Hydrological characteristics of the Dokriani Glacier in the Garhwal Himalayas

  • Published on
    17-Feb-2017

  • View
    212

  • Download
    0

Transcript

<ul><li><p>This article was downloaded by: [University of Connecticut]On: 11 October 2014, At: 14:17Publisher: Taylor &amp; FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK</p><p>Hydrological Sciences JournalPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/thsj20</p><p>Hydrological characteristics of theDokriani Glacier in the GarhwalHimalayasPRATAP SINGH a , K. S. RAMASASTRI a , U. K. SINGH a , J. T.GERGAN b &amp; D. P. DOBHAL ba National Institute of Hydrology , Roorkee, 247 667, Indiab Wadia Institute of Himalayan Geology , Dehradun, 248 001,IndiaPublished online: 24 Dec 2009.</p><p>To cite this article: PRATAP SINGH , K. S. RAMASASTRI , U. K. SINGH , J. T. GERGAN &amp; D. P.DOBHAL (1995) Hydrological characteristics of the Dokriani Glacier in the Garhwal Himalayas,Hydrological Sciences Journal, 40:2, 243-257, DOI: 10.1080/02626669509491407</p><p>To link to this article: http://dx.doi.org/10.1080/02626669509491407</p><p>PLEASE SCROLL DOWN FOR ARTICLE</p><p>Taylor &amp; Francis makes every effort to ensure the accuracy of all the information (theContent) contained in the publications on our platform. However, Taylor &amp; Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor &amp; Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to orarising out of the use of the Content.</p><p>This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms&amp; Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions</p><p>http://www.tandfonline.com/loi/thsj20http://www.tandfonline.com/action/showCitFormats?doi=10.1080/02626669509491407http://dx.doi.org/10.1080/02626669509491407http://www.tandfonline.com/page/terms-and-conditionshttp://www.tandfonline.com/page/terms-and-conditions</p></li><li>Hydrological Sciences -Journal- des Sciences Hydrologiques,</li><li><p>P. Singh et al. </p><p>hydrogrammes de dcrue a permis de montrer que le temps de rponse de la zone d'accumulation tait suprieur sept fois le temps de rponse de la zone d'ablation. Aucune relation entre le dbit et les matires en suspension n'a t observe. Durant la priode tudie, les valeurs moyennes de la concentration des matires en suspension et du transport solide ont t respectivement gales 350 ppm et 180 tonnes par jour. Les processus d'effritement ont t tudis en diffrentes zones du glacier afin de dterminer l'origine des sdiments entrains par les eaux de fonte vers le torrent. Il existe un coefficient de corrlation lev (r = 0.89) entre l'coulement spcifique du glacier et la temprature de l'air la station de jaugeage. Cela montre que la temprature peut elle seule expliquer la fonte du glacier et peut tre seule retenue pour la modlis-ation hydrologique de l'coulement de fonte. Sur la base de trois journes d'observation par temps clair et pour des blocs de neige isols, le facteur de fonte de la neige a t estim 5.4 mm/(C. 6 h). </p><p>INTRODUCTION </p><p>High mountain areas featuring glaciers and snow are widely distributed throughout the world. Himalaya is one of the regions where numerous glaciers exist. The water flowing in the Himalayan rivers is a combined drainage from rainfall, snowmelt and glacier melt runoff. Snow and glacier runoff play a vital role in making all the northern rivers of India perennial. The glacier contri-bution to the rivers originating from the Himalayas starts in July/August when seasonal snow cover melts and continues till October/November depending upon the prevailing climatic conditions in that region. In the regions where monsoon rain penetrates into the high altitude valleys containing glaciers and coincides with glacier melt runoff, the flow in the rivers is augmented suddenly and sometimes may cause havoc downstream. During winter these rivers con-sist of contributions from sub-surface flow and winter rains in the lower parts of the basins. Glacier melt runoff is negligible in the winter season because of very low temperatures over the glaciers. </p><p>Assessments of the melting rates and determinations of the drainage char-acteristics of glaciers in the high mountains have importance in harnessing the Himalayan river systems for hydroelectric power generation and irrigation, and lead to other benefits such as reservoir operation and the design of hydraulic structures. Himalayan glaciers provide a significant contribution to the flow in Himalayan rivers, but very limited studies have been carried out to understand the melt processes and other hydrological characteristics of the glaciers in the Himalayas. One of the basic reasons for such limitation is the difficulty in collecting data at high altitude for a long period because of inaccessibility and harsh weather conditions. Vohra (1980) has highlighted the problems associated with Himalayan glaciers. In the present study, results based on the analysis of data collected for a short period (August/September 1992) during an expedition to the Dokriani Glacier in the western Himalayas are presented. Efforts have been made to understand the hydrological behaviour of this glacier. </p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Uni</p><p>vers</p><p>ity o</p><p>f C</p><p>onne</p><p>ctic</p><p>ut] </p><p>at 1</p><p>4:17</p><p> 11 </p><p>Oct</p><p>ober</p><p> 201</p><p>4 </p></li><li><p>Hydrological characteristics of the Dokriani Glacier 245 </p><p>SALIENT FEATURES OF THE DOKEIANI GLACIER </p><p>The Dokriani Glacier is a valley type of glacier located in the western Himalayas. This section of the Himalayas is known as the Garhwal Himalayas (Fig. 1). It lies at about latitude 31N and longitude 79E and originates in the vicinity of the Janoli (6633 m) and Draupadi ka Danda (5716 m) peaks. The glacier elevation ranges from 3950 to 6400 m. The maximum length of the glacier is about 5.5 km and its width varies from 0.1 to 2.0 km from the snout to the accumulation zone. The glacier snout is situated at an altitude of 3950 m and is covered by huge boulders and debris. The lower portion of the glacier is almost totally covered by debris. The material of these moraines is derived from the valley sides through various processes such as debris slides, ava-lanches and weathering processes. The middle part of the glacier is highly fractured and consists of many glacial features such as crevasses, moulins, glacier tables and ground moraines. The crevasses are mainly of the transverse type and are wide and long. Sometimes longitudinal crevasses are also seen along the sides of the glacier. The glacier is bounded by two large lateral moraines about 200-250 m in height. Besides these lateral moraines, there are four other lateral moraines observed at different heights. These different levels of the moraines indicate past extensions of the glacier. The melt stream originating from the Dokriani Glacier is known as Din Gad which follows a narrow valley and meets the Bhagirathi River near Bhukki. </p><p>32' | HIMACHAL </p><p>Fig. 1 Location of the Dokriani Glacier in the Garhwal Himalayas. </p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Uni</p><p>vers</p><p>ity o</p><p>f C</p><p>onne</p><p>ctic</p><p>ut] </p><p>at 1</p><p>4:17</p><p> 11 </p><p>Oct</p><p>ober</p><p> 201</p><p>4 </p></li><li><p>246 P. Singh et al. </p><p>Geomorphological features </p><p>The geomorphological characteristics of a glacierized catchment influence the melting of the glacier and the drainage pattern of the glacier melt runoff. The primary characteristics of the catchment are its area, length, shape, elevation, slope, orientation, etc. The main geomorphological parameters of the Dokriani Glacier are given in Table 1 and the area-elevation curve of the glacier is illustrated in Fig. 2. </p><p>6500 n </p><p>6000 -</p><p>5500 -</p><p>: 5000 -</p><p>UJ 4500 i </p><p>4000 -</p><p>3500 </p><p>/ </p><p>12 0 2 4 6 8 10 </p><p>Cumulative area (sq. km) Fig. 2 Area-elevation curve of the Dokriani Glacier </p><p>Table 1 Geomorphological parameters of the Dokriani Glacier </p><p>Serial no. Parameter Value </p><p>Glacier area (km') </p><p>Drainage area (km2) </p><p>Glacier perimeter (km) </p><p>Glacier length (km) </p><p>Eccentricity of glacier </p><p>Circularity ratio of glacier </p><p>Elongation ratio of glacier </p><p>Glacier relief (km) </p><p>Average gradient of glacier (%) </p><p>10.0 </p><p>23.0 </p><p>23.0 </p><p>5.50 </p><p>0.55 </p><p>0.29 </p><p>0.57 </p><p>2.45 </p><p>44.54 </p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Uni</p><p>vers</p><p>ity o</p><p>f C</p><p>onne</p><p>ctic</p><p>ut] </p><p>at 1</p><p>4:17</p><p> 11 </p><p>Oct</p><p>ober</p><p> 201</p><p>4 </p></li><li><p>Hydrological characteristics of the Dokriani Glacier 247 </p><p>FIELD OBSERVATIONS </p><p>Glacier melt runoff observations </p><p>A survey of the melt stream starting from the snout to about 2 km downstream was made and finally a suitable gauging site was selected and established for streamflow measurements. This gauging site was about 800 m downstream from the snout of the glacier and about 1 km upstream of the confluence of several small nallahs joining the main stream. The flow was not greatly turbulent at this site and the total meltwater was confined to a single channel. A bridge over the melt stream was made with the help of wooden logs and using boulders as a bridge support at both ends. A view of the gauging site is shown in Fig. 3. </p><p>Fig. 3 Gauging site on the Dokriani melt stream. </p><p>The velocity-area method was used to estimate the discharge in the melt stream. Wooden floats were used to measure the velocity of flow. The time of travel of the floats was determined with a stopwatch. The straight reach at the gauging site was only 6 m long, forming the best possible straight reach which could be found along the channel. In fact, to get a long straight reach of flow is a great problem in this type of terrain. For accuracy, the velocity readings were repeated at least three times and an average value adopted for further computations. It was assumed that there was no change in the cross-sectional area of the gauging site during the study period. Atmospheric and water temp-eratures were also observed at the gauging site when flows were measured. </p><p>The observations of discharge, suspended sediment and air temperature were made for a period of 21 days (23.8.1992-12.9.1992). For this period hourly observations were made for all the parameters only during daytime and </p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Uni</p><p>vers</p><p>ity o</p><p>f C</p><p>onne</p><p>ctic</p><p>ut] </p><p>at 1</p><p>4:17</p><p> 11 </p><p>Oct</p><p>ober</p><p> 201</p><p>4 </p></li><li><p>248 P. Singh et al. </p><p>mean values of the parameters were computed. To obtain a complete hydro-graph at the gauging site, hourly observations of streamflow and air tempera-ture were made for 24 h on 10.9.1992/11.9.1992. </p><p>Runoff from isolated snow Mocks </p><p>In order to determine the snowmelt factor, snow blocks (60 cm x 60 cm x 30 cm) were extracted from the glacier snowpack at 4000 m altitude and studied for their melting rate. The observations were made from 0800 h to 1400 h on three days (21, 22 and 24.9.1992). The air temperature was observed each 15 min at 2.0 m above the surface of the snow block and used to compute the average temperature for each hour. The meltwater was collected in a bucket and measured every hour just after collection to minimize evaporation losses. The amount of meltwater lost via percolation was checked by putting a white plastic sheet under the snow block. This ensured that the total meltwater was collected in the bucket. The density of the snow blocks was measured to be 0.60 g cm"3. </p><p>The observations for the isolated snow blocks were restricted to clear weather conditions with a view to estimating the melt factor under fair weather conditions. Observations after 1400 h were not taken because after this time clouds formed and clear weather conditions did not persist. This phenomenon was observed regularly during the whole study period. One of the reasons for the formation of clouds in the afternoon is thought to be the availability of soil moisture for evaporation and vapotranspiration. As soon as sufficient solar radiation is available, vapotranspiration processes occur strongly and clouds are formed in the afternoon. </p><p>MELT FACTOR </p><p>The melt factor is also known as the degree-day factor when the time unit is a day. It is an important parameter and is used to convert the degree-days to snowmelt or ice melt expressed in depth of water. It is given in the following form: </p><p>M = Df(Ta -TJ (1) </p><p>where M = depth of meltwater (mm per unit time) ; Ta mean air temperature (C); T0 = base temperature (0C); and Df = melt factor (mm/(C. unit time)). </p><p>Information on the melt factor is required for glacier melt modelling studies. However, the melt factor is variable throughout the melt period because the changes in snow properties influence the melting process. It is possible to compute the melt factor at a point by measuring temperature and meltwater from the snowpack. The point measurements can be used for infor-</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Uni</p><p>vers</p><p>ity o</p><p>f C</p><p>onne</p><p>ctic</p><p>ut] </p><p>at 1</p><p>4:17</p><p> 11 </p><p>Oct</p><p>ober</p><p> 201</p><p>4 </p></li><li><p>Hydrological characteristics of the Dokriani Glacier 249 </p><p>mation on how well a specific station represents the hydrological characteristics of the given zone. </p><p>The observed values of average temperature and meltwater along with the computed melt factor for 6 h periods are given in Table 2. Details for the hourly basis are given in Table 3. </p><p>Values for D^have been given by several investigators. Anderson (1973) reported a seasonal variation in the melt factor and gave a range of 1.5-7.0 mm/(C. 6 h) using the mean air temperature on the same pattern as Male &amp; Granger (1978). From this study, an average value of D -was computed to be 5.4 mm/(C. 6 h). It is expected that values of Df derived from the snow block measurements may be slightly on the high side because of energy gained at the snow block walls. Very likely, melt rates at an undisturbed site would be lower. There are maximum contributions from glaciers to the Indian river systems in the months of July and August. Therefore, this value of the melt factor may be considered as the maximum melt factor for the glacier snow. </p><p>Table 2 Mean temperature and snowmelt factors for different dates; melt rates were observed between 0800 and 1400 h </p><p>Date (0800-1400 h) </p><p>21.8.92 </p><p>22.8.92 </p><p>24.8.92 </p><p>Mean (C) </p><p>i air temp. </p><p>12.5 </p><p>11.6 </p><p>10.5 </p><p>Depth (mm) </p><p>of meltwater </p><p>71.3 </p><p>65.1 </p><p>51.2 </p><p>D, (mni/CC. 6 h) </p><p>5.7 </p><p>5.6 </p><p>4.9 </p><p>Table 3 Hourly temperature, snowmelt water and snowmelt factors </p><p>Date Hours Average Ta Runoff from snow Dj </p><p>0800-0900 0900-1000 1000-1100 1100-1200 1200-1300 1300-1400 </p><p>0800-0900 0900-1000 1000-1100 1100-1200 1200-1300 1300-1400 </p><p>0800-0900 0900-1000 1000-1100 1100-1200 1200-1300 1300-1400 </p><p>CO </p><p>9.50 10.50 11.25 13.00 15.50 15.50 </p><p>8.00 9.50 </p><p>10.25 12.00 14.50 15.50 </p><p>8.00 8.50 </p><p>10.00 11.25 12.50 13.00 </p><p>blocks (mm ir') </p><p>3.33 6.20...</p></li></ul>

Recommended

View more >