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Photonirvachak
J. Indian Soc. Remote Sens. (March 2009) 37:119–128
RESEARCH ARTICLE
Land Degradation Mapping in the Upper Catchment of River Tons Gopal Krishan . S.P.S. Kushwaha . A. Velmurugan
Received: 26 December 2007 / Accepted: 15 December 2008
Keywords Land degradation . Remote sensing . Visual interpretation . Tons River
Abstract A study on land degradation in the upper catchment of river Tons, a tributary of Yamuna river, in Uttarkashi district of the Uttarakhand state, was carried out using on-screen visual interpretation of IRS LISS-III + PAN merged data. The study area, which is largely mountainous, includes Govind Wildlife Sanctuary and National Park. Vegetation cover, slope and erosion status were used as criteria for the delineation of four major land degradation categories viz., undegraded, moderately degraded, degraded and severely degraded. More than 50 per cent of the study area is reported to be covered with snow and grassland. The moderate to severely degraded area worked out to be 42.4 per cent of the
total area. The 32.8 per cent of area was found to be moderately degraded, followed by degraded (6.63%) and severely degraded (2.88%) areas. The depletion of vegetation cover on mountainous terrain and subsequent cultivation without proper protection measures is the reason for severe soil erosion and land degradation. In view of the existing land degradation situation, the catchment requires immediate treatment on priority for the sustenance of agriculture and wild life. It is expected that these measures will reduce the silt load in the river Tons and eventually, in river Yamuna.
Introduction
Gopal Krishan ( ) . S.P.S. Kushwaha . A. Velmurugan Indian Institute of Remote Sensing (NRSC), 4, Kalidas Road, Dehradun – 248001, India
email :
[email protected]
Land is one of the most important natural resources for the sustenance of life. It embodies soil, water, flora and fauna, and involves the total ecosystem. Land degradation is the temporary or permanent lowering of the productive capacity of land (UNEP, 1992). It includes various forms of soil degradation, adverse human impacts on water resources,
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deforestation and lowering of the productive capacity of rangelands. Land gets degraded when it suffers from loss of its intrinsic qualities or there is a decline in its capabilities as a consequence of forces, or the product of an equation, in which both human and natural forces find a place (Blaikie and Brookfield, 1987). Chisholm and Dumsday (1987) suggest that land degradation is something that can result from any causative factor or a combination of factors, which reduce the physical, chemical or biological status of the land and which may restrict the land’s productive capacity. Land degradation is universally recognized as a major problem for food security and sustainable development and was addressed at the 1992 United Nations Conference on Environment and Development (UNCES) in Agenda 21 (Koohafkan, 2000). Globally, 4706 million hectares (M ha) of land is affected by land degradation (Dregne, 1986). According to latest reports of the Department of Agriculture and Co-operation, 107 million hectares of area was classified under various types of degraded lands in India (DAC, 1994). It was also reported that land affected by water erosion, which results in loss of top soil, accounts for 80 per cent of degraded land. Land degradation is a major problem in the Himalayan region. Rapid increase in human population and the consequent increase in developmental activities during the recent past together with high rainfall, fragile geology, high relief, landslide debris, mine wastes and road cuttings have affected the flow regime in the river Tons. Overgrazing and deforestation have accelerated land degradation and the region is currently facing various degrees of degradation, that is seriously threating the already fragile Himalayan landscape. Though conventional soil surveys provide information on land degradation; these are slow, time-consuming and expensive. Among the new technologies for studying natural resources, spaceborne remote sensing proved to be powerful,
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because of the synoptic view of terrain features, repetitive coverage of the same area at regular time intervals, collection of data in visible through near infra red and the amenability of data to computer analysis. Quantification of a spatial extent during a particular time period is the first step in monitoring the progress of land degradation. Remote sensing data are handy for land degradation assessment and monitoring these periodically in time and space domain using multi temporal datasets in India (Venkataratnam and Rao, 1977; Venkataratnam, 1989; Rao et al., 1991; Venkataratnam and Ravisankar, 1992; NRSA, 1995). Most importantly, it helps to identify features and their conditions in inaccessible areas like that of Tons river catchment. It is essential to bring about a balance between economic development and environmental conservation. Needless to mention, up-to-date information on the state of natural resources is essential for planning the sustainable development of mountain regions. Rehabilitation of the Tons river catchment could reduce the sediment load in Tons and Yamuna rivers on the one hand and in situ conservation of monsoon water on the other. This study was undertaken keeping in view the above objectives.
Study area The upper catchment of river Tons (area: 1172 km2, 31°00' – 31°16' N and 78°00' – 78°38' E) lies in Purola tehsil of Uttarkashi district in Uttarakhand state of India (Fig. 1). It includes Govind Wildlife Sanctuary and National Park with Rupin, Supin and Sankari forest ranges. The study area is mountainous and the altitude varies from 1200 to 6387m. Forests, agriculture, grasslands, snow and glaciers are the major land use/land cover types. The Tons catchment exhibits an intricate pattern of mountain system consisting of high mountains covered with
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snow and glaciers in the north-east and moderate to very-steep sloping summits and peaks, with narrow valleys.
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October to May, more so, between November to March.
Fig. 1 Location of the study area.
The area with 3000m and above elevation could be classified as high mountains. The high mountains are further sub-divided into glaciated high mountains and seasonally snow-capped high mountains. This physiography consists of magnificent glaciers, viz., Bandarpunchh glacier, Jamdar Bamak, Deokiar Bamak glaciers. The tributaries of river Tons viz., Har Ki Doon gad, Maninda gad, Ruinsara gad, Obra gad, Liyari gad, Supin, Istar gad and Rupin are mainly fed by the mountain glaciers, valley glaciers and glacier lakes. The area is subjected to regular snowfall, interrupted by occasional cloud bursts of the higher elevations. The retreating movements of glaciers may be observed in the form of ‘U’ shaped valleys with moraines and aggradational slopes. The summits and peaks are permanently under snow cover. The rocky slopes and cliffs are mainly barren. Avalanches and landslides are regular phenomena along Maninda gad and other tributaries before they join river Tons at Har Ki Doon. The rainfall varies from 1000 to 1500 mm annually. Heavy snowfall occurs from
The great variation in altitude and aspect has resulted in a large variety of natural vegetation. Champion and Seth (1968) recorded five forest type groups viz., Subtropical Pine Forest, Himalayan Moist Temperate Forest, Himalayan Dry Temperate Forest, Sub Alpine Forest and Moist Alpine Scrub and 29 sub-groups in the region. Ten species of grasses, twenty four species of shrubs and twenty six species of trees are of high economic utility in the study area (Parmananda, 1998). Soils are formed either on moderate-to-steep slopes with vegetation cover or in narrow mountain valleys. At higher elevations and very steep slopes, soil development is lacking due to water erosion and colluvial movement of soil particles. At higher altitudes (above 4000m above m.s.l.), frost action is a common weathering agent and erosion is caused by glacial or glacio-fluvial water derived from melted glaciers. Soils on lower slopes are shallowto- moderately deep, well-to-excessively drained and loamy-to-loamy skeletal. Soils are generally, dark brown in colour and rich in organic matter.
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Materials and methods Resources at-1(P 6) LISS-III of 15th December 2005 with a spatial resolution of 23.5m and PAN data 5.8m were merged using Principal Component Analysis approach. Figure 2 shows merged False Colour Composite (FCC). Ancillary data viz., topo sheets and forest management plan documents were also used. Merged FCC, Global Positioning System (GPS) and topo sheets were used for ground truths. Data on the location of various ground features were collected and marked on the topo sheet. The accessibility is still the main problem. Details of the methodology are presented in Fig. 3. The database was generated using Geographical Information System (GIS).
Fig. 2 FCC of the study area.
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The image tone, texture etc., were used to delineate and map various land degradation categories on 1:25,000 scale. Terrain features were also used for improving the classification accuracy (Boyed et al., 1996; Malingreau et al., 1996). The interpretation key is depicted in Table 1. The following land degradation categories were delineated for the study area from remote sensing data: 1. Undegraded (D1): This class includes the very dense forests on moderate-to-gentle slopes, very slight erosion and intact top soil layer. 2. Moderately degraded (D2): Moderately dense forests, grazed and disturbed grass lands and agriculture in moderate-to-steep slopes with
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rills and small gullies and signs of root exposure is seen. 3. Degraded (D3): Sparse forests, modified natural grasslands and pastures, moderate-tosteep slopes and no big gullies or tree uprooting is seen. 4. Severely degraded (D4): Area having moderate-to-open forests, poorly cultivated, steep-to-very-steep slopes, severely eroded areas with or without gullies and tree cover uprooting.
5. Rock outcrop: Areas having rocks, rock-falls and moraines are categorized in this. 6. Snow: Areas having snow cover is kept in this category. 7. River: Rivers and tributaries in the study area are categorized in this. The interpreted details were field verified for accuracy assessment. Corrections were made wherever necessary and soil samples were collected from various land degradation types for soil characterization.
Table 1 Visual interpretation key Land degradation classes
Land use/Land cover status
Undegraded
Moderately degraded
Degraded
Severely degraded
Rock out crop
Snow
Image characteristics Tone
Texture
Pattern
Site
Association
Forest
Dark red
Smooth
Irregular
Lower to middle Himalayas
Moderate to gentle slopes
Agriculture
Grey to dark grey
Medium to coarse
Irregular
Lower to middle Himalayas
Moderate slopes
Forest
Red to bright red
Smooth
Irregular
Higher Himalayas
Moderate to steep slopes
Grassland
Light brown
Smooth to medium
Irregular
Middle to high Himalayas
Moderate to steep slopes
Wastelands
Light brown
Medium to coarse to fine
Irregular
Lower altitude to middle Himalayas
Moderate to steep slopes
Land slides
Light yellowish
Medium to coarse
Irregular
Low to high Himalayas
Ridges/Steep slopes to very steep slopes
Wastelands
Cyan
Medium to coarse
Irregular
Middle to high Himalayas
Steep slopes to very steep slopes
Low hills
Light blue
Smooth to medium
Regular/Irregular
Lower altitude
Steep slopes
High hills
Light brown
Medium to coarse
Regular/Irregular
High Himalayas
Steep slopes
White
Very smooth
Regular/Irregular
High Himalayas
Moderate to steep slopes
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J. Indian Soc. Remote Sens. (March 2009) 37:119–128 Table 2 Area under different land degradation categories
LISS III+PAN Merged Data
Topographic Map
Study Area Extraction
Reconnaissance Survey Ground truth
On-screen Visual Interpretation
Class
Area (km2)
Area (%)
1. 2.
Undegraded
264.03
22.53
Moderately degraded
385.32
3.
Degraded
32.89
77.66
6.63
4.
Severely degraded
33.80
2.88
5.
Rock outcrop
48.81
4.17
6.
Snow
348.53
29.75
7.
River
13.55
1.16
Total
1171.70
100.00
Interpretation keys
Ground checking
Land Degradation Map
Fig. 3
Sl. no.
appear grey-to-dark grey tone medium-to-coarse texture, irregular pattern in lower to middle Himalayas. The forests were red-to-bright red in tone, smooth texture, and irregular pattern on higher Himalayas. This was the most dominant land degradation category occupying about one third of the total area i.e., 385.32 km2 and representing 32.89 per cent of the total.
Approach of the study.
Degraded land Results and discussion Land degradation involves the strain and depletion of land resources due to the ever-increasing human and livestock population. Table 2 depict its status. Undegraded land This class includes the very dense forests on moderate-to-gentle slopes. The area appeared as dark red tone, with smooth texture, irregular pattern on lower to middle Himalayas. It was observed that the undegraded land in the study area is 264.03 km2 representing 22.53 per cent of the total area (Table 2). Moderately degraded land This category includes moderately dense forests and agriculture in moderate slopes. The agricultural areas
Alpine pastures on moderate-to-steep slopes on middle-to-high Himalayas and wastelands with moderate erosion on low-to-mid Himalayas are represented in this category. The alpine pastures and wasteland appeared light brown in tone. The alpine pastures were smooth-to-medium in texture with irregular pattern and the wastelands were mediumto-coarse-to-fine in texture. It was observed that this type of land occupied 77.66 km2, which is 6.63 per cent of the total area. Severely degraded land Areas having land slides with light yellowish tone, medium-to-coarse texture, irregular pattern and found in low-to-high Himalayas are known as severely degraded land. These were found on steepto very-steep slopes. The wastelands appearing cyan in tone, medium-to-coarse texture, irregular
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pattern middle-to-high Himalayas with steep-to-very high steep slopes were categorized in this class. As evident from Table 2 this category occupied 33.80 km2 area, which is 2.88 per cent of the total area. The removal of land cover on high slopes and cultivation without proper conservation measures leads to severe erosion and uprooting of trees. Normally, gullies and large-scale soil movement would be seen. The degraded land in the study area was assessed to be 496.79 km2, which is 42.40 per cent of the total study area. This calls for effective anti-degradation measures to be adopted in the study area. Others The study area is mostly covered with snow (348.53 km2), which was 29.75 per cent of the total area, and
Fig. 4 Land degradation map.
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incidentally, is the largest land cover class. The snow was observed to be with a white tone, very smooth texture, and regular-to-irregular pattern and found in high Himalayas with moderate-to-steep slopes. Rock outcrop occupied 48.81 km2 area and the river 13.55 km 2 area. The rock outcrop on low hills appeared light blue in tone, smooth-to-medium texture, regular-to-irregular pattern and on steep slopes, while in high hills these appear as light brown in tone, medium-to-coarse texture, regular-toirregular pattern and found on steep slopes. The river systems of the study area are fed by the numerous glaciers and the rivers are perennial. However, during the monsoon season they carry a lot of silt load from the degrading areas which calls for conservation measures in the catchment areas. Water erosion was observed to be the main cause
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of degradation apart from landslides and the decline of forest and grasslands. Water and gravity erosion are found to be the major cause of physically degraded land. Eroded land includes water erosion (gully, ravines, and stream bank) and gravity erosion (road slide, landslide, and debris fall). The main reason for landslide occurrence is gravity force involving failure of the earth material under shear stress i.e., the shear stress exceeds the shear resistance of the soil mass. The basic factors which may affect slope failure and landslides concern the geological material, geological structure, ground water and in situ stresses etc. The forest degradation was assessed (Fig. 5) and it was observed that the vegetated areas having dense tree canopy cover located mostly on the
Fig. 5 Forest degradation map.
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middle-to-upper hill slopes, are grouped under undegraded forest covering 25.87 per cent of the total area. The areas with moderately dense canopy cover are, generally, located on moderate slopes and the isolated patches on the middle-to-upper hill ranges located on the steep slopes are categorized in the degraded forest occupying 9.4 per cent of the total area. The soils are chemically degraded due to loss of bases and high soil acidity. Humans by way of extraction of timber, wood, fodder, etc., and animals by way of overgrazing, are the important factors causing degradation in the area. The major limitation found in the study area was gravel and shallow soils. Other soil properties do not limit much the vegetation growth in the area. Soil erosion in the
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cultivated and other disturbed areas is a major process leading to land degradation. This emphasizes the importance of soil and the need for conservation practices not only to sustain the production in hills and mountain areas but also to minimize the siltation of downstream reservoirs in the plains.
constant encouragement and necessary support. We express our gratitude to S.K. Chandola, Chief Wildlife Warden, Uttarakhand for allowing us to carry out the field work in the area.
References Conclusions The present study in the upper catchment of river Tons using remote sensing and GIS revealed that the soils are shallow-to-medium deep and that the depth of the soil is a major constraint in sustaining natural vegetation as well as crops. Soil erosion, reduction in forest density, over-grazing, forest fires and inadequate conservation measures are the main causes of land degradation. More than 50 per cent of the study area is covered by snow or grassland. Out of 42.40 per cent of degraded land, most of the land is moderately degraded, which is one third of the entire study area. There are pockets of severe land degradation throughout the catchment area, which would require immediate protection. In order to improve flow and water quality in river Yamuna, appropriate measures must be adopted for restoration of the degraded areas in the upper Tons river catchment. Prevention of logging and fires, reduction in grazing intensity, extensive plantation of suitable native species, installing physical and biological structures to check erosion and landslides are suggested in order to restore the land. It is also suggested to take up sub-watershed level sedimentation assessment and land cover-wise degraded areas to properly understand the interplay of various causes.
Acknowledgement Authors are thankful to the Ministry of Environment and Forests, Government of India for funding the project. We are grateful to the Dean, and Head, Agriculture and Soils Division, Indian Institute of Remote Sensing, Dehradun for
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