by This research is performed in partial fulfilment of the requirements for the degree of Master of Science in Hydraulic Engineering and Water Resources Management at Delft University of Technology and National University of Singapore. Delft, 14 January 2015 Arnold van ´t Veld [email protected] Prof.dr.ir. N.C. van de Giesen Delft University of Technology (chairman) Dr.ir. O.A.C. Hoes Delft University of Technology (daily supervisor) Nelen & Schuurmans Dr.ir. F. Nelen Nelen & Schuurmans Prof.dr.ir. G.S. Stelling Delft University of Technology National University of Singapore (co-supervisor) Prof. H.F. Cheong National University of Singapore (co-supervisor) Dr. S.Y. Liong National University of Singapore (examiner) This graduation thesis concludes the double degree programme “Hydraulic Engineering and Water Resources Management” started in August 2012 at the National University of Singapore and Delft University of Technology. The curriculum includes courses about the physical behaviour and modelling of water and sediments in sea’s, coastal waters, rivers and small channels. The research is proposed by the Filipijnengroep Netherlands and later on supported by Nelen & Schuurmans and Nationwide Operational Assessment of Hazards Project. I am greatly indebted to a lot of people, too many to mention all of them, for their help during this research. In this way, I want to thank the persons that are not mentioned below. In special I thank - Sir Hernando (Pampanga River Flood Forecasting Warning Center) and Sir Rigor (Angat Dam Operator) for their insides and detailed data about their River Basins; - NOAH with Sir Lagmay, Sir Tanjuakio, Sir Reyes and others for the support towards other agencies, providing laptop and accommodation and sharing all the knowledge and data in the project; - Sir Cruz and Madam Villanueva for using their network, arranging appointments, meetings and accommodation, and being a discussion partner for organizing thoughts; - Evert and Dick (Filipijnengroep Netherlands) for providing the subject; familiarizing me with the subject; introducing me to important contacts in the Philippines and reviewing the reports; - Colleagues at Nelen & Schuurmans for answering technical questions, providing a fruitful working environment and allowing me to use all the facilities; - Fons, Guus and Nick (Graduation Committee) for joining me to the Philippines (Fons and Guus) and for their feedback and encouragements; - Olivier (daily supervisor) for creating an obligation free relation with the company, a relax and fruitful supervision, giving insights in writing reports and improving presentations; - My friends in Rijnsburg and Delft for their support and encouragements during tough times during the research period; - My parents and brother for their support and encouragements and the reviews of the report, especially the in-depth reviews of my brother; - My fiancée for her love, being a discussion partner for organizing thoughts, reviewing and more; - and above all, God for guiding, protecting and blessing me during the whole research. Arnold van ’t Veld Delft, January 2015 Page | I The Pampanga and Angat River Delta, located on the northern side of the Manila Bay in a large alluvial plain, are regularly confronted with worsening fluvial and tidal floods. The fluvial floods are caused by typhoon and southwest monsoons and damages houses, roads and harvest of many rice paddies and fishponds. The tidal floods are caused by storm surges and high tides and are merely unpleasant because roads are not accessible and some houses are flooded. The large flood events, normally a combination of a fluvial and tidal flood, are causing an economic setback pertaining a vicious circle. Eight municipalities formed an alliance of coastal communities to tackle these flood related problems. The following research question is determined based on their problems: “What are the effects of potential measures to reduce the fluvial and tidal floods in the Pampanga and Angat River Delta, Philippines?” To assess the performance of potential measures, a 3Di model is used to estimate the current and future scenario with Pedring 2011 as representative storm event. A digital terrain model including sea and river bathymetry with a resolution of 1 x 1 m covering an area of 900 km2 is used as input for the model. The main inflows during Pedring 2011 are the Pampanga River at Mount Arayat with a peak discharge of 2800 m3/s and Manila Bay with a storm surge enhanced tide of 1.8 m above MSL. Subsidence rates up to 4.5 cm/year due to groundwater extraction are the main cause of the worsening floods. With subsidence, the flood extent in the populated areas increases from 80% to 87% in 50 years. The flood damage in the Pampanga and Angat River Delta increases from 1.5 to 2.1 billion pesos mainly due to the increase in damage in the populated area. Three measures have a positive impact on fluvial and tidal floods, have minor side effects, and are applicable in combination with all other measures. With precipitation predictions, the dam operation of Angat and Bustos dam could be improved by maximising the use of their flood storage capacities. This measure has the highest benefit-cost ratio of 21. The current levees protecting the city centres of Masantol and Macabebe are very lucrative to be monitored and maintained at the current elevation. The yearly costs are estimated at 11 million pesos/year. Groundwater extraction regulation and new potable water sources is an expensive measure with a maximum of 145 million pesos/year, but could stop the current subsidence. Two measures with large effects remain: fishpond dike height regulation and flood prevention with levees and tidal gates, like the Pampanga Delta Development Project. The former measure reduces the fishpond dike height just above spring tide, opens the gates during a fluvial flood and compensates the owners. This reduces the flood through the additional flow capacity towards Manila Bay making this measure beneficial. A fishpond flood channel consisting of around four neighbouring fishponds is advised to start with as first phase, because of its efficiency and feasibility. Flood prevention is possible by creating an expensive closed systems of levees, road elevations, tidal gates and fishpond dikes. This measure protects the area in the closed system, but enhances the flood outside the area. Page | III ABB-BP Alliance of Coastal Communities in Bulacan and Pampanga BODC British Oceanographic Data Centre CBDRR Community-Based Disaster Risk Reduction DEM Digital Elevation Model DTM Digital Terrain Model DREAM Disaster Risk Exposure and Assessment for Mitigation GEBCO General Bathymetric Chart of the Oceans JICA Japan International Cooperation Agency LiDAR Light Detection And Ranging MSL Mean Sea Level NIA National Irrigation Administration NOAH Nationwide Operational Assessment of Hazards Project PDDP Pampanga Delta Development Project PAGASA Philippine Atmospheric, Geophysical & Astronomical Services Administration PRFFWC Pampanga River Basin Flood Forecasting & Warning Centre SLR Sea Level Rise Page | V PREFACE .......................................................................................................................... I ABSTRACT...................................................................................................................... III LIST OF ABBREVIATIONS ................................................................................................ V 1 | INTRODUCTION ........................................................................................................ 1 1.1 Problem formulation .................................................................................................. 2 1.2 Relevance of the research .......................................................................................... 3 1.3 Outline........................................................................................................................ 4 2 | PAMPANGA RIVER BASIN ......................................................................................... 5 2.1 Geography .................................................................................................................. 5 2.2 Precipitation, rivers and dams ................................................................................... 6 2.3 Tide and surge ............................................................................................................ 9 2.4 Flood impact description ......................................................................................... 10 2.5 Typhoon Pedring ...................................................................................................... 11 2.6 Area description summary ....................................................................................... 13 3 | 3DI .......................................................................................................................... 15 3.1 Explanation .............................................................................................................. 15 3.2 Set-up ....................................................................................................................... 20 3.3 Performance............................................................................................................. 25 3.4 Sensitivity ................................................................................................................. 26 3.5 Model Summary ......................................................................................................