VNU Journal o f Science, E arth Sciences 28 (2012) 153-159
Influence factors to flood disaster and search and rescue capacity in Thua Thien Hue delta
Pham Thanh A n ’’*, Dao Dinh Bac^, N hu Thi Xuan^
^Search a n d R e sc u e T ech n ica l S e n i c e C en ter,
S u rv e y a n d A e r ia l M a p p in g C o rp o ra tio n -D e fe n c e M a p p in g A g e n c y 2 /1 9 8 Tran Cung, T u L iem , H an oi, V ietnam
^ G eo g ra p h y Faculty^ V N Ư U n iv e rsity o f S cien ce, 3 3 4 N g u y e n Trai, H a n o i, V ietnam
R eceived 05 July 2012; received m revised form 6 Auiiust 2 0 1 2
A b stra ct. Thua Thien Hue delta is one o f the strongest areas affected b y natural disasters, esp ecially disasters related to water disasters such as floods, landslides coast. T o have a scientific basis for the proposed m easures to prevent and respond to m itigate the dam age and assist in search& rescue in the event o f floods need to study the factors that affect stroke flood s and search& rescue capacity.
T his paper has identified the natural and man-made factors affecting flood disasters and search& rescue activities w hen disasters occur flood on Thua Thien Hue delta. In particular, major role as geographical location, the study area is located in the transition zone b etw een the Northern clim ate and Southern clim ate, the place where the dispute betw een the different air pressure, with m orphological characteristics o f terrain, exừ em e weather, resulting in Thua Thien Hue delta is often effected by various types o f natural disasters related to water disasters, esp ecia lly floods.
The result analysis o f the factors causing floods w ill be the scien tific b asis for early warning, prevention and response, efficien t support for search& rescue activities to reduce the lo ss o f life and property when flood disasters occur in Thua Thien Hue delta.
1. Context
Flooding is a natural hazard phenom enon, the result o f the concenfration o f w ater large am ounts and overflow ing into low teưain area m aking w ide flooding, causing dam age not only to people and property that also a long-term negative im pact on the environm ent such as w ater pollution, disease ...
* Corresponding author. Tel: 84-988528809.
E-mail; [email protected]
Thua T hien H ue delta is one o f the strongest areas affected by natural disasters, especially disasters related to w ater disasters such as floods, landslides coast. In flood history (X I/1999) w ith flood peaks exceeded the alaưning III level, T h ua Thien Hue has m ade plain im m ersed in w ater, d esừ oy ed several residential areas, killing hundreds o f people, dam ages estim ated trillion. It is the direct physical dam age, and the dam age to the ecological environm ent can not fully assess.
153
154 F T . A n et al. / V N U Journal of Science, Earth Sciences 2 8 (2012) 153-159
To have a scientific basis for the proposed measures to prevent and respond to m itigate the damage and assist in search& rescue activities in the event o f floods need to study the factors that affect sứoke flooding and the ability to search and rescue. This is the research content o f this paper.
2. The factors that affect flood hazard and the ability to search and rescue when disasters occur on Thua Thien Hue delta
The cause o f the flood disaster is derived from two basic factors, natural factors and man- made factors. These factors are affected both directly and indirectly to the flooding. Comm on factors independent nature, but in m any cases a com bination o f both nature and m an-m ade.
N atu ral fa c to rs: o f endogenous and exogenous origin.
Endogenous factors has a very im portant role, it indirectly affect flood on the earth's surface. Endogenous factors, tectonic activity and new tectonic new in the process o f formation o f the surface and hydrological netw ork and the form ation o f the delta is a very im portant role. Endogenous process usually takes very long geological cycles at a slower rate but there is a very decided, create the geological foundation o f a large basin.
Exogenous factors include landscape factors and the local landscape. They have both direct and indirect im pact to flood through the role o f vegetation and nature o f seasonal hydrological regim e o f rivers and oceanographic regim es rain - flood the continent, w aves, tides, ocean circulation, sea-level rise.
Natural factors interact w ith each other in the system consists o f tw o m ajor sub-system s to
generate flood or floo ding phenom enon in general. T he first su b -sy stem reflects the state o f atm ospheric p recip itatio n (rain, a com bination o f facto rs m onsoon with atm ospheric d istu rb an ce factors) and abnormal changes o f sea level for the coastal areas, such as w ater level, w a te r is draw n and unusually high tides. T h e secon d sub-system consists o f the factors reflectin g the p resen t state o f terrain buffer on tw o m ain aspects, w hich is the condition o f w ater to cause flooding or high flood level, o r even g en erate flash floods, flood debris. T h is is d eterm in ed p rim arily by the topography typ e is clearly on the digital elevation m odel (D E M ): the presence o f the surface form sm all abso lu te height, the low range relative to around, etc, the second characteristic o f th e te ư a in buffer is the perm eability or w a te r im p ed ir is defined by the characteristics o f the vegetation , the physical properties o f the m an tle and crust o f the soil, the surface layer o f the lithosphere, the characteristics o f the p aren t rock, etc. Both aspects o f the te ư a in b u ffer are reflected in the characteristics o f the source, or geom orphological ch aracteristics o f the terrain o f the area. So, co u ld be attributed to the analysis o f the in teractio n o f natural factors on fertility and flood in und atio n o f the analysis consists o f three co m po nents: state o f the atm osphere - the ph y sical te ư a in characteristics - arising terrain (g eo m o ip ho lo gical). In this interaction, i f the p ro cess o f w ater volum e win, will generate flo o d in g in varying levels, depending on the w ater v olu m e on the low terrain; co n ừ ary , w hen th e p rocess o f w ater drainage w in, ex trem e w ater levels w ill not appear. B y th at logic, for T h u a T hien H ue delta, we can see the sensitivity floo din g as follows:
- T he area is flo od ed ju s t no rm al due to the rainy season, th e m o st sensitive;
P.T. A n et al. / V N U journal of Science, Earth Sciences 28 (2012) 153-159 155
- The area flooded by rain in storm situations single season, second kind o f sensitivity;
- The area flo od ed by rain in storm situations seasons co m b in ed w ith tropical convergence circulation, th ird -sensitive type;
- T he area is floo ded b y rain in hurricanes husband situations co m b in ed w ith fropical convergence circu latio n and N E m onsoon circulation, the fourth categ ory sensitive;
Easy to u nderstand the depth o f flooding, duration o f flooding an d the level o f cause hazard also increased in the o rd er m entioned above [1].
M a n -m a d e fa c to r s : a very im portant decision factor to regu late the n atu ral flow from upstream is the rap id flu ctu atio n s o f w atershed vegetation due to deforestatio n, m ining and econom ic purposes o btain lan d for fanning, cattle breeding. T h e rap id d eclin e o f vegetation, especially in the cu rren t w atersh ed protection forests have lost the ability to slow dow n the flood, the flow o f surface w ater, and this is actually one o f the m ain causes o f the the flood disaster. In addition, the co nstructio n o f many w orks to regulate w ater reservo irs, dam s, dams regulate w ater, reco u n ts line, w h eth er they shore spillw ay, salty dam , dredging... has changed the n atu ral h y d ro lo g ical regim e o f the river, and the traffic system , housing... also im pede drainage causing flooding. O n the other hand, planning in the d istrib u tio n o f population, the civil, social and econ om ic decision likely hurt their d ifferent and th erefore also the dom inant direction o f search and rescue activities.
D ue to the to p o g rap h y and geom orphology o f T hua T hien H ue delta h as characteristics than even the n earb y co astal delta o f the central coast (as the T h u B o n R iv e r D elta) and the
dialectical relationship betw een they are for floods (flood left their m ark on the terrain, and then record the im pact o f the flo o d through various changes it has gone through), so the study o f the geom orphology fraces and w eather patterns causing floods will contribute to clarify the scale, causes and potential flood damage.
2.1. N atural fa c to rs
G eographical location: situ a ted in the clim atic transition zone betw een N orthern and Southern clim ate that ranges Bach M a is the natural clim atic boundary betw een the two regions, and is located in the boundaries o f the typical tropical areas w ith limited the 16 degrees latitude, the place w here the dispute betw een the air flow com es from the different air pressure center: from the N orth came down, from the W est pass, from the encroaching on the East and from the South move up, usually the com bination o f extrem e w eather phenom ena, and so located downsfream o f low and m edium m ountain ridges get wind, rain w elcom e in W estern Thua Thien Hue, a center o f heavy rain m ost o f Vietnam; boundary betw een typical ứ opical equatorial region should usually have m any strong w eather disturbances; located in the m iddle part o f the shoreline segm ents from Thanh Hoa to the exứem e South central perpendicular to the dom inant w ind direction N orthE ast coast often blocked by the estuarine sand trip and the sand bar extends parallel to the shore. These characteristics o f the geographical location is one o f the m ain causes for here regularly suffered the ravages o f stonns and flooding. As a result, there are often m any types o f natural disasters related to w ater disasters, especially floods. This set for the search and rescue activities w ith specific objectives is to focus
156 P.T. A n et al. / V N U Ịournal of Science, Earth Sciences 28 (2012) 153-159
energy and m aterial resources to respond m ainly to the flood disaster in the region.
Topography: if Southw est m ountains with very steep teưain beneath the coastal delta is both low and not slope. T hat m akes conditions for the flood took place so quickly in the study area.
A teưain quite com m on in Thua Thien Hue delta IS in the N ortheast o f the dunes running parallel to the coast w ith a height o f 5-30m, the two asym m etric ribs, ribs fairly large W estern slope 25"’-30°, the Eastern slopes laid over lO'’- 15°. These dunes make this delta having low trip after dune, estuarine is narrow , difficult to escape the w ater and the sand pressed into the estuary shore, forced to flow in the stream leads not slope, parallel to the coast, so that rapid flooding w hen there is heavy rain, w ater from the W est down.
Geology: the structure has decided to form the topography o f the delta by the parallel orientation o f the bar, the val-shore and estuarine sand trip extends in N W -SE direction, the same direction as the sand bar and m odem shore. It is also a very notable feature o f the Thua Thien Hue delta, because they m ake a
"grabens" valley and closed [2].
Climate: the interaction betw een the monsoon circulation and the topography o f South Truong Son m ountain did appear a special variable type the rain is hea\7 rain during the autum n and w inter and less rain in the spring-sum m er period, range pearling in the W est form a wall o f rain took alm ost the entire amount due to w eather disturbances caused when w inds from the east or in the w inter monsoon blow s from the N ortheast. The w eather is rainy situation even m ore pow erful com bination o f interference w ith operation o f the tropical convergence zone, and main
characteristics o f rain, storm s and tem perature, the characteristics o f the atm ospheric circulation and its interaction w ith the teưain did appear in this area disaster situations dangerous as flood floods, riv er bank erosion, coastal ...[3].
H ydrographic netw ork: in general, due to rain seasons, the rivers are short and steep, v e g e ta tio n c o v e r w a s b a d ly d a m a g e d , so the extrem e fluctuations in a flow ; the rainy season they are rivers full o f w ater, the w ater can repeatedly hit causing m ajo r floods bring disaster, while in the dry season, the v a lle y floor are usually shallow , rev ealin g the vast golden sand, his m asterpiece receiv er narrow, by rainfall concenừated on the narrow and steep, so the rivers are large flood p eak flow is usually very high. B esides the ancient river system, there is no recom m ended flood, so the flood waters, they reactivate and foHTi the large flow o f flood. A long w ith the rapid transition from steep m ountains to the low er thus accrue delta will very quickly, b ecau se there is flow not directly into the sea w h ich w as congestion in the lagoon due to the floating sand dikes high flood events here can happen v ery quickly.
O ceanographic regim e: sea salt contribute to speed up the process o f the t>pical brackish coastal lagoon on the T am G iang-C au Hai, affect the structure o f ửie ex isting species, prom ote agricultural im plem ent m ore thorough and salinity solutions, esp ecially solutions w orks and therefore also affect the ability to flood the region's natural m ig rato iy species groups. R ising sea levels also change the process variable te ư a in coastal and wetland expansion on the Tam G iang -C au H ai lagoon and the coastal plain, increasing the im pact o f floods on Thua Thien H ue d elta and the Huong river Basin [3].
P.T. A n et al. / V N U Journal of Science, Earth Sciences 28 (20Ì2) Ĩ53-159 157
S oil characteristics: barren hills m ainly in the m ountainous areas w ith steep slopes, the source o f the river, so the rainy season increases the risk o f d isaster phenom ena such as floods, flash floods and m ud rocks, erosion, landslides occur very serious.
Vegetation co ver a n d lakes: Forest area accounts for a large proportion o f natural land, but over the years the forest has been devastated, the coverage decreased significantly, from the ability to regulate flood basin fell, po or w ater holding capacity, com bined w ith slope increase flood flow coefficient. T he lag oo n area lakes in the province accounts for nearly 5% o f the territory, but m ainly n ear the sea so little to regulate.
G eom o rp hological characteristics: with geom orphologic characteristics w ith the characteristics o f the central region, may have noticed, we d eterm ine the structure o f these four countries, the d irection o f flow, the process o f accretion and erosio n direct reflection o f the operation o f the flood, inundation. Research and evaluate the ro le o f geom orphology o f the delta and Its inherent characteristics related to floods, really very u sefu l and effective for the proposed solutions to cope later. A pplying the achievem ents o f G IS w ill help, assist in analysis, calcu lation o f spatial data and associated rem ote sen sin g data, digital elevation m odels, esp ecially w h en com bined w ith expert know ledge analysis in geom orphology and flood characteristics can m ake m ore accurate judgm ents flood sensitiv e areas, the relationship
- this reflects that zo nin g areas at risk, build scripts p revention an d search and rescue plan in case o f flooding [2].
2.2. The m an-m ade fa c to r
It is an im po rtan t factor in prom oting or reducing the risk o f flood disasters. I f the
developm ent and im provem ent activities have calculated the risk o f com plications, the level o f risk is down, even if developm ent does not take into account the influence o f the level o f flood risk due to accidents, the result is incalculable.
Exploitation and im provem ent o f the natural teư ain for social life so grow ing human factor in increasing flood caused.
Due to pressure o f increasing coastal population and, o f course, is the economic developm ent needs requires more area under cultivation and housing, has led to the exploitation o f the teư itory o f a lack o f m anagem ent, serious encroachm ent coastal flood corridor. The uneven distribution o f population concentrated m ainly in the plain, on both sides o f the river downsfream. Along with econom ic activities such as sightseeing tourism, industry, agriculture, aquaculture fishing... have very sừong im provem ent o f virgin teưain.
Residential areas located along the high ridge along the river espécially Hue City including m any unique ancient architecture is built on alluvial o f H uong river along with high walls and drainage system s naư o w , the water overflow s the banks will cause huge damage.
D espite dense irrigation network, including rivers, canals dug in Huong Thuy, Phu Vang district, but by digging a long time, should not be dredged regularly now heavily sediment, making flood drainage capacity greatly reduced.
N o large-scale reservoirs, w ith a capacity o f about 55 m illion o f flood control level is not high. Existing irrigation in the plain key role to provide irrigation w ater, rather than drainage.
Therefore, in som e places this apparent draw back system like the roads to slow the drainage flood plain w hen surface runoff.
Roads often have higher than the natural terrain o f about 0.5m to 2m and m ain traffic
158 P.T. A n et a i Ị V N U ]ournal o f Science, Earth Sciences 28 (2012) 153-159
routes also play an im portant role in the process causing floods. 1A N ational Road w ith a height o f 1.5-2m runs parallel to the sea, n a ư o w drainage aperture form ed dam s prevent flood large parts o f the w estern plains units flooding in rainy season this is clear in the historic floods o f 1999: in many roads, flood who breached them to make escape routes flood erosion principle backw ards for geophysics online form located perpendicular to the direction o f spread transmission o f the flood.
In addition to the above factors affecting areas dow nsừeam is influenced by tides, stoư n surges. W hen flood to m eet surges, or surges will reduce downsfream flood w ater surface slope, the ability to drain the sea slow ed dow n, leading to rising flood w ater levels than norm al.
At low tide, the w ater surface slope as well as the flood flow rate increases, the m om ent the am ount o f flood w ater to drain faster, and the destructive pow er o f ửìe flood flow is also m ore dangerous - large flow rate will be w ashed away many houses, projects, river bank erosion, etc. All o f these features need to be included in the flood and disaster prevention plans, rescue scenario locally.
3. Conclusion
1. Research area, Thua Thien Hue delta is always potential risk o f flooding due to the natural geographical conditions w ith specific characteristics o f ửie region, especially the m orphological characteristics o f the topography associated with the arising in the process (ie the form directly and objectively reflect the operation o f flood and w aterlogging).
2. The w eather that caused flooding, storm , ữopical depression, tropical convergence zone (single operation or in com bination w ith cold
air m asses). T h at is the reaso n for the Thua T hien H ue d elta annual rainfall depending on the typ e o f the h ig h e st in the counữ y, but unev enly distribu ted , m ain ly in the rainy m onths, so floo din g w as b o m v ery intense. The distrib ution o f rainfall in space and tim e flood are very com plex, creatin g floods have m assive changes in the n atu re and in each section o f the riv er and its tribu taries. F lood flow w ith great speed, w hile the plain is a narrow , iow-lying areas, close to the fo othills o f the m ountain, it is blocked from th e sea by a typical lagoon system , the focusing speed IS very rapid ly from a n etw o rk o f sh ort riv ers and sư eam s, the average slope derived from the m ountains and foothills to the W est. In this context, the flow rate is u sually v ery large, w hen ro lled dow n’ve created large an d rap id ly rising w ater, causing serious flooding.
3. W e can n o t co m p letely allelopathic natural d isasters in general and flood disasters
in the reg io n in p articu lar, bu t can be active in the w ork o f early w arn in g (ie w arns practical areas w ill be flooded w ith tim e and depth o f flooding vary acco rd in g to geographical location and the w eath e r is rainy different flood), p rev en tio n an d resp onse, efficient su pp ort for search and rescue w ork to reduce low m ost dam age to p eo p le an d the flood disaster o ccm red.
References
[1] Pham Thanh A n, D ao Dinh Bac, Nhu Thi Xuan (2011), Integrated rem ote sensing and GIS technologies in support o f disaster search and rescue activities in V ietnam , Journal o f G eo d esy an d C a rto g ra p h y (Journal o f Geodesy and Cartography, ISN: 0 8 6 6 -7 7 0 5 ), Institute S cience o f G eod esy and Cartography, Ministry o f Natural resources and Environment, No. 9, September / 20 1 1 , page 54-58.
P.T. A n et a i / V N U Journal o f Science, Earth Sciences 28 (2012) 153-159 159
[2] Nguyen Hieu, D ang Van Bao (1 9 9 9 ), The stu dy o f landform ch a ra cter ừ tics affect sen sitivity f lo o d Hue delta on the b a sis o f rem ote sensing
an d GỈS application s, the report projects at the University o f S cien ce, 35 pages.
[3] Nguyen Thi Viet Lien (2 0 1 1 ), R isk A ssessm ent o f co a sta l Thua Thien - H ue due to sea level
rise and bu ild decision-support software.
Independent project report Cooperation between Institute o f Science and Technology o f Vietnam and the People's Committee o f Thua Thien Hue 2009-2010, Institute o f Mechanics.
