Integrated Water Induced Vulnerability Assessment of Lothar

Watershed, Chitwan/Makawanpur, Nepal.

A Dissertation work

For 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 OBJECTIVES

The general objective of the study is to assessing the overall water

induced 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

Desk Study

Collection of Maps and Imageries

Topographic maps (Sheet numbers 2784 -08A, 07D, 07B and 08C at a scale of 1:25,000) and Google images 2012

Collection of Hydro-Meteorological Data

Collection of Socio-economic Data

Field Study

Local consultation

Previous debris flow boundary and cultivation land loss were recorded

Old flood marks, old river course, channel shifting, old and young river terraces, and flood deposits

were collected

Active and old landslide were marked on the GPS

Walk over survey

ANALYSIS AND INTERPRETATION

The overall analysis consists of creating the indexes and summing with

certain weight.

Flood Vulnerability index (FVI, w=0.5)

Landslide Vulnerability index, (LVI, w= 0.25)

Debris flow vulnerability index

(DVI, w-0.25)

Combined physical Vulnerability index

(PhyVI), w=0.5

Previous loss index (PLIward), w=0.25

Potential loss index (PoLIward), w=0.25

Vulnerability index derived by Composite/multiple adoptive capacity index (ACI), w=0.5

Social Vulnerability index (SoVI), w=0.5

Integrated Vulnerability index

In Brief:

Flood Vulnerability Assessment

Flood frequency analysis Maximum instantaneous flow by WECS/DHM method

Flood hazard mapping

Ho

use

s un

it of

Do

S + Ad

ditio

nal

un

its from

G

oo

gle im

age

Flood depth (m) Hazard level

<.05 Low

0.5-2 Moderate

2-4 High

>4 Very high

Returning

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 & Faults

Aspect

Distance from Stream

Geology of Lothar watershed

Classified eight parameter

Landslide obtained from field +

Landslide from Google (100 of landslide having more than

400 m2 )

Digitalized (Arc GIS 9.3)

Landslide index method

Density Map = the landslide density within the entire map. A (Si) = Area, which contain landslide, in a certain parameter class. A (Ni) = Total area, in a certain parameter class.

Where, Wi = Weight assigned to certain parameters class. Density Class = the landslide 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 parameters

N= 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 zonation map

Saturation zone= Debris hazard zone

Validation

Houses unit

Combined physical Vulnerability index (PhyVI)

Calculated as done by Rod and et al. (2010):

Social vulnerability assessment

Socially 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 flow

damaged)ward/Total Cultivation land ward

Potential 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 index

Integrated vulnerability index was calculated by adding together

the min-max transformed index of combined physical

vulnerability and social vulnerability with giving weighted of 0.5

to 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

,6&7

23.41

Chitwan Lothar 1,2,3,4,5

,6,7,8 &

9

61.95

Makawanpur Kakanda 1,2,3,4,5

,6,7,8 &

9

62.32

Makawanpur Manaha

ri

1,2 11.95

Chitwan/Mak

awanpur

5 VDC 28

wards

168.37

Results 1. Hazard Assessment

1.1 Flood hazard assessment Flood frequency analysis

Table : Flood discharge with respect to returning period of tributaries of Lothar Khola

S.N Lothar Reach/

Tributaries

Instantaneous Flood discharge (m3/s)

Returning

period

5Yrs 10yrs 50yrs 100yrs

1 Upper reach 119 145 199 222

2 Reuti 83 111 184 219

3 Middle reach 190 240 383 408

4 Panthali 71 95 159 191

5 Lower reach 273 351 542 632

Some HecRAS Export

0 50 100 150 200 250320

330

340

350

360

370

380

390

Geom: Geometry data Flow: Lother flow data RS = 2997.765

Station (ft)E

levation

(ft)

Legend

EG 100yrs

WS 100yrs

EG 50yrs

WS 50yrs

EG 10yrs

WS 10yrs

EG 5yrs

WS 5yrs

EG 2yrs

WS 2yrs

Ground

Bank Sta

.035 .035 .035

Water surface profile of reach station

(2997.766) with respect to returning period Cross section develop from 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

Flood inundated area with respect to hazard level and returning period

05

101520253035404550

5 years flood 10 years flood 50 years flood 100 years flood

Tota

l fl

ood i

nundat

ed a

rea(

ha)

%

Returning Period

Low (<.5)m Moderate (.5-2)

High (2-4)m Very high (>4m)

1.2 Landslide hazard assessment

Landslide index in according to different classes of respective parameters

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 landslide

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

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100

Per

cen

tag

e o

f o

bso

rbed

lan

dsl

ides

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% .

78.67%

Saturation

Zonation

Area on

zonation

(km2)

Percen

tage of

Area (%)

Debris flow

occurrences

area (km2)

Percentage of

Debris flow

area (%)

Cumulative

summation of %

of zonation area

Cumulative

summation of % of

debris occurrences

area

Saturation 16.97 10.50 0.88 78.67 10.50 78.67

Threshold

Saturation

2.51 1.49 0.026 2.28 11.99 80.95

Partially

weighted

46.83 27.87 0.16 14.18 39.86 95.13

Low

moisture

101.94 60.19 .05 4.85 100 100

Total 168.25 100 1.12 100

1.3 Debris flow hazards assessment

Table : Saturation zonation areas with debris flow occurrences areas

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100

Per

cen

tag

e o

f o

bso

rbed

deb

ris

flo

w a

rea

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 assessment

Table : Digital representation of Houses unit with respect to wards of concern VDC within Lothar watershed VDC Ward No Total Number of

houses

VDC Ward No Total Number

of houses

Korak 1 261 Manahari 1 68

Korak 2 56 Manahari 2 230

Korak 3 94 Piple 6 352

Korak 4 70 Lothar 1 231

Korak 5 169 Lothar 2 85

Korak 6 54 Lothar 3 157

Kakanda 2 63 Lothar 4 122

Kakanda 3 12 Lothar 5 122

Kakanda 4 585 Lothar 6 115

Kakanda 5 131 Lothar 7 155

Kakanda 6 81 Lothar 8 153

Kakanda 7 180 Lothar 9 97

Kakanda 8 125

Kakanda 9 133

Total 3901

Physical vulnerability index

VDC-

Ward

Landslide

vulnerability

index

Debris flow

vulnerability

index

Flood

vulnerability

index

Combined

physical

vulnerability

index Korak-1 84.27 34.39 0.52 29.93

Korak-2 41.78 14.57 0 14.08

Korak-3 99.57 2.89 0 25.61

Korak-4 47.8 11.65 0 14.61

Korak-5 91.38 9.65 0 25.26

Korak-6 10.83 10.07 0 5.22

Kakanda-2 5.57 12.95 0 4.63

Kakanda-3 0 0 0 0

Kakanda-4 100 16.74 14.64 36.51

Kakanda-5 31.25 2.07 0 8.33

Kakanda-6 15.88 23.51 0 9.85

Kakanda-7 40.3 3.02 0 10.83

Kakanda-8 3.74 6.52 0 2.56

Kakanda-9 3.51 16.36 0 4.97

Manahari-1 0 100 100 75

Manahari-2 60.53 14.19 4.92 21.14

Piple-6 42.87 22.41 53.31 42.98

Lothar-1 33.93 6.87 19.03 25.36

Lothar-2 6.88 6.4 0 3.32

Lothar-3 20.86 27.72 3.17 13.73

Lothar-4 4.79 2.23 0 1.75

Lothar-5 7.67 0 0 1.91

Lothar-6 24.41 0 0 6.1

Lothar-7 3.02 1.75 0 1.19

Lothar-8 23.7 21.33 13.63 18.07

Lothar-9 2.8 2.8 0 9.14

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

Classes

Value

Minimum:

8.58

Median: 16.60 Low <15

Maximum:

52.65

Standard deviation:

111.84

Moderate 15-23.38

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

Classes

Value

Minimum:

5.17

Median: 15.86 Low <13.04

Maximum:

56.76

Standard deviation:

12.13

Moderate 13.04-27.88

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.

RECOMMENDATIONS

This 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.

ACKNOWLEDGEMENT

I 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 debris flow

Photo Plate: Google View of Reuti Landslide (Source: Google Earth image: 2012)