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
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,
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 203
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).
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 204
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.
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 205
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-
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 206
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
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 207
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).
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 208
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).
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 209
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.
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 210
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.
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 211
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.
Top Related