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Erodibility indices are important parameter that can be used to describe the intensity of the soil erosion problems causing environmental concerns. These indices are convenient to estimate the susceptibility to erosion where physical measurement is very difficult. Sikkim is one such state in India where measuring erosion is a tedious process due to its difficult and inaccessible terrain conditions. In the present study, spatial variation of susceptibility of erosion in East district of Sikkim was estimated by using indices such as clay ratio, dispersion ratio, mod clay ratio and critical level of soil organic matter. The result indicates soils in East district are mostly dominated by sand particles (40.5-81.06%) in majority of soil samples. The dispersion ratio values in most of the soils were >15% indicating very high vulnerability to erosion. The values of clay ratio (3.44-9), modified clay ratio (mean value of 6.9) and critical level of soil organic matter content (<5%) indicated high susceptibility to erosion. The trends of indices were generated by IDW interpolation method to understand the spatial variation of the susceptibility to erosion. The interpolated maps were overlaid on subwatershed maps to prioritize the subwatershed for planning treatment measures. Keywords. Erosion; erodibility indices; clay ratio; dispersion ratio; modified clay ratio; critical level of soil organic matter.

Heavy metal (Fe, Mn, Zn, Cu, Ni, Pb, and Cd) concentrations and their chemical speciations were investigated for the first time in bed sediments of Bharali River, a major tributary of the Brahmaputra River of the Eastern Himalayas. Levels of Fe, Mn, Pb, and Cd in the bed sediments were much below the average Indian rivers; however, Cu and Zn exhibit levels on the higher side. Enrichment factors (EF) of all metals was greater than 1 and a higher trend of EF was seen in the abandoned channel for most metals. Pb showed maximum EF of 32 at site near an urban center. The geoaccumulation indices indicate that Bharali river is moderately polluted. The metals speciations, done by a sequential extraction regime, show that Cd, Cu, and Pb exhibit considerable presence in the exchangeable and carbonate fraction, thereby showing higher mobility and bioavailability. On the other hand, Ni, Mn, and Fe exhibit greater presence in the residual fraction and Zn was dominant in the Fe-Mn oxide phase. Inter-species correlations at three sites did not show similar trends for metal pairs indicating potential variations in the contributing sources.

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Drought is a naturally occurring phenomenon affecting various aspects of life. Lack of understanding of the phenomenon is one of the reasons for its adverse impact. It is therefore of great importance to assess and characterize drought to plan appropriate management measures. In this study we attempted to characterize the droughts in the East District of Sikkim during the winter. Winter droughts (Oct–Mar) are a major cause of concern in Sikkim, responsible for reduction of productivity in high‐value horticultural crops, incidence of pests and diseases, forest fires and non‐availability of water for domestic purposes. For the characterization of drought the reconnaissance drought index (RDI) was applied using the data available for the period 1985–2012. From the analysis it could be seen that drought is experienced for 66.7 and 59.3% of time in the periods Oct–Dec and Jan–Mar. The droughts in the district followed the Wakeby frequency distribution function. The probability and return period were also estimated and it could be observed that every three years the district experiences drought. Specific management measures are necessary to minimize the adverse impact of drought. Some of the measures applicable to Sikkim are also discussed in the paper. Copyright © 2014 John Wiley & Sons, Ltd.

Sikkim is one of the constituent states of India, endowed with huge water resources. However, due to steep terrain and non availability of a groundwater aquifer, water conservation is a challenge. The water received as rainfall drains away through the steep terrain in the deep valleys, thereby creating a water stress after withdrawal of the monsoon. To overcome such a situation, a study was undertaken to design a suitable rain water harvesting system for the state. To design a suitable water harvesting system, we estimated the water demand of the end users, assessed the water availability during the non-rainy period, and designed the volume of storage structure. The study revealed that more than 80% of the respondents experienced water stress during the period from December to March. The average daily water demand of individual households was observed to be around 400 litres. The rainfall pattern indicated that 90% of the rainfall is concentrated during 6 rainy months. On average, 24 consecutive dry days were observed in the state. The volume of storage structure obtained, based on water availability and demand, was 5 m3 per household. It is felt that this volume can take care of the domestic water demand.

Many canal irrigation systems in India are found to have poor performance. Assessment of performance is a prerequisite for its improvement and achieve the desired objective of conceiving an irrigation project. We conducted a comprehensive performance assessment of the Kaldiya irrigation project (KIP) located in Assam in the north‐eastern part of India. The project was aimed at diversification and intensification of an agricultural scenario in a command of 10 000 ha. We performed the study by assessing parameters such as agro‐economic and system performance. The parameters were changes in cropping pattern, intensity, productivity, conveyance losses, delivery efficiency, water availability at source and demand–supply studies. Primary and secondary data were collected and field studies performed. Significant improvement in productivity (> 50%) in the head, middle and tail sections was observed. However, changes in intensity and area under production were comparatively less. The system performance indicated higher conveyance loss of 0.83–5.11 lps per 100 m. The average system delivery efficiency was only 35.3%. The water availability and demand analysis indicated that 43% of the time water availability in the source is higher than the design discharge of the main canal. Based on the findings, suggestions were formulated for modernization of the project. Copyright © 2013 John Wiley & Sons, Ltd.

This study was an effort to analyse the problems and prospects of water resource management and for suggesting strategies to meet the perceptive demand of 410 L of water per family during the winter period in South Sikkim district of Sikkim state, India. The district is of hilly terrain with an average rainfall of 1,500 mm per year, yet the district faces acute water shortage during the winter period. The hydro-geological and meteorological characteristics of the sub-watersheds were also studied. The district had very poor soil depth (&lt;50 cm), low water holding capacity of soils (27–28%) with mostly sandy-loam texture. The sub-watersheds were found to have more than 70% first-order streams, higher bifurcation ratio (3.31), higher drainage density (3.99 km/km2) and higher stream density (8.65/km2). Sub-watersheds are mostly elongated with average form factors of 0.21. The rainfall pattern, soil type and morphometry of sub-watersheds indicated poor in situ moisture storage and limited possibility of stream water harvesting. To mitigate the scarcity of water in South Sikkim, the only option left for the planners is to promote household roof water harvesting so that water demand can be met during the average consecutive dry period of 30 days.