Analysis of sedimentation in connection to grain size and shear stress at lower reach of the Rupnarayan river, West Bengal, India

1128-1137Bathymetric close grid survey of the lower reach of Rupnarayan River was made using Dumpy Level and Echo sounder interfaced with Position Fixing System (GPS). Simultaneous tidal observations were available at an interval of half-an hour. Velocity during high and low tide is measured by Digital water current meter and floating method. Rate of sedimentation in three seasons (Pre-monsoon, Monsoon and Post-monsoon) was measured by keeping the wooden tray on river bed for few days. Textural analysis of sediment grains by sieving technique reveals that sediments are mainly of fine sand to coarse silt in nature. Moderate to moderately well sorting of sediments indicate low and moderate energy condition in the depositional environment. Predominant positive skewness and mesokurtic to leptokurtic nature of the sediments indicate continuous addition of finer or coarser materials and retention of their original characteristics during deposition. Most of the sediments are transported by suspension with rolling, graded suspension and uniform suspension before deposition. Sediments are deposited by combined effects of marine and fluvial processes under shallow agitating environment and carried by turbidity action. Shear stress during swifter and stronger high tide is more than during slower and weaker low tide

Tidal impact leading to sedimentation at lower reach of Rupnarayan River, West Bengal, India

1349-1356During the last 20 years the lower reach of the Rupnarayan River has experienced a net shoaling of 26.57 million m3 (survey made by Kolkata Port Trust, 1992-2012) with 42.04 million m3 shoaling and 15.47 million m3 scouring. Bathymetric close grid survey of the study area was made using Leveling instrument and Echo sounder interfaced with Position Fixing System (GPS). Simultaneous tidal observations were available at an interval of one hour, velocity of high tide and low tide, tidal asymmetry and discharge of water etc. are measured at different Gauge Stations in the field. Swifter and stronger high tide results more available energy during high tide than as low tide. The incoming high tide brings a lot of sediments from the downstream and deposits it on the bed of the studied river in absence of any upland discharge during the non-monsoon months. During the freshet (July, August and September) the impact of high tide is felt less due to the voluminous anti-directional flow of the upland discharge. Tidal range is more near Geonkhali (4.5m) and decreases towards upstream, being lowest near Kolaghat (2.9m). Tidal asymmetry increases from downstream (2 hours at Geonkhali) to upstream (6 hours at Kolaghat). Tidal prism (volume of water that enters a tidal region during flood flow) is very high in that region

Sedimentation under variable shear stress at lower reach of the Rupnarayan River, West Bengal, India

The lower reach of the Rupnarayan River has been deteriorated and incapacitated due to continuous sedimentation (26.57 million m3 shoaling in last 25 years). Attempts have been made to explain the causes and mechanisms of sedimentation in connection to the seasonal fluctuation of shear stress. River depth and water velocity was measured by echo-sounder and current meter respectively. Textural analysis of grains was done by sieving technique. Available and critical shear stress (N/m2) have been calculated following Du Boys (1879), Shield (1936) and Van Ledden (2003) formula. The lack of available energy to transport a particular grain size during low tide (in dry season) is the main reason behind the rapid sedimentation in this area. Most of the places (>75%) having negative deviation of shear stress (available shear stress lesser than critical shear stress), during low tide are characterized by deposition of sediments. The presence of mud (silt and clay) above the critical limit (15%) in some of the sediment samples generates the cohesive property, restricts sediments entrainment and invites sedimentation

Hardening of Steel Through High-Voltage Low-Current Energy Input

A novel approach of high-voltage low-current energy input is applied for hardening of plain carbon eutectoid steel. Initial fine lamellar pearlitic structure disintegrates into four characteristic regions: lamellar pearlite often containing nucleated cementite spheroids (Region-I), fragmented cementite lamella in α-ferrite matrix (Region-II), submicroscopic cementite particles/clusters dispersed in α-ferrite matrix (Region-III), and supersaturated α-ferrite (Region-IV). At a particular applied voltage, structural refinement and matrix supersaturation (evolving martensite) progress concomitantly up to 5 min, followed by a reverse trend of coarsening and degeneration of martensite. The refinement effect and martensite-peak-broadening effect are augmented with increasing voltage up to 75 kV at which the highest hardness (429 HV) of the steel is achieved with treatment duration of 5 min. While primary hardening effect arises from the martensite region of stratified plate morphology (Region-IV), a secondary effect of hardening is resulted from the region containing dispersed submicroscopic cementite particles/clusters in α-ferrite matrix (Region-III). In addition, in the specimen exhibiting maximum hardening effect (at 75 kV, 5 min), as a unique feature, nanosized cementite particles also appear in Region-IV being dispersed in martensite matrix so as to provide further effect of dispersion hardening along with martensitic hardening

Comparative Study of Energy Utilization and Green House Gas Emission by Hybrid Rice Grown under Two Different Cultivation Systems in Red Lateritic Zone of West Bengal

A field experiment was carried out at Agriculture Farm, Palli Siksha Bhavana, Visva-Bharati, Sriniketan, West Bengal, India during kharif season of 2015 to compare rice cultivation in conventional transplanting (CT) and system of rice intensification (SRI) in terms of energy use, energy input output relationship and green house gas emission. Results showed that regardless of cultivars, conventional transplanting consumed 62.39% higher energy over SRI. Maximum energy input was associated with non renewable and indirect sources. Higher dose of nitrogenous fertilizer had contributed to 32.35% and 26.26% to the total input energy in CT and SRI respectively. Energy use efficiency (13.22), energy productivity (6.94 kg MJ-1), energy profitability (12.22) and energy intensity (4.60 MJ Rs-1) of hybrid rice varieties were noted higher in SRI. Maximum green house gas emission from rice field was also attributed to fertilizer nitrogen followed by diesel in both the system. Total green house gas emission in CT was estimated to 834.85 (kg CO2ha-1) i.e. 1.8 times of SRI. Engirdling different energy indices, total input energy and green house gas emission, the system of rice intensification was emerged as the most energy efficient and sustainable rice production system in resource stricken areas (Red Lateritic Zone).&nbsp