Vol. 4 No. 1-3 INTERNATIONALPathak JOURNAL./Int. J. L OFsld. LANDSLIDE Env.(2016) 4 (1AND-3),1 ENVIRONMENT-8 Dec embe r 2 01 6
Water Induced Disaster Mitigation from Watershed Management Perspective in Nepal - An Example from Dobhan Khola Watershed, West Nepal
Dinesh Pathak1
Central Department of Geology, Geodisaster Research Center, Tribhuvan University, Kathmandu, Nepal
ORIGINAL ARTICLE CorrespondenceCorrespondence to:to: DineshDinesh Pathak Pathak CentCentralal Department Department of of Geology, Geology, Geodisaster Research Center, Tribhuvan University Email: Kathmandu, dpathaktu [email protected] Email: [email protected]
Abstract Water induced disasters are common phenomenon in the mountainous region of the active Himalayan belt. It is the major cause of annual loss of lives and properties in Nepal. The water induced disaster management is generally carried out in basin, sub-basin or watershed level through watershed management approach. Exploration of water induced disaster and evaluation of appropriate watershed management in Dobhan watershed in Palpa district, west Nepal has been carried out. Water induced disaster events like landslide, bank cutting, flood and sediment transportation are common in the watershed. Around 20% of the Dobhan watershed is covered by agriculture land and majority of it is on the sloping terrace. Though more than 65% watershed area is covered by forest, there is significant encroachment leading to degradation of the forest area and natural condition of the forest. Watershed related information, like geology, geomorphology, river morphology, land use, socio-economic conditions of the people in the watershed are some of the factors to be considered in the watershed management leading towards water induced disaster risk reduction. This paper presents various parameters and approach required for watershed management of the Dobhan Khola watershed, which is equally important to deal with other watershed of the country in holistic manner for the mitigation of water induced disasters.
Keywords: Water induced disaster, watershed management, watershed atlas, Dobhan Khola
1. Introduction and ethical perspective (Newson, 1992; Marty, 1997). Each perspective corresponds with one or more The mountainous region of Nepal is facing loss of lives scientific disciplines, and each highlights some and property each year due to the water induced aspects of RBM. Watershed is a small component of disaster. The water induced disasters are taking place river basin. due to general tendency of underestimating the natural phenomena through deteriorating the environmental Disaster mitigation activities is essential
condition of the mountainous region. It has significant from various perspectives like protection of
impact also to the downstream areas. It has close environment in terms of natural resources and bio- relationship with poverty alleviation, natural resource diversity, protection of infrastructures, forced migration, management and sustainable development. conflict resolution that has eventual impact to the livelihood of people. This can be achieved through a There well managed watershed with conservation of are several perspectives on river basin management downstream. This situation will eventually minimize the (RBM). Some important ones are natural-science, watershed degradation thereby supporting to reduce engineering, social optimization, legal, decision-making sediment deposition as well as floods in downstream
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2 which will eventually create a favorable condition for 96 km . The watershed is elongated in east west direction reducing the water induced disaster. A harmonic and lies in the Siwalik region of Palpa district in Western relationship will be maintained between nature and the Development Region (Fig. 1). The watershed consists of people. Within river basins, land and water, surface mainly 4 VDCs, namely Dobhan, Kachal, Baldengadhi water and groundwater, and water quantity and and Juthapauwa. water quality interact in many different ways (Mostert, 1999). To prevent overuse and degradation, prudent management is necessary that pays due attention to these interrelations.
Watershed management
has been the priority of government of Nepal that is primarily focused to conservation of soil, water and other biological components within the watershed. However, it has given low priority for disaster risk reduction. For example, the huge mass wasting (either in the form of landslide or debris flow) in the upper watersheds are usually affecting both the upstream as well as the downstream population. The event could be either from the overexploiting natural resources or
purely a natural event. Therefore, watersheds need to be Figure 1 Location of Dobhan Khola watershed in western
studied to identify the natural and human induced Nepal. The location of Nepal in the Himalayan range is shown causes for the disaster. It can be done through the in inset at top right corner.
consideration of multi-layer components, multi-sectoral interaction and temporal information collection. The Dobhan Khola watershed is one of the most affected
The watershed ones in the Tinau river basin. Water induced disasters
management activities is typical in each watershed, resulting from severe cut banks, landslides and debris which should be identified through thorough study of flows are common in this area. There are a number of various factors. Educating people in the causes and shallow to deep-seated landslides developed due to toe consequences of various factors for water induced cutting by the Dobhan Khola. Likewise, the lower disaster, including proper land use practice, is necessary terraces of the Dobhan Khola are under a high flood to implement the activities. Water induced disasters in hazard. The Dobhan Bazar that lies near the confluence the Nepalese mountainous regions should be addressed of Dobhan Khola and Tinau River is at risk due to bank through the watershed management perspectives. cutting by the river.
The rainfall data as measured in The aim of this paper is to Butwal meteorological station maintained by the explore various interlinked components to reduce water Department of Hydrology and Meteorology, Government induced disaster from the watershed management perspective. A typical watershed in the southern of Nepal has been analyzed (Fig. 2). This is the nearest meteorological station lying south of the study area. It is Himalaya region has been considered in the study to justify the various data and aspects to be considered to observed that the maximum annual rainfall was 3251.9
address the issue. The importance of satellite imageries mm in 1996 and the minimum was 1399.2 mm in 1998. forE P relevantP of th e data ben c extraction,hmark mo d assessmentel (model 1) of landsharply use The 26 year average (1985-2010) being 2327 mm. The increasecondition,d as soon as evaluation the shaki n ofg e hazardvent in iti andated vulnerability and then lev e haveled maximum rainfall occurred between the months June to off. Whbeenile fo r carried model 2 out and in 3, the in w watershedhich this lo considered.cation was Variousin the September. parameters of the watershed to be considered for the water induced disaster mitigation activities are presented in the paper. The paper emphasizes on the necessity of dealing the entire watershed in a holistic manner for the reduction of water induced disaster. This approach of reducing the water induced disaster through watershed management perspective is supposed to be useful in other watershed in the Nepal Himalaya.
2. The study area Figure 2 Annual rainfall variation between 1985 and Dobhan Khola is one of the tributaries of approximately 2010 in the Butwal meteorological station. north south flowing Tinau River and covers an area of
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3. Geology of Dobhan Khola watershed area was digitized in GIS. This map consists of various geological formations with rock types and geological Though the watershed is distributed both in the Lesser structures. Likewise, the relevant documents were Himalaya in the north and Siwalik region in the south, collected from concerned organizations like Soil the present study is focused only in the Siwalik region Conservation and Watershed Management Field office, (Fig. 3). The Siwalik Group consists of fluvial deposits Water Induced Disaster Prevention Field Office, strongly influenced by the Neogene tectonics of the District Agriculture Development Office. Himalaya (Prakash et al. 1980). Rocks of Lower Siwalik (LS) and Middle Siwalik (MS) are distributed The primary in the area. The Lower Siwalik (LS) is characterized by data was basically extracted from the satellite imageries alternate beds of fine-grained sandstone, siltstone and and from field investigation. There is tremendous use of variegated mudstone. It is a mud and silt dominated the satellite imageries in watershed management. It is helpful right from the beginning of watershed sequence and is the oldest formation in the Siwalik management planning to execution stage. Various Group. The Middle Siwalik (MS) is characterized by information required for geo-disaster assessment can be alternate beds of thick bedded, massive, medium to coarse grained „salt and pepper‟ colored sandstone and extracted from the satellite imageries and aerial subordinately of mudstone, siltstone and conglomeratic photographs (Pathak, 2014, 2015b). The geological horizons at the upper part (e.g. Gansser 1964; Tokuoka boundaries as well as the geological structures were et al. 1990). The watershed is covered dominantly by updated from the high resolution satellite images and Middle Siwalik rocks (Shakya et al. 1998). later from field observation. Likewise, it is widely used in the assessment of flood hazard in an area (Pathak et al., 2009). Various thematic layers, like landslide distribution, gully erosion and bank cutting were prepared from the from the satellite images, which was further updated and verified during the field investigation. In addition, bifurcation ratio, stream order and drainage density in the watershed were calculated, which are important parameters related to stream morphology.
The field data collection was made through the observation, measurement and interaction with local people as well as stakeholder. Checklists were used for technical and social data collection in the field. The
technical data collection checklists included bio- physical (like settlements, geology, slope, land use, Figure 3 Geology of the Dobhan Khola. .watershed (modified after Shakya et al., 1998). stream order, drainage type and density and frequency, stream/river length, river bank cutting, erosion, Main Boundary Thrust (MBT) lies at the northernmost sedimentation and land degradation, landslide problem part of the watershed that borders the Siwalik Region areas, wetland, vulnerability to disaster etc.) that with the Lesser Himalayan Region. Likewise, the represents the watershed characteristics. The upstream-
Central Churia Thrust (CCT) is passing almost through downstream linkage was assessed so as to understand the centre of the watershed, north of the Dobhan Khola. the impact of activities soil erosion, landslide, CCT is mainly responsible for the formation of Doon deforestation etc. that is going on at the upper Valley. This thrust is the main cause of the repetition of catchment to the lower catchment. the Siwalik formations in the sequence. These geological structures play vital role in the The socio-economic geomorphological condition as well as terrain features data were mainly on the social composition, educational and on the slope stability. condition, water stress, livelihood and impact of disaster in the livelihood of people, economic activities of the 4. Materials and Methods people, energy sources etc. Likewise, the major agriculture products, cropping patterns, irrigation In order to assess the condition of watershed and facilities and livelihood strategy of the people living associated water induced disasters, primary and within the watershed was also assessed. secondary data have been utilized. The secondary data utilized in the study are geological map of the area The published by Department of Mines and Geology, digital primary and secondary data were compiled and topographic map of Department of Survey that consists analyzed. GIS database formed from the primary and of contours, drainage network, land use, and secondary data, which were analyzed and relevant maps administrative boundaries. The geological map of the were prepared. The location of gully erosion have been
11 Water Induced Disaster Mitigation from Watershed Manage ment Perspective in Nepal - An Example from Dobhan Khola Watershed, West Nepal
Vol. 4 No. 1-3 Pathak./Int. J. Lsld. Env.(2016) 4(1-3),1-8 Dec embe r 2 01 6 demarcated and landslide hazard map have been used to degree (Fig. 4a). The steeper area (> 50 degree) and the describe the landslide hazard condition in the gentle area (< 10 degree), respectively occupies around watershed. Likewise, the vulnerability from these water 7% and 10% of the study area. The northern part of the induced disasters have also been assessed. study area is mostly represented by the steeper hillslope.
The present land use condition have been considered as a basis for assessment of the appropriate use of land in the watershed and thereby propose for future measures to reduce the water induced disaster. Similarly, climate change is another issue to be considered in every planning and hence emphasized in the watershed management activities to be carried out to mitigate the Figure 4 (a) Slope map and (b) Relief map of the water induced disaster. The technical and social data watershed. collected from secondary source and from the field was carefully evaluated with respect to watershed The study area lies within the elevation from 250 m to management from water induced disaster perspective in 1750 m (Fig. 4b). The area with 750-1000 m elevation the watershed. A broader framework to deal with the occupies 35% of the study area followed by elevation water induced disaster through watershed management classes 500-750 m (31%) and less than 500 m (15%). activities have been proposed. The high elevation classes (<1000 m) occupies around 18% of the study area. The highest elevation areas lie in 5. Watershed Characteristics the north and western part of the study area. Interestingly, the study area has almost equal north Watershed characteristics mainly comprises of the facing and south facing sloping land (around 37.5% physical characteristics of the watershed. Certain each). The east facing and west facing slopes physical properties of watersheds significantly affect the respectively occupies 14.5% and 10.5% of the study characteristics of runoff and resulting river morphology. area. Morphometry is the measurement and mathematical analysis of the configuration of the earth‟s surface, The geomorphic feature of an area is controlled by shape and dimensions of its landforms (Clarke, 1966). lithology and geological structures, which are further The study of basin morphometry relates basin and modified by the drainage. Therefore, the resulting stream network geometries to the transmission of water landscape is the result of endogenic crustal movements, and sediment through the basin. The size of a drainage exogenic processes, and climatic condition. The rocks basin acts upon the amount of water yield; the length, are generally dipping towards north (Fig. 5). The shape and relief, affect the rate at which water is alternating layers of thick bedded mudstone and sandstone give rise to the hogback structures and strike discharged from the basin and total yield of sediments. ridges. Drainage area is a lumped variable as all the environmental variables are involved within it and specific sediment yield is an index of soil erosion intensity of some drainage basin. There is no specific relationship between the mass of the exported sediment and the size of the drainage basins (Cerdan et al. 2012; Carlos de Araujo and Knight 2005). The sediment yield from a watershed is a function of topographical, land use, and pedological parameters, which have been considered in the present study.
5.1. Geomorphology
The Siwalik Hills are the southernmost mountain range of the Himalaya that abruptly rises from the Terai Plain up to an altitude of 1687 m near Baldengadhi in the Dobhan watershed. Generally, the range exhibits very rugged terrain with deeply dissected gullies and steep Figure 5 Active Landslide with north dipping beds on the slopes. Low terraces, alluvial fans, badlands, thin soil left bank of the Dobhan Khola. cover are the characteristics of the Churia Range. Significant amount of sediments are generated from the In general, the MBT is responsible for creating gullies and tributaries. The slope class 10-30 degree a typical landform of a depression and a “pressure occupies almost 54% of the study area while around ridge” south of it. The CCT is another important thrust 20% of the study area is occupied by slope class 30-40
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running in east-west direction through the Siwalik farming, it is not practiced commercially rather aimed region. These thrusts are playing a vital role in creating to meet their domestic demand. the geomorphic features and drainage patterns. These are also responsible for creating slope instability There are 36 problems leading to landslides and debris flows. community forests handed over to the local community in Dobhan watershed indicating the good initiation to 5.2. Major morphometric parameter maintain the greenery of the watershed, which will be supportive to reduce the water induced disaster. However, the lower portion of the watershed is less The stream order in the Dobhan watershed have been calculated by Strahler (1964) method. The Dobhan diverse in biodiversity than the upper watershed due to
Khola is 4th order stream and the mean bifurcation ratio the increased encroachment from nearby settlements.
(BF) is 2.02. The total length of the stream in the
Dobhan Khola watershed is 156 km and watershed area The use of wood for fire is still a dominant (>93%) one
is 96. Drainage density is another morphometric for cooking purpose in the entire watershed (CBS, parameter that considers the amount of channels in a 2014). This requires careful forest management so that watershed (Horton, 1932). The calculated drainage it would not degrade due to excessive demand of wood density (Dd) 1.62 km/km2 indicates moderate drainage for domestic use. densities. The Moderate drainage density indicates the basin is having permeable subsoil and vegetative cover 6. Water induced disaster in the watershed that well reflects the field condition in Dobhan watershed. 6.1. Erosion, sedimentation and land degradation
5.3. Socio-economic condition Erosion has been taking place from the Dobhan watershed. The major factors that have contributed to Socio-economic condition of the people living in the induce high incidences of various types of mass watershed plays vital role in watershed degradation and movements in the area are fragile geological condition, vice-versa. The population of Dobhan VDC is highest prolonged and high-intensity rainfall, and various (6872) followed by Kachal (3699), Juthapauwa (3440) anthropogenic factors. and Baldengadhi (2043) VDC (CBS, 2014). The weak Siwalik rocks The Dobhan undergo extensive weathering and erosion process watershed is mostly resided by the Magars, followed by thereby producing significant amount of sediments to Chhetris, Brahmins and Dalits (CBS, 2014). Migration the gullies and then rivers flowing through the area (Fig. from ridge to the valleys like Kachal valley is 6). In addition, the scenario is much worse when there is increasing due to the availability of productive land. It significant deforestation in the area that removes the was noticed that the farm land is increasing with surface cover and increases the soil erosion activities. encroachment in forest, which is also evidenced by the new settlement observed inside the forests where trees were cut down for farming. The education level of the
people is highest in Dobhan VDC followed by
Juthapauwa, Baldengadhi and Kachal. Principally, it is
easy to make people aware about the watershed management if they are better educated, which is also indirectly lined with their better economic condition.
The agriculture product from their farm supports their round the year livelihood even without proper irrigation facility. Mainly, three type crops are grown in a year, which are paddy during monsoon, and maize, millet and buckwheat in winter and wheat and other crops during pre-monsoon. Vegetables are widely produced in the area, mainly cabbage, cauliflower, potatoes, beans etc. Figure 6 Gully erosion in the Dobhan.
Likewise, the livelihood of the people is also supported watershed. by the production of fruits like banana, peaches guava, mangoes. Cinnamon and Amliso are produced for The uncontrolled/unmanaged sand and gravel mining income generation. Local youths immigrate to India and activities from the river bed have disturbed the Arab countries for the employment in addition to major hydrological system of the river. Such activities also cities within the country. Producing local liquor is contribute for modification of the morphological another livelihood strategy, in which mostly women are condition of the river valley, including the upper engaged. Even though there is potentiality for livestock reaches of the catchment, in which the gullies plays
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active role in erosion of the rock and soil. The presence location. Further, the construction of rural road has also of numerous gullies and resulting erosion give rise to caused the occurrence of landslides. River bank cutting the formation of bad land topography. It is mainly has been one of the most serious problems in the taking place in south facing hill slopes in the Dobhan mountainous region where the river flows through watershed. narrow valley. It is taking place at the locations where river is meandered either due to the lithological 6.2. Landslide, bank cutting and flooding variation or due to structural control. Flooding problem is significant where there is wider flood plain. The
landslide and bank cutting problem in the Dobhan The northernmost boundary of the Dobhan watershed is traversed by the Main Boundary Thrust, (MBT) that watershed is shown on Fig. 7 and listed on Table 1.
forms the area geologically vulnerable to the occurrence
of landslide.
Landslide, river bank cutting and flood are
the common water-induced hazards in the area. The sediments derived from surface erosion, landslides and river bank cutting at the upper reaches of the rivers are transported downwards and deposited primarily on the relatively flat river valleys at downstream. This further supports for flooding and river bank erosion process.
Landslides are taking place either due to jointed rocks at steeper hill slope, increase in pore water pressure at the thick sediment deposits on slope or due to toe cutting by
the river. In the Dobhan watershed, all these phenomena are active, either one of the above mentioned factor Figure 7 Landslide and bank cutting in the Dobhan being dominantly active in the watershed.
Table 1: Locations of landslide and river bank cutting in Dobhan watershed.
S. N. VDC Ward No Problem No. of sites
1 Baldengadhi 4 Bank Cutting and Landslide 1 2 Baldengadhi 3 Landslide 1
3 Baldengadhi 4 Landslide 2
4 Baldengadhi 8 Landslide 4 5 Baldengadhi 9 Landslide 1
6 Dobhan 3 Bank Cutting and Landslide 1
7 Dobhan 6 Bank Cutting and Landslide 1 8 Dobhan 7 Bank Cutting and Landslide 3
9 Dobhan 9 Bank Cutting and Landslide 4
10 Dobhan 3 Landslide 3
11 Dobhan 7 Landslide 9 12 Dobhan 9 Landslide 10
13 Juthapauwa 2 Bank Cutting and Landslide 2
14 Juthapauwa 3 Bank Cutting and Landslide 3 15 Juthapauwa 7 Bank Cutting and Landslide 1
16 Juthapauwa 1 Landslide 1
17 Juthapauwa 2 Landslide 2 18 Juthapauwa 3 Landslide 4
19 Juthapauwa 7 Landslide 3
20 Juthapauwa 9 Landslide 3
21 Kachal 1 Bank Cutting and Landslide 3
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22 Kachal 5 Bank Cutting and Landslide 4
23 Kachal 6 Bank Cutting and Landslide 5 24 Kachal 7 Bank Cutting and Landslide 2 25 Kachal 8 Bank Cutting and Landslide 2
26 Kachal 9 Bank Cutting and Landslide 3
27 Kachal 1 Landslide 9 28 Kachal 4 Landslide 3
29 Kachal 5 Landslide 1
30 Kachal 6 Landslide 2 31 Kachal 7 Landslide 5 32 Kachal 8 Landslide 1
33 Kachal 9 Landslide 2
The field data shows that the Dobhan, Baldengadhi and , the Dobhan VDC is severely affected by the landslide Kachal VDC are severely affected by the landslide and with several events causing loss of lives and properties bank cutting problem. The number of households (Table 2). Between the year 1992 and 2013, total 17 affected by landslide and bank cutting problems in people died and 2 people injured due to landslide in the Dobhan, Baldengadhi and Kachal are respectively 280, Dobhan VDC alone. Likewise, the road was also 120 and 115. The presence of many landslides and bank damaged by the landslide in this VDC. However, in erosion sites within the VDC has increased the Kachal and Baldengadhi VDCs, the loss of lives due to probability of water induced disaster in the area. landslide event is low. There has been only two major flood event in the study area, that took place in Kachal
and Dobhan VDCs, respectively in the year 1998 and 6.3. Water induced disaster losses 2011. The flood at Kachal had death toll of one person
The water induced disaster, mainly the landslide and and another was injured.
flood are common in the study area. Among all VDCs,
Table 2: Water induced disasters in the Dobhan watershed (UN/ISDR, 2013).
Death Injured Road S.N. VDC Location Event Event date No. No. damaged
10/18/1973 1 Kachal Kalimati Landslide - 12 - 2 Baldengadhi Ward No. 4, Khule Landslide 9/5/2007 2 2 - 9/28/2013 3 Dobhan Ward No. 7 Landslide 1 1 - 7/1/2011 4 Dobhan Landslide 1 - - 5 Dobhan Ward No. 5 Landslide 1/3/2010 - 1 -
6 Dobhan Siddababa, Ward No. 5 Landslide 8/15/2008 2 - -
7/13/2006 - 7 Dobhan Siddhababa Landslide 1 - 10/8/2004 - 8 Dobhan Landslide 12 -
9 Dobhan Ward No. 5 Landslide 1/7/2004 - - 50 m
6/22/1992 - - 10 Dobhan Landslide 150 m 11 Dobhan Ward No. 5 Flood 8/30/2011 - - - 12 Kachal Ward No. 5 Flood 7/28/1998 1 1 -
7. Watershed Management significant implications in the structure and function of the other elements. Watershed Management is the
A watershed includes the human as well as the natural process of creating and implementing plans, programs,
system with their various elements and and projects to sustain and enhance watershed functions
interrelationships. The human system represents the that affect the plant, animal, and human communities social sphere whereas the natural system represents the within a watershed. The various components of
landscape sphere. The changes in one element can have watersheds that need to be managed include water
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resources conservation and utilization, protection from One step forward from hazard mapping is the river, catchment treatment, disaster mitigation, vulnerability mapping in the watershed. The conservation of farm land, greenery of the watershed vulnerability mapping requires identification of etc. The major components of the watershed potential hazards and the critical physical and management are briefly described below with reference anthropogenic factors that influence the anthropogenic to the Dobhan watershed as far as practicable. factors that influence the occurrences of such hazards. The settlements along the Dobhan Khola and on hill slopes are having high landslide vulnerability. This 7.1. Preparation of watershed atlas information is useful in the preparation of integrated
Preparation of the watershed atlas is a basic requirement watershed management plan of which the disaster
for watershed management planning. It consists of preparedness is an inevitable component. The field
maps, statistics and text about the bio-physical and study revealed that Dobhan VDC is highly vulnerable
socio-economic elements of watershed, which are from the water induced disaster problem followed by
required for the long-term sustainability of the Kachal and Baldengadhi VDC. Juthapauwa VDC is less watershed‟s natural resources. The content of watershed vulnerable among the VDCs within the study area. atlas are watershed boundary, VDCs and settlement within the watershed, topography, geology, location of 7.3. Appropriate use of land water bodies, conservation area, population, land use/land cover, major locations of mass wasting (gully Land use practice in the mountainous region has erosion, landslide/debris flow), flood affected area, prominent impact on the occurrence of slope instability. infrastructures etc. Such informations are vital in It is basic norm that land should be utilized according to planning and implementing the watershed management its appropriateness for particular purpose. For example, activities. The watershed atlas is quite useful in settlements should be avoided at the agriculture field at delineating basin, sub-basins, watersheds and providing the low land, the steeper hill slopes should be covered watershed management relevant information to the by vegetation, the area unsuitable for agriculture but not decision makers and general public (Pathak, 2015a). at steep slopes are suitable for settlement, the water bodies should be preserved and so on. This practice is 7.2. Hazard and vulnerability mapping called land use planning, which is essential not only for sustainable use of land resources but also for reducing Landslide hazard can be assessed considering several the geo-disasters. It is one of the major activities to be factors like slope angle, landform, relative relief, considered in watershed management. The land use map drainage density, hydrogeology, lithology, soil type and of the Dobhan watershed shows that the forest area thickness, geological structures, land use, dominantly covers the watershed (Figure 9). meteorological, anthropogenic etc. In the Dobhan watershed, the very high landslide hazard zone The area principally lies northwards of the Dobhan Khola (Figure covered by forest is around 75% of the watershed area. The 20% coverage of cultivated area is quite significant 8). The high hazard zone dominantly covers the study area, however, in the southern part of watershed, it is in the mountainous region. Cultivation in sloping
mostly distributed along the gullies. terrace is around 15% of watershed area, which is to be
Figure 8 Landslide hazard map of Dobhan Watershed (DWIDP, 2007).
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risk reduction should be to look at the upper watershed
areas and solve the issues with required treatment. Once these areas are intervened properly, the lower catchment area need to be considered for further management activities.
In the Dobhan watershed, the forest area is being degrading due to deforestation, grazing, fire,
queries and encroachment. The forest degradation at the
upper catchment has ultimately resulted in increased
sediment production and down slope transportation leading to sedimentation in cultivated land and bank erosion in downstream. This is in support of the
argument that conservation of upper watershed areas are
directly related to the livelihood support system of the Figure 9. Land use condition in the Dobhan lower watershed areas. watershed. considered with due care from disaster perspectives. 7.6. Address climate change related issue The crop type should be carefully selected and excessive irrigation should be avoided to control the soil The possible changes in the watershed condition due to erosion and slope instability. The 3% cultivated area at the impact of climate change need to be considered in the valley floor should not be used for the settlement as the watershed management planning. Climate change is it is the best location for agriculture. Grazing land and supposed to intensify the landslide and flood due to shrub land occupies, respectively 0.5% and 3.5% high intensity low duration precipitation, increase soil watershed area while settlement covers only 0.15% erosion leading to loss of vegetation; water shortage, watershed area. The proposed land use in an watershed prolonged drought leading to deceased crop production, should be prepared with reference to the present invasive and alien species affecting the crop production, practice so that it would be socially accepted and could changed pattern (intensity and duration) of be easily implemented. However, for the sustainable use precipitation; etc. (Pathak et al., 2010). of land, required changes need to be incorporated through a process of educating the people at pros and In order to cons of land use practice at various locations within the reduce the impact of climate change in the watershed watershed, which will facilitate to get their consent and ecosystem, necessary planning need to be carried out to support in materializing the proposed land use practice ensure the water availability for domestic and irrigation, in the watershed. adopt remedial measures to control soil erosion and maintaining greenery of the watershed. Likewise,
7.4. Identification of unstable areas change in cropping pattern and selection of suitable
crops that withstand in the changed climatic condition is
There are certain indicators of slope instability in any another approach to deal with the climate change. The area. Some indicators of slope instability have been water availability can be augmented through identified for the Dobhan watershed, which would be establishing the artificial recharge system and useful to meet the disaster risk reduction goal of the construction of storage ponds. In the Dobhan watershed, watershed management plan. Such unstable zones, drinking water in most of the settlement is provided mainly the gully erosion, landslide and bank cutting through the springs and streams at the upper catchment locations have been previously mentioned in detailed. area. These are supposed to have decreased discharge due to the climatic variations. The present approach of 7.5. Upstream and downstream linkages exploitation should be shifted towards construction of shallow wells penetration to water table in the hard rock In every watershed management planning process, the aquifer. Likewise, further treatment of gullies and river entire watershed need to be considered as a single entity banks is necessary to protect the areas from possible and required specific activities should be implemented. flash floods. These areas are primarily the areas that are The problem arising in the upper watershed area will affected by gully erosion, landslide and bank cutting have pronounced impact to the lower watershed areas. problems at present. Other vulnerable areas should also Sediments derived from surface erosion, landslides and be identified. gully erosion at the upper reaches of the rivers are transported downwards and deposited primarily on the 7.7. Adopt mitigation measures relatively flat river valleys at downstream and further transported downstream resulting in impact to bank Once the adequate understanding of the watershed in erosion and sedimentation. The optimum effort of terms of hazard, vulnerability and risk areas as well as watershed management practitioner focused to disaster land use condition is achieved, the site specific
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mitigation measures should be designed and The water induced disaster mitigation activities implemented. The landslide hazard maps of the should be carried out from the watershed watershed is useful for general planning purpose, like management perspective addressing all related identification of most hazardous areas within the component in an integrated manner. watershed and thereby making appropriate plan to protect infrastructure, agriculture, settlement and also References for catchment treatment activities. However, in many cases, there is requirement of site specific treatment like Carlos de Araujo, J. and Knight, D. W. (2005). A gully treatment and activities to control individual review of the measurement of sediment yield in landslide. It is to be noted that each landslide is unique by nature and the treatment practice adopted at one site different scales. R. Esc. Minas, Ouro Preto, 58(3),
may not be suitable at other landslide. Similarly, to 257-265.
control excessive soil erosion from the upper watershed CBS (Central Bureau of Statistics) (2014). National
areas, the degraded forest should be restored through population and housing census 2011-Palpa plantation and the forest encroachment should be (NPHC2011). National Planning Commission checked. The human activities should be controlled around the large landslide that can‟t be mitigated Secretariat, Government of Nepal, Vol. 6, 82p. instantly or require huge amount of investment. This Cerdan, O., Delmas, M., Négrel, P., Mouchel, Jean- will lead towards natural stabilization of the slope, Marie, Petelet-Giraud, E., Salvador-Blanes S.,
however, plan should be made to manage the landslide Degan, F. (2012). Contribution of diffuse hillslope debris without affecting the settlement, agriculture land erosion to the sediment export of French rivers. and river morphology at the downstream areas. Comptes Rendus Géoscience. Doi : 8. Conclusion 10.1016/j.crte.2012.10.011. Clarke, J. I. (1966). Morphometry from Maps. Essays in This paper summarizes the approaches to be considered Geomorphology. Elsevier Publ. Co., New York, to reduce water induced disaster in a watershed with an 235-274. example of Dobhan watershed in Palpa district, Nepal. DWIDP (2007). Preparation of water-induced hazard The Dobhan watershed is situated in the Siwalik region and traversed by two major geological structures maps of Tinau river basin. Department of water- namely Main Boundary Thrust and Central Churia induced disaster prevention (DWIDP), Disaster Thrust, forming the terrain fragile and vulnerable to mitigation support programme (DMSP), water induced disaster. The following conclusions are Government of Nepal. made to reduce water induced disaster in the Dobhan Gansser, A. (1964). Geology of the Himalaya, Wiley watershed from watershed management perspective: Inter Science, London, 289p.
Watershed related data like landslide, gully Horton, R. E. (1932). Drainage basin characteristics. erosion, bank cutting, land use practice etc. can Trans. Am. Geophys. Union., 13, 350-361. be extracted from the satellite imageries to Marty, F. (1997). International River Management - The form GIS database for further analysis. Political Determinants of Success and Failure; Introduction and Research Design, Studien zur Landslide, gully erosion and river bank cutting Politikwissenschaft Nr. 305, Universitat Zurich, is significant in the watershed leading to the Zurich. impact to settlement and agriculture land. Mostert, E. (1999). Perspectives on River Basin High water demanding crops like paddy should Management. Phys. Chem. Earth (B), 24 (6), 563- be avoided in the sloping agriculture land that 569. accounts around 15% of the watershed. Newson, M. (1992). Land, water and development; Instead, wheat and millet can be a better choice
on the steeper slope. Appropriate land use in River basin systems and their sustainable
the watershed will help to control the water development & Routledge, London and New
induced disaster. York.
Pathak, D. (2014). Geohazard assessment along the road The people residing in the watershed should be alignment using remote sensing and GIS: Case study made aware on the negative impacts of forest encroachment through providing alternatives to of Taplejung-Olangchunggola-Nangma road section, energy source and fodder to livestock. Taplejung district, east Nepal. Journal of Nepal Understanding the socio-economic condition in Geological Society, 47, 47-56.
the watershed would help to adopt appropriate Pathak, D. (2015a). Importance of watershed atlas in approach to aware the people.
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Shakya, T. R., Pradhan, U. M. S, Shrestha, R. B., Subedi, D. N., Sharma, S. R. & KC, S. B. (1998). Geological map of exploration Block-5, Chitawan, western central Nepal. Department of Mines and Geology, Kathmandu, Nepal. Strahler, A. N. (1964). Quantitative geomorphology of drainage basins and channel networks. In: V. T. Chow (ed.), Handbook of Applied Hydrology. McGraw Hill Book Company, New York, Section 4-II. Tokuoka, T., Takayasu, K., Hisatomi, K., Yamasaki, K., Tanaka, S., Konomatsu, M., Sah, R. B. & Rai, S. M. (1990). Stratigraphy and geological structure of the Churia (Siwalik) Group of the Tinau Khola-Binai Khola area, west central Nepal. Mem. Fac. Sci. Shimane Univ., 22, 71-88. UN/ISDR (2013), DesInventar-a free, open source Disaster Information Management System, UN/ISDR. (http://www.desinventar.net/DesInventar/profiletab.j sp?countrycode=npl). Accessed on March 15, 2016.
19 Water Induced Disaster Mitigation from Watershed Management Perspective in Nepal - An Example from Dobhan Khola Watershed, West Nepal