Sci. & Cult. 76 (11–12) 534–536 (2010)
Rivers in Arunachal Pradesh-the Eastern Himalaya Abstract : Water resources of the state Arunachal Pradesh is very rich and mostly drains into the river Brahmaputra, many streams/ rivers in the state are studied using DEM of the SRTM. Nearly 50% river length is under low and gentle stream gradient while about 64% falls under very low and low stream elevation. In the light of potentialities and bottlenecks it is found suitable for installation of mini over mega hydroelectric projects along with proper catchments treatment.
W
ater resources both ground and surface, of the state Arunachal Pradesh (AP) reclining in the Eastern Himalaya is very rich and most of the runoff drains into the river Brahmaputra cascading 41.9% of its basin area through very steep gorges in the state and finally debouches to Assam plain. With the decreasing trend of National per capita availability of water there is need of the hour for optimum utilization of this vital resource, indeed, there is a need of the proper inventory and assessment of water resource as well as identification of potentialities and bottlenecks. For this the application of remote sensing and Geographical Information System (GIS) is essential to predict the water quality parameters with accuracy1. The satellite images have been used to derive information on hydrogeomorphology of the terrain2. In recent past, development of stereo sensor in space platforms, capable of acquiring terrain information in 3dimensional form has added its unique potential for topographic analysis in relatively large area3. The present study covers the entire political land of the state AP located between 26º 39’ 59.67" N and 29º 22’ 44.83" N latitude and 91º 34’ 22.76" E to 97º 27’ 21.94" E longitude. There are 10 major river basins in AP consisting 46 major and medium rivers. These are Tawang, Kameng, Dikrong, Subansiri, Siang, Sisiri, Dibang, Lohit, Tirap-Dehing and Tissa river basins. Bountiful river/ streams winds in the hills of the state; which were studied for elevation and gradient wise lengths to through light on the potentialities and bottlenecks of water resource configuration. Methodology: The information about the water resources, river lengths, volume, flow characteristics are consulted from the various secondary sources. The InSAR Digital Elevation Model (DEM) of Shuttle Radar Topographic Mission (SRTM) is downloaded from the 534
United States Geological Survey (USGS) website (http:// seamless.usgs/gov). The tiles Z_55_7 and Z_56_7 containing 3 arc second DEM with a default pixel size of 87.413 metre are imported in the ILWIS 3.4 GIS. By using the ‘DEM hydro-processing’ operation the drainage network is extracted from the DEM. In order to reduce the computational robustness the drainages are extracted with a stream threshold value of 500 pixels. It also eliminates the ephemeral and other insignificant streams. The slope and elevation along the rivers are derived from the DEM using standard procedures and grouped into different category with suitable interval. The total length of the river in each category of slope and elevation is obtained for the analysis. Results and Discussion : Gradient wise Stream Lengths : The total length of the rivers with a threshold value of 500 pixels is found 29003.23 km distributed along the gradients varying from 0o to 39.900 falling under seven categories as shown in Table 1 and Figure 1. TABLE 1: Stream Gradient Vs Stream Length Gradient Category (degree)
Length (in km)
30
Extremely Steep
2.26
0.01
100
29003.23
100
Total
Length Cumulative (%) (%)
The maximum stream lengths i.e. 9897 km (32.12%) is found in the gradient below 20 which is put under very low category. It is followed by the low gradient (2-50) which accounts 6393 km (22.05%) stream lengths. The gentle and moderately gentle categories with gradient from 5 to 100 and 10 to 150 have stream length of 8119 km (27.99%) and 35.92 km (12.39%) respectively. The steep gradient varying from 15 to 200 and very Steep River having gradient between 20 to 300 have the stream length of 787.33 km (2.71%) and 210.85 km (0.73%) respectively. The extremely steep gradient with gradient of bed more than 300 comprises only 2.26 km of the river lengths which account 0.01% of the total. SCIENCE AND CULTURE, NOVEMBER-DECEMBER, 2010
TABLE 2: Stream Elevation Vs Stream Length Elevation (metre)
Category
5000
163.87
0.57
100
29003.23
100
Extremely High
Total
Figure 1. Stream Gradient Vs Length.
Figure 2. Stream Elevation Vs Length VOL. 76, NOS. 11–12
Elevation wise Stream Lengths : The elevation along the stream line in Arunachal Pradesh ranges from 107 metre in the southern part to 5699 metre in the northern margins. This elevation have been divided into very low, low, moderate, high, very high and extremely high elevations categories and presented in Table 2 and Figure 2. The elevations below 1000 m have been kept under the very low stream elevation category which accounts 11293.88 km (38.94%) river length. The low elevation category ranging between 1000 to 2000 m has the river length of 7668.34 km which accounts 26.44% of the total. The moderate stream elevation (2000 to 3000 m) and high stream elevation (3000 to 4000 m) constitutes 4954.20 km (17.08%) and 4000.75 km (13.79%) length of river respectively. The stream length in the very high elevation (4000 to 5000 m) and extremely high elevation (>5000m) progressively decreases to 922.18 km (3.18%) and 163.87 km (0.57%) respectively. Different geo-ecological zones in river Brahmaputra in AP have distinctive topographical, geological, climatological and floral characteristics4. The river is characterized by marked seasonality and high variability of daily flow. The highest recorded daily discharge at Pandu was 72, 726 m3s -1 in August 1962 while the lowest was 1,757 m3 s-1 in February 19685. The Dihing, Dibang, Lohit and Subansiri are estimated to contribute more than 60% of the average flow of the Brahmaputra6. Like wise all the rivers of AP discharge huge amount of sediments and suspended loads and receives by the river Brahmaputra- the second most heavily sedimentcharged large rivers in the 535
world after the Yellow (Hwang Ho) river in China. Its sediment transported per unit drainage area is 1,128 tons km-2 year-1 at Bahadurabad in Bangladesh. The river carries an average annual suspended load of 400 million metric tonnes at Pandu with an average daily rate of nearly two million metric tonnes in the rainy season5. Due to the hilly and mountainous nature of the area and very high monsoon rainfall, the discharges of the rivers are very high. This makes the state a potential power house of the country with about 50% of the power production capacity. However, the fragile geological structure and the rich biodiversity of the State stood in the way to tap the vast hydro-potentiality. Therefore, much precision is required before taking any step to harness the power potentiality. At the same time the sparsely distributed population over the geographical area of Arunachal Pradesh makes it difficult to ensure power distribution. Considering all these, mini hydel over the mega hydroelectric power generation project would be more ideal to meet the energy requirement of the people. On the other hand, these rivers also transport huge quantity of sediments and suspended loads hence proper measures of catchments treatment and land use planning in the
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watershed basins are imperative to check the sediments delivery. S J. S. RAWAT* AND B. A. LASKAR† 1 Department of Geography Rajiv Gandhi University, Rono Hills, Doimukh, Itanagar-791112, Arunachal Pradesh, E-mail:
[email protected] 2
Department of Zoology, Rajiv Gandhi University, Rono Hills, Doimukh, Itanagar-791112, Arunachal Pradesh, E-mail:
[email protected] Received : 21 December, 2009 1
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5
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SCIENCE AND CULTURE, NOVEMBER-DECEMBER, 2010
