Arup Kumar Sarma

Analysis of the change in temperature trends in Subansiri River basin for RCP scenarios using CMIP5 datasets

This study focuses on changes in the maximum and minimum temperature over the Subansiri River basin for different climate change scenarios. For the study, dataset from Intergovernmental Panel on Climate Change (IPCC) fifth assessment report (AR5) (i.e., coupled model intercomparison project phase five (CMIP5) dataset with representative concentration pathway (RCP) scenarios) were utilized. Long-term (2011–2100) maximum temperature (Tmax) and minimum temperature (Tmin) time series were generated using the statistical downscaling technique for low emission scenario (RCP2.6), moderate emission scenario (RCP6.0), and extreme emission scenario (RCP8.5). Trends and change of magnitude in Tmax, Tmin, and diurnal temperature range (DTR) were analyzed for different interdecadal time scales (2011–2100, 2011–2040, 2041–2070, 2070–2100) using Mann-Kendall non-parametric test and Sen’s slope estimator, respectively. The temperature data series for the observed duration (1981–2000) has been found to show increasing trends in Tmax and Tmin at both annual and monthly scale. Trend analysis of downscaled temperature for the period 2011–2100 shows increase in annual maximum temperature and annual minimum temperature for all the selected RCP scenarios; however, on the monthly scale, Tmax and Tmin have been seen to have decreasing trends in some months.

Optimal Ecological Management Practices (EMPs) for Minimizing the Impact of Climate Change and Watershed Degradation Due to Urbanization

Massive deforestation induced by unplanned urbanization in the hilly watersheds of Brahmaputra basin, India, has led to ecological imbalance and is gradually transforming this basin into a multi-hazard zone. Removal of green cover is also becoming a matter of global concern, as it can accelerate the adverse impacts of climate change. People coming in search of work generally reside in the hills, as they cannot afford the high cost of land in plains. This has led to deforestation of the hilly area and has resulted in increased surface erosion from the upper catchments. Though sediment and water yield from these degraded watersheds could have been minimized by implementing ecologically sustainable management practices (EMPs), such as grass land, forest land and detention pond, poor economic conditions of the people stands in the way of field implementation. On the other hand, major industries, which can be held responsible for emission of greenhouse gases, can be asked to finance greenery development in these hilly watersheds through implementation of selected EMPs to earn carbon credit for them. To convert this concept into reality, the EMP combination must be selected in such a way that it restricts sediment and water yield from the watershed within the permissible limit and maximizes its carbon sequestration capacity at minimum possible cost. Such optimal planning is a prerequisite for preparing an acceptable logical agreement between Government and private companies. Keeping this in mind, an optimization model was developed and applied to a micro watershed of Guwahati to explore its applicability in actual field. The model developed in this study provides most logical carbon credit negotiation, subject to the availability of reliable value of CO2 sequestration for different EMPs.

Assessing and mapping flood hazard, vulnerability and risk in the Upper Brahmaputra River valley using stakeholders’ knowledge and Multi‐Criteria Evaluation (MCE)

Assessing flood hazard, vulnerability and integrated risk has long been recognised as an important input for the formulation of policies aiming at flood risk management. This investigation is an endeavour to assess hazard, vulnerability and risk due to flooding, using an indicator-based methodology incorporating stakeholders’ knowledge and multicriteria evaluation in geographic information system (GIS) to achieve community-based assessment. The framework developed in this work is illustrated for the district of Dhemaji, a chronically flood-affected area in the Upper Brahmaputra River valley. Results show spatial distribution of hotspots of flood hazard and vulnerability and locations at risk at regional and subregional level. The emerged risk pattern indicates that vulnerability indicators are more significant contributors than hazard indicators while calculating risk for the Upper Brahmaputra River valley. The methodology provides a dynamic platform where the flexibility in uses of hazard and vulnerability indicators, depending on variation in physical and socioeconomic setup, is possible.

Optimal Ecological Management Practices for Controlling Sediment Yield and Peak Discharge from Hilly Urban Areas

AbstractSustainable mitigation of soil erosion and peak discharge from hilly urban watersheds in an ecologically and economically sound manner is a formidable challenge. This paper applies a linear programming optimization model for determining the best combination of ecological management practices that control sediment and peak discharge within permissible limits at a minimum cost. The linear programming model equations were solved with simplex method using a computer program. The model was applied to a hilly watershed of a rapidly developing city located in the northeastern part of India. The sediment yield and peak discharge were determined by well known equations. A mapping program was employed for extracting topographic parameters of the watershed. The best combination of three possible ecological management practices—grass, garden, and detention pond—was then established. Sensitivity analysis was performed for the assessment of physical parameters. While the sensitivity to rainfall intensity was ob...

Evaluation of Optimal River Training Work Using GA Based Linked Simulation-Optimization Approach

Use of structural measures for controlling a river to minimize its devastating effect and to utilize it for the benefit of mankind is a common practice all over the world. Because of high investment, such measures require prior investigation through model study. As lab based physical model study is very expensive and time consuming, mathematical modeling is generally used for investigating different alternatives of river training works. In this study, a new approach is proposed for deciding appropriate river training measure in a particular reach of a river or channel. In this methodology, an optimization model is linked with the hydrodynamic model for obtaining cost effective combination of groynes which will maintain a user defined flow speed in a pre-decided portion of a river reach. The optimization model is developed using binary coded Genetic Algorithm (GA) and the flow simulation model uses the Beam and Warming scheme for solving the two dimensional (2D) hydrodynamic equations of unsteady flow. The performance of the model is tested by applying the methodology in a rectangular channel for attaining different target speed values at a pre-defined portion of the channel and logical results have been obtained for all the tested scenarios.

Dam Break Hydraulics in Natural Rivers

An investigation is carried out for numerical computations of dam break hydraulics in Natural Rivers with Explicit Finite Difference (EFD) Schemes. Although computational Dam Break Hydraulics is a topic of interest over more than 100 years, numerical simulations of dam break flow in relatively simple channels are found more often compared to real river flood simulations. Natural River channel with wide floodplains make the computation cumbersome as Natural River channels are highly non-prismatic with significant variations in River bed slope and friction. In this study, first order Diffusive Scheme, second order modified two-step Predictor Corrector scheme and Total Variations Diminishing (TVD) McCormack Predictor Corrector using Venn Leer Flux limiter are analyzed by solving unsteady flow equations in conservative and non conservative forms for simulating a hypothetical dam break situation in a Himalayan River in India . The height of the dam is 245 metres. Upstream length of the channel is 40,000 m and downstream is 64,000 m, the elevation of the bed of the channel changes from 545 m to 126.95 m, change in the channel width ranges from 300 m to 5650 m and Manning’s roughness coefficient varies from 0.03 to 0.035 depending on the channel characteristic. The numerical solutions of the EFD are relatively tested for their performances giving special emphasis to some parameters such as the flood depth at different sections and inundated area at different time periods after the failure of the dam and travel time of the flood waves; which are most important for the practicing engineers for efficient flood management. The computational aspects of the numerical models i.e. the implementation efforts of the schemes, run time required are compared. The applicability of the complex numerical corrections such as TVD in the numerical model for refinement in the solutions of dam break hydraulics in Natural Rivers is also examined. The stability and accuracy of the numerical solutions for both conservative and non conservative formulations are analyzed, and it is observed that numerical simulation of flows for complex real River topography in conservative forms with simple EFD schemes are advantageous from practical point of view compared to the higher order Explicit or Implicit Finite Difference or Finite Element schemes which increase the run time significantly and make the implementation complex.

Model-based analysis of urban settlement process in eco-sensitive area of developing country: a study with special reference to hills of an Indian city

Rapid and unplanned expansion of a city into its eco-sensitive areas like hills, wetlands, and forests is becoming a major concern, particularly in developing countries. Understanding the process and causes of such unplanned urban expansion is of paramount importance for framing sustainable urban development policies. This paper presents a modelling concept that relates urban settlement in such eco-sensitive areas with potential socio-economic, demographic and geographical factors. The model is applied to an Indian city Guwahati, which is experiencing serious environmental degradation due to unplanned urban settlement in its eco-sensitive hilly areas. While topographical and settlement data were derived using satellite data in GIS platform, all other necessary data were collected from relevant government organizations. On validation of the multi-linear regression model, the coefficient of determination and the root mean square error are obtained as 0.938 and 1.7, respectively. Model results show that geographical parameters are less influencing as compared to the other socio-economic and demographic factors. Sensitivity analysis of urban settlements in hills of Guwahati city carried out with respect to the considered factors reveals that land value and free space availability in the surrounding area of a hill are the most sensitive parameters. This indicates that city development plans should give more importance to outward spatial expansion in plain areas with regulated land value and zoning scheme to minimize unauthorized settlement in eco-sensitive hilly areas of Guwahati city.

Turbulent flow structures and geomorphic characteristics of a mining affected alluvial channel: Turbulence in Mining Affected Alluvial Channel

Sediment mining in rivers may have a major impact on river geomorphology and research is required to quantify these impacts. In this research, experimental studies were conducted to analyse the morphological changes of channel bed and the turbulent characteristics of flow in the presence of mining. The channel bed profile shows erosion at the bank of the pit and that the erosion expands to the whole width of the channel and propagates downstream with time. The deposition of sediment occurs along the upstream edge of the pit and the depth of the pit decreases with time. Velocity reversal occurs at the central bottom of the pit related to a recirculation zone. Reynolds shear stress and the turbulent intensities become higher in the mining pit region and downstream of it as compared to the upstream section, causing a more rapid movement of bed particles. Analysis of the bursting phenomenon shows that the contribution of sweep and ejection events to the total Reynolds shear stress is more dominant over outward and inward interaction events. The dominance of the sweep event over ejection is observed at the near-bed region for all the sections, but the depth range of dominance of sweep events in the pit and downstream of the pit is found to be more than the upstream. The increase in thickness is responsible for the increase in bed material transport. The increased sediment transport capacity at the mining pit and downstream of it caused the deformation and lowering of channel bed downstream. An empirical formulation of bedload transport for mining induced channels is derived from two different sized uniform bed materials. Copyright

Impact of Spatial Data Availability on Climate Change Prediction in the Weyib River Basin in Ethiopia

Impact of spatial data availability on the temperature and precipitation prediction characteristics of Weyib River basin in Ethiopia has been investigated using CMIP5-CanESM2 model for the RCP8.5, RCP4.5 and RCP2.6 scenarios. The objective of the present study is to characterize how future temperatures and precipitation prediction under CMIP5-CanESM2 model output varies against diverse averaged arbitrary spatial weather stations found in the basin. The statistical downscaling model tested and verified using the observed daily data for twelve, six and three averaged arbitrary spatial weather stations as well as for a single weather station was used to predict the future climate scenarios. The results revealed that the mean annual daily maximum and minimum temperature and precipitation for twelve, six and three arbitrary spatial stations have revealed an increasing trend in the upcoming periods until the end of the century. In single station analysis, the trend itself has changed from increasing trend to decreasing trend in case of maximum and minimum temperature. In case of precipitation, no visible trend has been observed in case of single station analysis. Therefore, the variation in amount and distribution of precipitation and temperature among the four averaged spatial stations in the same study area might affect the water resources and agriculture of the basin and also instead of using a single weather station to predict future climate variables for a particular study basin, it is more reliable using averages of numerous spatial weather stations data.

An Implicit Scheme for Shallow Water Flow with Wet Dry Interface

A finite difference implicit scheme is presented in this paper for solution of the shallow water equations in one dimensional (1D) form. The present model has many advantages like, handling of discontinuous and complex bed topography, satisfying C-property (preservation of motionless water surface over a wet or dry bed) and capability of handling large value of temporal step etc. Another very important feature of the present model is that, no special treatment of the source vector of the governing equations is required here to deal with very less water depth. To investigate the performance of the present model in diverse situations, it is used to replicate four different problems of known analytical solution, and the model is found to be quite capable for varied situations.