Channel form and processes of the flood-dominated Narmada River,India

The 1300 km long Narmada River flows along a structural lineament, alternating between constricting rocky gorges and rapids, and meandering wide alluvial reaches. Channel forms and processes were studied in a 120 km long section of an alluvial reach. Channel size, shape and bedforms in the Narmada River are related to very large floods which have occurred three times in this century. During such floods the entire 400 m wide channel is utilized and 10–15 m high cliffs on both sides operate as riverbanks. Normally, even the high flows of the south-western monsoon are insufficient to fill the whole channel, and hence their effects are limited to building of discontinuous floodplains between the cliffs and modifying bedforms and bars. A channel-in-channel topography is thus created. The very large floods are also responsible for erosion of the rocky stretches and building of point bars. The river meanders, but its movement is restricted because of (1) rocky gorges and scablands operating as anchor points at intervals, and (2) the presence of high alluvial cliffs which are topped on extremely rare occasions. In spite of being located in a tectonically active zone in a monsoon setting, it is the exceptional high-magnitude floods at irregular intervals which control the form and behaviour of the Narmada River.     

Rapid eco-physical impact assessment of tropical cyclones using geospatial technology: a case from severe cyclonic storms Amphan

The tropical cyclones are very destructive during landfall, generating high wind speeds, heavy intensive rainfall, and severe storm surges with huge coastal inundations that have massive socioeconomic and ecological catastrophic effects on human beings and the economic well-being. The sizable ecological effects of cyclonic storms cannot be ignored because of the uncertainty of impact, intensity induced by a warming ocean, and sea level rise. The Super Cyclonic Storm Amphan which falls under the category five classifications under the scheme of the India Meteorological Department (IMD), on the basis the maximum sustained wind speeds gusting up to 168 km/h affected parts of West Bengal and Odisha in India, and south-west Bangladesh between May 16 and 20, 2020. In this work, we have focused on the coastal districts of Kendrapada, Bhadrak, Balasore in Odisha, Purba Medinipur, and South Twenty-Four Parganas in West Bengal, India and, Khulna, Barisal division of Bangladesh that have been seriously affected by the Super Cyclonic Storm Amphan. The objective of the study is to analyze the eco-physical assessment of tropical cyclone Amphan using geospatial technology. Therefore, shoreline change detection and enhance vegetation index have been used in this research work to systematically analyze the eco-physical impact parameters of Cyclonic Storm Amphan using ortho-rectified Landsat 8/OLI imagery and MODIS dataset of USGS with high spatial resolutions of 30–500 m. The result highlights that about 60.33% of the total transects of the study area was eroded, but only 24.99% of the total transects experienced accretion, and 14.68% of the total transects depicted stability. The scientific study will benefit coastal managers and policymakers in formulating action plans for coastal zone management, natural resilience, and sustainable future development.

     

Correction to: A Size-Dependent Bonded-Particle Model for Transversely Isotropic Rock and its Application in Studying the Size Effect of Shale

Geotechnical and Geological Engineering -     

Seasonal and spatial variations in the scaling and correlation structure of streamflow data

Seasonal and spatial variability in scaling, correlation and wavelet variance parameter of daily streamflow data were investigated using 56 gauging stations from five basins located in two different climate zones. Multifractal temporal scaling properties were detected using a multiplicative cascade model. The wavelet variance parameter yielded persistence properties of the streamflow time series. Seasonal variations were found to be significant in that winter and spring seasons where large‐scale frontal events are dominant showed higher long‐term correlations and less multifractality than did summer and fall seasons. Coherent spatial variations were apparent. The Neches River basin located in a subtropic humid climate zone exhibited high persistence and long‐term correlation as well as less multifractality as compared with other basins. It is found that larger drainage areas tend to have smaller multifractality and higher persistence structure, and this tendency becomes apparent in regions that receive large amounts of precipitation and decreases towards arid regions. Copyright © 2012 John Wiley & Sons, Ltd.     

Coda Q Estimates in the Andaman Islands Using Local Earthquakes

The attenuation property of Andaman Island has been investigated analyzing coda waves from 57 local earthquakes in the magnitude range of 2.0–4.9, using the single backscattering model. These earthquakes waveforms, recorded on five broadband seismographs sited over the island from north to south during Nov. 2003 to March 2004, have been used to calculate the frequency dependent Coda Q (Q _c ) applying the time domain coda-decay method. The Coda Q, computed at central frequencies from (0.5–12) Hz and five-lapse time windows from 40 to 80 s, progressively increases from 105 f ^0.88 in the north Andaman to 135 f ^0.79 in the south Andaman with an average of 119 f ^0.80. The average Q _c values vary from 75 ± 42 at 0.5 Hz to 697 ± 54 at 12 Hz central frequency for 40 s lapse time window, while for 80 s lapse time window its variation is from 117 ± 38 at 0.5 Hz to 1256 ± 115 at 12 Hz. The Q _c estimated at different lapse times manifests a significant variation from 122f ^0.75 to 174f ^0.73, corresponding to lapse time window lengths of 40 and 80 s, respectively. The variation of Q _c with frequency, lapse time and also with the location of seismograph reflects the marked structural and compositional inhomogeneity with depth along the Andaman Islands. These observations are well correlated with the seismicity pattern and distinct high angle subduction beneath the island.     

On the propagation of wave from a cylindrical cavity

Summary This paper discusses the disturbance produced in an infinite layer of non-homogeneous elastic material characterised by =0 ⁿ and =0ⁿ(n>0) where and are the density and shear modulus respectively of the material, due to periodic torsional force applied on the wall of a cylindrical hole in the layer. The variation of the displacement component with the radius vector is shown graphically and compared with the corresponding homogeneous case.     

Sharing academic space

This paper is a personal reflection on my participation in the panel “The Spaces of Critical Geography” at the ICGC in 2002, where my position as an European Americanist working in Asia was helpful in disrupting any tendency towards conflation of location, nationality, identity, and academic practice. These reflections focus on three topics: my interactions with various hegemonies and hierarchies; my relationship with the English language; and the contribution I believe critical geography can make to contemporary academic practice across the disciplines.     

Satellite-based monitoring of recent heavy flooding over north-eastern states of India in July 2019

Natural Hazards - South-west monsoon of 2019 advanced towards northern parts of India during the first week of July. Heavy-to-very-heavy rainfall events during July 05–16 resulted in severe...     

Response of ionospheric electric fields to variations in the interplanetary magnetic field

The STARE system (Scandinavian Twin Auroral Radar Experiment) provides estimates of electron drift velocities, and hence also of the electric field in the high-latitude E-region ionosphere between 65 and 70 degrees latitude. The occurrence of drift velocities larger than about 400 m/s (equivalent to an electric field of 20 mV/m) have been correlated with the magnitude of the Interplanetary Magnetic Field (IMF) components B_z and B_y at all local times. Observation days have been considered during which both southward (B_z<0) and northward (B_z>0) IMF occurred. The occurrence of electric fields larger than 20 mV/m increases with increases in B_z magnitudes when B_z<0. It is found that the effects of southward IMF continue for some time following the northward turnings of the IMF. In order to eliminate such residual effects for B_z<0, we have, in the second part of the study, considered those days which were characterized by a pure northward IMF. The occurrence is considerably lower during times when B_z>0, than during those when B_z is negative. These results are related to the expansion and contraction of the auroral oval. The different percentage occurrences of large electric field for B_y>0 and B_y<0 components of the IMF during times when B_z>0, clearly display a dawn-dusk asymmetry of plasma flow in the ionosphere. The effects of the time-varying solar-wind speed, density, IMF fluctuations, and magnetospheric substorms on the occurrence of auroral-backscatter observations are also discussed.