Flooding Impacts on Dong Thap Muoi Region: Cause and Mitigation

International Journal of Research and Innovations in Earth Science Volume 6, Issue 1, ISSN (Online): 2394-1375

Quoc Huy Nguyen2*, Tien Yin Chou1, Mei Ling Yeh1, Thanh Van Hoang1, Yao Min Fang1 and Xuan Linh Nguyen2 1 GIS Research Center, Feng Chia University, Taiwan R.O.C. 2*, 2 PhD program in Civil and Hydraulic Engineering, Feng Chia University, Taiwan R.O.C. Corresponding author email id: Date of publication (dd/mm/yyyy): 10/03/2019 Abstract – Dong Thap is one of the 13 provinces of the Mekong Delta, located in the upstream of the Tien River, in the province of Dong Thap within the confines of 10 ° 07 '- 10 ° 58' north latitude and 105 ° 12 '- 105 ° 56' East longitude. The North is bordered by Long An province, to the north-west by Cambodia's Preyveng province, to the south by An Giang and Can Tho. This paper focus to analyze the flooding events in the province, causing and designing flooding map, population distribution in the flooded areas by applying geospatial tools. It is useful references for the decision makers in disaster prevention mitigation and strategies. Keywords – MeKong River, Dong Thap Province, Natural Disaster, Flood and Flood Mitigation.

I. INTRODUCTION

Dong Thap Muoi (DTM) is a low-lying land located on the left side of the Mekong River, in the north it borders Cambodia, southwest by Tien River, east and northeast by Vam Co Dong River. Dong Thap Muoi (DTM) in the Mekong Delta has a natural area of about 696, 946 ha, accounting for 17.7% of the natural area of the Mekong Delta [1], spread over 3 provinces of Long An, Dong Thap and Tien Giang. Of which more than 50% is in Long an province (Figure 1).

This is an area of alum (about 39.27%) with low-lying terrain, is suitable for growing rice, growing more than other crops, so rice is the main crop. From the country liberation with modest rice yields of 700-800 thousand tons (mainly of winter rice) to date the area of rice cultivation is about 350,000 ha, the output of rice is from 3.0 to 3.4 million tons/year (Statistic Year Book 2015, Dong Thap province, in Vietnamese). Leading the DTM to an important position, contributing to the rice export of the Mekong Delta and ensuring a stable food security in the region. At present and in the future, DTM remains and will be a major rice producer.

The interaction among natural factors: geomorphology, sediment, soil, water and other factors have formed natural landscapes with typical ecosystems of the DTM area.

Before being explored, the DTM has a diverse ecosystem such as primary melaleuca, cajuput, river bushes, etc. The vegetation with communities varies with the natural environment in each area such as Xyris indica, Eleocharis, Panicum repens, Ischaemum, Cyperus. And other Nymphaea spp, and aquatic plants.

Since the DTM is taken with the large scale in the last part of the 20th century and special from 1980s to the present DTM has changed from wilderness ecology to short-term intensive rice ecosystem.

Since 1983, the Chairman of the Council of Ministers has issued a decision on basic Mekong Delta baseline investigation. It can be said that starting from this point, the Government officially concentrates on studying and investing in DTM reclamation.

In 1984, the central canal was dug, draining alluvium fresh water from the Tien River through the DTM to the

Vam Co Tay River to accelerate the alum and soil improvement. Where fresh water leads, people gather on the canal side of the canal, reclaim land, settle down there.

Some other canals were excavated years ago and this time also began to promote the removal of acidity. Measures addressing the status of soil contaminated alum by digging canals, sawed ditches are all agree, recognized. The irrigation movement leads to fresh water spreading everywhere in the DTM area.

For people to come and stick to the headland, the localities also pay attention to investment in infrastructure, transportation, new production techniques. As a result, from an area of "dead land" flooded with reeds and reeds, 312,587 ha of rice was planted in 1987, nearly 700,000 ha in 1996. Rice yields from 1-2 tons/ha increased 5-7 tons/year after 2000 [3, 4].

From the wilderness to the granary, which are extremely important to human life, the lost ones are also enormous.

It can be said that the natural ecosystem together with the wetland biological diversity of the DTM has been seriously reduced, the natural landscape has changed after a time of exploration for the purpose of economic development, especially is the development of the common agricultural economy for the downstream of Mekong delta.

II. IMPACTS OF FLOODING IN DONG THAP PROVINCE

A. Study Site

Fig. 1. Map of Dong Thap Muoi region.

Recently global climate change in the current does not only a forecast but also a reality. The Earth's greatest climate changes is the Arctic and Antarctic, where temperatures rise fastest. Then to the high mountains like the Himalayas, Tibetan, etc. According to research the coldest areas with the fastest increase in temperature [7].

In Vietnam, the annual average temperature has increased by 0.10C and sea level has risen by 2.5-3 cm over the past decade. The temperature forecast in Vietnam will increase from 10C to 20C by 2020, from 1.50C to 20C by 2070. The areas with the highest temperature increase are North West and Viet Bac [5, 6, 8, 9].

Changes in rainfall patterns with increasing rainfall in the rainy season but decreases in the dry season cause more frequent floods and droughts occur every year in most areas of the country [10, 11]. Current climate change impacts on the DTM are becoming increasingly apparent and the risk of climate change impacts is increasingly detrimental to the region.

Since 1996, floods from the upstream of the Mekong Delta have been recorded to be occurred early, increased flooding frequency and short flood retention times. Flooding was occurred in three years (2000-2002) in the Mekong Delta with the flood peak is more than 4.5 m). The historical flooding at Tan Chau (upstream of Tien river) reached 5.06 m (in 2000) and 1.91 m (in 2002) at My Thuan. At Chau Doc (upstream of Hau river) reached 4.9 m (in 2000) and 1.95 m in Can Tho (2002) [6].

Between 2003 and 2010 continuous floods (flood peaks of less than 4.5 m) also caused difficulties for rice production in the DTM area.

Flood season in 2011 flood peak at Tan Chau station reached 4.87 m is the seventh highest in the chain measured the last 85 years [6]. In general, floods in the Mekong River Delta are becoming more and more irregular.

Oceanographic data show that the average sea level in the South China Sea has increased by about 5-10 centimeters over the last 40 years. In the present, the problem of tides has affected the production and life Ho Chi Minh City and in the Mekong Delta.

In DTM region, tidal erosion causes the flood to drainage slowly and salinity intrusion in the dry season is a problem need to be warned.

B. General Characteristics of Floods in Dong Thap (i) Flood and stability: the flood discharge during the flood season is very large but it is regulated by low-lying areas of Cambodia, especially Tonle Sap, so when it arrived at the Dong Thap causes its mass and flood discharge are reduced to about 20,000-25,000 m3 / s (Table 1). Flood level is increasing slow, average flood intensity is 6cm/day, maximum is not over 30cm/day, Overflow floods should not exceed 0.5 - 0.8m/s. (ii) Time of flood peak and duration of flood water retention: High level of 3.0m per day (at alert level I) in Tan Chau and in the Dong Thap province about 2, 3 months (Figure 1). However, in the early XXI century, floods are quite complex (time, level, etc).

Table 1. The largest flood discharge and the highest water level in Tien river at Tan Chau station (Source: Vietnam Southern Institute of Water Resources Planning) [3, 4, 6].

Year 1961 1978 1984 1991 1996 2000 2001 2011

Largest Flood Discharge - 25900 22400 24300 23600 25500 23800 -

Highest Water Level 5,12 4,94 4,96 4,80 4,99 5,06 4,78 4,86

C. Reason of Flooding

The cause of floods in the Mekong Delta in general and Dong Thap province in particular is due to rainstorms, tropical low pressure, tropical convergence associated with the Southwest monsoon. This weather pattern is usually active from the end of July to September, causing heavy rain in Truong Son mountain (Central and South Laos, Cambodia, Central Highlands, Vietnam).

There are three main causes of flooding in the Mekong Delta are: (i) Area of downstream in Mekong Basin is small (about 5% of total area), the flow of upstream water with large discharge should be able to drainage slowly; (ii) Effects of tides, most semi-diurnal tide; (iii) Internal rain coinside with the flood season.

D. Causes of Some Major Floods

The history of the floods in September, October 1961 was the result of five typhoons entering Vietnam, the largest Hurricanes No.8 and No.10 cause heavy rain in Vietnam, Laos and the rain center is Draivy - Cambodia. With monthly rainfall of 737mm. Flooding in September 1978 caused by three consecutive storms in the central caused heavy rains in Central and South Laos, Northeastern Thailand in July, August, September. July's rainfall in Thakhek (Laos) is 667mm, August's rainfall in Pakse (Cambodia) is 900mm. Large floods in 1996 caused by 5 storms and tropical depression.

The history of the 2000 floods is very unusual: floods with two flood peaks, the flood form is rare in the Mekong Delta (1978, 1984), two flood peaks 51 days apart; Flood early with high peaks; Flood events are complex. The direct cause of this flood was identified as storm No. 2 and No. 4 causing heavy rain on the whole region but the underlying cause is the impact of global climate change, La Nina phenomenon is strong stretching (from 1999 to 2000).

Floods in 2011 due to continuous storms (4, 5) and strong Southwest monsoon activity, the frequent occurrence of tropical convergence bands. Therefore, rainfall in the middle and downstream of Mekong basin (from Chieng Saen - Thailand to Stung Treng) is very large, it is exceeded the average annual rainfall over the same period (2010) many times.

E. Damage

Floods occur in Dong Thap along with the benefits (alluvial accumulations, exploitation Aquatic products, bauxite wash alum, reduce the operation cycle of pests, supply Water, etc) also causes a lot of damage to the locality. Early flooding affects the produce Summer-autumn crop, the main flood affecting Autumn-Winter (crop 3), fruit orchards, infrastructure, increased river bank erosion, affecting people's lives, etc.

Floods in 2011, according to the Steering Committee for Flood and Storm Control, Rescue and Search Work - Dong Thap province, flood caused damage: 23 people dead, 7000 km road was overflowed water causing landslides, road damage, 24 bridges destroyed, 2,000 hectares of Thu Dong rice (Crop 3) (2015 Annual Report on Disaster prevention and Search, Secure Work) and the economic damage over 300 billion Vietnamese Dong.

III. FLOOD DISASTER MANAGEMENT AND FLOODING MITIGATION

A. Forecasting, Disaster Warning and Information Dissemination

Forecasting, disaster warning and information dissemination: (i) The Center of Hydro-Meteorology of Dong

Thap province sends forecasts and warnings on hydro-meteorological situation so that people and offices at all levels can actively prevent them. Issueing newsletters about hurricanes, tropical cyclones and dangerous weather phenomena; (ii) The Standing Office of the Steering Committee for Natural Disaster Prevention and Control and Provincial Rescue and Search Work issued the notices on the hydrometeorology and natural disaster in the beginning and middle of the month, the reports on storms and tropical depression; (iii) Completion of the project on survey and construction of the 2011 flood marking system in the province: Investigate and build 26 new landmarks at population clusters; The elevation according to the Dong Thap system for inland hydrological stations built by the Hydro-Meteorological Station of South Vietnam in 2010-2011 but not high; To build a map of water level in flood peak 2011 in the province; (iv) Implement the Lightning Prevention Project: Building 2 Early Warning Lightning Stations in Phu Cuong Commune - Tam Nong District and Truong Xuan Commune - Thap Muoi District; (v) Implementation of the project "Surveying and forecasting the evolution of river banks in Dong Thap province" has been decided by the provincial People's Committee; (vi) Dong Thap Broadcasting and Television Station, Dong Thap Newspaper, local radio stations regularly report on floods and disaster response activities of localities; (vii) All sectors and mass organizations at all levels will intensify information dissemination activities in response to natural disasters, especially community awareness raising, children protection and disaster mitigation.

B. Building for Water Reservoirs

Water reservoirs have an important place in regulating the flow of water to serve for different water demand. On the other hand, the reservoir is also a disaster prevention resolution. In addition to providing water to the downstream area during the dry season, the water reservoirs also regulate floods in downstream areas. However, need to proper flood water regulation will bring new benefits to the project.

In the Mekong Delta, there are many low-lying areas, they had been overwhelmed by flooding into these areas to make the flow speed slow down and digging large ponds and lakes to raise the ground for flooded residential clusters, those lakes are also like water reservoirs for fresh water.

C. Human Resource Training and Community Awareness Raising

(i) The Center for Natural Disaster Prevention and Mitigation - The General Department of Irrigation organized training courses for 05 provincial trainers and training workshops to implement a project "the Public Awareness Raising and Risk Management based community (Project 1002); (ii) Implementing the Community and Disaster Risk Management based on in 2014 to train 10 commune-level lecturers with 335 participants; 07 training courses (Office of the Steering Committee for Natural Disaster Prevention and Rescue and Search Work six classes and Lai Vung district - one class) on disaster prevention and natural disasters management for 293 commune staff; purchasing equipment for education and training 2015 Annual Report on Disaster prevention and Search, Secure work).

According to the Disaster prevention system from Vietnam Government, each of province has set up Irrigation department that is belong to Provincial of Agriculture and Rural Development. There are 5 divisions such as Administrative; Legal inspection, Dyke, Irrigation work management, and disaster prevention division. Those divisions are in charge of each dyke in the region (Figure 2).

Fig. 2. General diagram of disaster prevention system in Vietnam (Source: Vietnam Ministry of Agriculture and Rural Development) [2].

IV. RESULTS AND DISCUSSION

A. Input Data

The documents used to study and analyze the flash flood, and digital data 2015 include: (i) Surveying data on historical of all floods events in the region. (ii) Documentation of meteorological rainfall in meteorological stations in Dong Thap province. (iii) Digital data include: + Vegetable cover + Slope terrain + Soil map + Geology: degree of weathering of soil

Those above maps have a scale of 1:500,000 provided by the Center for Geodesy and Cartography, so the map quality is relatively good. Therefore, these types of maps are completely reliable as input data for the mapping of flood as a warning map that useful for resident people and local government.

The information collected is based on a primary analysis of the natural condition. Local conditions, which sometimes determine the likelihood of occurrence, and the nature of flash floods, need to be surveyed.

B. Output Data In this study, Map Info version 12.5 is using for establishing some maps for the flood management, and flood mitigation management. Firstly, we identified the flooded areas in this province that is shown by Figure 3, 4, 5:

The map showing population density in flood prone area was illustrated the population live in a flooded area is less than the population are living in high areas. Hong Ngu, Tam Nong, Thanh Binh is always in inundation areas with the population density is under 400 people/km2. Lap Vo, Lai Vung have a high population density with over 600 people/km2 are living in a higher than an inundation area about 60 cm.

The study focus to establish the map of population distribution on the flooded area. Therefore, we can forecast the flooded areas always affected on the living areas, showing the disaster management strategy for Dong Thap province.

Fig. 5. Map of population distribution on the flood area.

Based on the digital map, local government and all the related officers can use those maps or update information for the flooding events (Figure 6), and send the early warning to resident people via broadcast like radio, or TV channel.

There are need to be checked the public engineering, irrigation works, flooding prevention to create synergy in deleting the erosion, decreasing floods blocking of new floodplains. The local government should plan to prevent and respond to storms, floods, tropical low pressure, natural disasters, organized 24/24 hours on duty during storms, tropical low pressure, timely catch the situation to prepare the appropriate response, to ensure the safety of life, property for guests and the nature of the units.

Fig. 6. Evaluation of flood risk information layers in Dong Thap province.

V. CONCLUSION AND FUTURE WORKS

Based on surveying of flash flood, and analyze the database by ArcGIS, the authors have developed a flood map, map showing population density in flooded areas, map of population distribution in flooded areas in quickest way, high precision for Dong Thap province.

A. Results Achieved Scientifically

This article has built a potential flash flood map for Dong Thap as the basis for the timely planning of flood prevention policies, limiting damage to people and properties when the floods occurred, the subject is well suited to the study area.

B. Results Achieved in Terms of Application

This is a new technique with high accuracy and can improve the range of the area to be implemented. Knowing the technique of stacking maps also helps solve many other problems. Research results of the project will help Dong Thap Flood control committee, meteorological and hydrographical experts to apply for early warning alert of floods and storms in the mountainous areas in time. Provinces, districts, and communes in the study area are more active in directing the prevention of flash floods, promptly responding when flash floods occurred, having specific plans and response consequences of flash floods.

The study created a data bank on the dynamics of flash floods as a basis for the design of construction of traffic works, health and irrigation and planning of residential areas where have potential flash floods.

By integration of multiple layers of information on the map, applying Flooding depth control station, it is easy help for the decision makers can decide to avoid when a disaster strikes.

Based on the results of the study on the risk of flash floods, it is a first step for the authors to be continue to research on flooding, landslides to develop a Flooding depth control station for disaster warning systems for Dong Thap province in the future.

REFERENCES [1] People committee of Dong Thap Province, Statistical Office: https://ctk.dongthap.gov.vn/wps/portal/cucthongke (accessed 29.01.19). [2] Vietnam Ministry of Agriculture and Rural Development. http://www.mard.gov.vn/Pages/home.aspx. (accessed 29.01.19). [3] Dong Thap Statistical Office. Statistic Year Book 2002-2007, Dong Thap province, in Vietnamese. [4] Dong Thap Statistical Office. Statistic Year Book 2007-2015, Dong Thap province, in Vietnamese. [5] United Nation in Vietnam. Vietnam and Climate Change: A discussion paper on policies for sustainable human development. 2009. [6] Vietnam Southern Institute of Water Resources Planning. Annual Report on Disaster prevention and Search, Secure Work. 2015. [7] The World Bank. (2009). Climate adaptation and development. Washington, DC: The World Bank Group [8] Ministry of Natural Resources and Environment. Viet Nam Initial National Communication under the United Nations Framework Convention on Climate Change. 2003, http://unfccc.int/resource/docs/natc/vnmnc01.pdf (accessed 29.01.19) [9] Ministry of Natural Resources and Environment of Vietnam (MONRE). Climate Change, Sea Level Rise Scenarios for Viet Nam. 2009, http://www.preventionweb.net/english/professional/publications/ (accessed 29.01.19). [10] Dinh, Q., Balica, S., Popescu, I., Jonoski, A. Climate change impact on flood hazard, vulnerability and risk of the Long Xuyen Quadrangle in the Mekong Delta. 2012, Int. J. River Basin Manag. 10, 103-120. [11] Tri, V.P.D., Trung, N.H., Thanh, V.Q. Vulnerability to Flood in the Vietnamese Mekong Delta: mapping and uncertainty assessment. 2013, J. Environ. Sci. Eng. 2, 229-237

AUTHORS PROFILE’ MSc. Quoc Huy Nguyen obtained Bachelor on Mathematics – Informatics at VNU University of Science, Vietnam National University in 2011. He graduated on Master of Software Engineering at VNU University of Engineering and Technology, Vietnam National University in 2016. His major field includes Data Mining, Software Engineering and Geographic Information System. Currently, he is studying on PhD program in Civil and Hydraulic Engineering, Feng Chia University, Taiwan. Email: [email protected].

Prof. Tien Yin Chu had his PhD degree from Department Resources Development at Michigan State University in 1990. He has been the Director of Geographic Information Systems (GIS) Research Center at Feng Chia University (FCU), Taiwan for above 20 years, and honored as Distinguished Professor at Dept. of Urban Planning and Spatial Information and Dept. of Land Management. With his profession and enthusiasm, Prof. Chou has performed an outstanding achievement with his 250 full time staff members at GIS Research Center to bring the GIS.FCU as one of the leading role in the GIS- related academic and industry fields domestically and globally. Email: [email protected].

Dr. Mei Ling Yeh received her MSc and PhD degree from PhD program of Civil and Hydraulic Engineering, Feng Chia University, Taiwan (2015). She is an Assistant Professor at GIS research Center, manager of the Department of Geospatial Information-Environmental Planning, Feng Chia University, Taiwan. Her major is Geographic Information Systems, Geographic Information Systems Practices, Geospatial Information and Environment Planning. Email: [email protected].

Dr. Thanh Van Hoang received her MSc in Geography Department at Thai Nguyen University, Vietnam (2008) and PhD degree from PhD program of Civil and Hydraulic Engineering at Feng Chia University, Taiwan (2015). Currently, she is an Assistant Professor at GIS Research Center, Feng Chia University, Taiwan. Her major includes Geographic Information Systems, Agriculture Model, Climate Change Impact Analysis. Email: [email protected].

Dr. Yao Min Fang received the Ph.D. degree from Feng Chia University, Taichung, Taiwan, in 2006. Before he joined the Department of Civil Engineering, Feng Chia University (FCU), in 2006, he worked as a Postdoctoral Researcher with the Geographic Information Systems Research Center, FCU. Currently, he is a Research Professor with the Geographic Information Systems Research Center. His research interests include disaster monitoring and civil engineering. Email: [email protected].

MSc. Xuan Linh Nguyen obtained Bachelor, Master on Land Administration at VNU University of Science, Vietnam National University in 2011, 2016. His major field includes Land Administration, Spatial Analysis and Geographic Information System. Currently, he is studying on PhD program in Civil and Hydraulic Engineering, Feng Chia University, Taiwan. Email: [email protected].