Application of GIS and Remote Sensing for Identifying Flood Risk in Ho Chi Minh City, Vietnam Vo Le Phu and Luu Dinh Hiep Faculty of Environment Ho Chi Minh City University of Technology volephu@hcmut.edu.vn ASEAN Japan Seminar and Workshop on Satellite Data Applications on Floods, 30-31 July 2012, Chulalongkorn University
Outline Overview of Flood Problems in Ho Chi Minh City Remote Sensing Image Data Image Interpretation Changes in Coating Surface Conclusion
Ho Chi Minh City: Background Located at the downstream section of the Dong Nai and Sai Gon rivers; Biggest agglomeration and fastest urbanization (~ 9 M); Affected by semi-tidal regime; Mean elevation is +10m and slopping from Northwestern to Southeastern.
1975-2005 8 M 1950-1975 2 M 1700-1950 0.5 M Urbanization and Typography 2020 12 M Mean elevation: +10m; Lowest elev. 0.5m 60% of the City is low land (South and Southwest) and is below +1.5m
Hydrology and Drainage System Ave. rainfall: 2000mm/year; Max: 200mm/day. Semi-diurnal regime; Max. +1.5m; Min.-1.2m. Dong Nai River Tri An Reservoir. Sai Gon River Dau Tieng reservoir. The City has 6 drainage basins: Central North West South Northeast Southeast. Drainage Basin Planning 2020
Drainage Systems West bank of the Sai Gon River, 4 areas: - Northern Area: 136 km 2, Elev: +8.0m - +10m. - Western Area: 80 km 2, Elev: +0.7m - +1.0m. East bank of the Sai Gon River, 2 areas: - Northeast Area: 65 km 2, high Elev. +2.0m - +30.0m. - Central Area: 106 km 2, including: Tan Binh, Phu Nhuan, Dist 1 (+2.0m - +8.0m) and low-lying dists: Binh Thanh, Dist 6, Dist 8 <+2m). - Southeast Area: 119 km 2, low Elev. +0.5m - +1.5m. - Southern Area: 82 km 2, low elevation: +0.5m -+1.2m.
Urban Drainage Projects Master plan JICA (6/2001) Tham Luong-Ben Cat (USD 400 M., under construction ) Nhieu Loc-Thi Nghe (USD 150 M., under construction) Tan Hoa-Lo Gom (USD 200 M., under construction) Tau Hu Ben Nghe (USD 250 M., under construction) Hundreds of small projects since 1990. USD 1 B has been spent for the last decade. USD 5 B is needed for the next 20 years.
Upstream flood Upstream flood Flood Problems Upstream flood Tidal effect and sea level rise Heavy rains; Tidal surge; Rain Tidal surge; Sea level rise
Urban Flood Issues Heavy rains flooded many streets Hundreds of houses were flooded by 40 cm. Water receded after three or five hours Traffic congestion and environmental pollution More than 100 locations were reported flooded repeatedly.
Causes of Flooding: urbanization and infrastructure development obstruction of the drainage system Existing slums along canals The encroachment of canals is one of the reasons leading to urban flooding. 1990 2005: About 40% of waterways/canal systems was narrowed/filled up by human activities
Heavy Rain Combined with Tidal Surges The highest water level had reached >1.50m (2011) Residents in many wards were suffered Inundation between 0.4-0.5m. Most of the outlying dykes and embankments are in poor condition Tidal Surges and Heavy Rain Events
Upstream Floods Reservois Forests Climate Change Land Use Conflicts Urbanization Industrialization Coastal mangroves Sea Level Rise Agriculture Downstream
Causes of Flooding in Ho Chi Minh City Natural conditions low land; Land use changes increases in impermeable surfaces; Urbanization changes in coating surface Serious Storm Surge and Floods How to do?
Lesson Learned? Kasetsat University Mega Flood in Bangkok, 2011
Lesson Learned: Thailand Mega Flood 2011
Urban Expansion in Ho Chi Minh City
Urban Expansion in Ho Chi Minh City
Urban Expansion in Ho Chi Minh City
Driving Forces of Flood Risks Rapid urbanization changes in land use changes in urban hydraulic issues urban planning becomes outdated. Human-induced climate change/climaterelated disasters current urban designs become inappropriate future plan to deal with flood risks. Rapid changes in urban coating surface is the main factor causing exacerbated floods
Remote Sensing Image Data Type Date Resolution Landsat TM 01-01-1985 30m Landsat TM 16-01-1989 30m Landsat TM 03-03-1995 30m Landsat TM 06-11-2000 30m Landsat ETM + 04-01-2005 30m Landsat ETM + 20-01-2005 30m Landsat ETM + 02-04- 2010 30m
Process of Image Interpretation Satellite Images Adjusting Geometric Field Survey for Getting Samples Developing Key Interpretation Image Interpretation Coating Status Selection of Sample Areas to Collect Factual Database and Adjustment Interpretation Map of Land Cover
Objects of Interpretation in practice Water bodies: Rivers, streams, lakes, canals... Traffic routes: paved, concrete, paving materials Grass: Paddy rice fields, grass/parks Greenery areas: perennial trees, green belts, planted/natural forests Roof: Tile/ corrugated roofs Bare land: unplanted land, not concrete transport roads
Image Interpretation
Changes in Coating Surface: Pervious VS Impervious Waterways versus Transport roads Grass and Greening areas Roofs versus Bare land
Roofs 4.083 5.753 8.949 15.099 25.621 29.219 Type of Surface Area (%) 1985 1989 1995 2000 2005 2010 Rivers 15.344 13.741 13.050 11.025 9.065 6.755 Roads 2.455 3.344 5.236 6.720 8.657 11.182 Plants 31.863 30.228 34.034 36.065 33.458 28.915 Trees 24.233 25.790 24.132 20.642 20.989 22.444
CONCLUSION Causes of floods in Ho Chi Minh City are complex; High rainfall; Semi-tidal regime & tidal surge; Heavy rain combined with tidal surge; Urbanization and land use changes changes in coating surface. Rising of sea levels (climate change) is also contributing to flood risk in Ho Chi Minh City; The coating surface has significantly changed over 6 periods: 1985-1989-1995-2000-2005-2010 1985 2000: permeable surface areas are dominant in Ho Chi Minh City.
CONCLUSION 2005 2010: impermeable surface has sharply increased, about 30% - 40%. Impervious surface areas has increased in parallel with urbanization changes in urban hydraulic the need for controling coating surface to prevent flood risks/inundation. Classification method (by using RS images) was initially applied for identifying changes in coating surface with high benefits (quick, high accuracy).
CONCLUSION Mapping changes in coating surface areas assists the authorities to re-shaping policy for urban planning reasonable coating surface (covered with self-absorbed surface) Further research on RS and coating surface mapping is needed b/c flood risk remains high even structural measures (drainage projects) are completed Application of remote sensing for mapping surface coating is very convenient for updating along with new developments and changes.
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