S.K. Bartarya

Hydrochemistry and rock weathering in a sub-tropical Lesser Himalayan river basin in Kumaun, India

Abstract Major ion chemistry of the water of the Gaula catchment — a medium-sized Lesser Himalayan basin in Kumaun, was measured in 1983 and 1984. The results show the influence of rock weathering on the concentration of major constituents in the ground water and surface water. The catchment lithology contributes a large part of the major constituents in the waters; Ca and Mg account for 40–73% of the cations and HCO 3 accounts for 48–98% of anions, and the equivalent ratio of Ca + Mg to Na + K is about nine. Cl + SO 4 accounts for 12–16% in the anion balance and does not represent a contribution from soil salt. The low Mg:Ca ratio (0.1–0.4) and high bicarbonate suggest the possibility of carbonate precipitation between the upper and the lower reaches. The excess Na over Cl, low Mg:Ca ratio and relatively high abundance of silica in the upper reaches indicate weathering of aluminosilicate minerals of crystalline rocks (granite, mica schist and quartz porphyry), and particularly of Na- and K-feldspar and quartz. Intense weathering of pyrite and or gypsum associated with the carbonate rocks is reflected by the substantially higher abundance of SO 4 , low silica and the low Na:Cl ratio. In comparison with the Indian peninsular rivers, the low concentrations of the major constituents in the water of this Lesser Himalayan catchment indicate rapid infiltration and quick outflow of the rainwater and thus a short residence time for water, during which interaction with the rocks could occur, because of the steep slopes.

Catastrophic mass movement of 1998 monsoons at Malpa in Kali Valley, Kumaun Himalaya (India)

Abstract A devastating landslide on 18 August 1998 near Malpa Village in Kali Valley of Higher Kumaun Himalaya killed 221 persons. The landslide was a complex rock fall–debris flow. The mass movement generated around one million cubic metres of debris and partially blocked the Kali River, Malpa Gad (a tributary of Kali) being blocked completely. The rock mass failed primarily due to the near vertical slopes hanging over the valley along joints, the formation of structural wedges along the free face, the sheared rock mass due to the close proximity of major tectonic planes, and the enhanced pore–water pressure due to prolonged heavy precipitation in the preceding days. The mesoscopic shear zone, exhibiting ramp and flat structure in quartzites, shows a southward thrust movement that might have generated shear stress in the rocks. The slide clearly demonstrates the distressed state of the rock mass in the Himalayan region due to the ongoing northward drift of the Indian plate.

Radon in groundwater of eastern Doon valley, Outer Himalaya

Abstract The radon content in water may serve as a useful tracer for several geohydrological processes. The hydrodynamic factor, presence of radium in host rocks, as well as the soil porosity and permeability control its concentration in groundwater. In order to understand the factors that control the occurrence of radon in groundwater of Doon valley in Outer Himalaya, a total of 34 groundwater samples were collected from handpumps and tubewells covering three hydrogeological units/areas in the eastern part of Doon valley. Radon variation in tubewells and handpumps varies from 25.4±1.8 to 92.5±3.4 Bq / l with an average of 53.5±2.6 Bq / l . A significant positive correlation between radon concentration and depth of the wells was observed in the Doiwala–Dudhli and Jolleygrant areas suggesting that radon concentration increases with drilling depth in areas consisting of sediments of younger Doon gravels, whereas samples of the Ganga catchment show negative correlation. The high radon levels at shallower depths in the Ganga catchment (consisting of fluvial terraces of Ganga basin) indicate uranium-rich sediments at shallower depth.

Interactions between forest and landslide activity along new highways in the Kumaun Himalaya

Abstract Forest cover and landslide activity were surveyed along two hill roads crossing steep hillsides in the Kumaun Himalaya. The Kilbury Road is cut through reserved forest (29°24′N 79°28′E, altitude 2100 m). The Almora Bypass crosses a suburban fringe (29°16′N 79°40′E, altitude 1650 m). Tree canopy cover upslope of the road cut was 56.8% along the Kilbury Road and 14.1% along the Almora Bypass. Tree canopy cover downslope of the roadbed was 35.7% and 7.6% respectively. Ground vegetation cover downslope of the road was also much reduced. In 1990 (and 1985), landslides affected 80.9% (76.5%) of the roadcut in the forest and 42.5% (43.1%) along the suburban roadcut. Statistical correlation of forest cover and landslide attributes recorded for each 200 m reach of roadbed demonstrate that, in the suburban case study, forest cover correlates positively with landslide activity—because forest survives mainly on sites which are too steep and unstable for development. However, in reserved forest, negative correlations link forest cover and landslide activity. Correlation of the ratio between forest cover downslope and upslope of the road with environmental and landslide activity attributes produces little that is significant from the combined or Almora data sets. However, along the undeveloped forest road, low ratios, indicating a greater proportional reduction of tree cover downslope of the road, are significantly associated with steeper slopes, higher roadcuts, increased slumping onto the roadbed, and increased undermining of the roadcut by landslide and erosional processes.

Landslide induced river bed uplift in the Tal valley of Garhwal Himalaya, India

A large scale landslide occurred in the Tal valley of Garhwal Himalaya in late January, 1990. The most interesting feature associated with this slide was the 4 m uplift of a 200 m long and 25 m wide part of the river bed (at an average rate of 13.8 cm/day) between 28 January and 25 February 1990. Studies revealed that the slide occurred because of complex slope processes consisting of rotation and slump movement attributable to the accumulation of pore water pressure in extremely shattered and pulverized rocks during prolonged surface moistening. The process of movement was triggered by the gravitational force exerted upon the sheared material which dislocated a block at the upper part of the slide along a slip plane which terminated below the river bed. Counter resistance was provided by the rocks below the river bed to subdue the further movement of the slide. This indicates that uplift of the river bed and formation of terraces is also related to the nature of the slide and the volume of slumped material.

Environmental correlations of landslide frequency along new highways in the Himalaya: Preliminary results

Abstract Variables which correlate with accelerated landslide activity are identifed in a study of two new hill roads at Almora and Nainital, U.P., India. Cumulatively, 32% of the roadcut is affected by rockfall and 27% by the slumping of rock and/or regolith. Correlation and discriminant analyses suggest that rockfalling may be predictable from measures of the frequency of enlarged joints in the roadcut supported by members of an inter-related complex of variables including slope angle, roadcut height, apparent dip, rock strength, and upslope vegetation cover. Direct measures of environmental instability, such as the undermining of the roadbed by erosion, were also shown to have value. However, the study found few useful environmental indicators of slumping. A positive relation between slumping and tree cover upslope may reflect the fact that forest survives as a relict landuse in locations which are undeveloped because of their instability.

Occurrence of Radon in the Drinking Water of Dehradun City, India

In this paper, the results of measurements of radon (222Rn) in the drinking water of Dehradun City are pre sented. The radon was measured in water samples taken from the tube wells and hand pumps which are the usual sources of water supply in the city. The recorded radon concentrations in 19 water samples from different hand pumps were found to vary from 27 to 154 Bq.l-1 with an average of 67 Bq.I-1, while radon concentrations in 49 water samples from different tube wells were found to vary from 26 to 129 Bq.l-1 with an average of 59 Bq.I-1. The results are compared with international recommen dations for human exposure. These recorded values were found to be above the average of the recommenda tions but well below the highest recommended value of 400 Bq.l-1. In general, the drinking water of Dehradun city is contaminated by radon at a concentration which is reasonably uniform over the study area.

Measurement of Radon and Thoron Concentrations in the Indoor Atmosphere and Drinking Water of Eastern Doon Valley, India

Radon and radium content were measured in water samples from tubewells and handpumps in the eastern Doon valley, India. Activity due to the radon concentration was found to vary from 25.4 to 72.3 Bq L-1, whereas activity due to radium in selected water samples varied from 0.10 to 0.84 Bq L-1. The values recorded for radon were generally higher than those reported by various other workers for drinking water but well below the maximum levels that have been recorded. Measurements of indoor radon, thoron and their daughter products were also made in the houses in the same area for all the four seasons of a year on a time integrated cycle using twin chamber dosimeters. Concentrations of indoor radon and thoron varied from 28.4 to 63.7 Bq m-3 and 0.01 to 15.9 Bqm-3, respectively. The total resultant radiation dose to occupants in the houses surveyed in the eastern Doon valley varied from 0.03 to 0.11 μSv h-1. A detailed analysis of the radon and thoron distribution in different houses with seasonal variation and ventilation conditions and a description of the geology of the area is presented in this paper.

Environmental influences on landslide activity: Almora Bypass, Kumaun Lesser Himalaya

Landslides are self-organizing and self-referenced systems. The conditions which lead to their emergence along Himalayan highways are not the same as those which govern their subsequent evolution. Landslides originate at sites which differ from average conditions by having significantly higher, steeper roadcuts, carved into steeper hillsides, with more finely bedded but less steeply dipping rocks, and fewer trees upslope. These variables do not correlate with measures of landslide size. Landslide morphometric variables correlate with other landslide variables and with few external factors. The system exhibits independence (autopoiesis) from its environment. Additionally, landslides dominated by rock-mechanical processes tend to produce lower angle outfalls from higher, north-facing, roadcuts than those dominated by soil-mechanical processes which are associated with greater depths of below-soil regolith. However, the outfall volumes produced by the landslides of different type are similar. These findings are generated from statistical (correlation/T-test/stepwise discriminant) analyses of data produced by a field survey of average environmental conditions, and the morphometry and environmental contexts of 88 landslides, on 7.6 km of the Almora Bypass.

Post-glacial landform evolution in the middle Satluj River valley, India: Implications towards understanding the climate tectonic interactions

Late Quaternary landform evolution in monsoon-dominated middle Satluj valley is reconstructed using the fragmentary records of fluvial terraces, alluvial fans, debris flows, paleo-flood deposits, and epigenetic gorges. Based on detailed field mapping, alluvial stratigraphy, sedimentology and optical chronology, two phases of fluvial aggradations are identified. The older aggradation event dated between ∼13 and 11 ka (early-Holocene), occurred in the pre-existing topography carved by multiple events of erosion and incision. Climatically, the event corresponds to the post-glacial strengthened Indian summer monsoon (ISM). The younger aggradation event dated between ∼5 and 0.4 ka (mid- to late-Holocene), was during the declining phase of ISM. The terrain witnessed high magnitude floods during transitional climate (∼6.5–7 ka). The fluvial sedimentation was punctuated by short-lived debris flows and alluvial fans during the LGM (weak ISM), early to mid-Holocene transition climate and mid- to late-Holocene declining ISM. Based on the terrace morphology, an event of relatively enhanced surface uplift is inferred after late Holocene. The present study suggests that post-glacial landforms in the middle Satluj valley owe their genesis to the interplay between the climate variability and local/regional tectonic interactions.