Sediment response to tropical storms in singapores residential catchments

SEDIMENT RESPONSE TO TROPICAL STORMS IN SINGAPORE’S RESIDENTIAL CATCHMENTS BY LEE WAN AIK, DESMOND (M.Sc.) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF GEOGRAPHY NATIONAL UNIVERSITY OF SINGAPORE 2009 Acknowledgements It has been a meaningful experience to work with people who has offered valuable advice and help in this Ph.D. program. I would like to thank A/P Lu Xixi my supervisor for his help and understanding during this period and his contributions in making this thesis possible. I would also like to convey my deepest gratitude to A/P David Higgitt for his guidance and help in the thesis too. I would also like to take this opportunity to convey my thanks to the administrative staff at the Geography Department. Special thanks go to Miss Pauline Lee for her help in student administrative matters; Mr Tow Fui, for his help in sourcing for available equipment for this study has been phenomenon; Mr Yong Sock Ming for his help in GIS and Mrs Lee Li Kheng for her help in map drawing. From the time we met, till now, my wonderful wife, Jane Chan has been the pillar of support in all aspects. She has helped in many ways including laboratory work, samples collection and providing undying encouragement during my entire doctorate degree. When I am feeling down, she is always there for me. Thank you so much!! I would also like to thank my family members for the encouragement they have offered, especially my Mum and Dad for their patience and support during this period of study. There are several friends who have given lots of help in this study. I have to thank Daryl Lam for the several late nights of help in laboratory work, sample collection and his numerous comments on this study. I would also like to offer my gratitude to Shurong for sparing time in reading the thesis. I would also want to thank Miss Yolanda Chin, Miss Katherine Quah, Woon Chih Yuan and Brian Tan for proof-reading my chapters, and Sovan for his help in statistics. I would also like to thank several other friends for their constant motivation. They are May Tan-Mullins, Songguang, Harng Luh and Seeta. The times in the graduate room and drinking sessions are wonderful. The “Fieldstudies” group has been great support too in several ways. Finally, I would to thank the university for this research scholarship opportunity and the Geography Department in making this a wonderful learning experience. I Dedication This study is dedicated to my wife, Jane Chan and in special remembrance of my Grandma and Father-in-law, Chan Han Pooi for his selfless guidance in every aspect of my life. II Table of Contents Acknowledgements…………………………………………………………………… I Dedication ………………………………………………… .………………………. II Table of Contents ……………………………………………………………………. III Brief Summary…………………………………………………………………… .… IX List of Tables ………………………………………………………………………… XI List of Figures ………………………………………………………………………. XIII List of Plates …………………………………………………………… .…….…. XXIII Glossary .XXIV Introduction …………………………………………… ……………………………1 1.1 Background ……………………….…………………………………….… 1.2 Significance of the study in Singapore ………………………….… ………4 1.3 Relevance of this study to urban management …………………… .……8 1.4 Aim and objectives of research ………………………………… …………10 1.5 Arrangement and structure of the dissertation …………………… …….…14 Study area and methodology …………………………………………… …… 17 2.1 Introduction ……………………………………………………………… .17 2.2 Jurong West and Ang Mo Kio urban residential catchments ……… …17 2.3 Land cover mapping …………………………………………… ………26 2.4 Measurement of rainfall …………………………………………….………30 2.5 Measurement of discharge …………………………………………….……31 2.6 Measurement of suspended sediment concentrations…………………….…36 III 2.7 Continuous turbidity measurements ……………………………… … …38 2.8 Dissolved organic carbon analysis ……………………………….… .……39 2.9 Soil compaction measurements ………………………………… ….……41 2.10 Soil infiltration measurements …………………………………………… 43 Storms characteristics ……………………………………………… … ………45 3.1 Introduction …………………………………………………… …….……45 3.2 Individual storm events ………………………………………….…………46 3.2.1 Magnitude, intensity and duration…………………….…………47 3.2.2 Antecedent dry period …………………………………… ……54 3.3 Monthly rainfall …………………………………………………….………56 3.4 Annual rainfall …………………………………………….…… …………61 3.5 Conclusion ………………………………………………………….………62 Runoff response to storms ……………………………………………….……… 64 Abstract …………………………………………………………… …….……… 64 4.1 Introduction ……………………………………………………… ……… 65 4.2 Estimate of runoff response time during storm events ……………… ……74 4.3 Storm hydrographs …………………………………………………………76 4.4 Lag time and time to peak …….……………………………………………79 4.5 Storm runoff ratio ……………………………………………………… …84 4.6 Conclusion and management implications …………………………………87 Appendix 4A ………………………………………………………………….…92 IV Pervious and impervious runoff …………………………………………………93 Abstract ………………………………………………………….…………………93 5.1 Introduction ……………………………………………… …….…………94 5.2 Directly connected impervious area ………………………… …….… .…99 5.3 Identification of pervious runoff events …………………………… .……104 5.4 Factors influencing pervious runoff …………………………………….…108 5.4.1 Catchment characteristics ………………………… …….……108 5.4.2 Storms characteristics …………………………………….……108 5.4.3 Antecedent dry period …………………………………………114 5.4.4 Temporal contributions of pervious runoff ……………………116 5.5 Conclusion and management implications ……………………….…….…119 Appendix 5A ……………………………………………………….……… …124 Appendix 5B ………………………………………………………….…… …126 Suspended sediment concentrations ……………………….………… …… …128 Abstract ………………………………………………………………… …… …128 6.1 Introduction ………………………………………………………… ……130 6.2 Suspended sediment concentrations during storm events …………… … 136 6.2.1 General characteristics ……………….………….………… …136 6.2.2 Individual storm events ………….……………………….….…143 6.2.3 Seasonal variations ……………………………………… ……159 6.3 Turbidity as a surrogate for suspended sediment concentrations ……… 162 6.3.1 Turbidity levels …………………………………………… .…162 V 6.3.2 Turbidity rating curves …………………………………………165 6.3.3 Assessment of turbidity as suspended sediment concentration surrogate …………………………………………………… …170 6.4 Conclusion and management implications …………………………… …176 Hysteretic and flushing patterns of suspended sediment …………… .………183 Abstract ……………………………………………………………………………183 7.1 Introduction …………………………………………………………… …185 7.2 Suspended sediment flushing magnitude ……………………………….…204 7.3 Suspended sediment hysteresis patterns ……………………………… …221 7.4 Factors influencing suspended sediment hysteresis patterns and shape … 230 7.4.1 Storm characteristics ……………………………………… …230 7.4.2 Catchment characteristics ……………………………… .……239 7.4.3 Construction activities and bare soils surfaces …………… .…242 7.5 Conclusion and management implications ………………………… ……246 Appendix 7A ………………………………………………………….… ……250 Appendix 7B ………………………………………………………………… 254 Appendix 7C ……………………………………………………………… .…257 Appendix 7D ………………………………………………………….… ……258 Appendix 7E ………………………………………………………….… ……260 Appendix 7F ……………………………………………………………………261 Appendix 7G …………………………………………………………… .……264 VI Sediment load estimate …………………………… ……………………………266 Abstract ……………………………………………………… .………………….266 8.1 Introduction ………………………………………… ……………………268 8.2 Fitting of sample-based sediment rating curves …………………… .……279 8.3 Accuracy of sample-based sediment rating curves ……………….….……289 8.4 Event-based sediment rating curves ………………………………….……300 8.5 Conclusion and evaluation of applicability of rating curve ………….……317 Appendix 8A ……………………………………………………………… .…322 Appendix 8B ………………………………………………………… .………327 Dissolved organic carbon ………………………………………… ……………332 Abstract …………………………………………………………………… .…….332 9.1 Introduction ………………………………………………………… ……333 9.2 Dissolved organic carbon concentrations …………………………………342 9.3 Relations with water discharge ……………………………………………345 9.3.1 Impact of large and small storm events ……………….….……347 9.4 Relations with suspended sediment concentrations …………………….…348 9.4.1 Antecedent dry period …………………………………….……351 9.5 Dissolved organic carbon load and flux …………………………… ….…353 9.6 Conclusion and management implications ……………………….….……361 Appendix 9A …………………………………………………………….… …366 Appendix 9B …………………………………………………………… .……368 Appendix 9C …………………………………………………………… .……370 VII Appendix 9D ……………………………………………………………… .…372 Appendix 9E ……………………………………………………………… .…375 Appendix 9F ……………………………………………………………………377 Appendix 9G …………………………………………………………….…… 379 Appendix 9H ………………………………………………………… ……….381 10 Conclusions ………………………… .…………………………………….…….383 10.1 Brief overview of the study ………………………………………………383 10.2 Major findings and achievements …………………………………… …384 10.2.1 Pervious and impervious runoff separation ………………… . 384 10.2.2 Variations in temporal suspended sediment response in tropical storms …………………………………………………… ……390 10.2.3 Sediment yield estimate ……………………………………… 395 10.2.4 Dissolved organic carbon response to tropical storms ……… 399 10.3 Prospects in future research …………………………………… .………402 10.3.1 Stormwater monitoring program ……………………….………402 10.3.2 Assessment of polluting sources …………………………….…404 10.3.3 Expansion of urban tropical studies ……………………………405 10.3.4 Improvements in field set-up and data collection methods 406 10.4 Research limitations …………………………………………… ………407 10.4.1 Sampling period ……………………………………….………407 10.4.2 Manpower and research funds ………………………… .……408 10.4.3 Data availability …………………………………………….…408 References ……………………………………………………………………………409 VIII Brief Summary Urbanization impacts have been strongly recognized as a threat to the sustainable management of urban water resources, especially to developing countries in the tropics. At the moment, little information on urban tropics is available. This research aims to investigate high density urban residential catchments’ impacts on runoff, sediment delivery and dissolved organic carbon in the tropics. A sampling period of 20 months was carried out in two catchments namely, Jurong West (JW) and Ang Mo Kio (AMK). JW is 69 in size and is 84% impervious while AMK is 35 in size and 60% impervious. Quick runoff responses are observed in 120 and 106 storm events sampled in JW and AMK respectively. JW has shorter runoff lag time, longer time to peak timing and higher runoff ratios than AMK. Large storm events, coupled with poor urban soil conditions have led to immediate pervious runoffs (Saturation Overland Flow and Hortonian Overland Flow) during storm events. Higher abstraction loss and hydrograph evidence indicate pervious runoff in AMK is contributed in delayed form (Throughflow) too. 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(2005) “Uncertainty of Simulated Catchment Runoff Response in the Presence of Threshold Processes: Role of Initial Soil Moisture and Precipitation”, Journal of Hydrology, 315, pp. pp. 183 – 202. 430 [...]... storm magnitude and duration in Jurong West 47 Figure 3.2: Relation between storm magnitude and duration in Ang Mo Kio 48 Figure 3.3: Quantile values of storm magnitude in Jurong West and Ang Mo Kio 50 Figure 3.4: Changes in storm intensity from the 5th to 30th minute in Jurong West 51 Figure 3.5: Changes in storm intensity from the 5th to 30th minute in Ang Mo Kio 51 Figure 3.6: Changes in storm... flushing magnitude with relation to storm magnitude in Ang Mo Kio 214 Figure 7.13: Scatter plot of flushing ratio against storm magnitude in Jurong West 216 Figure 7.14: Scatter plot of flushing ratio against storm duration in Jurong West 216 Figure 7.15: Scatter plot of flushing ratio against storm magnitude in Ang Mo Kio 216 Figure 7.16: Scatter plot of flushing ratio against storm... management plans, Singapore’s flood prone area was reduced from 6900 ha in the 1960s to 297 ha in 1997 and currently stands at 130 ha although small scale flooding in low-lying areas still occurs during extreme storm events (Lim 1997 and Singapore PUB 2007) 4 Another challenge facing Singapore pertains to meeting the water demands of its increasing population and growing economy Singapore relies on... Non-point sediment sources like construction sites and pervious cover also contribute sediment into stormwater Small construction upgrading works are frequently carried out, especially in residential catchments Unplanned removal of pervious cover and open exposure of construction materials have resulted in sediments being transported into drainage network during storm events Heavy compaction from machinery... This study seeks to investigate runoff response and runoff type during storm events Emphasis is also given to sediment generation and delivery during storm events and variations in dissolved organic carbon (DOC) in two small, high-density residential urban catchments in Singapore – Jurong West (JW) and Ang Mo Kio (AMK) In Singapore, 80% of the population is housed in high-density housing (Kwame 1999).This... potential sediment source 142 Plate 6.2: Suspended sediment contribution from bare soil patches during storm event 142 Plate 6.3: Photos showing detachment and mobilization of deposited sediment from bare soil during a storm event 155 Plate 6.4: Photos showing sediment deposited beside a drainage inlet after a storm event, awaiting to be transported at the next storm event... contributes to sustainable water resource management in Singapore The key weakness of most sediment management programs in the tropics has been their limited capacity to identify key problem areas and focus efforts in addressing them Hence, like other tropical cities, Singapore is still deficient in its urban sediment management program In order to proper design sediment reduction programs, information... bringing the two (people and water) closer together (Singapore PUB 2007) Given the current situation, a study which examines the impact of urbanization on Singapore is useful and complements the government’s efforts in protecting Singapore’s limited resources The delivery of sediment into receiving waters has been made easier under tropical conditions than temperate areas This is because tropical storms. .. taps to meet its water needs The first is water imported from Malaysia The second is stormwater runoff collected from local catchments that is diverted into reservoirs The third is NEWater which is recycled water used for drinking and industrial purposes The fourth is desalination Desalination is the process of removing salt from seawater and treating it for industrial and drinking purposes The Singapore... is needed to resolve the problem of land use management in Singapore A Singapore Green Plan 2012 has been formulated by the Ministry of Environment to muster efforts towards sustainability (ENV 2003) The main goals in the green plan consist of effective waste management, nature conservation, maintaining clean air, ensuring sufficient water supply, excellence in public health, improvement in environment . Changes in storm intensity from the 5 th to 30 th minute in Jurong West 51 Figure 3.5: Changes in storm intensity from the 5 th to 30 th minute in Ang Mo Kio 51 Figure 3.6: Changes in storm. SEDIMENT RESPONSE TO TROPICAL STORMS IN SINGAPORE’S RESIDENTIAL CATCHMENTS BY LEE WAN AIK, DESMOND (M.Sc.) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY. storm intensity in Jurong West 52 Figure 3.7: Changes in storm intensity in Ang Mo Kio 52 Figure 3.8: Daily rainfall during dry months in Jurong West 55 Figure 3.9: Daily rainfall during