Precipitation-runoff simulation for a Himalayan River Basin, India using artificial neural network algorithms

In the Himalayan regions, precipitation-runoff relationships are amongst the most complex hydrological phenomena, due to varying topography and basin characteristics. In this study, different artificial neural networks (ANNs) algorithms were used to simulate daily runoff at three discharge measuring sites in the Himalayan Kosi River Basin, India, using various combinations of precipitation-runoff data as input variables. The data used for this study was collected for the monsoon period (June to October) during the years of 2005 to 2009. ANNs were trained using different training algorithms, learning rates, length of data and number of hidden neurons. A comprehensive multi-criteria validation test for precipitation-runoff modeling has been undertaken to evaluate model performance and test its validity for generating scenarios. Global statistics have demonstrated that the multilayer perceptron with three hidden layers (MLP-3) is the best ANN for basin comparisons with other MLP networks and Radial Basis Functions (RBF). Furthermore, non-parametric tests also illustrate that the MLP-3 network is the best network to reproduce the mean and variance of observed runoff. The performance of ANNs was demonstrated for flows during the monsoon season, having different soil moisture conditions during period from June to October.     

Geology, petrochemistry, and genesis of the bimodal lavas of Osham Hill, Saurashtra, northwestern Deccan Traps

The Saurashtra region in the northwestern Deccan continental flood basalt province (India) is notable for compositionally diverse volcano-plutonic complexes and abundant rhyolites and granophyres. A lava flow sequence of rhyolite-pitchstone-basaltic andesite is exposed in Osham Hill in western Saurashtra. The Osham silicic lavas are Ba-poor and with intermediate Zr contents compared to other Deccan rhyolites. The Osham silicic lavas are enriched in the light rare earth elements, and have ε_Nd (t = 65 Ma) values between −3.1 and −6.5 and initial ⁸⁷Sr/⁸⁶Sr ratios of 0.70709-0.70927. The Osham basaltic andesites have initial ε_Nd values between +2.2 and −1.3, and initial ⁸⁷Sr/⁸⁶Sr ratios of 0.70729-0.70887. Large-ion-lithophile element concentrations and Sr isotopic ratios may have been affected somewhat by weathering; notably, the Sr isotopic ratios of the silicic and mafic rocks overlap. However, the Nd isotopic data indicate that the silicic lavas are significantly more contaminated by continental lithosphere than the mafic lavas. We suggest that the Osham basaltic andesites were derived by olivine gabbro fractionation from low-Ti picritic rocks of the type found throughout Saurashtra. The isotopic compositions, and the similar Al₂O₃ contents of the Osham silicic and mafic lavas, rule out an origin of the silicic lavas by fractional crystallization of mafic liquids, with or without crustal assimilation. As previously proposed for some Icelandic rhyolites, and supported here by MELTS modelling, the Osham silicic lavas may have been derived by partial melting of hot mafic intrusions emplaced at various crustal depths, due to heating by repetitively injected basalts. The absence of mixing or mingling between the rhyolitic and basaltic andesite lavas of Osham Hill suggests that they reached the surface via separate pathways.     

http://www.sciencedirect.com/science/article/pii/S1674987111001277

A numerical model is developed for investigating the evolution of fracture permeability in a coupled fracture-matrix system in the presence of fracture-skin with simultaneous colloidal and bacterial tr...     

Three-dimensional temporally dependent dispersion through porous media: analytical solution

A three-dimensional model for non-reactive solute transport in physically homogeneous subsurface porous media is presented. The model involves solution of the advection-dispersion equation, which additionally considered temporally dependent dispersion. The model also account for a uniform flow field, first-order decay which is inversely proportional to the dispersion coefficient and retardation factor. Porous media with semi-infinite domain is considered. Initially, the space domain is not solute free. Analytical solutions are obtained for uniform and varying pulse-type input source conditions. The governing solute transport equation is solved analytically by employing Laplace transformation technique (LTT). The solutions are illustrated and the behavior of solute transport may be observed for different values of retardation factor, for which simpler models that account for solute adsorption through a retardation factor may yield a misleading assessment of solute transport in ‘‘hydrologically sensitive’’ subsurface environments.     

Impact of the 2004 Sumatran tsunami on the diversity of intertidal brachyuran assemblages of Maavah, Laamu Atoll, Maldives

A 2-year spatio-temporal survey of intertidal brachyuran crabs involving five sites was conducted in the Maavah reef system, Laamu Atoll, Maldives, from April 2001 to March 2003. In December 2004, the sites were hit by the catastrophic Sumatran tsunami. An 8-month-long study was carried in the same five sites after the tsunami, and the data obtained were compared with the pre-impact baseline data. A sand dune formed at the north-eastern side of the island as a result of the tsunami was also included in the post-tsunami study (site 6). Nine brachyuran crab species not recorded during pre-tsunami sampling in the five study sites were collected after the event. Of these, six species were recorded in site 6 during January 2005, and they started to appear in the other sites in the following months. Nine species of crabs collected during the pre-tsunami periods from four sites were not represented in the post-tsunami collections. Abundance, evenness and diversity of the post-tsunami brachyuran communities of sites 1 and 2 exhibited downward trends, and the evenness and diversity of the post-tsunami communities of site 4 exhibited upward trends when compared with pre-tsunami patterns. Multivariate analyses revealed that the tsunami had changed the post-tsunami brachyuran communities of sites 1?C4. However, tests revealed that in site 4, the pre-tsunami brachyuran assemblage 1 (2001?C2002) differed from pre-tsunami assemblage 2 (2002?C2003) and post-tsunami assemblages. The roles of tsunami-transported species and site-specific dominant species in contributing to faunal dissimilarities between the pre- and post-tsunami brachyuran assemblages were found to be patchy. Further studies would reveal whether the population of any newly added species increases or decreases in the long term.     

Seismicity and source parameters of moderate earthquakes in Sikkim Himalaya

In this study, we accurately relocate 360 earthquakes in the Sikkim Himalaya through the application of the double-difference algorithm to 4?years of data accrued from a eleven-station broadband seismic network. The analysis brings out two major clusters of seismicity??one located in between the main central thrust (MCT) and the main boundary thrust (MBT) and the other in the northwest region of Sikkim that is site to the devastating Mw6.9 earthquake of September 18, 2011. Keeping in view the limitations imposed by the Nyquist frequency of our data (10?Hz), we select 9 moderate size earthquakes (5.3????Ml????4) for the estimation of source parameters. Analysis of shear wave spectra of these earthquakes yields seismic moments in the range of 7.95?×?10²¹ dyne-cm to 6.31?×?10²³ dyne-cm and corner frequencies in the range of 1.8?C6.25?Hz. Smaller seismic moments obtained in Sikkim when compared with the rest of the Himalaya vindicates the lower seismicity levels in the region. Interestingly, it is observed that most of the events having larger seismic moment occur between MBT and MCT lending credence to our observation that this is the most active portion of Sikkim Himalaya. The estimates of stress drop and source radius range from 48 to 389?bar and 0.225 to 0.781?km, respectively. Stress drops do not seem to correlate with the scalar seismic moments affirming the view that stress drop is independent over a wide moment range. While the continental collision scenario can be invoked as a reason to explain a predominance of low stress drops in the Himalayan region, those with relatively higher stress drops in Sikkim Himalaya could be attributed to their affinity with strike-slip source mechanisms. Least square regression of the scalar seismic moment (M ₀) and local magnitude (Ml) results in a relation LogM ₀?=?(1.56?±?0.05)Ml?+?(8.55?±?0.12) while that between moment magnitude (M _w ) and local magnitude as M _w ?=?(0.92?±?0.04)Ml?+?(0.14?±?0.06). These relations could serve as useful inputs for the assessment of earthquake hazard in this seismically active region of Himalaya.     

Estimation of heavy rainfall during cyclonic storms from microwave observations using nonlinear approach over Indian Ocean

In this study, an effort has been made to study heavy rainfall events during cyclonic storms over Indian Ocean. This estimate is based on microwave observations from tropical rainfall measuring mission (TRMM) Microwave Imager (TMI). Regional scattering index (SI) developed for Indian region based on measurements at 19-, 21- and 85-GHz brightness temperature and polarization corrected temperature (PCT) at 85?GHz have been utilized in this study. These PCT and SI are collocated against Precipitation Radar (PR) onboard TRMM to establish a relationship between rainfall rate, PCT and SI. The retrieval technique using both linear and nonlinear regressions has been developed utilizing SI, PCT and the combination of SI and PCT. The results have been compared with the observations from PR. It was found that a nonlinear algorithm using combination of SI and PCT is more accurate than linear algorithm or nonlinear algorithm using either SI or PCT. Statistical comparison with PR exhibits the correlation coefficients (CC) of 0.68, 0.66 and 0.70, and root mean square error (RMSE) of 1.78, 1.96 and 1.68?mm/h from the observations of SI, PCT and combination of SI and PCT respectively using linear regressions. When nonlinear regression is used, the CC of 0.73, 0.71, 0.79 and RMSE of 1.64, 1.95, 1.54?mm/h are observed from the observations of SI, PCT and combination of SI and PCT, respectively. The error statistics for high rain events (above 10?mm/h) shows the CC of 0.58, 0.59, 0.60 and RMSE of 5.07, 5.47, 5.03?mm/h from the observations of SI, PCT and combination of SI and PCT, respectively, using linear regression, and on the other hand, use of nonlinear regression yields the CC of 0.66, 0.64, 0.71 and RMSE of 4.68, 5.78 and 4.02?mm/h from the observations of SI, PCT and combined SI and PCT, respectively.