này được hy vọng sẽ góp phần hiểu biết tốt hơn về hệ thông đê sông Hỏng ở Việt Nam những hướng nghiên cứu mới

cũng được mở ra trng lĩnh vực đa ngành giữ ÿ thuật và thủy công, đồng thời

‘Tom Tar xiii

cũng mở ra những triển vọng ứng dụng phương pháp tính toán dựa vào xác suất ở

Việt Nam và các nước đang phát triển khác.

235 Review of dike engineering in four periods ,

2.3.6 Typical floods in Viet Nam from the 1900s

4.24 Relations of reliabilty-based and conventional design „46

4.3.1 Understandingofunceraintym geotechnical engineering „47

„50

„50 _-

2 82 sản

at 78

„8l

„8M

xvii CONTENTS:

D Soil Property along the Red River dike

E_ Observed Sand Boils at Sen Chieu in the Red River

F Model Factor for Uplift Test on the Thaibinh Formation

G Reduction of Seepage Length During High Water Level

H Solutions for Groundwater Flow

I Decay and Delay of Groundwater Flow

J Observed Phenomena During Flood Seasons in the Red River Dike

1.1 BACKGROUND AND PROBLEM STATEMENT

HE Red River Delta (RRD), located in northern Viet Nam with an area of around 15,500 km? and a population of nearly 20 million people, is protected by approximately 3000

km of dikes which are classified into four grades from 111, II, {to “special’, indicating the increase of the safety levels In the past, the main cause of dike failure was overflow due

to limited height Of the 38 cases of dike failures in the 19" century most were related to overflow, as for instance was the case in the floods in 1910, 1915, 1925, 1945, 1971 (Khanh

es al,, 1995; GDM, 1995), Currently, the flood mitigating measures, which are expected to lower flood risk in the RRD, includes the reforesting in the upper basins, the constructing dams and reservoirs to store flood water, the strengthening of dikes, and the raising of pub- lic awareness of flood protection By doing so, the safety of flood defence in the delta has been significantly improved, indicated by the design water level that has increased from 1/5

to 1/500 years for one hundred year

‘The assessment of flood defences in Viet Nam currently has some limitations, determin- istic evaluation and inadequate hydraulic boundary conditions The deterministic evalua- tion is the so-called “deterministic framework" that treats load and resistance as standard values This approach also relies on the Factor of Safety (FS) but the determination of the values of FS is still implicit The inadequate hydraulic boundary conditions refer the assess- ment of flood defence at the highest water level in the flood frequency from 1/50 years to 1/250 years in the past, while the current designed flood frequency is 1/500 years (LYVïtU, 2009; Khoi, 2010) Therefore, the safety margin of the Red River dike system in the new boundary conditions fascinates many researchers in this field

To resolve the mentioned problems, we apply the “reliability-based framework” to as- sess the Red River dike system, in which uncertainties of load and resistances are taken into account, and the flood defences are considered in the new hydraulic boundary conditions (van Gelder, jjling and van Gelder, 2002) In the reliability-based approach, water level and soil properties, which respectively represent the load and strength in the assess- ment, are modelled as random processes and these can be integrated in the risk-based anal- ysis The new hydraulic boundary is also investigated in the flood frequency of 1/500 years that wil threat the dike system with a long duration flood wave From such input boundary

ø 1,]NTGDUCTION

conditions, the reliability indices of the whole dike system can be figured out probabi

cally Figures || & |.2 illustrate the differences between the deterministic and probabilistic approach

‘and factors of safety are empirically given, acteristic values, or probability of failure is caleu-

lated in thisform Pp= ff fig, (R<LdRat-

~ To understand the background conditions and related issues, including natural con- ditions, socio-economic issue, and flood defences development;

~ To clarify the hydraulic boundary conditions in a flood frequency of 1/500 years;

- To synthesise the applicable probabilistic-based framework in geotechnical engineer- ing and to analyses the geotechnical conditions of the Red River dikes in the area of

In order to answer the main research question, the following key questions are gener- Ga

ated:

1 What are the natural and socio-economical conditions these influence the assess-

ment of the Red River dike in the Ha Noi area?

2 What are the hydraulic boundary conditions of the Red River in the area of Ha Noi?

3 How does the probabilistic-based approach take the uncertainties in geotechnical en-

gineering into account?

4, How do the geotechnical conditions influence the assessment of the Red River dikes

in the Ha Noi area?

How to assess the reliabi

of the Red River dike during a long duration flood?

6 How safe is the Red River dike during the flood with a frequency of 1/500 years?

1.4, APPROACHES AND METHODS

1 obtain the objectives, we devised a numerical modelling approach to apply to the hy-

draulic boundary conditions, the geotechnical engineering conditions, and the reliabil-

ity analyses The hydraulic boundary conditions were modelled to figure out the stage dis-

charge relationship from observed data, and to predict the flood frequency of 1/500 years

On the other hand, the geotechnical data, gathered in different geological investigations

from both in situ and laboratory, were statistically analysed, The reliability analysis was

based on the Monte Carlo simulations

Sections in Chapters 5, (and 7 concern the hypotheses on the spatial variation of soil

properties and the piping failure mechanism Soil data in the study area are inadequate to

elaborate the spatial distributions, therefore several assumptions have been made to sim-

plify the ground conditions Nevertheless, the developed framework in this research can be

applied to another case studies if the in-situ tests are adequately obtained

1.5 CONTRIBUTIONS AND SCOPE

HE study demonstrates a reliability-based assessment framework for the Red River dike

T system with special consideration of the hydraulic boundary condition and spatial vari-

ation of soil properties The flood frequency of 1/500 years was elaborated to figure out its

effects to the safety margin of the Red River dike The spatial variability of soil parame-

ters was probabilistically evaluated to model the inherent uncertainties from ground con-

ditions

Several models have been applied to elaborate the geotechnical failure mechanisms in

dike assessment (e.g piping, uplift, internal erosion, and instability), Both theoretical and

experiment method in combination with observed data have been adopted to calibrate the

new models, becoming the reliable and applicable models

‘The assessment framework was adapted for the case study in the Red Riverand italso es-

tablishes a new research direction in an integrated field (hydraulic-geotechnical engineer-

ing) from reliability-based point of view, The research focuses on the dike system itself ex-

cept other hydraulic structures such as dams, reservoirs, weirs, etc A risk-based framework,

with attention to consequences of failure of the flood defence system, can in the future be

investigated based on these research results

4 1, ]NTRODUCHON

1.6 ORGANIZATION OF THE DISSERTATION

HE dissertation is organized into eight chapters, and the detailed outline is given in Fig- Tai Chapter 2 synthesises the background conditions of the Red River Delta, includ- ing natural conditions, socio-economic issues, and flood defences development Chapter

5 presents the analysis of hydraulic boundary conditions, by taking the system operation

of reservoirs and combination of flood discharge of three tributaries into account The re- sulting water level and flood duration will be integrated in the calculations in Chapters ( and 7, Chapters 4 and 5, in turn, demonstrate the theoretical probabilistic-based frame- works in geotechnical engineering and the applications to the geotechnical conditions in the Red River dikes Aims of Chapters ( and 7 is to develop an assessment framework for river dikes during a long duration flood, and to apply to the Red River dikes in the area of

Ha Noi Finally, Chapters | and 8 contain the introduction, and the conclusions and recom- mendations respectively

Figure 1.3: Structure of the dissertation.

THE RED RIVER DELTA

‘The Red River Delta (RRD) is the second largest delta in Viet Nam with an area of around 15,500! km? and a population of nearly 20 million The flood defences in the RRD have been established for several centuries with thousands of kilometres of dikes along the Red River system,

This chapter provides an overview of the flood defence and water management in the RRD Section 2.! describes the natural conditions, including the meteorological and the topographic conditions Section 2 2 presents several socio-economic issues which could influence the dike assessment in term of flood risk analysis Section 2.3 shows how the flood defence and its safety standard have been improved over time; the current management

of flood defence will be presented in Section 2.4 This chapter will be concluded with a discussion section

2.1 NATURAL CONDITIONS

IETNAM, a country in Southeast Asia, has a shape of the letter “S”, and is located be- tween latitudes from 8°27' to 23°23'N, and longitudes from 102°8! to 109°27'E The total mainland area is around 330,000 km?, which is divided into eight regions, namely the Northeast’, the Northwest, the Red River Delta, the North Central Coast, the South central Coast, the Central Highlands, the Southeast and the Mekong River Delta, with a total of fifty eight local provinces and five municipalities The Red River Delta is located in Northern Viet Nam with an area of around 15,500 km’, its latitude and longitude varies from 19°05!

to 21°34! and from 10517! to 107°07' respectively, see Figures 2.| and 2.2

‘The Red River delta is the second biggest delta in Viet Nam, after the Mekong River Delta

in the South, but itis also the most crowded area in the country, including eleven provinces namely Vinh Phuc, Ha Noi, Bac Ninh, Ha Nam, Hung Yen, Nam Dinh, Thai Binh, Hai Duong,

Hai Phong, Ninh Binh, and Quang Ninh Ha Noi is the heart of the Delta of enormous po- litical, cultural and economic value, created through centuries of history In 1010, a king named Ly Thai To chose Thang Long (the former name of Ha Noi) as the capital of the coun- try at that time There have been many changes during these thousands years, but this area

is still a political, economical centre of Viet Nam

Figure 2.2; Study area in the Red River Delta

ments areas In the upstream part of the Red River, over 47% of the catchment area is

high mountains, of which in the area of Viet Nam, the elevation is higher in the northwest

(over 1000 nz’) and lower in the southeast (around 600 - 700 m) It is similar in the north-

west basin of the Thai Binh River with over 60% area of low hills (elevation in a range of

50180 m) In the delta area, elevation varies from 715 m in the area of Ha Noi to0.5-2 m

on the coast, and around 50% of the whole delta is lower than 2.0 m, However, there remains

several rocky hills with an elevation of around 20-50 m in eight out of eleven provinces in

the RRD (except Thai Binh and Hung Yen province) The rocky hills lead to the variation of

ground conditions in the Red River dikes, for more details see {Wt (20009); Khoi (2010) and

Figure 2.“ (adapted from the data of U.S Geological Survey http://glovis.usgs.gov/)

SAUl the elevations mentioned here is above the mean sea level, which is known as the national datum at the Hon

Daustation

‘The annual evaporation rate is relatively high, around 1000 mm, with a maximum value

in June of 100 mm and a minimum in February of 56 mm The annual average temperature

is around 24 degree Celsius, but the average maximum temperature is 33 degree Celsius in July and the average minimum temperature is 14 degree Celsius in January The dominant wind directions in the rainy season are south and south-east, and the average monthly wind speed is around 1.6-2.1 m/s, See Figure 2.4 and QCVN-2:2009/ EXD (2009) for more infor- mation

As previously mentioned, the characteristics of topography and meteorology will affect the hydraulic boundary conditions in the Red River, for instance the peak discharge and the increased rate of the water level in a flood wave The Da River reaches its peak discharge in July, while the peak discharge of the Thao and Lo River are in August (see Figure 3.3) This leads to a peak flood discharge in the Red River in August as well The lag time of the peak discharge is due to the differences of topographic characteristics in the upper basin and the climate patterns, which are also changed due to the regional atmospheric conditions

(IAP, 200%; Khoi, 2010), The inerease rate of water level in a flood wave is relatively high

in the upstream river with a range of 3—7 m per day, while it is around 0.5 ~ 1.5 m per day in

the delta area, Recently, this increasing rate has changed due to the operation of reservoir

systems

‘Table: 1: Maxim rainfall in one day t stations in the catchment areas ofthe Red River system, data from (QUVN-2:2000/8ND (2009

‘Meteorology ‘Maximum rainfall (mmm) in different periods of time (minute)

Tại Chau Da 233/962 469/962 684/971 83/971 56/1971 IH6/71 I51/1871 174/1971 229/1971

Dien Bien 22/1972 SLANI97S —69.7/1972 896/975 94.3/1975 126/1975 I6B/A97S — 175/975 - 200/1975 Son La - 294/79 588/979 654/979 IH4/I979 12/1979 135/1979 137/1979 13/1979 171/1873

Hoa Bình © 3HR/IBBẢ 643/963 862/965 96.7/1965 101/185 146/1962 203/1962 238/1982 - 283/1875 lao Cai Thao 296/1961 7.I/I961 937/860 03/1960 105/160 51/1971 185/971 185/971 - 191/1971

SaPa River 29/1983 683/963 106/1963 NHA 41/1963 160/1963 163/963 186/1971 - 30/1968 Yen Bat > 294/881 701/961 943/961 101/196 I30/964 149/I964 1759/1973 187/1973 1989/1966

Ha Giang lo 26.8/1974 58/1979 776/979 9544/4979 14/1968 14/1973 183/961 200/1965 - 239/965

‘Tuyen Quang River 324/196 6L5/1463 94/1988 989/969 108/1964 122/961 130/1961 15/1961 211/1960

Viet TH - 3H4/973 388/977 24/975 —99.7/1975 106/975 128/175 190/975 292/173 - 372/1876 Son Tay, Red 307/970 625/970 897/970 1201970 I33/1966 232/971 281/971 41271971 5308/1971

Ha Noi River 352/1968 568/1969 94/1967 14/1967 116/1967 1390/1972 17/1972 180/1972 - 23/1972 Nam Dinh - 307/965 631/965 15/1977 I81/M37 Â9UVIS77 2181977 222/977 236/197 250/1975 Ninh Bình = 40/1878 808/974 IHUIWZB I6O/IS7B IÐ2/I978 232/1978 248/1978 3401978 529/1878

It is believed that the most critical situation will coincide when there is an extreme flood

inall three rivers, in combination with heavy rain in the downstream and a high storm surge

on the coast; however, the probability of this event is not investigated in this study, and even

it is expected to be very small (Kivi, 2010)

2.1.3 RIVER SYSTEMS

‘The Red River and the Thai Binh River systems influence the water management in the

RRD with their total annual water volume of around 120 billion cubic metres The Red River

system constitutes the major part! of the delta, which has a total length of 1150 km and

a basin area of 143,000° km? at Son Tay, including the Da River, Thao River, and Lo River,

‘The characteristics of these rivers will be discussed in more detail in Chapter 3 In the Thai

Binh River system, the total length is around 388 km and basin area is about 15,180 km?,

including the Cau River, Thuong River, and Luc Nam River, which forms a minor part of

the delta Interestingly, the Thai Binh River system is named after Thai Binh although only

around 5 km of river flows through the area of Thai Binh province, see Figure 2.5 and Table

22

From the Red River, water will be diverted into the Duong River and the Luoc via the

Thai Binh river system The diversion rate at the Duong River is around 28 - 30% while

that of the Lược River is around 10 — 14% of the total discharge from Son Tay Recently,

these diversion rates have been increased and led the dike system in the Thai Binh River

to overload with flood water (Kho, 2010; WAP, 2009) Typical flood discharges in different

gauge stations along the Red River indicate the decreasing discharge rate from the Ha Noi

area to the downstream, see Figure 2 for more information

‘in the flood season, the peak discharge at Son Tay (the Red River) is about 1216 times of the peak discharge

at Pha Lal (three tributaries ofthe Thai Binh River, including the Cau River, Thuong River, and Luc Nam River,

exclusive the diverted discharge from the Duong River, see Figure 2»), a

The total basin area of the Red River and the Thai Binh River is around! 169,000 kmn?, of which 51% is in the Viet

‘nam area, 48% isin the China area and 1% in the Laos area

12 2 FLooD DEFENCES MANAGEMENT IN THE RED RIVER DELTA

Figure2.5: Simplified scheme of the Red River and Thai Binh River systems in the Red River Delta

‘Table22i Maximum flood discharge and water levelin the Red River system, data from iol (2010; WI? GO,

Station 89” (km?) — QmaxmDi) — Hmaxim) - Month-year

(C) the predieted values by taking the dike filures into account:

(¢*) see the simplified scheme of the River systems in Figure 25

2.2 SOCIO-ECONOMIC CHARACTERISTICS

2.2.1 RELEVANT SOCIAL CHARACTERISTICS

Asa result of the practising agriculture and the cultivation of water-rice in the RRD, the Viet people have close-knit communities During thousand of years of fighting against water,

Red River system “Thai Bình River system

Pha Lai (100%) +

=

2 [) 50-54%

Tra Ly River 124m ® | Luce River

Figure 2.6: Distribution of river discharge in the Red River and Thai Bình River system,

people have organised themselves and have created a modus of living with water, from a

small embankment to protect the low land for cultivation to a complete flood defence sys-

tem

‘The population of Viet nam, in 2010, was around 87 million people; of which in the Red

River Delta around 19.7 million, and in Ha Noi over 6.7 million people ‘The population

growth rate is around 1.03% per year and around 60% of population is in the age group of

15~60 years old The young population isa potential labour resource, but the population

pressure may also lead to the unemployment of the young people, see GSO (20! |) and Table

2 for more details,

During the economic reform, the urbanization has been expanded through areas with

different industrial zones, factories, and resident areas As a result, there will be signifi-

cant changes in land use and infrastructure, and the real estate will become more valuable,

‘Therefore, a demand of a higher safety standard for the flood defences has been increasing

in the public

To raise the awareness of flood protection, education is supposed to be the key measure

providing not only public education but also higher level training for staff and professionals,

Anumber of training projects have been conducted to help the Vietnamese Government to

strengthen their administration, governorship and research work (Binniie-Poriners, 194,05

Dijkman et al, 1996),

ca Delis Mountain -CentralCoast Highland Population, mil 9770 11603

62MB 51207 3/00

After 1986, the Doi Moi renovation helped to expand both size and quality of the economy

in Viet Nam, from the majority of state owned enterprises to the dominant non-state owned sectors, The economic value varies in proportion between agriculture, service, and industry, for instance agriculture values 19%, followed by service 38% and industry 43% respectively

‘The GDP growth rate and GDP per capita are illustrated in Figure 2.7

From the previous discussion, it is apparent that the growth rate of the economy has

(20 owe ft)

igure 2.7: Economic growth in the past 25 years in the period of 1996~2012, data from World Bank

‘huip://data.worldbankorg/country/vietnam

increased the standard of living of the citizens in the RRD, but it has also lead to problems

in terms of water management People in the RRD now have a higher income, and the in- frastructure has been expanded into villages The values of real estate and other properties

in the protected regions have also increased Furthermore, the politically and economically important role of the capital of Ha Noi will also lead to a catastrophic consequence if the area is flooded Therefore, the demand of a higher standard of safety in this area is created However, the over-expansion of residents on the flood plain leads to the increase of water level at the same discharge, which will threaten the dikes by overflow, see Chapter 3

2.3 DEVELOPMENT OF FLOOD DEFENCES AND SAFETY STANDARD

2

‘The imperial period of Viet Nam started in the 11" century" However, the ancient Viet

already knew, in the centuries BC, how to build dikes to protect themselves in the low-lying

land of the RRD, as described in the Chinese historical documents (Klianh, 1981) Dur-

ing the approximately one thousand years under Chinese rule, there was no noticeable im-

provement of the water management From the 1000s, the Ly emperors encouraged people

to construct dikes around the area of Ha Noi, the new country capital, and along the rivers

Subsequently, the following dynasties continued their fights against flooding in combina-

tion with protecting their country from the Northern invasions

Significant progress in hydraulic knowledge can be noted from the beginning of the 19"

century during the Nguyen dynasties, when people measured the water levels and strength-

ened the dikes after each flood Hundreds of kilometres of dikes were built throughout this

period, and most of them located in the major municipal areas in the Red River Delta In

1857, Mandarin Nguyen Tu Gian proposed an integrated measures for flood protection, in-

cluding dams, reservoirs, and river dredging instead of heightening the dike crest level only

(Khanh, 1981; Khanh et al., 1985)

‘A number of dike construction programs were undertaken by the Nguyen Emperors,

and therefore, the last geometry measurements of dikes and the typical flood in 1893 were

selected for the calculation of this period There were 38 dike-failures years during the 19'!

century with catastrophic economic damage and fatalities; in contrast, only 8 years of river

dike-failures were observed in the 20"” century Atthe end of this period, the dike systems in

the RRD were partly constructed, but at least it could protect against a water level of 10.5 m

equal to flood frequency of 1/2-1/5 years (see Khuinh, 1981; Khanh et al., 1995; PPD, 2000)

1 IMPERIAL PERIOD

2.3.2 FRENCH PERIOD

‘The French period is from the 1890s to 1945 when France fully established their rule in Viet

Nam At that time, the French were concerned with the construction of hydraulic structures

to protect cities from flooding, especially in the Ha Noi area The French engineers were

involved in the water management plan at that time, namely Norinandin, Peytavin, Rouen,

whose plans set a foundation for the flood mitigation in the Red River Delta Hundreds of

kilometres of dikes were built and strengthened following the dike improvement programs,

mainly from 1915 to 1926 such as the 1*' and 2"¢ dike programs (Gauthier, 191; GDM,

1995; Khanh, 1981)

‘The amount of earthwork carried out in the French period is the second biggest compare

to all four rehabilitation strategies, see Figure 2 Consequently, the noticeable progress in

flood protection was made during this period, for instance the increase of the dike crests

from 10 5m to 13.0 m, and the construction of the Day flood gate to divert water to the

Day River in 1937 On the other hand, the safety levels were not equally established for

the whole delta, as for instance the flood in 1945 leading to dike failures in many locations

outside the Ha Noi area The French engineers also realized that it should be important to

deal with different safety criteria for each of the protected regions, but these plans had not

been completed because of the Vietnamese revolution in 1945 In other words, the dike

programs were accomplished as far as possible in 1945

This period is only defined for the assessment of the flood defences inthe Red fiver Dela

2.3.3 Vier NAM WAR PERIOD

‘The third period is the Viet Nam war’, which resulted in the anomalies of the river dikes; the dikes, at that time, could be bomb targets or were excavated to slow down the enemies’ assaults In terms of dike engineering, the anomalies of dike embankment came not only from its very construction, but also from such war activities, Although, many rehabilitation projects have since then been carried out in different dike systems in the RRD, they were still threaten in high flood waves After the declaration of a new Viet Nam (by Ho Chỉ Minh and the pro-communist people), the new government also paid attention to strengthen the flood defences with the design water level equivalent to a flood frequency of 1/50 years Millions of man-days had been mobilised for the earthworks from 1954 to 1965 It led the amount of the earthwork in this period to the first proportion, see Figure 2 0,

In 1971, the flood frequency of approximately 1/75 - 1/100 years, affected the Red River Delta with serious damage and fatalities, but the dikes around Ha Noi were safe After that, the Vietnamese engineers developed a plan to strengthen the flood defences by the construction of dams and reservoirs to redistribute river water discharge This is supposed

to be the most important measure of the flood mitigation in this delta, because the dike crest heightening is limited due to its soft foundation and land-use in the highly populated delta

‘The Hoa Binh hydro-power station was constructed in 1979 under the support from the Soviet Union It is estimated to cut down the flood discharge to 7 billion cubic metres (Shoi, 2010) Consequently, the safety standard was established, for the Red River dikes, equivalent to the design water level of 13.3 m in Ha Noi (around the water level in Ha Noi in the 1971 flood)

2.3.4 DoIMol PERIOD

‘The last period is the Renovation-of-Economy period (known as Doi Moi in Viet Nam) from

1986 till now, Economically, the non-state enterprises were established and equally treated

as the state-owned sectors As a result, new technologies have been applied to the dike safety in the projects funded by the Asian Development Bank (ADB) and by local govern- ments The safety level of the flood defence system has been significantly improved due

to the application of effective measures such as the reforestation in upper basins, the con- struction of dams and reservoirs to store water, the rehabilitation of dikes, and the raising public awareness of flood protection, The Hoabinh hydro-power station was completed in

1989 and others finished in 2007 and in 2012, which upgraded the total maximum storage volume to around 8.5 billion cubic meters, In short, the Red River dikes are now able to withstand a flood frequency of 1/250 years to 1/500 years compared to 1/50 years in the Viet Nam war period (Khoi, 2010)

2.3.5 REVIEW OF DIKE ENGINEERING IN FOUR PERIODS During the past hundred years, overflow and the resulting erosion of the inner slope, which came from the limited height of the dike systems, caused many dike failures From the imperial period until now, the dike embankments have been heightened many times, and

“The Viet Nam war is widely recognized inthe period of 1955~1975; hereafter, we use this definition for the periods ofbolh 1945-1954 (the French restored their colonial rule tillthe end of the Dien Bien Phu Battle), and 1955—1975 {involvement of American Army -after the Geneva Conference tothe fall of the South Viet Nam government)

‘The dikes protect the old square ofthe Ha Not area on the right bank ofthe Red River

properties and their distributions, which play important roles in the dike safety assessment, also change underneath the dikes, particularly during a long flood wave

‘As can be seen from Figure 2.0, the earthwork has been undertaken for hundreds of years From 1955 to 1975, most of the earthwork had been done, followed by that of the French period (1905 ~ 1945); the rest took place in the Doi Moi and the Imperial period Figure 2.9 demonstrates how a dike has been constructed in different periods, from a very low dike to a current massive dike (Gauthier, 1931; GDM, 1995; Khanh, 1981; Khanh et at, 1995) Figure 2 10 presents the decrease of the flood frequency and flood water levels, in different periods of dike rehabilitations at a dike section at Km54 +200, from 91% in the

18905 to 0.2% in 2000, See Tui et al (2012b) for more details

160 E10

2.8.6 TYPICAL ELOODS |N VIET NAM FROM THE 1900s

There are several typical floods such as the flood in 1905, 1915, 1925, 1939, 1945, 1968, 1969,

1971, 1986 and 1996, which lead to the catastrophic damage for the RRD In this study, we describe the details of the flood in 1971 (before the operation of the Hoabinh reservoir) and the flood in 1986 (after the operation of the Hoabinh reservoir), which also caused the two dike failures at Cong Thon and Van Coc on the Red River dike system in the area of Ha Noi

dey

Compaction ratio K = P42 with pary isdry density of Sol pqs bs maximum censty whichis found by plotting

a density ~ moisture curve in compaction laboratory test (ASTM D698 & ASTM D1S57 ).

be 37,800 m/s after the restitution analysis, by taking the dike failures into account, The flood frequency was around 1/75 ~ 1/100 years and the measured water level at Ha Noi was

13.9 m, The Red River dike protected zone 1 (see Figure 2.2) was safe but the dikes at others

locations failed (e.g, Khe Thuong - the Da River, Cong Thon - The Duong River, and Nhat

‘Trai — the Thai Binh River) The inundated areas were 2500 km? and resulted in 594 fatali- ties, affecting of around 2.7 million people (see Tinh (2000) and Figure A.2

‘The dike failure at Cong Thon in Gia Lam district of the city of Ha Noi took place at 20:00

on August 23, 1971, lagged 18 hours after the peak flood, and the water level was decreased

by 22 cm, see Figure 2 ¡1 & Table 2.5 Termite activity and piping were believed to be the main causes of this failure In Gia Lam district, the catastrophic damage included the in- undation area of 9.1 km?, and 20 fatalities, see Appendix \ and DMD-1iN (2002) for more details

THe 1986 FLo00

‘The flood in 1986 was a result of the very large floods in both the Thao and Lo rivers and

in combination with the medium flood in the Da River Consequently, 165 people lost their lives, and a large area of the Phu Tho, Vinh Phuc, Bac Ninh, Bac Giang, and Ha Noi provinces were inundated

‘The dike failure at Van Coc happened at 1:25 on July 28, 1986, when the water level

‘was 12.m lower and 17 hours earlier than the peak of flood (see Figure 2 11) Piping was observed and believed to be the cause of the dike failure The consequences of failure were the inundation of an area of 22.9 km? with a huge damage See Appendix \ for more details,

station with indications ofthe dike failures at Cong Thon and Van Coc

(On the state level, the Ministry of Agriculture and Rural Development (MARD) has full re-

sponsibilities for the water management and flood defence in the flood season The Min-

ister of MARD is also the vice-president of the National Committee for Flood and Storm

Control (NCFSC) '" which will carry out the management of emergency actions to deal with

flooding and storms in the rainy season The General Water Management Office (GWMO)

under MARD, and the Department of Dike Management and Flood Control (DDMEC) under

GWMO, are responsible for dike management and technical support of the flood defences

in Viet Nam The DDMEC is also incharge of the new research and construction projects for

One Vice Prime Minister wil be incharge as the president of NCPSC,

the dike improvement and flood protection

On the provincial level, the governor of each province will create the same system to deal with disaster and water management The Provincial Committee for Flood and Storm Control (PCESC) is set up from the different representatives of Departments on the provin- cial levels The Dike Management Division (DMD) under the Department of Agriculture and Rural Development (DARD) has the similar duties and responsibilities as the DDMEC, but in the lower level DMD may carry out new projects for dike improvement under the approval of the DDMEC or the provincial government

On the district level, similar schemes will be established for both flood defence manage-

‘ment (dike brigade) and the District Committee for Flood and Storm Control (DCFSC) In each dike brigade, engineers are incharge of the local flood defence management and the maintenance work The dike brigade may be divided into smaller groups to deal with the actual situations during the flood season

On the commune level, the Commune Committee for Flood and Storm Control (CCFSC)

is also established but there is no organization of dike management at this level However, the local authorities have responsibility to coordinate the local dike brigade (if present) Figure 2.12 presents a framework of the water management, disaster management systems;

‘see Vrolijk (2002); [WAP (2009) for more information

2.4.2 FLOOD DEFENCE MANAGEMENT

Having discussed in the previous sections, the strengthening of the dike systems in the RRD has been mentioned in the management of flood defences, considering it as a part of the water management plan (e.g surface water, ground water, waste water, and drinking wa- ter), The flood risk in the RRD may come from both rivers and coast, as a result of heavy rainfall from typhoons, fronts, and tropical depressions However, high precipitation also comes from downstream areas, which leads to inundation inside the protected regions The Red River flood defence system is defined asa system of dikes, and hydraulic structures (e.g culverts, dams, reservoirs, flood gate, flood retention area), In this study, we will pay atten- tion to the system of dikes; the hydraulic structures are discussed in other research projects Currently, the management of flood defences in the RRD follows the guideline in 1! 1CN

{22 (2002) with the following features:

~ Design water levels of the dike in Ha Noi are equivalent to a discharge with frequency

of 1/500 at the Son Tay gauging station, under the system operation of a series of reservoirs in the upstream rivers;

~ Incase of an extreme condition, water will be diverted into the Day River (if the water level at Ha Noi is predicted to be higher than 13.4m and the storage capacities of the reservoirs reach their limit:

~ The flood mitigation measures for the RRD include:

+ Strengthening dike system;

+ Dredging river bed (to increase flow discharge);

+ Constructing reservoirs;

+ Diverting flood discharge;

+ Reforesting in the catchment;

+ Intensifying awareness of flood protection

Figure 2.12: Scheme of flood management and disaster management in relation to th

in which, MARD is the Ministry of Agriculture and Rural Development: NCFSC is the National Committee for

Flood and Storm Control; GWMO is the General Water Management Office; DDMEC is the Department of Dike

‘Management and Flood Control; PCESC is the Provincial Committee for Flood and Storm Control; DMD is the

DARD s the Department of Agriculture and Rural Development; DCESC isthe District Committee for Flood and Storm Control, and CCPSC is the Commune Committee for Flood and Storm Control

administrative system;

Itis clear that human errors may lead to the failure of the system operation of the flood de-

fences, including failure of dams, culverts, flood gates, and/or emergency measures How-

ever, the question of how to reduce human errors in system analysis will not be answered in

this study

2.5 DISCUSSION

Te natural conditions play an important role in the flood defence management in the

RRD because of its typical topography and meteorological characteristics ‘There is

around 50% of the delta area is lower than 2 m andit is surrounded by high mountains Con-

sequently, the flood will be routed through the tributaries systems and affects the lowland

areas Furthermore, the monsoon climate with its typhoons, fronts, and tropical depres-

sions, leads to heavy rainfall in both the upstream and delta area The extreme conditions

The flood defences in the RRD have been established for hundreds of years and the safety standard has been increased from a design water level of 1/2 years to 1/500 years The design water level at Ha Noi is 13.4 m while it will be 13.1 m for the dikes in other provinces (the design water level will be routed from the Ha Noi gauging station) The dike manage- ment system is created in cooperation with the administrative governance and the disaster management system, It is suggested that the management, improvement, and planning of the flood defences should be carefully considered from scientific studies

CONDITIONS OF THE RED RIVER

DELTA

In this chapter, the hydraulic boundary conditions for the Red River dike assessment are considered, First, a system description of the water management scheme, including river tributaries, dikes, dams, and reservoirs, is provided in Section 3 | In Section #2, the river discharge is analysed, and its changes due to the redistributed effects of reservoirs systems will be presented, followed by an analysis of flood routing The final sections pose the chal- lenges for the future (Section 3.3) and a chapter discussion (Section 3.4) The calculation results of this chapter will be incorporated in Chapters 5, 6, and 7

‘The Da River begins in the high mountain area in the south of the Yunnan province of China with a total basin area of around 53,000 km®, in which the catchment area belonging

to China takes 49% and to Viet Nam 51%, see Eigtire 3.1 The landforms of the basin in the Viet Nam area are characterized by steep mountains and elevations vary from location to location Consequently, the highest flow discharge of the Da River is 1.75 times higher than that of the Thao River in spite of the fact that the catchment area of the two rivers are equal

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