SOLUTION FOR ADAPTION TO FLOOD HAZARD DUE TO CLIMATE CHANGE IN HO CHI MINH CITY

Quoc Thai NGUYEN,Thinh Diep NGUYEN

Ho Chi Minh City Urban Drainage Company Limited

ABSTRACT

Climate change is the most serious challenge to Vietnam in implementation of sustainable development purposes, hunger elimination and poverty reduction. Among which, Mekong delta and Ho Chi Minh City are most vulnerable to impacts of climate change. Assessing and being seriously aware of consequences of climate change, typically, more and more complicated flood and pollution occur, which remarkably affects the building and the sustainable development of Ho Chi Minh City, the Government of Ho Chi Minh City have intensively directed departments, committees, sectors, business associations and the whole population to make joint effort in solving and minimizing the adverse impact of flood and pollution in the City. In this article, authors, as one of the direct management and operation organizations of the City drainage system, present some assessments, judgments, proposed sustainable solutions as well as urgent solutions to scope with flood in background of climate change

1. INTRODUCTION

Ho Chi Minh City is the locomotive in development of economy, science and technologies of the whole nation and with dense population. Subject to impact of climate change, sea water rise, heavy rains, high tide conditions occur more frequently, flood in Ho Chi Minh City will more likely occur unless comprehensive flood solutions are soon and timely implemented (according to statistics, from 2013, tidal peak reached history record 1.68m, from 2011 to 2014, tidal peaks higher than 1.5m occurred 76 times, meanwhile 63.5% of the City area is lower than 1.5m so flood occurs more frequently)

2. CONTENTS

2.1 Overview of drainage network

2.1.1 Natural conditions

Ho Chi Minh City has total area of  2.095 km², in downstream area of Dong Nai river, Sai Gon river, has network of river, canals with total length of 5.075 km (among which, 1.177 km is for drainage purpose), average precipitation of 1.949 mm. The City has low terrain slope from North-Northeast downhill to West-Southwest, 876,3 km² (41,8%) with elevation < +1,0 m, 455 km² (21,72%) with elevation from +1,0 m to +1,5 m, 783,44 km² (37,39%) with elevation > +1,5 m, especially in center of the City of 106,4 km² , 43,15 km² (40%) with elevation < +1,6 m; therefore, high tide frequently causes flood, and has more and more adverse impact in background of more and more unpredictable climate change.

2.1.2 Current condition of drainage system

Total length of the City’s drainage system is 3.099 km, which is divided into 06 basins: center basin, West basin, South basin, North basin, Northeast basin and Southeast basin according to Decision no. 752/QĐ-TTg by the Prime Minister on approval of Master Plan of drainage system of Ho Chi Minh City  Minh to the year 2020.

Figure 1. Map of drainage basins in Ho Chi Minh City

Sewers being combined sewers (collecting both storm water and wastewater) have been constructed over several periods, many sewer pipes are aging, deteriorated, small in cross section, which do not meet required drainage capacities of individual basins; no complete drainage system in suburban areas. Channels, canals are filled up during urbanization, encroachment, dumping of trash which causes blockage and pollution still occur, which has not been solved thoroughly     

2.2 Rain and tide in climate change

2.2.1 Rain

According to statistics, for the past 40 years (1962-2001), 09 three-hour rains with precipitation of over 100mm occurred (once every 4 years). In last 10 years alone (2002 til now), 29 rains of the precipitation occurred (three times in one year). Especially, in 02 years (2013-2014) 03 rains occurred with precipitation of 100mm-122mm in only 01 hour 

2.2.2 Tide condition

In 27 years (1980-2007) highest tidal peak only reached less than +1.50m at Phu An. But in 8 years (2008 tile now) due to effect of climate change, tidal peak has exceeded +1.50m, meanwhile frequency of high tide is higher and higher. Statistical figures of tidal water level at Phu An station shows that from 2006-2010, frequency of tidal peaks exceeding +1.50m is 15, but in 05 years (2007-2015), tidal peak has 79 times reached current record +1.68m.

According to master plan 752, design frequency for drainage system is for rains with precipitation of 95.91mm in 03 hours (channel, canals – sewer level 1), 85.36mm (sewer level 2) and 75.88mm (sewer level 3), so the real condition has much exceeded input data used for preparation of master plan of the City’s drainage system, therefore, master plan-based parameters for design are no longer appropriate for actual situation, which leads to the fact that some  sewer lines though newly built have become overloaded.