RESEARCH COMMUNICATIONS Reprinted from Current Science

Received 14 May 2001; revised accepted 30 May 2002

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GIS and remote sensing-based studyof the reservoir-induced land-use!land-cover changes in the catchmentof Tehri dam in Garhwal Himalaya,Uttaranchal (India)

Piyoosh Rautela*, Rahul Rakshit,. V. K. Jha, RajeshKumar Gupta and Ashish MunshiIndian Institute of Remote Sensing, 4, Kalidas Road, Dehradun 248 001,India

Large dams, though necessary for national growth,adversely affect the life-support strategy of a largenumber of people living in the submergence zone andthe hinterland of the reservoir. With the help of GIS-based techniques and land-uselland-cover map pre-pared with the help of satellite remote sensing tools, itis estimated that the Tehri reservoir in the upper catch-ment of Ganga river would directly affect 2687 ha ofagricultural land and another 3347 ha around thereservoir rim would be rendered unfit for cultivation.

THE importance of water resources has increased withindustrialization and growth of population, as these areneeded for sustaining crop productivity, meeting the ever-increasing needs of the domestic, industrial and powersector. Dams are therefore being constructed for harness-ing water resources.

The Himalayan terrain provides cost-effective condi-tions for dam construction - deep gorges with wide valleyson the upstream; but the inherent fragility and pronenessof the terrain to seismic tremors is the bone of contentionbetween environmentalists and policy implementers. What-ever the concerns, water resources need to be tappedbecause, despite being endowed with vast land and waterresources, India faces severe scarcity of water in relationto agriculture, municipal and industrial needs, as also forpower generation.

The present study concentrates upon the reservoir rimarea of Tehri dam that is coming up in the catchmentof Ganga river a little downstream of the confluence ofBhaghirathi and Bhilanganga rivers (Figure I). The Tehridam site is located in a narrow and deep gorge (Figure 2)and has a wide vaHey with extensive fluvial terraces onthe upstream side. Work on this dam started in 1978 andis envisaged to produce 2000 MW of electricity, besidesirrigating 270,000 haof land and providing drinkingwater to the tune of 500 cusecs to the Indian capital, NewDelhi.

The Tehri dam is approaching its final stages and withthe closure of the lower level diversion tunnels, the water

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*For correspondence. (e-mail: piyooshrautela@rediffmail.com)

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level has started to rise; therefore it is important to studythe land-use/land-cover changes in the area due to thereservoir and its overall impact upon the life-supportsystem of the masses.

Land-use/land-cover pattern is the result of anthropo-genic interaction with the natural environment. Besidesaffecting the quality of life of the people living in thearea, it also affects surface run-off as also erosion inten-sity that control the reservoir life.

The inhabitants of the area traditionally maintained alarge number of animals. Increasing restrictions upon forestresources in the previous decades have, however, led tosubstantial reduction in cattle headcount. This at thesame time has increased human pressure upon land.Marginal lands, traditionally left barren hitherto, havetherefore been terraced with 65% of the total area under

agricultural activity falling under slopes steeper than 20°.Remote sensing techniques are particularly suited for

providing reliable, up-to-date and comprehensive data onland-use/land-cover. Apart from the field investigations,IRS LISS III multispectral and PAN data were used forpreparing the land-use map of the area (Figure 3).

Forest types identified along the slopes of the Bhaghi-rathi and the Bhilanganga valleys are classified into(i) dense/fairly dense mixed, (ii) open mixed, and (iii)scrub. The dense mixed forest accounts for 71% of the

Figure 1. Location map of the study area.

CURRENT SCIENCE. VOL. 83. NO.3, 10 AUGUST 2002

total forest cover delineated in the area, while open forestaccounts for another 26% (Figure 4).

Southerly slope aspects have less of dense and openforest, but majority of the scrub forest. This observationis in keeping with the vegetation distribution pattern inthe Himalayan terrain and reflects differential solar inso-lation on the two slopes. With the gentler slopes beingcleared for cultivation, forests are mainly confined to thehigher reaches; high (20-30°), very high (30-40°), andsteep (> 40°) slope class accounting for 30 and 25, 15%of the forest cover respectively.

Chir (Pinus roxburghii) is the predominant species ofthe region, while the other communities include banj(Quercus leucotrichophora), kaphal (Myrica esculenta),burash (Rhododendron arboreum), and deodar (Cedrusdeodara). In the Bhaghirathi valley, barring a few poc-kets, there is mostly open forest between Tehri and theconfluence of Jalkur with Bhaghirathi. Beyond this thesteeper slopes are clad with dense mixed forest that iswell developed on the left bank. Open forest is observedto border the dense forest along the right bank. In theBhilanganga valley between Tehri and Dewal, a similarsituation prevails as between Tehri and the Jalkurconfluence in the main valley. However, occurrence ofdense and open forests is encountered in this valley. Theslopes are not bare continuously, but are randomlycovered with vegetation patches of mixed varieties.Beyond Pilkhi the area is thickly wooded, but the Dewal-Pilkhi sector is intercepted with open and dense forestsand scrub forest.

The entire Bhaghirathi catchment area is mountainousand rugged, with poor infrastructure development. Thearea is therefore sparsely populated, with the populationbeing concentrated in the river valleys where agricultureis being practised in river terraces.

Apart from the increasing anthropogenic pressure uponthe forests, the region until recently witnessed large-scale

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Figure 2. View of the deep gorge of Bhaghirathi river.

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LEGEND

" Agriculture LandDense ForestOpen ForestScrub ForestOpen ScrubSettlementMass Wastage ZoneRiverSandArea under Dam Construction

Figure 3. Land-use/land-cov~r map of Tehri dam reservoir rim.

Dense Mixed Forest

-Open Forest

Scrub Forest

Figure 4. Statistics of forest distribution in the area.

commercial felling of forests and there is no system ofcounter-treatment of used-up forests. Thus, one-way traf-fic of deforestation, soil erosion and degradation ofenvironment has been going on unabated. This is reflec-ted in the following parameters that affect the quality oflife of the masses in the region: reducing forest cover;degrading pastures; increased use of steep slopes foragriculture and low agriculture yield; uncontrolled torrentand streams; frequent landslides; soil moisture deficiencyduring dry period and communication failure.

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Figure 5. Water layer draped over the digital elevation model show-ing impoundment of the area.

The Tehri dam is designed to be 260.5 m high andwould submerge everything below the critical 840.5 mlevel on the upstream side. Digital elevation model (DEM)of the area together with the land-use/land-cover map(Figure 3) prepared with the help of satellite data havebeen utili~ed for studying the likely land-use changes inthe area.

Under the GIS environment, a dam with 260.5 m heightwas simulated to assess the storage capacity of thereservoir as also the extent of the area that is likely to beimpounded (Figure 5). This submergence zone layer wasthen used for assessing the various land-use/land-cover

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N4 0 4 Kilometers,

\700600

I

E 500.J<CT

400..f« 300

200

100

0

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AgrIculture Land62%

SeItIem.nt2%

Figure 6. Statistics of the land-use typcs likely to be impounded byTehri reservoir.

SCNb Foreet Op.n SCNbSetll8ment 8% 1%

1%

Open Foreet26%

Den.. For.et17%

M... Weetege Zone1°'"

Figure 7. Details of the land-use types falling within the buffer zoneof 500 m around the reservoir.

types likely to be affected by the impoundment of waterin the lake. These studies show that the Tehri reservoirwould cover an area of 5170.21 ha and would have astorage capacity of 4345.44 million m3.Agricultural landaccounts for almost 52% (2687 ha) of the total area likelyto be submerged (Figure 6) by this dam. A number ofhabitations in the river valley, including the township anderstwhile district administration centre at Tehri would besubmerged by the reservoir waters.

The reservoir would affect the land around the reser-voir rim. The introduction of a huge reservoir would bedisturbing the delicate balance between soil, water andplants through rise in groundwater table (water-logging),and disturbing the natural salt distribution in the soil,thereby affecting the biomass productivity in comingyears; and the agricultural fields around the reservoir rimwould be rendered unfit for cultivation. For the purposeof the present study, with conservative estimates, the areafalling within a distance. of 500 m from the reservoirlevel is being considered most likely to be rendered unfitfor cultivation. A buffer zone of 500 m is thus createdaround the reservoir and with the help of the land-use/land-cover map, various-types of land-use, falling within thiszone, have been marked out (Figure 7). It is observed that3347 ha of prime agricultural land (46% of the total areawithin the buffer) on the upper terraces falls within thiszone. This land would have to be left barren even if not

affected by salinity or water-logging, and the marginalfarmers owning these lands would have to be rehabilita-ted. To add to it, 42% of the area within the buffer zonefalls in dense mixed forest and open forest categories.

Water sources of a large number of habitations on thereservoir rim are likely to be flooded by reservoir watersand this poses a threat of an epidemic in the region. Thecivic authorities have not cared to clear the debris andgarbage dumps around Tehri, and this would furtherdeteriorate the water quality of the reservoir.

The reservoir would be providing a vast area (5170.21 ha) for atmosphere-water interaction that would inducemicroclimatic changes in the region by way of increasingthe humidity levels. The evaporation rates in thesurroundings are quite high (- 2.7 mm daily averagedover two years; Data Hill Campus, Ranichauri) and on anaverage 0.14 million m3 of water would be evaporatingdaily from the reservoir. This would influence the bio-mass availability of the region besides enhancing masswastage rates in the catchment area and adversely affect-ing the stipulated reservoir life.

Besides this, regional-level effects include: (a) Displace-ment of labour from agriculture; (b) Widening incomedisparities; (c) Declining sustainability of secondary andtertiary sectors; (d) Enhanced ecological pressure uponthe catchment due to the migration of people; (e) Increa-sed erosion due to engineering activities; (f) Scarcity. ofdrinking water due to water sources getting inundatedand (g) Invasion of new pathogens due to enhancedmoisture.

At present agriculture is the mainstay of economy inthe region and the studies show that the reservoir wouldaffect 6034 ha of prime agricultural land (mostly irriga-ted) of the river valleys. The dam would affect 3663 haof mixed and open forests, with 2990 ha falling in thebuffer zone of 500 m. With increased humidity, biomassavailability in the region would increase together withincreased incidences of water-borne diseases. Anthropo-genic pressure upon the available natural resources wouldat the same time be increasing and the displaced peoplemay resort to terracing of the steeper slopes hithertounder forest cover.

There is an urgent need of promoting non land-basedeconomic activities in the region apart from promotingthe industrial infrastructure, so that the affected peoplecould easily find suitable economic rehabilitation. .ACKNOWLEDGEMENTS. We thank Dr P. S. Roy. Dean, IndianInstitute of Remote Sensing (IIRS), Dehradun and the faculty of theGeosciences Division. IIRS for extending infrastructure support for thestudy. P.R. acknowledges financial assistance from the Council of .Scientific and Industrial Research, Government of India under theScientists Pool Scheme. We thank the anonymous referee for importantsuggestions which have greatly improved the original manuscript.

Received 13 March 2002; revised accepted 18 June 2002

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