Numerical modelling of rheological properties of landslide debris

Debris flow has caused severe human casualties and economic losses in landslide-prone areas around the globe. A comprehensive understanding of the morphology and deposition mechanisms of debris flows is crucial to delineate the extent of a debris flow hazard. However, due to inherent complex field topography and varying compositions of the flowing debris, coupled with a lack of fundamental understanding about the factors controlling the geomaterial flow, interparticle interactions and its final settlement resulted in a limited understanding of the flow behaviour of the landslide debris. In this study, a physical model was set up in the laboratory to simulate and calibrate the debris flow using PFC, a distinct element modelling-based software. After calibration, a case study of the Varunavat landslide was taken to validate the developed numerical model. Following validation with an acceptable level of confidence, several models were generated to evaluate the effect of slope height, slope angle, slope profile, and grain size distribution of the dislodged geomaterial in the rheological properties of debris flow. Both qualitative and quantitative analysis of the landslide debris flow was performed. Finally, the utility of retaining wall and their effect on debris flow is also studied with different retaining wall positions along the slope surface.

     

A geospatial analysis of Samudra Tapu and Gepang Gath glacial lakes in the Chandra Basin,Western Himalaya

Geospatial studies carried out in two major proglacial lakes of Samudra Tapu and Gepang Gath (Chandra Basin, Western Himalaya) showed substantial expansion in their area and volume over the last four decades (1971–2014). The linear and areal expansions for the lakes Samudra Tapu and Gepang Gath were 1889, 1509 m and 1, 0.6 km², respectively. The results show that increased melting of the feeder glaciers over this period is major contributor to expand the volumes approximately 20 times of both the lakes Samudra Tapu and Gepang Gath. This expansion of lakes volume of Samudra Tapu and Gepang Gath from 3.4 × 10⁶ to 67.7 × 10⁶ and 1.5 × 10⁶ to 27.5 × 10⁶ m³, respectively, is quite significance in terms of hazards generated from glacial lake outburst floods (GLOF). This kind of climate change induced increase in the rate of glacial melting is a cause of concern, as the Himalaya Mountains may turn out to be vulnerable to natural hazards like GLOF.     

Magnetotelluric impedance tensor analysis for identification of transverse tectonic feature in the Wagad uplift,Kachchh, northwest India

The 2001 Bhuj earthquake (Mw 7.7) occurred in northwestern region of Indian peninsula has reactivated a couple of transverse faults to its surroundings. Intermediate to moderate magnitude earthquakes are occurring along these faults which includes recent Dholavira earthquake (Mw 5.1, 2012) suggesting distinct tectonic scenario in the region. We present the results of magnetotelluric (MT) impedance tensors analyses of 18 sites located along a profile cutting various faults in the uplifted Wagad block of the Kachchh basin. The MT time series of 4–5 days recording duration have been processed and the earth response functions are estimated in broad frequency range (0.01–1000 s). The observed impedance tensors are analyzed by using three decomposition techniques as well as by the phase tensor method constraining with the induction arrows. The analyses suggest distinct tectonic feature within the block bounded by the South Wagad Fault (SWF) and the North Wagad Fault (NWF) particularly in the period band of 1–10 s. In the south of NWF, the telluric vectors and the major axes of the phase ellipses are aligned in the NNW–SSE to NW–SE direction where as a dominant E–W strike is obtained for northern side of the NWF. The transverse geo-electric strike coincides with the prominent clustering of seismicity after the Bhuj earthquake and trend of the Manfara transverse fault is located in close vicinity of the study area. We therefore suggest the presence NNW–SSE trending transverse structural feature in the Wagad uplift of the basin appears to play significant role in the current seismicity of the active intraplate region.     

Determining shallow aquifer vulnerability by the DRASTIC model and hydrochemistry in granitic terrain,southern India

Shallow aquifer vulnerability has been assessed using GIS-based DRASTIC model by incorporating the major geological and hydrogeological factors that affect and control the groundwater contamination in a granitic terrain. It provides a relative indication of aquifer vulnerability to the contamination. Further, it has been cross-verified with hydrochemical signatures such as total dissolved solids (TDS), \(\hbox {Cl}^{-},\, \hbox {HCO}_{3}^{-},\, \hbox {SO}_{4}^{2-}\) and \(\hbox {Cl}^{-}/\hbox {HCO}_{3}^{-}\) molar ratios. The results show four zones of aquifer vulnerability (i.e., negligible, low, moderate and high) based on the variation of DRASTIC Vulnerability Index (DVI) between 39 and 132. About 57% area in the central part is found moderately and highly contaminated due to the 80 functional tannery disposals and is more prone to groundwater aquifer vulnerability. The high range values of TDS (2304–39,100 mg/l); \(\hbox {Na}^{+}\)(239– 6,046 mg/l) and \(\hbox {Cl}^{-}\) (532–13,652 mg/l) are well correlated with the observed high vulnerable zones. The values of \(\hbox {Cl}^{-}/\hbox {HCO}_{3}^{-}\) (molar ratios: 1.4–106.8) in the high vulnerable zone obviously indicate deterioration of the aquifer due to contamination. Further cumulative probability distributions of these parameters indicate several threshold values which are able to demarcate the diverse vulnerability zones in granitic terrain.     

Multivariate modeling of droughts using copulas and meta-heuristic methods

This study investigated the utility of two meta-heuristic algorithms to estimate parameters of copula models and for derivation of drought severity–duration–frequency (S–D–F) curves. Drought is a natural event, which has huge impact on both the society and the natural environment. Drought events are mainly characterized by their severity, duration and intensity. The study adopts standardized precipitation index for drought characterization, and copula method for multivariate risk analysis of droughts. For accurate estimation of copula model parameters, two meta-heuristic methods namely genetic algorithm and particle swarm optimization are applied. The proposed methodology is applied to a case study in Trans Pecos, an arid region in Texas, USA. First, drought severity and duration are separately modeled by various probability distribution functions and then the best fitted models are selected for copula modeling. For modeling the joint dependence of drought variables, different classes of copulas, namely, extreme value copulas, Plackett and Student’s t copulas are employed and their performance is evaluated using standard performance measures. It is found that for the study region, the Gumbel–Hougaard copula is the best fitted copula model as compared to the others and is used for the development of drought S–D–F curves. Results of the study suggest that the meta-heuristic methods have greater utility in copula-based multivariate risk assessment of droughts.     

Some features of the arid area variations over India: 1871–1984

Spatial variability of the annual rainfall over drier regions of India is studied by examining the variations in the arid areas. A long period (1871–1984) arid area series has been prepared for the entire country, including the two broad subregions of North India and Peninsular India, using annual rainfall data from 306 well distributed stations. Following an objectively determined criterion based on rainfall amount alone, the yearly area under arid conditions is obtained by totalling areas which received annual rainfall totals less than 560 mm. The interannual variability of the arid area series is large and its distribution is highly right-skewed, demonstrating large spatial variations in the annual rainfall over India. Statistical tests do not suggest any significant long-term trend in the arid area series, but persistently low values of the arid area after 1941 are noteworthy. Implications for the study of risk analysis and assessment of drought and desertification processes are discussed.     

Generalized flux law,with an application

A generalized flux law, which can specialize into power‐ and diffusive‐type flux laws, is proposed. When coupled with the continuity equation, a generalized flow equation is the result. The generalized equation specializes into several cases, one of which is the kinematic wave equation. By applying the generalized flow equation and its variants to flow routing in two rivers, the usefulness of the generalized flux law is evaluated. Copyright © 1999 John Wiley & Sons, Ltd.     

Calibration and validation of a general infiltration model

A general infiltration model proposed by Singh and Yu (1990) was calibrated and validated using a split sampling approach for 191 sets of infiltration data observed in the states of Minnesota and Georgia in the USA. Of the five model parameters, f_c (the final infiltration rate), S_o (the available storage space) and exponent ‘n’ were found to be more predictable than the other two parameters: m (exponent) and a (proportionality factor). A critical examination of the general model revealed that it is related to the Soil Conservation Service (1956) curve number (SCS‐CN) method and its parameter S_o is equivalent to the potential maximum retention of the SCS‐CN method and is, in turn, found to be a function of soil sorptivity and hydraulic conductivity. The general model was found to describe infiltration rate with time varying curve number. Copyright © 1999 John Wiley & Sons, Ltd.     

Design of a Low-Cost Bamboo Well

Bamboo wells are an economical alternative for water supply wells in developing countries. The design of the bamboo well described in this article was developed based on field tests. Following field experiments, the screen in the bamboo well was fabricated with seven 3-m-long bamboo strips, each 2 cm wide and 1 cm thick. The strips were bolted on 1-cm-wide mild steel rings spaced 30 cm along the length of the bamboo strips, with 9-cm-long galvanized iron pipe end pieces. Pipes used in the bamboo well were fabricated by wrapping polythene sheets on the bamboo screens. Excellent performance, low cost, and good service life justify the use of a bamboo well for ground water withdrawal in developing countries.