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INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 7, No 2, 2016

© Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0

Research article ISSN 0976 – 4402

Received on January 2016 Published on September 2016 201

Use of earth observation data for disaster mitigation planning in an Inner

Terai watershed of central Nepal Dinesh Pathak

Central Department of Geology, Tribhuvan University, Kathmandu, Nepal

[email protected]

doi: 10.6088/ijes.7018

ABSTRACT

The problem of mass wasting, landslide and soil erosion is common in hills and mountain

areas while the plain area is affected by flood and sedimentation problem. In addition to this,

the failure of timely formulation and implementation of land use regulation as well as

increased human intervention have further deteriorated the watershed. The problem can be

addressed by preparation of integrated watershed management plan and its effective

implementation. It is always desirable to have well managed watersheds including

conservation of downstream areas. This is required to minimize degradation in the

watersheds for reducing sediment deposition as well as flashfloods in downstream areas The

earth observation data can be used to access the geological disaster, prepare management plan

thereby implement it through participatory integrated watershed management. Watershed

management is necessary to have an environmentally sustainable watershed through

watershed rehabilitation and disaster reduction activities. The present study identifies

issues/problems/threats and underlying causes behind degradation of the Riu watershed.

Landslide susceptibility map of the watershed and flood hazard map of the Riu River shows

the areas vulnerable to landslide and flood, which is a vital tool for watershed management

through appropriate planning to reduce the disaster risk in the watershed.

Keywords: Earth observation data, disaster mitigation, Riu watershed, Inner Terai, Nepal.

1. Introduction

The mountains of Nepal Himalayas are geologically young and tectonically active with steep

and unstable landscape. Intense and prolonged rainfall causes erosion, slope failure, river

bank erosion and flooding during the monsoon period. The result is the loss of agricultural

lands damage of properties, infrastructures and loss of lives each year (Aryal, 2012). The

Siwalik region at the southernmost part of the Himalayas, has been constantly suffering from

the problems of degradation (natural and anthropogenic) and over exploitation. This lead to

the overexploitation of valuable watershed resources of Siwalik region and has become

unable to meet the demand of natural resources of a growing population in and around

Siwalik region (also called Churia region in Nepali).

The extensive soil erosion and landslide from the Siwalik watershed leading to sediment

deposition on riverbed as well as desertification of agriculture land at the downstream has

taken place. In addition, it has caused flashfloods thereby damaging the agriculture land,

which eventually reduces the fertility and productivity of farm lands. In comparison to the

erosion rates of other regions of the Himalaya these rates are significantly higher (Ghimire et

al., 2013; Ghimire et al., 2006). This disastrous consequences and other cross cutting issues

(loss of biomass and biodiversity, inappropriate agriculture practices, overgrazing, forest

Use of earth observation data for disaster mitigation planning in an Inner Terai watershed of central Nepal

Dinesh Pathak

International Journal of Environmental Sciences Volume 7 No.2 2016 202

encroachment, haphazard settlements etc.) has resulted in the reduced sources of livelihood

and deprivation of the people.

A proper management of river basin is the only solution for reduction of soil erosion,

landslide mitigation, sedimentation control and disaster mitigation, which will eventually

support for better livelihood and overall development of the area. In order to identify the

critical area to the landslide and flood hazards as well as vulnerable areas and proposing

appropriate preventive and mitigation measures the earth observation data can best be utilized

(Pathak, 2014a; Pandey et al., 2007; Khan et al., 2001). The present study carried out study

on gully erosion, landslide susceptibility and flood hazard mapping that are quite useful for

the disaster mitigation planning in the watershed.

2. Study area

The study area lies in the southern part of Chitawan district, central Nepal. It is a part of the

Churia range (also known as Siwalik) that extends along the south of the Mahabharat range

from the east to west continuously. The study area is traversed by Riu River through Madi

valley, which borders India in the south (Figure 1).

Figure 1: Location of Riu River watershed in the Chitawan district. The position of Chitawan

district in Nepal is shown in the index map at top left

The Riu River valley (Madi valley) is situated within the Chitawan National Park. Forest area

lie at the right bank of the river while four Village Development Committees (VDCs),

namely Gardi, Baghauda, Kalyanpur and Ayodhyapuri VDCs lie at the left bank. The

protected area (Chitawan National Park) covers an area of 960 km2 and hence is quite

important from wild life conservation and touristic aspects. The four VDCs (Ayodhyapuri,

Kalyanpur, Baghauda and Gardi) lie within the Buffer Zone of the national park and hence

the people are continuously threatened by the wildlife. The population densities of

Ayodhyapuri, Baghauda, Gardi and Kalyanpur VDCs are 87, 261, 251 and 181 per square km,


Dinesh Pathak


respectively with an average of 196/km2, which is very close to the national average of

197/km2 for the year 2014 (The World Bank, 2015).

The study area lies in the humid tropical climatic zone with very hot summer. The monthly

rainfall pattern observed in Rampur meteorological station (near Bharatpur) from the year

2001 to 2005 shows the usual trend of Nepal with the highest rainfall between June and

August. The highest maximum temperature recorded at this station ranges from about 33

degrees to 37 degree in the months of April to June and the lowest minimum temperature

ranges from 4 degree to 9 degree in the month of December and January. More than 80% of

rainfall occurs during the months of June-Sept associated with the summer monsoon. The

proportion of summer monsoon to total precipitation is around 85%. The monthly rainfall

pattern observed in Rampur meteorological stations from the year 2001 to 2005 also shows

similar national trend.

2.1 Drainage

The SE-NW flowing Riu River originates at Someswor hill in Siwalik range and discharges

to the Rapti River. The Riu River Basin covers an area of 460 km2 at Confluence with Rapti

River in the west. Several tributaries that originate from the Siwalik range covered by dense

Sal forest joins the Riu River at left bank, while few tributaries are at the right bank (Figure

2).

Figure 2: Drainage network in the Riu watershed

The width of the river varies from 1300 m at upstream to 200 m in the downstream part (near

the confluence with Rapti River). There is about 230 m elevation difference between the

originating point and Riu-Rapti River confluence point. The slope varies from 1:320 at the

upper reaches to 1:3000 at the lower reaches. Around 28 km long stretch of the river

(upstream of Rapti-Riu confluence) is the critical stretch that occupies an area of 285 km2.

The higher catchment areas are represented by high drainage density showing the significant

presence of gullies at those localities (Figure 3).


Dinesh Pathak


Figure 3: Drainage density map of the study area

The drainage density in the catchment area has significant role in the soil erosion and

landslide activities in the area when the other parameter favors the situation.

2.2 Geology of the study area

The Riu River catchment is consisting of rocks of Siwalik Group, aged between Mid.

Miocene to Lower Pleistocene (DMG, 1998; Gansser, 1964). The Siwaliks thrust over the

Quaternary sediments of the Indo-Gangetic Plain in the south along the Main Frontal Thrust

(MFT), and is separated from the Lesser Himalaya in the north by the Main Boundary Thrust

(MBT). The whole Siwaliks consist of an alternation of mudstone, sandstone, and

conglomerate, but at varying proportions and textures. This Group is sub-divided into Lower

Siwalik, Middle Siwalik and Upper Siwalik. The Lower Siwalik is characterized by fine

grained sandstone with inter-bedding of red coloured mudstone, shale and siltstone, while the

lower part of Middle Siwalik is dominated by fine to medium grained sandstone with inter-

bedding of siltstone and mudstone. The upper part of Middle Siwalik consists of medium to

coarse grained pebbly sandstone. Conglomerate with subordinate sandstone and mudstone

occurs in Upper Siwalik. Besides, surficial material of alluvium in origin (Quaternary to

Recent in age) the Siwalik Group of rocks are exposed at several locations.

Lower Siwalik rocks are exposed at the mountainous parts in the upper reaches of Riu River,

mostly in the southern part of the area, near Indo-Nepal border (Figure 4). The alluvial

materials ranging in size from clay to boulders are widely distributed in the lower elevation

areas, mostly covering the right bank of the river. The area between Riu River and Rapti

River is entirely covered by these materials. The Upper Siwalik rocks are exposed in

easternmost part of the watershed while the Middle Siwalik is distributed around the left bank

of the River. The Siwalik rocks are thrusted/faulted and folded with the development of joint

sets and differential erosion is one of the reasons for contributing significant sediment load to

the river during monsoon season.


Dinesh Pathak


Figure 4: Geological map of the Riu River watershed (modified after DMG, 1998)

The Lower Siwaliks is exposed around right bank of the Riu River and the Middle Siwaliks

consisting dominantly of thick-bedded, massive, medium- to coarse grained, ‘salt and pepper’

sandstone and subordinately of mudstone, siltstone, and conglomerate occupies southern part

of the Riu watershed. The Siwalik Group on the whole displays a coarsening upward

sequence, forming an archive of the Himalayan uplift. There are many faults within the

Siwalik. Central Churia Thrust (CCT) that passes through the Churia Range is mainly

responsible for the formation of Dun Valley. Such geological control is playing dominant role

in the drainage network, physiographic condition, natural hazard (landslide, flood, bank

cutting etc.) and biodiversity/ecological units. The flora and fauna are also varying in

different physiographic regions. The Dun Valley Occupies recent sediments derived from the

surrounding mountains. It is a tectonic valley formed due to the presence of faults. The Riu

River Valley represents the southern part of the Chitawan Dun Valley. The sediments are

relatively coarser along the mountain foothill that gradually becomes fine towards the valley

centre.

3. Materials and methods

A general assessment of the Riu River watershed was done through the study of available

literature as well as satellite imageries. The Riu River watershed has been assessed through

the utilization of primary data collected in the field, information extracted from the satellite

image and secondary information. The data used in the study are geological map of the area,

digital topographic map and satellite imageries. The geological map of the area published by

Department of Mines and Geology (DMG, 1998) was digitized in GIS. This map consists of

different geological formations with rock types and geological structures. Various thematic

layers like slope, aspect, drainage density, land use, landslide distribution, physiography etc.

were prepared from the digital topographic data as well as the information extracted from the

satellite images and field data. The data were integrated in GIS and bivariate statistical

method was applied to prepare the landslide susceptibility map of the area.

Hydrological analysis was carried out followed by hydraulic modelling to prepare flood

hazard map of the Riu River. The results form vital source of information regarding geo-


Dinesh Pathak


hazard condition in the area. Appropriate mitigation measures have been proposed to reduce

the impact of geological disaster in the study area.

4. Results and Discussion

4.1 Watershed characteristics

The Riu watershed is represented by a typical doon valley, which is surrounded by

mountainous regions. The watershed area is mostly covered by hill slope with less than 15

degree (92%), while the area covered by hill slope between 25 and 40 degree is less than 1%,

indicating that the watershed is having low to moderate hill slope (Figure 5).

Figure 5: Slope map of the Riu River watershed

The Riu watershed is dominantly covered by forest area (76%) followed by cultivation (16%),

grass land (4%) and sand deposition (3%). The remaining 1% of the watershed area is

covered by water body, barren land and settlements (Figure 6). This parameter is useful

because the landslide occurrence and land use changes have direct connection (Glade, 2003).

Fortunately, the mountainous areas are mostly covered by the vegetation, which is playing

positive role for the soil erosion and landslide control. However, the left bank of the valley

region is mostly occupied by the agriculture land. It has been annually affected by the Riu

River flood during the monsoon season.

Figure 6: Land cover map of Riu watershed


Dinesh Pathak


4.2 Basin morphology

The Riu River is sixth order stream. The total length of the first order stream in the Riu

watershed is 770 km, while the lengths of second, third, fourth and fifth order streams are

respectively 324, 187, 100, and 49 km (Figure 7). The length of highest stream order (i.e.

sixth order) is 43 km.

Figure 7: Stream network and order in the Riu watershed.

Majority of the tributaries of Riu River are of the order up to third at the right bank while it is

up to fifth order at the left bank. The mean bifurcation ratio of the Riu watershed is 1.94,

stream frequency is 7.7, and drainage density is 3.21. The bifurcation ratio generally ranges

between 3 and 5 for natural drainage basins without differential geological controls and only

reaches higher values where geological controls favor the development of elongated narrow

basins (Strahler, 1964). Chorley (1969) had noted that the lower the bifurcation ratio, the

higher the risk of flooding, particularly of parts and not the entire basin. The low bifurcation

ratio of the Riu watershed of 1.94 is an indication that parts of its segments are liable to

flooding. Likewise, the circulatory ratio 0.41 is an indication that the basin is not circular in

shape. Chow (1964) had noted that strongly elongated basins have circularity ratios of

between 0.40 and 0.50.

4.3 Landslide susceptibility mapping

Delineation of the landslide susceptible zones in an area is helpful towards landslide disaster

risk reduction. Various methods are in use for the preparation of landslide susceptibility map

(e.g. Pathak, 2016, Pathak, 2014b; Park et al., 2013; Dahal et al., 2012; Regmi et al., 2010;

Yalcin, 2008; Dahal et al., 2008; Chen and Wang, 2007; Van Westen et al., 2003). The

present study carried out knowledge based landslide susceptibility mapping in which weight

for each theme and rank for each class within the theme were assigned. Each thematic layer

was given weight ranging from 0 to 10 depending upon the degree of their effect for the

occurrence of landslide. Likewise, in each thematic layer, the ranks to individual classes were

also assigned within the value of 0 to 10 (Pathak, 2016). The derived map was validated with

the existing landslides and mass wasting data. The resulting map shows that the north eastern

part and southern part of the study area is having high landslide susceptibility (Figure 8).


Dinesh Pathak


Figure 8: Landslide susceptibility map of the Riu watershed.

The landslide susceptibility condition within the watershed is important for watershed

management purpose, which is required to reduce the disaster risk in the area.

4.4 Flood hazard mapping

Flood hazard mapping was carried out through hydrological and hydraulic analysis, the later

was carried out in GIS platform. The river is ungauged so the flood flow estimation was

carried out using three different methods, namely Water and Energy Commission Secretariat

(WECS, 1990), Department of Hydrology and Meteorology (Sharma and Adhikari, 2004) and

Modified Dickens methods.

Table 1: Computation of Riu River discharge at various return periods.

S.

No.

Computation

Method

Riu River Discharge (m3/sec) at Various Return Periods

2

years

5

years

10

years

20

years

50

years

100

years

200

years

1 WECS

Method 429.37 654.10 815.03 977.21 1193.53 1373.54 1556.40

2 DHM

Method 467.86 758.73 976.81 1203.18 1513.84 1778.92 2053.52

3

Modified

Dickens

Method

471.05 758.58 976.09 1193.59 1481.12 1698.63 1916.13

It is realized that the WECS method gives low discharge in comparison to other methods and

the other two methods gives very close discharges. Since the Modified Dicken’s Method is

widely used, the discharge value obtained from this method for 50 years return period has

been used as the design discharge for the hydraulic modeling of Riu River. HEC-RAS

software has been be used for hydraulic analysis and the output is the flood level on the

cross-section of the river, which was used to generate flood hazard (in terms of flood depth)

using HEC Geo-RAS application. The flood hazard map shows that the entire stretch of the

Riu River is having flood problem (Figure 9).


Dinesh Pathak


Figure 9: Flood hazard map of the Riu River.

The settlements at the left bank of the river are prone to river flooding and hence required

mitigation measures are required for flood disaster risk reduction in the area.

5. Conclusions

Riu River originates from Siwalik range in the south western part of the Chitawan district and

flows through the Chitawan National Park, with settlements at the left bank of the river. The

Riu River watershed is very fragile as it completely lie within the Churia (Siwalik) Region.

The river is of aggrading nature, which is braided in the upper reaches while it is meandered

at the lower reaches in the study area. Channel shifting of the river is a common phenomenon.

The river is narrower at the upper reaches and becomes wider as it approaches the valley part

thereby depositing the sediment derived from the upper catchment. The river is inflicting

damages to the settlements lying at the left bank thereby causing damages to houses and

agriculture fields lying on the river bank. The damages by the river are mainly in terms of

bank erosion, sediment deposition and flooding or inundation during the monsoon period.

Landslide susceptibility mapping of the watershed and flood hazard mapping of Riu River

has been carried out which has identified the areas vulnerable to landslide and flood. This

information is useful for planning the required mitigation measures so as to reduce disaster

risk in the watershed.

Acknowledgement

The author wish to express sincere thanks to Professor V. Dangol and Dr. R. K. Dahal,

Department of Geology, Tribhuvan University, Nepal, for going through the manuscript and

providing constructive suggestions that has greatly enhanced the quality of the manuscript.

6. References

1. Aryal, K. R., (2012), The history of disaster incidents and impacts in Nepal.

International Journal of Disaster Risk Science, 3(3), pp 147-154.


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2. Chen, Z. and Wang, J., (2007), Landslide hazard mapping using logistic regression

model in Mackenzie Valley, Canada. Nat Hazards, 42, pp 75–89.

3. Chorley, R. J., (1969), The drainage basin as the fundamental geomorphic unit. In R. J.

Chorley (Ed.), Water, earth, and man: a synthesis of hydrology, geomorphology and

socio-economic geography, pp 77-99. London:Methuen.

4. Chow, V. T., (1964), Handbook of applied hydrology: a compendium of water-

resources technology. New York:McGraw-Hill.

5. Dahal, R.K., Hasegawa, S., Bhandary, N.P., Poudel, P.P., Nonomura, A., and Yatabe,

R., (2012), A replication of landslide hazard mapping at catchment scale. Geomatics,

Natural Hazards and Risk, 3(2), pp 161-192.

6. Dahal, R. K., Hasegawa, S., Nonomura A., Yamanaka, M., Dhakal S., and Paudyal, P.,

(2008), Predictive modelling of rainfall induced landslide hazard in the Lesser

Himalaya of Nepal based on weights-of-evidence, Geomorphology, 102(3-4), pp 496-

510,

7. DMG, (1998), Geological Map of Exploration Block-5, Chitawan, Western Central

Nepal (1:250,000), Department of Mines and Geology, Petroleum Exploration

Promotion Project, Government of Nepal.

8. Gansser, A., (1964), Geology of the Himalayas. London/New York/Sydney: Wiley

Interscience, p. 289.

9. Ghimire, S., K., Higaki, D., and Bhattarai, T. P., (2013), Estimation of Soil Erosion

Rates and Eroded Sediment in a Degraded Catchment of the Siwalik Hills, Nepal.

Land, 2, pp 370-391.

10. Ghimire, S., K., Higaki, D., and Bhattarai, T. P., (2006), Gully erosion in the Siwalik

Hills, Nepal: estimation of sediment production from active ephemeral gullies. Earth

Surface Processes and Landforms, 31 (2), pp 155-165.

11. Glade, T., (2003), Landslide occurrence as a response to land use change: a review of

evidence from New Zealand. Catena, 51, pp 297-314.

12. Khan, M. A., Gupta, V. P., and Moharana, P. C.,(2001), Watershed prioritization

using remote sensing and geographical information system: a case study from Guhiya,

India. Journal of Arid Environments, 49(3), pp 465-475.

13. Pandey, A., Chowdary, V. M., and Mal, B. C., (2007), Identification of critical

erosion prone areas in the small agricultural watershed using USLE, GIS and remote

sensing. Water Resources Management, 21(4), pp 729-746.

14. Park, S., Choi, C., Kim, B. and Kim, J., (2013), Landslide susceptibility mapping

using frequency ratio, analytic hierarchy process, logistic regression, and artificial

neural network methods at the Inje area, Korea. Environ Earth Sci, 68, pp 1443–1464.


Dinesh Pathak


15. Pathak, D., (2016), Knowledge based landslide susceptibility mapping in the

Himalayas. Geo Environmental disasters, 3(8).

16. Pathak, D., (2014a), Geohazard assessment along the road alignment using remote

sensing and GIS: Case study of Taplejung-Olangchunggola-Nangma road section,

Taplejung district, east Nepal. Journal of Nepal Geological Society, 47, pp 47-56.

17. Pathak, D., (2014b), Water Induced Disaster in Tamor River Sub-Basin, East Nepal,

DWIDP Bulletin, Series XV, pp 6-11.

18. Regmi, N., Giardino, J.R., and Vitek, J.D., (2010), Modeling susceptibility to

landslides using the weight of evidence approach: Western Colorado, USA.

Geomorphology 115, pp 172–187.

19. Sharma, K. P, and Adhikari, N.R., (2004), Hydrological Estimations in Nepal.

Department of Hydrology and Meteorology, Government of Nepal, Kathmandu.

20. Strahler, A. N., (1964), Quantitative geomorphology of drainage basins and channel

networks. In V. T. Chow (Ed.), Handbook of Applied Hydrology. New York:

McGraw Hill.

21. The World Bank, (2015), Population density (people per sq. km of land area.

http://data.worldbank.org/indicator/EN.POP.DNST, assessed on 15 May, 2016.

22. van Westen, C. J., Rengers, N. and Soeters, R., (2003), Use of Geomorphological

Information in Indirect Landslide Susceptibility Assessment. Natural Hazards, 30, pp

399–419.

23. WECS, (1990), Methodology for estimating hydrological characteristics of ungauged

locations in Nepal, His majesty’s Government of Nepal, Ministry of Water Resources

Water and Energy Commission Secretariat and Department of Hydrology and

Meteorology, Kathmandu, Nepal.

24. Yalcin, A., (2008), GIS-based landslide susceptibility mapping using analytical

hierarchy process and bivariate statistics in Ardesen (Turkey): Comparisons of results

and confirmations. Catena 72, pp 1-12.

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