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MINISTRY OF EDUCATION AND TRAINNING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT VIETNAM ACADEMY FOR WATER RESOURCES SOUTHERN INSTITUTE FOR WATER RESOURCES RESEARCH ==================== DANG THANH LAM DEVELOPMENT OF A SUITABLE MODEL FOR HYDRAULIC SIMULATION OF THE INTEGRATED URBAN DRAINGAGE SYSTEM IN TIDAL AREA Research Sector: Water Resources Engineering Sector Code: 62 58 02 12 PHD THESIS SUMMARY Ho Chi Minh city-2015 Study is done at: Southern Institute for Water Resources Research Supervisor: Prof.Dr Nguyen Tat Dac Review Expert 1: ………………………………………………… Review Expert 2: ………………………………………………… Review Expert 3: ………………………………………………… Thesis will be presented at Evaluation Board of the Academy organized at : ……………………………………………………… ……………………………………………………………………… At hour of the date month year 2015 Thesis is available at: National Library of Viet Nam Library of the VN Academy for Water Resources Research Library of the Southern Institute for Water Resources Research 1 INTRODUCTION Scientific research and practical application of effective drainage and solving inundation depends on several factors of which the application of urban hydrological and hydraulic modelling is a very important one for planning and design of drainage system. A technical tool namely DELTA-P has developed to compute complex interactions of river and sewerage system under the influences of rainfall, flood and tide. Study purpose: To find scientific solutions for urban drainage issues and to improve river and pipe hydraulic coupling model for suitable urban application under specific conditions of strong tidal impact, heavy rainfall and rapid urbanization in Viet Nam. Findings: (1) Development of a computer module P for urban hydraulic modelling; (2) Coupling of module P and existing river hydraulic model DELTA; (3) Simultaneously run model for surface rainfall-runoff, pipe flow and tidal river hydraulic computation; (4) Capable application of coupling model for an actual drainage network. Scientific values: The research study has developed a new model DELTA-P for coupling model on urban surface-pipe-river simulation. The model has been successfully tested. Practical values: Provide a new capable modelling tool for solving urban drainage problems. 2 CHAPTER 1 : OVERVIEW OF URBAN FLOODING URBAN DRAINAGE MODEL 1.1. FLOODING CITIES AND MITIGATION MEASURES FOR It is said that the urban drainage work began in thousands of years ago. By the 1980’s, application of computational technique for simulation of drainage network had been improved economic benefit and more technical transparent. However, statistical reports shows still rapidly flood damages in the world . Annual flood damage estimate is at 100 millions USD in the first half of the XX century and it reaches 1 billions USD in the second half, especially about 10 billions in the latest 10 years. Urban flooding in Viet Nam is mainly caused by seasonal heavy rainfall, tropical storm and high tide. Some historical events are as follows: - Serious flood damage of Ha Noi capital city in November 2008. - Hue city is annually flooded 3-4 times with highest depth about 4 meters. - Da Nang city is often flooded at about 30 locations during heavy rain. - Can Tho in the Mekong delta is suffering from flooding in wet season. - Largest Ho Chi Minh is now hardly fighting against flood problems caused by upstream flood, heavy rain and high tide (Figure 1-1). Causes of flood: - Objective causes: low land, heavy rain, big upstream flood, 3 degradation of sewerage and rapid urbanization; - Subjective causes: ineffective urban planning, urban river encroach, protective forest degradation. Figure 0-1: Main causes for urban flooding of Ho Chi Minh city Mitigation measure: Urban flood mitigation planning is developing with active contribution of scientists, public and technology. Application of a capable model is defined in the integrated urban drainage strategy as follows: - Comprehensive analysis on causes, impact and mitigation 4 measures on urban flooding; - Providing detailed information on impact of each factor on sewerage; - Strong support on infrastructure development plan and drainage works; - Evaluating the past damage and predicting future risk; - Development of emergency action plan; - Analysis on impact of drainage system on rivers; - Climate change and sea level rise adaptation. Hydrological and hydraulic models are developed to simulate single or complex issues as follows: - Under ground pipe and open river interaction; - River and flood plain hydraulic; - Surface runoff, under ground pipe and open river interaction; - Surface and ground water interaction; - Under ground pipe flow and tide interaction. The surface runoff, under ground pipe and open river interaction package is strongly recommended for integrated strategy. General approach for drainage system modelling is defined as (i) One dimensional (1D) model for in bank flow and (ii) Two dimensional model (2D) for over land flow. The river and pipe flow are typically 1D and surface flow is possibly 1D or 2D. The world wide modelling tools are available such as SWMM (US), WASSP (UK), MOUSE and MIKE (Denmark), SOBEK URBAN (The Netherlands). Some of them are applied in urban drainage studies for Ho Chi Minh city. In Viet Nam the F28 model is developing and testing. Currently practical application of separated single module for each river or pipe modelling for the studies mentioned above is big disadvantages. Technical and practical situations of Viet Nam 5 require an integrated package of coupling model for ‘outer layer’ (rivers) and ‘inner layer’ (under ground pipes) simulation. 1.2. MODELS FOR URBAN DRAINAGE a) Basic definitions Impact of urbanization on hydrological cycle A complete hydrological cycle on the earth is described by the water path from rainfall, runoff and river flow routing to the ocean. In the urban catchment natural flow routing is significantly modified by drainage work, man-made storage and concreted surface causing more lag time and less infiltration rate. Urban catchment characteristics Urban catchment boundary is both naturally defined by topography and artificially separated by human made structures such as roads. 1.3. URBAN HYDROLOGICAL MODEL Some methods applied for rainfall-runoff computation are including: a/ Experimental equations: - The Rational Method and Unit Hydrograph. b/ Popular mathematical models: - Mike RR package contains NAM, SMAP, FEH and DriFt modules - HEC-HMS model. Remaks: The Urban-B type is most suitable for Viet Nam urban modelling with full data set and Urban-A type for lack of data. 1.4. URBAN HYDRAULIC MODEL Urban flow: Runoff forms street flows, enters manholes, flows through under ground pipe and discharge into river. Street flow plays 6 an important role as a main flow path and temporary storage basin in the case of extreme rainfall. A standard urban hydraulic model must contain and couple rainfall runoff, pipe routing and river flow modules. SWMM model: SWMM model computes pipe and river flow by using SaintVenant equation for unsteady 1D condition. Numerical method for pipe network is presented in detailed in the model manual . Many hydraulic structures (pump, weir, gate) can specifically be schematized. The model was applied to simulate a pilot drainage system of Tham Luong-Ben Cat in Ho Chi Minh city. The pilot model showed rain water drainage in the pipes, but no tidal impact. MIKE model package: The MIKE package contains single MOUSE, MIKE11 and MIKE21 model or coupling sets of MOUSE-MIKE21 (MIKE URBAN) and MIKE11-MIKE21 (MIKE FLOOD) Examples of pilot studies of MIKE package are as follows: - MIKE FLOOD application for flood simulation of Nhue-Day rivers in Ha Noi. - Urban drainage model for Dhaka city in Bangladesh using MOUSE simulates surface flow and under ground pipes. F28 model: The model contains rainfall runoff, street and pipe flow modules. Pilot model application for urban area of Thu Thiem (Ho Chi Minh city) simulates pipe system and river network and generates urban flooding caused by heavy rain. VRSAP model: VRSAP model is widely applied for flood control study in sub- 7 urban and delta area. The model is typical 1D hydrodynamic routing for open rivers. CHAPTER 2: DELTA-P MODEL FOR COUPLING PIPE AND RIVER HYDRAULIC DELTA-P model (a river hydraulic model DELTA and additional pipe model P) is developed with clear theoretical basic and applied for a pilot study to test the model functions and model outputs. Pilot study is done to verify model simulation and to analyze structural urban drainage measures utilizing pipe and river network. Modelling activities are as follows:: - Calibration of the model by using simulated and observed data for both river stage and Tan Hoa-Lo Gom catchment inundation. River network covers entire lower Dong Nai-Sai Gon river basin from downstream of Dau Tieng, Phuoc Hoa and Tri An dam to the sea and is capable to simulate upstream flood and tidal impact, local flood plain regulation. - Urban drainage model network covers underground pipes of Tan Hoa-Lo Gom catchment and is capable to simulate rain water discharge and tidal impact on pipes. - Testing simulation of pipe network and canal improvement to reduce urban flooding. - Capable simulation of integrated river tidal barriers and underground pipes. 2.1. NUMERICAL BASIC OF RIVER HYRDAULIC MODEL Numerical method of river hydraulic model DELTA-P presents strong mathematical and fluid dynamic basic. Recent improvement on database, GIS application and user interface were made. 8 2.2. NUMERICAL BASIC OF PIPE HYRDAULIC MODEL Drainage pipe is applied for long round and rectangle shape types. Main regimes of pipe flow are schematized as follows: - Pressure flow for full pipe; - Semi-pressure flow for submerged upstream inlet and free downstream outlet; - Non-pressure flow for un-submerged upstream inlet or nonfull pipe. Non-pressure flow can be submerge or free mode which depends on water depth (higher or lower than critical depth respectively). Flow equations presented on Figure 2-1 contain function of discharge (Q) and water head variables Q = f(H,h). The equations are solved by differential and numerical methods in DELTA-P. Figure 2-2 illustrates the pipe flow regimes. The linear relation between Q and water head (H in two pipe inlets or pipe outlet and river) is formed at pipe inlets or outlets. By using reduction algorithm for Q we can obtain the systems of linear algebraic equations for variable H. Figure 2-1: Scheme of pipe flow regimes and respective equations