E2993 V3 Viet Nam Managing Natural Hazards Project (VN-Haz/WB5)
Total Page:16
File Type:pdf, Size:1020Kb
Environmental Assessment (EA) E2993 v3 Viet Nam Managing Natural Hazards Project (VN-Haz/WB5) ANNEX 3 Background on Key River Basins Public Disclosure Authorized 1. This annex provides environmental background in key river basins (Ma, Ca, Ha Vang-Rac, Gianh- Nhat Le, Thach Han, Vu Gia - Thu Bon, Tra Khuc - Tra Bong, Kone, and Dinh). The data includes natural features (climate, flow and flood, salinity intrusion), ecological features and cultural sites, water quality, and socio-economic conditions. This information was used as the basis in assessing the potential impacts of the Project. A3.1. Environmental Background in Ma River Basin A3.1.1. Natural features 2. Ma River originates from the Northern side of Pu Huoi Long mountain range at an elevation of 2,179 meters (m) in Tuan Giao, Dien Bien province, continues in northwest – southeast direction across Son La, Sam Nua (Lao PDR), Hoa Binh, Thanh Hoa, and discharges into the Pacific Ocean through the Sung, Lach Truong and Cua Hoi tributaries. The Ma River basin system also includes three rivers, Chu River, Buoi River, Public Disclosure Authorized and Cau Chay River, all joining Ma River in Thanh Hoa Province in the Central Vietnam. 3. Ma River is a 512 kilometers (km) long river, with a basin area being the fifth largest in Vietnam, after Mekong River, Hong – Thai Binh River, Dong Nai River and Ca River. The total drainage area of the basin is 28,400 square kilometers (km2), of which 17,720 km2 lies within Vietnam’s territory, making up 62% of the total river basin area. Climate 4. The average temperature in the Ma River basin is relatively high throughout the year. The average temperature recorded at the 14 meteorological stations within the Ma River basin varies spatially ranging from 20.9-23.oC, reflecting the topographical characteristics and altitudes of the locations. 5. Annual rainfall is substantial with dominant winds from south and southeast during May to September months. The historical data recorded in the Ma River basin (1961-2007) show some special Public Disclosure Authorized variability in climatic conditions in annual rainfall of 1,165-1,966 millimeters (mm) with 80% of the rainfall occurring during the monsoon (May to September) season. The average annual rainfall ranges from 1,200 to 1,700 mm per year (mm/year) in the upstream area, 1,500-1,600 mm/year in the middle stream area, 2,000- 2,200 mm/year in the upstream area of Chu River, and 1,600-1,800 mm/year in the lowland area. The rainy season in the upstream areas begins in May and ends in October, while that in the Chu river basin is from late August to early November. 6. There are two factors that influence the wind characteristics in the Ma River basin: the southeast winds in summer, originating from the Bay of Bengal, which increases the density of water vapor leading to monsoon rains; and the presence of two parallel mountain ranges surrounding the Ma River basin that partially blocks incoming air from the southwest in summer or from the north in winter. The average annual wind speed in meters per second (m/s) in the Ma River basin indicates no big spatial variations in wind speed: on an average, the lowest value corresponds to Tuan Giao (0.7 m/s) and the highest value to Moc Chau (2 m/s). Public Disclosure Authorized 7. The river flow varies greatly in time and space. In general, the distribution of flow of large and medium rivers follows a one-peak pattern with the highest flow rate occurring in September or August. However, the flow of small rivers in Chu river basin follows a two-peak pattern, with a second peak in May or June. The river flow in cubic meters per second (m3/s) varies quite greatly in Cam Thuy. The average discharge in April (111 m3/s) is only one-third of the annual discharge (334 m3/s) and one-seventh of the 1 Environmental Assessment (EA) Viet Nam Managing Natural Hazards Project (VN-Haz/WB5) highest average discharge (in August). Data show that the highest discharges monitored at Cua Dai, Xuan Khanh and Cam Thuy are 442 m3/s and 1,713 m3/s, respectively, and 258 times higher than the lowest discharges at the same gauging station. Flow and floods 8. The flood season varies across the Ma River basin, from June to October across Ma River, from June to November in the upper area of Chu river, and from July to November in the Chu River’s lowland area. The total runoff in flood season accounts for 65-80% of the total annual runoff. Each year, Ma River’s total runoff to the sea equals 18 billion m3/year. The flow is unevenly distributed. 9. In the dry season, the runoff is only 4,76 billion m3, making up 26% of the total annual runoff. Meanwhile, the 4 months of the flood season make up 74% of the total annual runoff. The driest period is between February and April, which comprises 8% of the annual flow. March tends to have the lowest flow rates, contributing only 2.4% of the total. The total runoff per person in the Ma river basin is over 4,100 m3/person, only slightly higher than the standard (4,000 m3/year), however, this number will be considerably reduced if the flows coming from outside the country (22% of the runoff) are excluded, and the average total water supply per person goes down to only 1,080 m3/person. Salinity intrusion 10. Salinity intrusion is influenced by tides and river flows. In the dry season, the salinity intrusion in the downstream part of Len River can extend up to 20-25 km from the river mouth. Salt water intrusion reaches Yen On along Len River, Mi Quang Trang along Can River and Tuan T-junction along Ma River. The entire Lach Truong River always saline in the dry season. On Ma River, at Ham Rong, the salinity rises up to 6 %o in 2-3 hours when the tides peak, up to 0.1%o half tide at Tuan T-junction. On Len River, the salinity is at 0.1%o. The intrusion even reaches Bao Van in several years. The salinity intrusion in Lach Truong River often reaches Xiphong Cu Da in the dry season. A3.1.2. Ecological features and cultural sites 11. Ma River basin’s ecosystem is characterized by both Northwest and North-Central ecosystems. Evergreen forests are the typical type of natural forests of the basin. There are 7 conservation areas within the river basin: i) Pu Hu Nature Reserve (35,089 ha); ii) Pu Luong Nature Reserve (17,662 ha); iii) Ben En National Park (16,634 ha); iv) Xuan Liem Natural Reserve (23.61 ha); v) Xuan Nha (38,069 ha); vi) Pa Co- Hang Kia (7,091 ha); vii) Cuc Phuong National Park (22,200 ha). Conversation area index is estimated at 5.66%, which is of low-medium level compared to other basins. The index indicates that the conservation value and environmental assets in the basin are at low-medium level. 12. Basin forest cover rate is estimated 44% at medium level, compared to other basins. The rate indicates important role for sustaining river basin processes. Basin native forest rate is high 77.3% that indicates good forest quality and good catchment processes for runoff and water quality. However, it is generally acknowledged that the quality of natural forests continues to be more fragmented and degraded. Most of the natural forests are considered poor or under recovery; significant forest fragments remaining are mostly in Nature Reserves, National Parks. 13. There are 4 Historical/Cultural Sites approved by The Government in the Basin. Heritage Index of Ma basin is of medium level. Table A3.1: Ecological features of Ma river basin Total area: 28,400 km2 of which 17,720 km2 are located in Vietnam Environmental health: Biodiversity and ecosystems 2 Environmental Assessment (EA) Viet Nam Managing Natural Hazards Project (VN-Haz/WB5) Characteristics Included: terrestrial and aquatic ecosystems Ma river basin’s ecosystem is characterized by both Northwest and North-Central ecosystems. Evergreen forests are the typical type of natural forests of the basin; lowland evergreen forests now only remain in some areas of Ben En National Park Conservation There are 4 Conservation areas, including National Parks, Nature Reserves recognized by areas The Government in the Basin Conversation area index is estimated at 5.66%, which is of low-medium level compared to other basins. The index indicates that the conservation value and environmental assets in the basin are at low-medium level Historical/ There are 4 Historical/Cultural Sites approved by The Government in the Basin Cultural Site Heritage Index of Ma basin is of medium level (4), compared to other basins. Major water 1. Sop Cop Nature Reserve related Location, area, water source environmental Area: 27,886 ha assets Sop Cop Nature Reserve is located in Song Ma district in the mountainous north-west of Vietnam. The topography of the nature reserve is steep and mountainous, and elevations range from 450 to 1,940 m. The nature reserve is fed and drained by tributaries of the Ma river. The natural vegetation has been extensively cleared and replaced by scrub. However, it appears that areas of evergreen forest still remain at high elevations. The fauna was previously very rich, and the site supported a high diversity and abundance of large mammal species, including, in the 1950s, a species of rhinoceros.