Integrated water induced vulnerability of Lothar watershed
Integrated Water Induced Vulnerability Assessment of Lothar Watershed, Chitwan/Makawanpur, Nepal. A Dissertation workFor the partial fulfillment of requirements for completion of Master Degree in Environmental Science Submitted by Niroj Timalsina TU Regd No: 5-1-283-42-2002 Roll No : 6410
INTRODUCTION Landslide, debris flow and flood are prominent water induced hazards of Nepal. Total 7,809 people’s were killed by flood and landslide in between (1983-2010), (DWIDP, 2010). Landslide and debris are prominent in mountainous parts and while reaching plains of Terai it created wide spread flood. Disaster preparedness plan can be implemented on the basis of Vulnerability assessment. Integrated water induced vulnerability assessment aims to integrate physical vulnerability (flood, landslide and debris flow) with social vulnerability.
STATEMENT OF THE PROBLEM Disaster occurred in 1993 reflected that high intensity rainfall have high implication for triggering the flood, landslide and debris flow. Many times these hazard (Flood, landslide and debris flow) became the dependent event. Eg: Khosi flood caused by huge amount of sediments derived from upper catchment (Dixit, et al., 2009). Seti flood was caused from debris mixed snow avalanches (Dahal, et al., 2012). Individual vulnerability assessment of respective hazards in a single watershed would insufficient.
RESEARCH OBJECTIVESThe general objective of the study is to assessing the overall waterinduced vulnerabilities of Lothar watershed.The specific objectives are as follows: To prepare hazard zonation maps of flood, landslide and debris flow of Lothar watershed in 1:25000 scales. To create flood, landslide and debris flow vulnerability index in the ward level (lowest local governmental administrative units). To prepare composite physical vulnerability map by combining flood, debris flow and landslide vulnerability index. To estimate and map social vulnerability as directed by water induced hazard. To prepare the overall vulnerability map by integrating physical vulnerability and social vulnerability index.
SCOPE OF STUDY Varnes (1984): “the past & present are keys to the future” If GCMc projection holds true, it can easily excepted that water induced hazards will take more often & with more consequences. This integrated vulnerability map of places can easily be understood. Place based vulnerability map will fruitful to concern agencies tasked with DRR.
METHODOLOGY Collection of Maps and ImageriesDesk Topographic maps (Sheet numbers 2784 -08A, 07D, 07B and 08C at a scale of 1:25,000) and Google images 2012Study Collection of Hydro-Meteorological Data Collection of Socio-economic Data Local consultation Walk over Previous debris flow boundary and survey cultivation land loss were recordedField Old flood marks, old river course, channel shifting,Study old and young river terraces, and flood deposits were collected Active and old landslide were marked on the GPS
ANALYSIS AND INTERPRETATIONThe overall analysis consists of creating the indexes and summing withcertain weight. Flood Vulnerability index (FVI, w=0.5) Combined physical Landslide Vulnerability Vulnerability index index, (LVI, w= 0.25) (PhyVI), w=0.5 Debris flow vulnerability index Integrated Vulnerability (DVI, w-0.25) index Previous loss index (PLIward), w=0.25 Social Vulnerability index Potential loss index (SoVI), w=0.5 (PoLIward), w=0.25Vulnerability index derived byComposite/multiple adoptivecapacity index (ACI), w=0.5
In Brief:Flood Vulnerability Assessment Flood frequency analysis Maximum instantaneous flow by WECS/DHM method DoS + Additional Houses unit of Google image Flood hazard units from mapping Flood depth (m) Hazard level <.05 Low 0.5-2 Moderate 2-4 High Returning >4 Very high period: 5, 10, 50 &100 yr
Houses units located in more than 0.5 m flood depth from each wards Flood vulnerability index Calculated as (Rod et al., 2010):FloVI= Where r are the return intervals, Hr are the houses within inundated zones of a 1/r flood and Hward are the total houses in each wards within Lothar watershed.
Landslide Vulnerability assessment Landslide Hazard mapping: Statistical bivariate was performed Selected eight Parameter taken are: Land use/land cover Slope angle
Relief Factor Internal relief Distance from thrust Aspect & Faults Geology of Lothar watershedDistance from Stream
Classified eight Landslide obtained from field parameter + Landslide from Google (100 of landslide having more than 400 m2 )Landslide index method Digitalized (Arc GIS 9.3) Density Map = the landslide density within theWhere, entire map.Wi = Weight assigned to certain parameters A (Si) = Area, which contain landslide, in aclass. certain parameter class.Density Class = the landslide A (Ni) = Total area, in a certain parameter class.density within the parameter class.
LHI is determined by summation of each factor’s ratings using equation (Lee and Min, 2001; Lee and Pradhan, 2006): LHI =Where,Wi = Weight assigned to each i parametersN= Total number of parameters Classification of landslide hazard zones: low, moderate, high with predictive rate evaluation. Then returning period was assigned as 50 and 100 yrs in regard to high hazard zone and moderate hazard zone respectively as a fictive probability. Similar to FoVI at a ward level, the landslide vulnerability index is calculated as: LVI =Where, Hr is the number of houses within hazard level r.
Debris flow vulnerability assessment DEM SINMAP Saturation Saturation zonation map zone= Debris hazard zone Validation Houses unit
Combined physical Vulnerability index (PhyVI)Calculated as done by Rod and et al. (2010):
Social vulnerability assessmentSocially vulnerability, SoVI calculated as:SoVI = ½ (PLI +PoLI) + ½ Vulnerability index derived from capability index (ACI)Previous lost index (PLI):PLIward = (Flood damaged + Landslide damages + Debris flowdamaged)ward/Total Cultivation land wardPotential loss index (PoLI):Vulnerability index derived by Composite/multiple adoptive capacity index(ACI) from climate change vulnerability mapping for Nepal, MoEn,2010.: In accordingly each ward of respective VDC of Chitwan districts was assigned with 16.66 vulnerability indexes and that of Makawanpur was 33.67
Integrated vulnerability indexIntegrated vulnerability index was calculated by adding togetherthe min-max transformed index of combined physicalvulnerability and social vulnerability with giving weighted of 0.5to each:Int VI = PhyVI + SoVI (Rod et al, 2010)
Study Area District VDC Wards Area (sq. km) of VDC Chitwan Piple 6 8.74 Chitwan Korak 1,2,3,4,5 23.41 ,6&7 Chitwan Lothar 1,2,3,4,5 61.95 ,6,7,8 & 9 Makawanpur Kakanda 1,2,3,4,5 62.32 ,6,7,8 & 9 Makawanpur Manaha 1,2 11.95 ri Chitwan/Mak 5 VDC 28 168.37 awanpur wards
Some HecRAS Export Geom: Geometry data Flow: Lother flow data RS = 2997.765 .035 .035 .035 390 Legend EG 100yrs 380 WS 100yrs EG 50yrs 370 WS 50yrs E levation (ft) 360 EG 10yrs WS 10yrs 350 EG 5yrs WS 5yrs 340 EG 2yrs WS 2yrs 330 Ground Bank Sta 320 0 50 100 150 200 250 Station (ft) Water surface profile of reach stationCross section develop from (2997.766) with respect to returning period HEC- GeoRAS
Flood inundated map with respect to returning period 5yrs,10yrs, 50yrs and 100yrs were prepared:
Relation of Flood inundated area with returning period 50 Total flood inundated area(ha)% 45 40 35 30 25 20 15 10 5 0 5 years flood 10 years flood 50 years flood 100 years flood Returning Period Low (<.5)m Moderate (.5-2) High (2-4)m Very high (>4m)Flood inundated area with respect to hazard level and returningperiod
1.2 Landslide hazard assessment Total weight is positive, the factor is favourable for landslide Class with lesser distance from drainage (50m) has only assured the positive weight. Elevation (1000-1500m) and south and south-west facing slope of study area were landslides prone Distance from the faults and thrust have positive weight so it reveals the situation of places nearby the trust and faults to be more susceptible towards landslideLandslide index in according to differentclasses of respective parameters
Quantitative bivariate analysis was done to obtain hazard map, which is then reclassified into three hazard zones
118.544 km2, 40.668 km2 and 8.6504 km2 located under low, moderate and high zone respectively. Probability rate Percentage of obsorbed 100 90 80 70 landslides 60 50 40 78.67% 30 20 10 0 0 20 40 60 80 100 Percentage of pridicted landslides from high to low hazard Figure : Predictive rate of landslide occurrence The probability rate was calculated by trapezoid rule, resulted with 78.67% .
1.3 Debris flow hazards assessment Table : Saturation zonation areas with debris flow occurrences areasSaturation Area on Percen Debris flow Percentage of Cumulative CumulativeZonation zonation tage of occurrences Debris flow summation of % summation of % of (km 2) Area (%) area (km 2) area (%) of zonation area debris occurrences areaSaturation 16.97 10.50 0.88 78.67 10.50 78.67Threshold 2.51 1.49 0.026 2.28 11.99 80.95SaturationPartially 46.83 27.87 0.16 14.18 39.86 95.13weightedLow 101.94 60.19 .05 4.85 100 100moistureTotal 168.25 100 1.12 100
100 Percentage of obsorbed debris 90 80 70 flow area 60 50 40 30 20 10 0 0 20 40 60 80 100 Percentage of pridicted Saturation zone from high to low hazard Debris flow hazard zonation map and occurrences of previous debris flow recorded area to respective zonation resulted 88.53% of success .
2. Vulnerability assessmentTable : Digital representation of Houses unit with respect to wards ofconcern VDC within Lothar watershedVDC Ward No Total Number of VDC Ward No Total Number houses of housesKorak 1 261 Manahari 1 68Korak 2 56 Manahari 2 230Korak 3 94 Piple 6 352Korak 4 70 Lothar 1 231Korak 5 169 Lothar 2 85Korak 6 54 Lothar 3 157Kakanda 2 63 Lothar 4 122Kakanda 3 12 Lothar 5 122Kakanda 4 585 Lothar 6 115Kakanda 5 131 Lothar 7 155Kakanda 6 81 Lothar 8 153Kakanda 7 180 Lothar 9 97Kakanda 8 125Kakanda 9 133Total 3901
Fig: Physical Vulnerability index spider chart
Social vulnerability index Social vulnerability map was prepared on the basis of natural break (Jenks) classification with basic statistical value: Count: 26 Mean: 20.09 Vulnerability Value Classes Minimum: Median: 16.60 Low <15 8.58 Maximum: Standard deviation: Moderate 15-23.38 52.65 111.84 Sum: 522.49 High >23.38
Integrated water induced vulnerability index Integrated water induced vulnerability map was prepared on the basis of natural break (Jenks) classification with statistics as: Count: 26 Mean: 18.15 Vulnerability Value Classes Minimum: Median: 15.86 Low <13.04 5.17 Maximum: Standard deviation: Moderate 13.04-27.88 56.76 12.13 Sum: 471.85 High >27.88
DISCUSSION Integrated water induced vulnerability assessment was based on the use of indices. HDI of UNDP, Indicator of development of districts of Nepal created by the ICIMOD (2003), Climate change vulnerability mapping for Nepal, MoEn (2010) has been an inspiration sources for such calculation. Lothar watershed characterized by the higher threat of landslide and debris flow in hill parts which also possesses serious risk of flood in lower reach (DWIDP, 2011). Proper water induced hazards preparedness in this watershed would only be possible when three prominent hazards are focused at once.
o Since people of Lothar watershed has prioritized the disaster prevention as development issues (DWIDP, 2011), previous agricultural loss and potential loss were incorporated here for SoVI calculation.o Integrated vulnerability map displayed here reliable for judging the place based vulnerability and helpful for disaster preparedness within study areas. The map display here indicated that Panthali watershed needs emergency response for DRR.
CONCLUSION Flood inundated area will increase with returning interval. 118.544 km2, 40.668 km2 and 8.6504 km2 of watershed is under low, moderate and high landslide hazard zone respectively with probability rate 78.67%. Debris flow hazard is also prominent in the study area which was mapped with having success rate 88.53%. Ward no:1 of Manahari VDC and ward no:6 of Piple VDC are more vulnerable towards flood while ward no: 4 Kakanda VDC, wards no: 3,1 and 5 of Korak VDC and ward no: 2 of Manahari VDC are vulnerable to landslide. Ward no: 1 of Manahari VDC which together with higher potential flood inundation and debris flow made the place to assure higher physical vulnerability. Panthali and Retuti Khola possesses higher influence on social vulnerability index. Integrated vulnerability map revealed that wards no: 1 and 2 of Manahari VDC, ward no: 4 of Kakanda VDC, and ward no: 1 of Korak VDC are most water induced vulnerable places within Lothar watershed.
RECOMMENDATIONSThis study offers several practical applications: Lothar bazar area including the places of Panthali watershed needs immediate planning of risk management and lower reach of Reuti as well as places nearby Ganawachok Khola should prioritize for disaster preparedness.For further study: To overcome from the deficiency of digital terrain data, new technology such as LIDAR (Light Detection and Ranging), which improves the quality of the digital terrain representations can be used for further study. Digital data layers which has dynamic characters should be updated continuously and thus study strongly suggests to responsible Governmental agencies for regular updates the houses unit, road coverage, landcover etc. Moreover, GPS could use for further study to delineate household units and wards boundary. Assessment is recommended to be carried out for formulating the returning period of landslide. Detail study of Social vulnerability assessment needs to incorporate the lowest scale (wards) and more concisely at households level.
References Dahal R.K., Bhandary N.P. and Okamura, M., 2012. Why 1255 flash flood in the Seti River? Retrived from www.ranjan.net.np. In July, 2012. DWIDP: Department of Water Induced Disaster Prevention, 2011. Study of Lothar watershed, Chitwan/Makawanpur District. NAPA: National adaptation programme of Action, 2010. Climate change vulnerability mapping of Nepal. Lee, S., and Pradhan, B., 2006. Probabilistic landslide hazards and risk mapping on Penang Island, Malaysia, Earth System Science, v. 115(6), pp. 661-672. Rod, J. K. and et.al (2010). Mapping Climate Change , Natural Hazards, and the vulneability of Districts in Central Norway. Norwegian University of Science and Technology (NTNU), pp. 6- 12.
ACKNOWLEDGEMENTI express my heartiest gratitude to : Associate Prof. Kedar Rijal, Ph.D., HOD of CDES My thesis supervisor, Mr. Ananta Man Singh Pradhan My co-supervisor Mr. Gyan Kumar Chhipi Shrestha All the members of Central Department of Environmental Science, TU. My family, friends and everybody who was important to the successful realization of research.
Some Photo Plate Photo Plate: Local Consultation During field Visit
Photo Plate: Place where 15 persons of single family were killed by debrisflow
Photo Plate: Google View of Reuti Landslide (Source: Google Earth image: 2012)