Dissertation summary: Evelopment of a suitable model for hydraulic simulation of the integrated urban draingage system in tidal area

Research objectives: 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.

MINISTRY OF EDUCATION MINISTRY OF AGRICULTURE AND TRAINNING 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

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

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

CHAPTER 1 : OVERVIEW OF URBAN FLOODING URBAN DRAINAGE MODEL

1.1 FLOODING AND MITIGATION MEASURES FOR CITIES

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

Causes of flood:

- Objective causes: low land, heavy rain, big upstream flood,

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

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

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

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

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

VRSAP model:

VRSAP model is widely applied for flood control study in

sub-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

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 full pipe Non-pressure flow can be submerge or free mode which depends on water depth (higher or lower than critical depth respectively)

non-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

The DELTA-P has an advantage by using same algorithm for all types of connections of river sections and pipes Figure 2-3 illustrates

a connection of a pipe and river junction (I)

Figure 2-2: Scheme of pipe flow regime

Rainfall-runoff simulation in P module: Runoff generated in the catchment is stored in basins, routing along streets and drain away via manholes Drainage discharge depends on street width, manhole area and water depth

Variation of water depth above manholes is expressed by the equation (2-1):

Where F i is storage area, R i (t) is rainfall, Q i,k (Z i , h k ) is discharge of

sub-catchment k draining via manhole i

Water level at junctions or manholes is a combination of river stage and flood depth Z then it can present inundation depth caused

by rain or tide

Figure 2-3: Pipe connection to river junction I

CHAPTER 3 : APPLICATION OF DELTA-P FOR MODELLING RIVERS OF HO CHI MINH AREA AND DRAINAGE PIPES OF TAN HOA-

LO GOM CATCHMENT

3.1 URBAN FLOODING IN HO CHI MINH CITY

Ho Chi Minh is the biggest city in Viet Nam with existing population of 8.6 million people and land area of 2095 square kilometers

Topography: A large part of area is low at about less 1.0 meter

above mean sea level (MSL) and surrounded by dense branches of lower Dong Nai river

Climate: Annual temperature and humidity are high There are

two seasons of the year: wet and dry Average annual rainfall is 1915

mm and rainfall amount in wet season shares 93% of annual total

River system and hydrological regime: All of river branches of

Ho Chi Minh city are influenced by semi-diurnal tide from east sea The high tide level is at 1.55-1.60 meter above MSL

Main rivers: including Dong Nai and Sai Gon branches those flow through the central part of the city and Vam Co, Long Tau, Thi Vai branches surround the south-east side

Urban rivers/canals: including Nhieu Loc-Thi Nghe, Tan

Hoa-Lo Gom, Tau Hu-Ben Nghe, Kenh Doi-Kenh Te, Nuoc Len-ben Cat and Cau Son-Vam Tat branches

Sub-urban rivers/canals: several branches in Thu Duc and southern city area

Sewer pipes: existing under ground pipes for domestic waste and rain water drainage Classification of sewerage is as follows: Primarily/class I: are rivers and canals

Class II, III and IV: are underground pipes with about total 1000

km long

Urban flooding

In period 2007-2008 there were about 4011 ha of flooded area

in both central and sub-urban zones Of which, 2861 ha of construction land and 1150 ha of agriculture land Flooding in central city is 100cm deep and 24 hours long

After 2008 to present the flood points and flooded area are decreased by 2/3 and 1/2 respectively

Flood problem is most critical in the case of heavy rain and high tide

Sub-urban flooding:

Occurred in the case of: high tide, heavy rain and big upstream flood Flooded area is 4348 ha mostly in Nha Be and Can Gio districts Annual flood damage is 371 billion VND and highest is 500 billions VND

Flood mitigation measures:

Are defined by the Ho Chi Minh city urban drainage planning study as follows:

Improvement of sewerage system from every building to the rivers with high design rainfall intensity

Construction of complete ring dykes and tidal barriers

Flood mitigation projects of HCM City

There are available studies at two levels: master plan and local projects, listed as follows:

- Master plan and Feasible study on waste and rain water drainage for Ho Chi Minh city by 2020

- Water work planning study for flood mitigation of Ho Chi Minh city

- National research study on flood mitigation measures for Ho Chi Minh city

- Pre-feasibility study for environmental improvement of Tau Hu-Ben Nghe and Kenh Doi-Kenh Te canals

- Project on sanitation and infrastructure improvement of Tan

Hoa-Lo Gom canal

- Project on environmental improvement of Hang Bang canal

3.2 RIVER HYDRAULIC MODEL

Model schematization of DELTA-P for downstream branches of Dong Nai-Sai Gon rivers in Ho Chi Minh city area is developed with sufficient available topographic data, river stage time-series and boundary conditions (upstream discharges and sea tidal level time-series) Model is calibrated against river water level in October 2005 (example of hydrograph is presented in Figure 3-1)

High computational speed is a big advantage of DELTA-P for simulating large scale network

Figure 3-1: Hydrograph of observed and simulated water level time

series at Phu An station in October 20015

3.3 PIPE HYDRAULIC MODEL

(1) Model extent

Sewerage system of Tan Hoa–Lo Gom (THLG) covering an area of 2500 ha is one of five drainage systems in central part of Ho Chi Minh city

The main Tan Hoa-Lo Gom canal is about 7600m long

Sewerage pipes are installed along main streets and they connect to main canal Diameter of pipes is in range of 60-100cm

(2) Flood issues and mitigation measures

Flooding is caused by some main reasons such as big rainfall, poor sewerage pipes, obstacle of drainage canal and low land elevation

Inundation mitigation measures are proposed as follows:

- Improvement of main drainage canal of THLG;

- Installation of new pipes to increase drainage discharge

(5) Boundary conditions:

Model boundary conditions are upstream discharge at Dau Tieng, Tri An, Phuoc Hoa dams and sea level at Vung Tau

Rainfall data is at Tan Son Nhat (airport) station

Model is calibrated against water level at Nha Be, Phu An and Bien Hoa stations

However, there are lack of observed water level and discharge data for THLG canal

(6) Pipe network

The pipe model consists of 106 sections with determined flow directions, junctions, pipe diameter and inlet/outlet elevations

(7) Rainfall

Testing simulation uses 10-year design rainfall in 120 minutes

of Tan Son Nhat station