ISSN 00978078, Water Resources, 2010, Vol. 37, No. 5, pp. 623–637. © Pleiades Publishing, Ltd., 2010.
WATER RESOURCES AND THE REGIME OF WATER BODIES
Use of Geoinformatics for InterBasin Water Transfer Assessment1 Niladri Guptaa, Petter Pilesjob, and Ben Maathuisc a
School of Geography, University of Southampton, +44(0) 7919315113 Southampton, Highfield, Southampton S0171BJ, UK b G1S Centre, Lund University, +4646222954 Solvetrotan 12, S223, 62, Lund, Sweden c International Institute for GeoInformation Science and Earth Observation, +31534874391 7500 AA, Enschede, the Netherlands Received July 2, 2009
Abstract—Fresh water availability and demand are unevenly distributed both temporally and geographically. Furthermore, the availability of fresh water has remained more or less constant, while the demand for clean water is steadily increasing. With demand surpassing supply, an integrated water resource management approach is required to ensure even distribution of potable water to all levels of society while protecting the environment. Interbasin water transfer (IBWT) is an approach being applied in various countries around the world, with varying environmental and social implications. The Interlinking of Rivers (ILR) scheme is an example of such a project being planned in India. The research described in this paper was based on the ILR project and includes an assessment of the IBWT programme in some of the tributaries of the Brahmaputra and Ganga Rivers in the eastern part of India, covering the district of Jalpaiguri, West Bengal, India. Geoin formation has been used in association with physical and socioeconomic factors to identify potential dam and reservoir sites and to delineate the optimal route for canals to transfer water from the Brahmaputra basin to the Ganga basin for further transportation to the waterdeficient regions of India. Keywords: environment, interbasin, reservoir sites, canal. DOI: 10.1134/S0097807810050039 1
In some areas of the world, especially regions with high population density and intense economic activity, the demand for fresh water has overtaken the supply. An integrated water resource management approach is required to balance environmental, social and eco nomic issues, rather than the conventional technique of “hydraulic mission” [9], It was suggested that such an approach would increase the efficiency of water use and enable society to achieve sustainability, while opti mising the economic return on water. They also pointed out that, in river basins where demand exceeds supply, new sources of water could be found either by desalinating sea water or transferring water from a neighbouring basin where there is a surplus using interbasin water transfer (IBWT), which is becoming a common solution. IBWT has been undertaken in several countries with various environment and socio economic implications, for instance the USA, China and Russia. India is a large subcontinent and, as a result, the challenges it faces are also on a large scale. Water resources are unevenly distributed due to variations in the geographical and temporal distribution of rainfall. This leads to drought in some parts of the country and floods in others. Providing water during droughts and
1 The article is published in the original.
preventing floods in the monsoon season have always been a challenge. The Indian river system, which forms the lifeline of the country, can be divided into two components: the Himalayan component, the sources of which are the glaciers of the Himalayas and the monsoon rains, and the peninsular component, consisting of water mainly from the monsoon rains. There is surplus water in the Himalayan component and partial deficit in the pen insular component, especially during the dry season, resulting in inundation of agricultural land in areas with high precipitation and water scarcity and crop failure in areas with low precipitation. Recently, the national water policy of Government of India points to a national perspective to undertake such interbasin water transfer. Water transfer is based on the view that the transfer of surplus water from one river basin to another, could permanently solve the problems of droughts and floods, thus increasing food grain production [1]. Thirty possible links between the major rivers in India, 14 in the Himalayan component and 16 in the peninsular component, have thus been proposed. These were based on earlier proposals, in 1972 by K.L. Rao for the National Water Grid [20], and in 1977 by Captain Dastur for the Garland Canal Project. These earlier projects were shelved due to a
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lack of technical feasibility, desirability and economic viability [3]. The Ganga and Brahmaputra basins (the two major river basins in India) constitute a major part of the Himalayan component. There is a surplus of water in these two river basins and floods are therefore a recur ring phenomenon. A significant reduction in regional imbalance could be achieved by storing these water resources in reservoirs, and transferring the excess water to other parts of the country via canals. However, it is not known whether such a project would actually prevent drought, or merely move the problem from one place to another. Many other questions also remain. Will it be necessary to relocate people, and if so, how many? Are there any smallscale alternatives to engineer ing on this grand scale? Is the terrain suitable for building canals to transfer the water? What types of engineering structures are required, and where can they be located? What will the effect of the project be on the envi ronment? How much water will actually be made available? The project thus requires a multidisciplinary approach. Presently, IBWT accounts for about 540 × 109 m3 water per year, i.e. 14% of all global withdrawal, and there are proposals for an additional 940 × 109 m3 per year [11]. These volumes together form only a quarter of the projected need for water withdrawal by 2025, and are thus not considered significant in terms of water resource management. Interbasin water trans fer has effects on both the donor and recipient basins. Such projects are also limited by the geoenvironmen tal and socioeconomic conditions in the area. Expe riences of water transfer projects such as the Central Valley Project in the USA and the Aral Sea Project in the former USSR have revealed some of the limita tions and consequences of such projects [14, 18, 4, 8]. Experts in the field have acknowledged that there may not be any real surplus of water despite the fact that there are real shortages [12]. Thus, an integrated water resources management plan is required to ensure that both water and profits are properly distrib uted. The sustainability of IBWT programmes must be assessed in terms of design, operation and manage ment. According to the ILR project, the excess water from the Ganga and Brahmaputra rivers and their trib utaries must be transported through the Himalayan foothill region, which is structurally characterized by EW trending faults/lineaments parallel to the Hima
layan trend, and transverse faults trending NS, NW SE and NESW running across the Himalayan trend (see Fig. 1). A few of these faults have been shown to be active in geologically recent times, while others are only thought to be active. These networks of faults/lin eaments are considered to be a major contributor to the instability of this region [5]. Any movement or adjustment along these structural elements will have an effect on river geomorphology in the area, e.g. shift ing river courses, which can be observed in the rivers included in the ILR project. The aims of this study were to investigate the geomorphology, geology, land use and drainage characteristics of the area using multi temporal and multisensor satellite data; to identify suitable reservoir sites and to determine the storage capacity of the major tributaries traversing the study area using a numerical method and available elevation data from a Digital Elevation Model (DEM) of NASA’s Shuttle Radar Topographic Mission (SRTM); to determine possible routes of the link canal for IBWT; to evaluate the possible benefits of the transported water in terms of usage assuming a specific transfer rate, and taking losses during transportation and decrease in reservoir capacity into account. STUDY AREA The area studied is located in the Jalpaiguri district in the state of West Bengal, in the eastern part of India (Fig. 1). The area is located between 26°16′ and 27°0′N and 88°4 and 89°53′E, covering an area of about 6190 km2. It is bounded by the foothills of the Himalayas in the north and northwest and by the alluvial plains of the Ganga and Brahmaputra rivers in the south and east. The climate varies from sub tropical in the northern part to humid sub tropical in the southern part. The annual rainfall is unevenly distributed. The mean annual rainfall varies from 3160 mm in the monsoon season (May–October) to 201 mm in the dry period (November–April). The Mahananda River is the only major river of the Ganga basin and the Teesta, Jaldhaka, Torsa, Raidak and Sankosh are the major rivers of the Brahmaputra basin within the area stud ied. Geomorphologically, the area is part of the Teesta, Jaldhaka and Torsa interfluve belt of North Bengal. Locally, the northern part of the area is called “Duars” and is part of the Piedmont plains at the foothills of the Himalayas. These are gradually transformed into allu vial plains further south. The Piedmont region is dis sected by the major rivers and the tributaries consid
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ered in this study. The northern part of the area is char acterized by faninfan morphology and the ancient deposits are fluvioglacial in origin, as evidenced by huge boulders. Later fluvial activity can be observed in the form of terraces, where coarse pebbles to clay size materials are found. Rill and gully erosion over a long period of time has produced deposits with a dissected undulating surface. In the alluvial plains levees, back swamps and oxbow lakes are dominant, and all consist mainly of recent sediments. The area is distinctly dif ferent from the rest of the frontal Himalayas and is characterized by the absence of large EW flowing riv ers like the Ganga to the west and the Brahmaputra to the east. Instead, huge fans and flood plains have evolved from southerly flowing rivers such as the Teesta and the Mahananda [5]. Geologically, the Piedmont zone, which forms the northern part of the study area, can be divided into 5 morphostratigraphic units based on their oxidation index, the colour of the sediments in the weathering zone and the colour of the topsoil [5]. The study area has been influenced by tectonic activity that took place in the eastern Himalayas from the Pliocene to recent times [10]. The northern part of the area is characterized by alluvial fan deposits which have coa lesced to form the Piedmont zone. The land use and land cover of the study area also reflect the characteristics of the terrain. The northern part is mainly covered by dense forest with occasional degraded forest, encroachments and tea plantations in the hills and the fan lobe areas, while the southern part is used for agricultural purposes, with one or two crops a year, and occasional scrubland. METHODOLOGY The methodology was based on the problems, aims, the data available, and technological knowhow and its implementation. Various methods can be used to identify possible locations for dams and reservoirs, and to determine the best route of canals. The choice of method depends on the drainage characteristics and the terrain, as well as the technology appropriate for a particular environment. Details of the approach adopted are shown in the form of flow diagram in Fig. 2. The procedure was divided into 3 stages. Stage I deals with the terrain analysis (TA) required for reser voir location. Thematic maps were generated from remote sensing data and a multicriteria analysis was undertaken using the thematic information to identify possible dam and reservoir sites. Stage II deals with the estimation of reservoir storage capacity in a GIS framework in which SRTM data were used as the input for an iterative numerical propagation method to determine the spatial extent of the reservoir and fac tors related to reservoir capacity. The final stage is con cerned with identifying the best route for canals to transport the water from the reservoirs, with the ulti
mate aim of joining the new canal to the existing canal system between the Teesta and the Mahananda basins. Terrain Analysis and Reservoir Location The method used to identify potential sites for res ervoirs takes into account both the physical suitability and the socioeconomic suitability of the location. Available IRS 1D LISS III, IRS P6 LISS III, and LANDSAT TM data were processed together with Survey of India (SOI) topographical maps and other ancillary data, using visual or digital classification techniques to generate prefield thematic maps per taining to geomorphology, land use/land cover and drainage of the area on a scale of 1 : 50000. The geol ogy map was generated by scaling up the Geological Survey of India (GSI) geological map on the scale of 1 : 250000 to 1 : 50000 and updating it using satellite data. The prefield thematic maps thus generated were then validated by ground truthing to generate the final geomorphology, geology, drainage and land use/land cover maps. These thematic maps were used to asses the physical suitability of potential reservoir sites and were used as input to the multicriteria analysis. The canal transport network and the village maps were derived from the SOI topographical maps updated with satellite data. These were used as socioeconomic suitability inputs for the multicriteria analysis (MCA). The detailed methodology is illustrated in Fig. 3. Two GISbased approaches can be adopted for ter rain analysis and multicriteria analysis (TA and MCA) to evaluate spatial features and suitable loca tions for reservoirs [16]: one, a subjective, knowledge driven approach that emphasizes expert knowledge in the matter, and the other a datadriven approach employing objective criteria and weighting. In the present case a datadriven approach was adopted as it provides adequate information to identify the section of the river suitable for the location of the dam and the reservoir. Table 1 lists the criteria applied in the MCA to identify suitable locations for dams and reservoirs based on certain considerations. Calculation of the Reservoir Volume A dam was created at each potential reservoir loca tion identified in Stage I of the procedure, taking into consideration dam height, freeboard and designed water level. The dams at each potential reservoir loca tion were converted into a raster and then integrated with the available DEM data (SRTM Version 3) [21]. The SRTM data had already been preprocessed to fill the voids using an interpolative technique, i.e. the TOPOGRID algorithm of Arc/Info, providing a seamless elevation dataset of 5 by 5 degree tiles. To determine the areal extent of the reservoir, a neigh bourhood connectivity function of ILWIS software [13] was used to help identify all neighbouring pixels in WATER RESOURCES
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Fig. 2. Overall research methodology.
the DEM with an elevation lower than or equal to the specified water level of the reservoir behind the dam [7, 2, 15]. Figure 4 illustrates the process. The reservoir depth was calculated by subtract ing the elevation contained in the DEM from the reservoir water level. The reservoir capacity was WATER RESOURCES
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then determined by integrating the reservoir depth (the value for each pixel) over the total inundated area. The most suitable dam and reservoir locations were selected based on the output of the neighbour hood function. The detailed methodology is illus trated in Fig. 5.
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Visual interpreatation and/digital classification
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Updation Final drainage map Final land use/land cover map Final village map Final transport map
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Fig. 3. Method used for terrain analysis and the identification of sites suitable for the location of dams and reservoirs.
Criteria for Optimal Canal Routing After determining the suitable locations for reser voirs based on estimates of the dam height and reser voir storage capacity, possible canal routes were iden tified based on the gradient of the terrain for the trans port of water by gravity. The ultimate aim was to join the proposed canal to the existing TeestaMahananda canal. The fan lobes of the region were also taken into consideration as it is not always possible to build canals through the lobes. A transfer rate from each reservoir was estimated based on the storage capacity of each reservoir and the number of days the flow rate could be maintained to accommodate the dry season’s lower flow. The dimensions of the proposed main link canal, divided into 5 sections, were based on the water trans fer rate from each reservoir to the main link canal. The
calculation was carried out assuming normal flow depth in a rectangular channel where the slope of the water surface and channel bottom is same, depth remaining constant and no acceleration of flow occurs. A MS Excel based application which uses an iterative process and Secant’s method was used for this purpose [17]. RESULTS AND DISCUSSION Terrain Analysis and MultiCriteria Analysis Both the physical and the socioeconomic suitabil ity were considered in the terrain analysis and the multicriteria analysis. The information on which physical suitability was determined included the land use map, the geomorphology map, the geology map, WATER RESOURCES
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Table 1. Key Criteria for dam site selection and the underlying condition considered for different thematic information used for MCA Thematic Layer
Criteria for dam site selection
Underlying condition
Settlement Transport Network DEM
Not to be located near or within 1 Km settlement area Safety (to avoid flooding) Not to be located within 1 km of major roads or railroad Safety (to avoid flooding and disruption of commu nication) To be located above 110 m elevation New canal alignment is to be connected to the exist ing Teesta – Mahananda link canal. Slope To be located in a slope <12% Hydraulic condition/Stability Structure To be located at a distance >500 m Stability of an existing lineament/fault scarp Drainage Preferably on river bed To have sufficient reservoir capacity Geomorphology To be located avoiding low altitude fan/alluvial plain Hydraulic condition/Stability
the structural map, the slope map and the DEM. The socioeconomic suitability was assessed based on the settlement map and the transport network map. The multicriteria analysis involved raster analysis in which all the input maps were converted into rasters. Each geomorphic unit was weighted with a value from 0 to 5: a value of 0 being assigned to alluvial plains (least suit able) and a value of 3 to midaltitude intermediate fans (reasonably suitable). Of the 15 land use classes iden tified, 5 major classes were considered to be likely to be affected by the reservoir, and agricultural land was assigned a weight of 0 (least suitable), and river beds a weight of 5 (most suitable). A Boolean operation was applied to the elevation and slope data in which it was required that the reservoirs be located above an alti tude of 110 m and the slope <12%. The pixel values that satisfied the criteria were given assigned the value 1 (suitable) and those that did not were assigned a value of 0 (unsuitable) to identify the physically suit able locations for reservoirs and dams. Similarly, to identify sites that were socioeconomically suitable a buffer zone was created around roads and railways and settlements (as listed in Table 1). Areas within the buffer zone were considered unsuitable (and assigned a value of 0) while those outside the buffer zone were considered suitable (and assigned a value of 1). The
outcome was presented in the form of a composite suitability map showing the potential dam and reser voir locations as can be seen in Fig. 6. TA and MCA were used to identify potential dam and reservoir sites in the study area. Five sites were found. The existing barrage on the river Teesta (Dam 1) was used to test the iterative propagation method and the capacity of the existing reservoir was estimated. Other potential reservoir locations were identified on the tributaries of the Jaldhaka (Dam 2), Murti (Dam 3), Torsa (Dam 4) and Kaljani (Dam 5) rivers. According to the results of the TA and MCA, one of the five identified sites was not suitable (Dam 3) as the land cover on both sides of the river was forest, which has a high weighting factor. However, the site was suitable with regard to the slope and drainage characteristics, so a dam was proposed here and the reservoir volume was estimated. Although Dam A was suitable according to the multicriteria analysis, the reservoir capacity was not sufficiently high and this location was therefore not considered. Lower but not connected
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Fig. 4. Determination of the areal extent of a reservoir using topography and a neighbourhood connectivity operator [7]. WATER RESOURCES
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Storage capacity/ Reservoir volume Fig. 5. Methodology for reservoir map creation and volume calculation from the DEM using the iterative propagation method [7].
Estimation of Reservoir Capacity A cell was defined behind the dam, and an algo rithm was used to identify all the neighbouring cells with an elevation lower than or equal to the specified reservoir water level. The cells that satisfied this condi tion were labelled. The algorithm was then applied to
the labelled neighbouring cells. The process was repeated until no more connected cells had an eleva tion lower than or equal to the required level. All the identified cells were labelled as being flooded. The extent and capacity of the reservoirs were determined for dams with three different levels, and WATER RESOURCES
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Reservoir Capacity (milion m3)
three reservoir extent maps were created for each potential site. The catchment area of the rivers and the tributaries from the dam locations were determined from the drainage map generated from the DEM. The “DEM Hydroparameterization” module of ILWIS was used [13]. The dam location was used to delineate the catchment area upstream of the dam. Figure 7 shows the extent of the reservoir when Dam 1 on the River Teesta has three different levels. The calculated volumes of the reservoir at different dam height on the river Teesta (Dam 1) are shown in Fig. 8. Similar plots were made for the reservoirs on the other rivers. In all cases an almost linear relationship was found between the dam height and the reservoir capacity, and there fore no intermediate levels were calculated, as shown by the regression equation in Fig. 8.
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Similar reservoir extent maps were generated for three different dam heights at the other four potential locations. The runoff was assumed to be 50% of the mean annual precipitation. The mean annual precipi tation was assumed to be the same for all the catch ment areas and was determined as the mean of the mean annual precipitation recorded at four weather stations in the study area (3517 mm per year). The present Teesta barrage has a transfer rate of about 30 m3 s–1, which is equivalent to about 946 million m3 per year. The total runoff available (50% of the mean annual precipitation in the study area) is about 15360 million m3. Thus, the total volume of water transferred is about 6% of the total runoff. The volume of water available through runoff, the maximum stor age capacity of the reservoir and the percentage of run off utilized for storage was estimated for each of the five reservoirs. Assuming a flow rate of 20 m3 s–1 from the other 4 reservoirs ~ 5 m3 s–1 from each (that from the River Teesta being 30 m3 s–1 ) the amount of water available each day would be about 50 m3 s–1. With a total available reservoir capacity of 972 million m3, water would be available for only 225 days in a year. Since this scenario did not provide sufficient water for a whole year, another configuration was investi gated. Two of the existing reservoirs, one on a tributary of the River Jaldhaka (Dam 2) and the other on River Torsa (Dam 4), were relocated upstream at the north ern edge of the study area, and one of the reservoirs on the River Kaljani (Dam 5) was rejected. Correspond ing estimates were made of the volume of water avail able through runoff, the maximum storage capacity of the reservoirs and the percentage of runoff being uti WATER RESOURCES
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lized for storage in each of the four reservoirs. The assumptions were the same as used above. In this case, it was found that, assuming a water transfer of 50 m3 s–1, it would be possible to supply water for a maximum of 276 days. A third alternative was then investigated in which two more reservoirs were located at two new locations, one on the River Raidak (New Dam 5) instead of River Kaljani (Dam 5) and the other on the River Sankosh (Dam 6). Both these rivers flow through the study area, but no suitable reservoir site was found within the study area using TA and MCA. The new reservoirs were thus located on these two rivers further upstream, outside the study area. Besides being outside the study area, the reservoir extended over the international boundary into Bhutan. In this case, it was found that the stored water would be able to supply water for a maximum of 345 days, which is almost the whole year. Estimates of the water availability from each of the six proposed reservoirs in the third alternative can be found in Table 2. The calculations indicate that the reservoirs behind Dam 1 on the River Teesta could supply water for almost a year with the present flow rate of the Teesta canal, while the reservoirs at Dam 4 and Dam 6 could supply water at a flow rate of more than 5 m3 s–1. The reservoir at Dam 5 could supply water on a continuous basis if the transfer rate were 3 m3 s–1, while those at Dam 2 and Dam 3 could supply water almost all the year with a combined flow rate of 5 m3 s–1. It was found in all the alternatives that the percent age of runoff stored for transfer from each reservoir did not exceed 8% of the total amount of water available from runoff, which was about 2% more than the value assumed (6% runoff being transferred from the present Teesta reservoir at a rate of 30 m3 s–1). This indicates that the natural flow of the river downstream would not be hampered to any great extent. The only excep tion was the reservoir behind Dam 2 on the tributary of the River Jadhaka, which had about 22.5% of runoff transferred. In this case as the reservoir and the dam were located on one of the tributaries of the main River Jaldhaka, the water available downstream in the river would not be affected to any great extent as the other tributaries would still feed the main river. Optimal Route for the Link Canal The ultimate aim is to merge the proposed canal with the existing TeestaMahananda link canal (TMLC). An optimal route was found, taking into consideration the slope, roughness and character of the terrain, especially the midaltitude intermediate fan, which was avoided as far as possible. Although the land use in the area should be taken into consider ation, especially forested areas, tea plantations and agricultural land, it was not possible to avoid all the above land use categories due to the location of the reservoirs (see Fig. 9). The proposed main link canal WATER RESOURCES
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Table 2. Water availability from each reservoir in 3rd Scenario considering different transfer rates Dam no. 1 2
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Teesta Jaldhaka Tributary (Upstream new location)
3
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Torsa (Upstream new location) Raidak (Outside area)
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Sankosh (Outside area)
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3 5 2 3 5 5 3 5 5
197 118 124 82 49 453 416 250 446
was divided into five sections of different dimensions according to the amount of water being transferred from each reservoir. As the total transfer rate was assumed to be 50 m3 s–1 and the existing TMLC had a capacity of about 30 m3 s–1, the rest of the reservoirs would contribute about 20 m3 s–1. Taking this into consideration a trans fer rate of 6 m3 s–1 was assumed for the first section of the canal with input from the River Sankosh (Dam 6) to the proposed main link canal. An additional flow of 4 m3 s–1 was added to the second section of the canal from the River Raidak (New Dam 5), while a flow of 5 m3 s–1 was added to each of the third and fourth sec tions of the canal, from the River Torsa (Dam 4) and combined transfer from the River Murti (Dam 3) and the tributary of the River Jaldhaka (Dam 2), respec tively. Section 5 of the canal was assigned a flow rate of 50 m3 s–1 considering the input of 30 m3 s–1 from the River Teesta (Dam 1). A schematic diagram of the link canal and the contributions from each reservoir on the rivers is shown in Fig. 10. Based on the flow rate from each reservoir the dimensions of the canal were calcu lated using an iterative process by considering normal flow depth in a rectangular channel using Secant’s method [17]. The estimated dimensions of the pro posed link canal are given in Table 3. An average flow velocity of 1 m s–1 was assumed in the proposed link canal. Assessment of IBWT An assessment of the possible utilization of the water available in the three alternatives described above was made, based on the following two assump tions:
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Dam 4 New T
A
J
E
U
N
Dam 1
D A R
26°45′0″N
E S
Section 4
Section 3
Dam 5
Dam 6
Section 1
Section 5 Section 2
A S S A M
Torsa Mahananda
Jaldhaka
Raidak
B Teesta Sankosh
A
26°30′0″N
N
G L
A H
D
E
26°15′0″N 0 3.75 7.5
Scale 15
22.5
88°30′0″E
S 30
Kilometrs
88°45′0″E
Legend Link Teesta (DAM1) Jaldhaka Tributary (DAM2 NEW) Murti (DAM3) Torsa (DAM4 NEW) Raidak (DAM5) Sankosh (DAM6) Distriet Boundary
89°0′0″E
Abandoned Channel Land wih scrub Urban Area Open Spaces River Island Canal Kharif River Scrub Forest Dense Forest Forest Plantation Villages Kharif + Rabi Tea Gardens (double Cropping) Ponds/Tanks Source: IRS P6 LISS III 2005, Jan 2006 SOI Topo Map 1975 (1: 50000 scale)
89°15′0″E
89°30′0″
INDIA
WEST BENGAL
89°45′0″E
Fig. 9. Map showing proposed canal route superimposed on the land use and land cover map.
the amount of water required for irrigation was 2 mm per day (based on a requirement of 2 cm over a 10day period); 70–135 litres of water are consumed per person per day for domestic use, the lower value in rural areas and the higher value in urban areas [22]. The loss of water due to evaporation and during conveyance was also considered, and was assumed to be 10%, although the actual loss would vary with changing seasons, climatic conditions and the aging of the canal. Reductions in reservoir capacity over time were assumed to vary from 10 to 40% as it has been found in earlier studies that the rivers in the study area
carry a great deal of sediments [5, 6]. As the reservoirs are located in the Piedmont zone heavy silting can be expected. Figure 11a shows the area that can be irri gated if 40% of the available water is used for irrigation and Fig. 11b – the number of days per year water will be available if 20% of the available water is used for human consumption. The results indicate that if water were available at a discharge rate of 50 m3s–1 then a total of 4.32 million m3 water would be available daily. If 40% of the available water were used for irrigation a total of 2160 km2 could be irrigated daily and if 20% were used for human con sumption, water could be provided for 12.34 million
Table 3. Estimated dimensions of the proposed link canal using reiterative method Canal Sections Factors Transfer Rate, m3 s–1 Manning Roughness, n Slope m m–1 Width of Canal m Flow depth m Flow Velocity m s–1
Section 1
Section 2
Section 3
Section 4
Section 5
6 0.04 0.002 3 1.99 1.01
10 0.04 0.0017 4 2.31 1.08
15 0.04 0.00125 5 2.81 1.07
20 0.04 0.001 6 3.16 1.05
50 0.04 0.00055 9 5.25 1.06
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635
DAM 6 (R. Sankosh)
DAM 2 NEW (R. Jaldhaka Tributary) DAM 5 (R. Raidak)
DAM 4 NEW (R. Torsa)
6 m3/s DAM 1 (R. Teesta) 4 m3/s 5 m3/s
3 m3/s DAM 3 (R. Murti) 30 m3/s 2 m3/s
LINK L CANA
Section 1 Section 2 Section 3
Section 4 Section 5
Fig. 10. Estimated dimensions of the proposed link canal.
people if they used 70 litres per day, or 6.4 million peo ple if they used 135 litres per day. In reality, the water would be used for many other purposes apart from irrigation and human consump tion, such as power generation and in industry, but this preliminary assessment gives an idea of the benefits of the planned ILR project. Limitations of the Methodology The present methodology has the following main limitations. The terrain analysis and multicriteria analysis included only some of the factors affecting site selec tion such as slope, drainage, geomorphology, geology, structure and land use regarding physical suitability and village location and transport networks regarding socioeconomic suitability. In reality, other factors such as the kind of drainage, drainage discharge, soil type and soil character would be required in the multicri teria assessment. The SRTM data used as the input for elevation had a resolution of 90 m and were taken from a global dataset. This type of dataset is useful for preliminary assessments of possible reservoir locations, but when WATER RESOURCES
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considering specific potential reservoir locations, highresolution elevation data are essential as the SRTM data may underestimate slope steepness [19] resulting in over or underestimation of the reservoir capacity. The uncertainties related to elevation infor mation and the effects of radarreflective surfaces were not considered in the present study. Neither the slope nor the condition of the terrain was considered in detail when determining the most suitable route of the link canal. The alternative pro posed was the result of using a methodology with lim ited ground data. The assessment of the utilization of the water made available was based on certain assumptions regarding water transfer and reservoir capacity. The actual avail ability in the study area was not determined. The transfer volume was also assumed and only irrigation and human consumption were considered. In reality, the water will also be used for other purposes. CONCLUSIONS AND RECOMMENDATIONS Interbasin water transfer is being considered a dominant solution to cope with the deficit of water in some major river basins of the world. The ILR project
10% + 10% 20% + 10% 30% + 10% 40% + 10%
0.30 0.25 0.20 0.15 0.10 0.05 0
1
2 Scenario
3
No. of Days of Water Avalability
NILADRI GUPTA et al. Irrigated Area (million km2)
636
10% + 10% 20% + 10% 30% + 10% 40% + 10%
300 250 200 150 100 50 0
1
2 Scenario
3
Fig. 11. a Estimates of the area that can be irrigated in 3 scenarios assuming 40% of the available water is used for irrigation, and b estimated number of days of water availability in 3 scenarios for a rural population of 12.34 million consuming 70 litres/day or an urban population of 6.4 million consuming 135 litres per day, taking into consideration a reduction in reservoir capacity (10⎯40%) due to silting and a 10% loss due to evaporation and conveyance losses.
is an example of this. In this study, an approach was developed to make a preliminary assessment of IBWT using geoinformatics. Terrain analysis and multicrite ria analysis were used to identify potential reservoir locations. SRTM data were used to provide elevation information to determine reservoir capacity. The required canal dimensions were estimated, and the optimal route for the canal was proposed. Utilization of the water in terms of irrigation and human con sumption was also assessed. The study showed that multitemporal and multi sensor satellite data can be used to map the relevant geomorphology, as well as the geology, land use and drainage characteristics of a study area, and these can be used as input for terrain analysis and multicriteria analysis to identify potential reservoir sites. A combi nation of elevation and slope data and the abovemen tioned thematic information improves the identifica tion procedure of the potential reservoir sites. The method presented here could be used for preliminary terrain analysis and multicriteria analysis in large river basins. However, more data must be collected for more precise identification of potential reservoir sites. We used SRTM Version 3 data [21] as the input for the characterization and estimation of the reservoir capacity in an iterative propagation model. This method has previously been used to model flood inun dation due to dyke failure [7] and storm water surges in urban areas [15]. SRTM data are thus useful for pre liminary reservoir characterization and volume calcu lation. The use of field data collected by GPS survey ing, or other local elevation information of much higher resolution, for example, GDEM (30 m resolu tion) from ASTER Stereo, would provide better char acterization of potential reservoir sites. The optimal route of the canal linking the reser voirs was determined by taking into account the eleva tion, slope and the characteristics of the terrain, including the geomorphology and land use. The canal route proposed here was based only on the above men
tioned factors. The iterative process used indicates that to maintain a flow of about 1 m3 s–1, the channel slope should not exceed 2 m km–1. Detailed topographic information is therefore required to determine slopes. No hydrological information on the river discharge or silting was available for the study area. River dis charge information will enable more accurate esti mates of the water availability in the rivers. Silting data will be useful to calculate the reduction in reservoir capacity over time. The latter is important as the suit able sites are located in active flood plains. An assessment of the utilization of the available water for irrigation and human consumption was made, taking into consideration losses due to evapora tion, conveyance and reduction in reservoir capacity. It can be concluded that this type of assessment enables water utilization to be estimated in the differ ent scenarios of water availability prevailing in the real world. Information on actual water requirements in various sectors is essential for better feasibility assess ments of the use of water stored in reservoirs. The information gathered and the results obtained can be used in a preliminary costbenefit analysis, to obtain an indication of the cost of the ILR project pro posed by the Indian Government. In conclusion, many issues are involved in inter basin water transfer programmes apart form reservoir site identification, capacity estimation, canal routing and the possible utilization of the available water. The research described above provides a stepping stone for more detailed studies. ACKNOWLEDGMENTS Niladri Gupta would like to express his thanks to the European Union and the Erasmus Mundus con sortium (University of Southampton, UK, Lund Uni versity, Sweden, Warsaw University, Poland and ITC, the Netherlands). This paper evolved from a disserta tion by Niladri Gupta, who would like to express his WATER RESOURCES
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special thanks to Mr. Sanjoy Nag, Senior Scientist, and Dr. Parthasarathi Chakrabarti, Chief Scientist, at the Department of Science & Technology, Govt. of West Bengal, India for their invaluable support and suggestions during the field work and primary database generation.
10. 11.
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