Flooding Impacts on Dong Thap Muoi Region: Cause and Mitigation
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International Journal of Research and Innovations in Earth Science Volume 6, Issue 1, ISSN (Online): 2394-1375 Flooding Impacts on Dong Thap Muoi Region: Cause and Mitigation 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 Copyright © 2019 IJRIES, All right reserved 1 International Journal of Research and Innovations in Earth Science Volume 6, Issue 1, ISSN (Online): 2394-1375 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]. Copyright © 2019 IJRIES, All right reserved 2 International Journal of Research and Innovations in Earth Science Volume 6, Issue 1, ISSN (Online): 2394-1375 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 Copyright © 2019 IJRIES, All right reserved 3 International Journal of Research and Innovations in Earth Science Volume 6, Issue 1, ISSN (Online): 2394-1375 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.