Homotopy Perturbation Method‐Based Analytical Solution for Tide‐Induced Groundwater Fluctuations

The groundwater variations in unconfined aquifers are governed by the nonlinear Boussinesq's equation. Analytical solution for groundwater fluctuations in coastal aquifers under tidal forcing can be solved using perturbation methods. However, the perturbation parameters should be properly selected and predefined for traditional perturbation methods. In this study, a new dimensional, higher‐order analytical solution for groundwater fluctuations is proposed by using the homotopy perturbation method with a virtual perturbation parameter. Parameter‐expansion method is used to remove the secular terms generated during the solution process. The solution does not require any predefined perturbation parameter and valid for higher values of amplitude parameter A/D, where A is the amplitude of the tide and D is the aquifer thickness.     

Effects of disturbance intensities on vegetation patterns in oak forests of Kumaun, west Himalaya

In order to realize the significance of oak forests for ecology and economy of the Himalayan region,the present study attempts to objectively characterize disturbance intensities and their impacts on compositional features of identified Oak forests, i.e.Banj-oak(Quercus leucotrichophora A.Camus), Tilonj-oak(Q.floribunda Lindley)and Kharsu-oak(Q. semecarpifolia J.E.Smith)in west Himalaya. Amongst studied forests,Q.leucotrichophora and Q. semecarpifolia forests exhibited high sensitivity towards disturbance intensities.In both forests, increasing level of disturbance significantly lowered tree density,dominance and natural recruitment (seedling and sapling density).Q.floribunda forests, however,appeared relatively more resilient to anthropogenic disturbances.Amongst studied oak forests,Q.semecarpifolia forests with overall poor natural regeneration are in a most critically endangered demographic state.However,a slightly improved regeneration(i.e.,seedling density)in moderately disturbed plots is indicative that such plots may be utilized most suitably for in situ revival of these forests.Effect of disturbance intensities on tree population is an important subject for forest ecology and management and the present study highlights a need for adopting different management strategies across disturbance intensities in diverse oak forests of west Himalaya.     

A new approach to the determination of methane content of coal seams

Summary An approach to the determination of methane content of coal seams is proposed. The method utilizes the transformed Airey's empirical equation on desorption of methane from coals. The methane content values estimated by this method correspond well with actual values from laboratory experiments. In the case of Indian coals, the applicability of the relationship for the calculation of the gas lost from coal lumps during long periods of time loss appears to be limited due to poor agreement with the experimental values.     

IMF BY dependence of the extent of substorm westward electrojet

In this paper the duskward extension of the westward auroral electrojet is investigated for substorm intervals on the basis of magnetograms recorded at the Indian Antarctic station, Maitri. The database comprises three years from 1998–2000. Based on an initial study of the magnetograms, an arbitrary local time of 2030 MLT is fixed to define the early manifestation of the substorm westward electrojet. Using this criterion 12 substorms are identified and the possible causes examined. Many of these events are observed to be associated with a moderate to intense ring current. The hourly average of the GSM B_Y-component of the interplanetary magnetic field (IMF) for the hour preceding the substorm onset at Maitri is negative for most of the events. It is suggested that the azimuthal shift of the auroral electrojets in the southern hemisphere resulting from a negative B_Y-component of the IMF influences the extent of the substorm westward electrojet. This finding implies that the IMF may have a role in controlling the longitudinal extent of substorm occurrence.     

On some characteristics of severe rainstorms of India

Summary Detailed examination of daily rainfall data for India (and other relevant publications regarding severe rainstorms) show that during the last 110 years, the Indian region recorded 231 severe rainstorms. Of these, 27 were of 2-day duration and the rest (204) were of 3-day duration. Within a rainstorm, maximum rain fell on the 2nd day on 63% of occasions. It was also observed that the average raindepths obtained from slow moving rainstorms were greater in magnitude than those of fast moving rainstorms. All these rainstorms, during their movement through the country, had their rain centres at about 308 locations. This study has shown that only 19 locations recorded severe rainstorm centres on five or more occasions. Maximum number of rain centres recorded for one location was 13.With 2 Figures     

Geochemical and hydrogeological contrasts between shallow and deeper aquifers in two villages of Araihazar, Bangladesh: Implications for deeper aquifers as drinking water sources

Sediment and groundwater profiles were compared in two villages of Bangladesh to understand the geochemical and hydrogeological factors that regulate dissolved As concentrations in groundwater. In both villages, fine-grained sediment layers separate shallow aquifers (< 28 m) high in As from deeper aquifers (40-90 m) containing < 10 μg/L As. In one village (Dari), radiocarbon dating indicates deposition of the deeper aquifer sediments > 50 ka ago and a groundwater age of thousands of years. In the other village (Bay), the sediment is < 20 ka old down to 90 m and the deeper aquifer groundwater is younger, on the order of hundreds of years. The shallow aquifers in both villages that are high in As contain bomb-³H and bomb-¹⁴C, indicating recent recharge. The major and minor ion compositions of the shallow and deeper aquifers also differ significantly. Deeper aquifer water is of the Na⁺-HCO₃^- type, with relatively little dissolved NH₄⁺ (76 ± 192 μmol/L), Fe (27 ± 43 μmol/L) and Mn (3 ± 2 μmol/L). In contrast, shallow aquifer water is of the Ca²⁺-Mg²⁺-HCO₃^- type, with elevated concentrations of dissolved NH₄⁺ (306 ± 355 μmol/L), Fe (191 ± 73 μmol/L), and Mn (27 ± 43 μmol/L). In both villages, the quantity of As extractable from deeper aquifer sands with a 1 mol/L phosphate solution (0.2 ± 0.3 mg/kg, n = 12; 0.1 ± 0.1 mg/kg, n = 5) is 1 order of magnitude lower than P-extractable As from shallow deposits (1.7 ± 1.2 mg/kg, n = 9; 1.4 ± 2.0 mg/kg, n = 11). The differences suggest that the concentration of P-extractable As in the sediment is a factor controlling the concentration of As in groundwater. Low P-extractable As levels are observed in both deeper aquifers that are low in As, even though there is a large difference in the time of deposition of these aquifers in the two villages. The geochemical data and hydrographs presented in this study suggest that both Holocene and Pleistocene deeper aquifers that are low in As should be a viable source of drinking water as long as withdrawals do not exceed recharge rates of ∼1 cm/yr.