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Ho Chi Minh City Ho Chi Minh City growing with waterrelated challenges TRAN NGOC, T. D. 1, 2 PERSET, Morgane 3 STRADY, Emilie 1,4 PHAN, Thi San Ha 1 VACHAUD, Georges 4 QUERTAMP, Fanny 3 GRATIOT, Nicolas
Ho Chi Minh City Ho Chi Minh City growing with waterrelated challenges TRAN NGOC, T. D. 1, 2 PERSET, Morgane 3 STRADY, Emilie 1,4 PHAN, Thi San Ha 1 VACHAUD, Georges 4 QUERTAMP, Fanny 3 GRATIOT, Nicolas 1,4 1 Centre Asiatique de Recherche sur l'eau CARE, Ho Chi Minh city University of Technology, VNU HCM ( 2 Faculty of Environment and Natural Resources FENR, Ho Chi Minh city University of Technology, VNU HCM 3 Centre de prospective et d études urbaines PADDI, Région Auvergne- Rhône- Alpes/HCMC People Committee/Métropole de Lyon 4 Laboratoire d Etude des Transferts en Hydrologie et Environnement LTHE UMR5564, Université Grenoble Alpes/CNRS/IRD 1 Part A : General context Geography and growth evolution Ho Chi Minh City (HCMC), formerly Sai Gon is a lowland city located in south of Viet Nam and is crossed by the Sai Gon River. It is bordered by the lower Mekong delta on its south- west side and by 15 km of coastline, in front of the East Sea in the south east direction (Figure 1). The city covers a surface of 2096 km 2 with a N- S (North- South) distance of ~104 km and a E- W (East- West) distance of ~47 km. The city is built up in a low land area with 65% of ground surface at less than +1.5 m above sea level. Founded in the 17 th century (administrated officially in 1698), the city emerged from an urban- embryo located in a deltaic plain, like other Southeast Asian and Indian megacities. Water is omnipresent in HCMC with a crisscrossing network of water bodies reported in Figure 1. This network first provided favorable conditions for water transport and trading, which enabled the city development. Also, as the city was already prone to flooding, canals allowed water drainage. In the 18 th, the network of canals was improved and developed in order to increase water trading with the Lower Mekong delta region. Later on, during the French colonial occupation, from mid- 19 th to mid- 20 th, some canals were deepened and widened to allow deep- draft ships to navigate. The perception of urban waterways changed during the 20 th century. At this period, demographic and urban pressure turned water into a critical issue for the city. As canals were used to dump waste along residential areas, French colonial authorities decided to fill all canals running inside the city center for health purposes. The urbanization of HCMC since the 20 th century is depicted in Figure 2. From the 1950 s until late 1970 s, the city received successive waves of immigration in the context of colonial war against France, then against USA. The city experienced a 76 % demographic growth between 1945 and 1954, moving from inhabitants to 1.7 million in less than ten years (Gubry and Le, 2002), and reached 2.7 million inhabitants in In the 1990 s, after the 1986 Đổi Mới, an economic reform policy launched to transit to a socialist- oriented market economy, HCMC has become the main economic, industrial and tertiary center of Viet Nam. Since 2003, HCMC is composed of 19 urban districts ( Quận ) surrounded by 5 rural districts ( Huyện ). The so- called urban city center composed of inner districts and new urban areas forms an urban surface of ~600 km 2 (Figure 1). According to the UN- definition for a city with benchmark of 10 million inhabitants, HCMC is a megacity. With an urban growth of about 3 % per year (GSO, 2013) and an economy area representing 35% of Vietnam GDP, HCMC is becoming one of the main megacities of the southeast asian region. HCMC's population is officially a census over 8 million of hộ khẩu thường trú (permanent resident) (after HIDS, ) with 81 % of urban inhabitants (living in the 19 urban districts). Nevertheless, its de 1 See PADDI. 2016a. Planification et stratégie économiques. Les Ateliers du Centre de Prospective et d'études Urbaines, p facto population is most likely more important considering an unquantified floating population of temporary inhabitants, workers and students (Gubry, 2014). This rapid demographic growth has a strong impact on HCMC spatial development. On average, 16 km² of its 2096 km² territory are urbanized on a yearly basis, since 2000 (Department Of Natural Resources and Environment, DONRE, 2013). The city expands filling up waterways, wetlands and converting them into urban areas (PADDI, 2014). This rapid urbanization has combined effects that need to be taken into account such as: urban fringe development, denser central core, inundation, water quality, subsidence, soil sealing. Hydrology and related forthcoming issues HCMC falls in tropical monsoon climate. Its annual average temperature is o C. Annual average rainfall is of ~1900 mm harvested by almost 93% during rainy months from May to November. The dry months occur from December to April. HCMC is encompassed in the Dong Nai River Basin which has a total area of km 2 (Figure 1). The hydrological network is composed of four main rivers: Dong Nai, Sai Gon, Nha Be and Vam Co Dong rivers. With about 8000 km of rivers, channels, and creeks, the water surface of HCMC reaches ~33500 ha, i.e. 16% of the total city area. The Dong Nai River (~890 m 3 /s of average flow) and Sai Gon River (~54 m 3 /s) are the main sources of water supply. There are 4 canal networks inside city acting as main water drainage systems: Nhieu Loc Thi Nghe (9 km); Tau Hu Kenh Doi Kenh Te Ben Nghe (25.4 km); Tan Hoa Lo Gom (7.2 km); and Tham Luong Ben Cat Vam Thuat (14 km) (source: hochiminhcity.gov.vn). By the end of the 1980 s, two reservoirs have been constructed upstream of HCMC. The Dau Tieng Reservoir (storage capacity of 1.58 billion m 3, built in1985) was built up on Sai Gon River and a few years later the Tri An Reservoir was built up on Dong Nai River (2.55 billion m 3, 1989). These reservoirs are mainly used for irrigation (Dau Tieng) and hydroelectric power supply (Tri An). They also provide some sources of fresh water for HCMC. The regulation of their water discharge contributes to the limitation of salt intrusion from the East Sea during the dry season. The two rivers are influenced by a strongly asymmetric semi- diurnal tide cycle, with an average magnitude of +1.4 m for maximum water level at the Phu An station (10 o 46'N 106 o 42'E, located in District 2) on Sai Gon River (the historical tide peak of m was recorded in 2013, source: phongchonglutbaotphcm.gov.vn). The tidal influence is a main forcing factor that leads to a maximum saline intrusion from February to May. Sea water rising The city is subjected to two forcing winds from the southwest (Indian Ocean) and northeast (East Sea) that blow during the rainy and dry seasons, respectively. HCMC is rarely affected by typhoon; however, the Intergovernmental Panel on Climate Change (IPCC, 2014) reported that without a very drastic reduction (50%) of emission of greenhouse gases at planetary scale, the south of Viet Nam will be probably impacted by an increase of the occurrence of typhoons and extreme rainfalls (by 10 to 20%), with a strong impact on river flow and banks erosion. There is already a clear tendency of increase for the tropical storms hitting HCMC in the last 50 years (VCAPS, 2013). The experts also pointed out that an elevation of the sea surface temperature of +5 C or higher in the South Pacific zone will produce a possible sea- level rise of 0.6 to 1 m (MONRE, 2008) by the end of this century, as a result of sea- water dilatation (for 1/3) and melting of polar ice (for 2/3). Knowing that 65% of HCMC ground 3 surface is below +1.5 m above sea water level, HCMC ground surface and soils are facing serious flooding risks. Soil subsidence The quaternary topsoils of HCMC are distinguished by a transition between the Pleistocene and the Holocene for the northern - northeastern parts and the southern - southwestern parts, respectively. HCMC undergoes major changes driven by human- activities. Like Bangkok and Jakarta, HCMC is founded on a soft deltaic deposit with about 200 m thick of soft clay and sand layers (tertiary alluvial and marine soils consisting of Miocene and Pliocene formations, Tran et al., 1991) where compaction predominates, so that land subsidence is inevitable (Pham and Ta, 2015; Erkens et al., 2015). This subsidence is exacerbated in the region, as a result of intensive water pumping in groundwater for civil engineering purposes (building foundations, construction of tunnels, metro lines ), together with the large number of high- rise buildings (Pham and Ta, 2015; Nguyen et al., 2015). Rate of land subsidence as high as 0.44 m within 10 years were monitored in the southwestern area of the city (Pham and Ta, 2015) and confirmed locally by RADAR imagery observations (interferometry with synthetic aperture) (Ho Tong et al., 2014). Consequently, at the end of this century, the subsidence of the soil level could be of the same order of magnitude or higher than the sea- level rise. The relative elevation of the megacity could thus tend towards zero, or worse, become negative. The conjunction of extreme rainfall intensities, upstream river floods and downstream tide flows will certainly result in serious flooding risks threat (ADB, 2010) and possible permanent submersion of several districts of HCMC in a near future. Drinking water Water sources, treatment and network Drinking or domestic water 2 has been distributed at the rate of 0.01 m 3 /day since 1880, from reservoirs and water towers filled mainly from groundwater. Water supply is divided into six zones in HCMC: zone 1 covering Districts 1, 3, 5 and 10; zone 2 for Districts Tan Binh and Tan Phu; zone 3 for Districts 12, Phu Nhuan, Binh Thanh and Go Vap; zone 4 for District 2, 9 and Thu Duc; zone 5 for Districts 4, 7 and Nha Be; and zone for Districts 6, 8 and Binh Tan. Domestic water is produced under the control of SAWACO (SAigon WAter COrporation), a state- owned company that can provide ~2.1 million m 3 per day from 7 water treatment plants (their locations presented in Figure 1): 1.5 and 0.5 million m 3 /day of this total are pumped from surface water of Dong Nai and Sai Gon Rivers, respectively; and an additional 0.1 million m 3 /day extracted from groundwater (see details in Table 1). Distributed by pipelines for a cumulated length of 5460 km, the network supplies water to ~85% of the population. Its maintenance is worrying as 80% of the network is more than 20 2 The HCMC drinking water supplied by the SAWACO meets the standards for domestic use as bathing/washing, but it is usually re- treated by micro- filters at households for human consumption. Unlike European and North American countries, it could not be drink directly, so that, the term domestic water is preferred. 4 years old (Vo, 2015; Dao, 2015). According to SAWACO, water leakage on distribution network is estimated to reach a loss of nearly 34% of the total water supply (~ m 3 /day) (in Vo, 2015). While domestic water is guaranteed for urban dwellers, only 20% of suburban dwellers have access to it. Actually, the city network has not been extended over all the areas of new inner districts and suburban districts, so that some holdhouses are using individual groundwater wells or purchase commercial water for their daily consumption. The pattern described here above clearly points out inequity in the supply of water. The city authority does intend to supply drinking water for 100% households by the end of According to the Master Plan 2025 of HCMC water supply 3, the total water demand would increase by nearly two fold (3.296 million m 3 /day). Thus, the city should supply 3.7 million m 3 /day of water, 2.25 million of which coming from Dong Nai River, 1.35 million from Sai Gon River, and 0.1 million from groundwater (Table 1). Water quality monitoring Although the HCMC is located in a well- watered region, fresh water shortage is occasionally occurring during the dry season. As the domestic water relies mainly on the Dong Nai and Sai Gon Rivers, the good quality of surface waters is becoming a crucial issue, in a context of severe drought, where saline intrusion is causing disrupted operation of water treatment plants and in a context of increasing industrial and urban effluents towards the rivers. SAWACO is in charge of the quality survey of the domestic water. The company focuses on the presence of parameters related to sewage effluent discharges (ammonia, COD, BOD, E.coli, total coliforms) and on the level of turbidity, chloride and manganese in water, which may impact directly the water treatment processes (Table 2, SAWACO and Vitens Evides 2015). Concerning riverine surface water quality issues, the DONRE is settling a long term monitoring program of basic parameters based on monthly sampling in several sites of the Sai Gon and Dong Nai rivers. The data being not public, it is thus difficult to state on the water quality of these two rivers. However, research projects evidenced the presence of Endocrine Disrupting Compounds (EDCs) in the two river watersheds (Le et al., 2016) and trace metals in the Saigon River (Strady et al., 2016), with systematic higher concentrations in the urban area and nearby the water treatment plant in the Saigon River. Apart from the basic parameters, emerging contaminants (e.g. urban trace metal, pesticides, EDCs, PCB, HAP, antibiotics ) should be now monitored in the surface water to ensure the quality and security of water consumption. Groundwater uses HCMC groundwater is exploitable from the Pleistocene and deeper aquifers (ancient alluvial sediments), but not from the Holocene, new alluvial sediment, which is exposed to high iron concentration and low ph in groundwater (Nguyen et al., 2007). The confined sandy aquifers of the 3 distinguishable soil types (Pleistocene, Pliocene and Miocene) are lying at average depth of 2 65 m, m, and m, respectively (Pham and Ta, 2015). Three Pleistocene aquifers are already over- exploited by an underestimated number of individual pumping wells (Figure 3). The average density is about 50 wells/km 2 (the highest density of 3 Decision N o 729/QĐ- TTG approved by the Prime Minister on June 19 th ~900 wells/km 2 in Phu Nhuan District). The water extraction was of about m 3 /day in 2010 and reduced to m 3 /day in 2015 (Bui et al., 2015; WWAP, 2015). A sustainable exploitation of m 3 /day is preconized by the Division for Water Resources Planning and Investigation of the South of Viet Nam (DWRPISV). It is worth noting that SAWACO exploits only m 3 /d; the remaining 80% being pumped by industrial and household wells. Most of the pumping wells are illegally pumping the groundwater resource. This results in a clear decrease of the groundwater table (Figure 4), as well as a degradation of water quality due to pollution from near surface seawater intrusion (Vo, 2007). In the meanwhile, natural recharge is not more than m 3 /day which is 5% of precipitation (Ha, 2015), due to soil sealing increase. The Dau Tieng Reservoir also contribute to the burden of HCMC groundwater (Nguyen et al., 2007). The Master Plan 2025 of HCMC limits the groundwater exploitation to m 3 /d, under the exclusive control of SAWACO. Water price The HCMC drinking water sector has been listed on stock exchange by SAWACO. However, water price is fixed by the People Committee with the aim of being affordable for the largest number of households. Thus, low prices are preconized, sometimes against the opinion of private partners. Water prices have been increased at a rate of 10 % per year between 2009 and The company offers prices for different categories with a fixed quota of 4 m 3 /month/person at a price of 5300 VND/m 3 (~0.4 USD). To promote water regulation, the price doubles if the consumption exceeds this quota. For private companies, the price of water is 4 fold higher. Wastewater fee is 10% of piped water price and is payed directly to SAWACO. This water policy is different from the one existing in most of the European countries, where the waste water price is more expensive than drinking water price. Sanitation and storm water Sanitation and drainage sewers were installed in the 1870 s, under the French colonial period (Coffyn, 1927). Nowadays, waste water and rain water are collected and transported by a 4745 km long network of canals and creeks and an additional 3095 km long network for combined sanitary and storm sewerage network (PADDI, 2012). As population needs are growing, the sanitation and storm water infrastructures become undersized. For instance, only ~ 10% (capacity of 2 water treatment plants in operation) of over 2 million m 3 /day of wastewater are treated (disinfection) before discharging into Sai Gon River (Table 3). To face this situation, ten water treatment plants should be constructed in the near future (Figure 5). The existing network will also need some rehabilitation. More than 50 km of the French- era- built sewers need to be repaired or renewed (Figure 6, Tran Ngoc et al., 2002). According to the city authority, a budget of 3000 billion VND (~140 million USD) is required for this rehabilitation. It is worth noting that some important works have already been made to improve and develop it. Thus, between 2001 and 2011, the network was expanded from 516 km to its actual length. The ambitious environmental sanitation projects which aim at building four main drainage basins inside the city have been engaged (end of the first phase) and the second and third phases are now ongoing. The first phase was devoted to the installation of sewers and the refreshing of infrastructures, whereas the next phases mainly aim at establishing waste water treatment plants. In these projects, one of the most popular works 6 consists in cleaning up slums along the canals (Figure 7). This point will be detailed in section B. During the 1990 s and 2000 s, the city authority agreed to fill up many waterways or replaced them by rectangular sewers for residential projects, Bau Cat (Tan Binh District), Van Thanh (Binh Thanh District), Binh Phu (District 6), for example. In the other hand, several cases of illegal canal occupation were reported each year, especially on drainage basins of new urban areas. According to the HCMC Company of Urban Drainage (UDC), 38% of canals and creeks managed by UDC for drainage were violated in 2012, and nearly 50% for this year (2016). Consequently, inundation is worsening in the city. In the same time, sewerage network is reducing its capacity because of a poor awareness of local people. In 2012, the UDC identified m of sewers and 306 drain- holes violated. A lot of collectors have been covered or sealed in front of shop houses along busy streets because of hygiene and landscape problems. Localized urban inundation Urban inundation is exacerbated by urbanization which alters infiltration and evaporation. Impervious surfaces now exceed 80% of the city core area (Tran et al., 2015) and concomitantly, the volume of run- off reach about 7% of the annual rainfall in HCMC (~120 mm/y; Rujner and Goedecke, 2015). Rain intensity can be severe, some extreme rain events of 100 mm within 3 hours being gauged occasionally (Ho, 2007). Inundations deteriorate private and public goods, but also threaten life activity and safety of townspeople. During severe events, water depth can reach up to 1.2 m in some particularly exposed streets. To face this yearly disasters, several infrastructure- engineering projects with huge budget have been undertaken. The conjunction of extreme monsoon rainfalls and tides constitute a technical and economic issue that is hard to solve for HCMC urban inundation. The inundation problem is complicated by the fact that HCMC experiences many types of inundations (including pluvial vs. fluvial flood) depending on location: permanent (old) inundation; new inundation; re- appeared inundation. Especially, HCMC has been suffering recurrent localized inundation events caused directly by heavy tropical rains and/or tides. In 2015, the whole city listed 68 localized inundation locations (Tran Ngoc, 2015). Na
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