Harinarayan Tiwari

Turbulence study in the vicinity of piano key weir: relevance, instrumentation, parameters and methods

This research paper focuses on the need of turbulence, instruments reliable to capture turbulence, different turbulence parameters and some advance methodology which can decompose various turbulence structures at different levels near hydraulic structures. Small-scale turbulence research has valid prospects in open channel flow. The relevance of the study is amplified as we introduce any hydraulic structure in the channel which disturbs the natural flow and creates discontinuity. To recover this discontinuity, the piano key weir (PKW) might be used with sloped keys. Constraints of empirical results in the vicinity of PKW necessitate extensive laboratory experiments with fair and reliable instrumentation techniques. Acoustic Doppler velocimeter was established to be best suited within range of some limitations using principal component analysis. Wavelet analysis is proposed to decompose the underlying turbulence structure in a better way.

Interaction between flow hydrodynamics and bed roughness in alluvial channel

The present study describes the methods of bed shear stress estimation, numerical estimate of velocity distribution and quadrant events on different hydraulic roughness. Quadrant events of velocity signify the contribution of velocity to generate shear. Experimental data sets of velocities were collected over bed with different hydraulic roughness. In the present work, a turbulent kinetic energy method is anticipated as more reliable to describe the bed shear stress in open channels. These data analysis express that the quadrant events associated with flow is influenced inherently by the bed roughness. Percentage distribution of first and fourth quadrant looks like a wine cup which is wider in the case of hydraulically smooth conditions and getting narrower as the bed roughness increased. It is also a sign of increasing randomness throughout the depth with increased roughness. It is found that at same relative depth for three different roughness conditions, eddy motions are displaying more uncertainty for hydraulically rough condition. Increase in bed roughness augments randomness of Reynolds stress at relative depth 0.05–0.4. The analysis relies on relative depth, which can for imply the local phenomenon and this local phenomenon of velocity on different bed roughness condition was also investigated in this paper.

Trend analysis using discrete wavelet transform (DWT) for long-term precipitation (1851–2006) over India

ABSTRACT This study is an attempt to determine the trends in monthly, annual and monsoon total precipitation series over India by applying linear regression, the Mann-Kendall (MK) test and discrete wavelet transform (DWT). The linear regression test was applied on five consecutive classical 30-year climate periods and a long-term precipitation series (1851–2006) to detect changes. The sequential Mann-Kendall (SQMK) test was applied to identify the temporal variation in trend. Wavelet transform is a relatively new tool for trend analysis in hydrology. Comparison studies were carried out between decomposed series by DWT and original series. Furthermore, visualization of extreme and contributing events was carried out using the wavelet spectrum at different threshold values. The results showed that there are significant positive trends for annual and monsoon precipitation series in North Mountainous India (zone NMI) and North East India (NEI), whereas negative trends were detected when considering India as whole. EDITOR A. Castellarin ASSOCIATE EDITOR S. Kanae

Rainfall erosivity factor for India using modified Fourier index

Spatio-temporal average rainfall erosivity factor map has been generated for India. This study on rainfall erosivity makes use of 101 years monthly rainfall data and 52 spatial points. The results presented here provide the much needed guidance to remove ambiguities regarding the rainfall erosivity factor in the Indian context. This study has a variety of applications in erosion prediction technology, such as Universal Soil Loss Equation or Revised Universal Soil Loss Equation, or in rainfall-data-deficient regions. In-depth observations can develop a deeper understanding of rainfall variation to estimate the erosivity factor. Rainfall erosivity factor map can facilitate agriculturists and soil conservationists to identify rainfall erosivity potential at diverse locations, and thereby apply obligatory safety measures to minimize soil erosion. The rainfall erosivity factor map has been used to provide a more rational value of the average rainfall erosivity factor covering India, in regions where rainfall distribution patterns is of the same order.

Nonlinear and entropic velocity distribution in open channel

Abstract The present study describes the nonlinear vertical velocity distribution in an open channel (with and without hydraulic structure). Conventionally, velocity distribution is based on shear velocity normalization. In this study, maximum velocity has been applied for normalization. Von-Kármán logarithmic distribution (based on Kármán constant), its proposed analogous models, and entropy-based nonlinear velocity distribution have been compared for both the cases (with and without hydraulic structure). An entropy-based nonlinear velocity profile model has been also suggested to describe the velocity field in open channels. The suggested approach has been validated by means of controlled laboratory tests, executed in flume under steady flow conditions and at hydraulically smooth surface. The higher equivalence between the estimated velocity profiles using entropy and the observed ones. Entropy model has found best replicating model with respect to other four models (based on analogous of Prandtl–von Kármán model with the use of maximum velocity parameterization) but it also acquired difficulties regarding its higher number of numerically calculated coefficients. Power analogous model (based on maximum Reynolds number) and entropy model has been suggested as overall robust velocity distribution model and it is performing equally for both (with and without hydraulic structure) conditions.

Non-parametric characterization of long-term rainfall time series

The statistical study of rainfall time series is one of the approaches for efficient hydrological system design. Identifying, and characterizing long-term rainfall time series could aid in improving hydrological systems forecasting. In the present study, eventual statistics was applied for the long-term (1851–2006) rainfall time series under seven meteorological regions of India. Linear trend analysis was carried out using Mann–Kendall test for the observed rainfall series. The observed trend using the above-mentioned approach has been ascertained using the innovative trend analysis method. Innovative trend analysis has been found to be a strong tool to detect the general trend of rainfall time series. Sequential Mann–Kendall test has also been carried out to examine nonlinear trends of the series. The partial sum of cumulative deviation test is also found to be suitable to detect the nonlinear trend. Innovative trend analysis, sequential Mann–Kendall test and partial cumulative deviation test have potential to detect the general as well as nonlinear trend for the rainfall time series. Annual rainfall analysis suggests that the maximum changes in mean rainfall is 11.53% for West Peninsular India, whereas the maximum fall in mean rainfall is 7.8% for the North Mountainous Indian region. The innovative trend analysis method is also capable of finding the number of change point available in the time series. Additionally, we have performed von Neumann ratio test and cumulative deviation test to estimate the departure from homogeneity. Singular spectrum analysis has been applied in this study to evaluate the order of departure from homogeneity in the rainfall time series. Monsoon season (JS) of North Mountainous India and West Peninsular India zones has higher departure from homogeneity and singular spectrum analysis shows the results to be in coherence with the same.

Emerging Methodologies for Turbulence Characterization in River Dynamics Study

River engineering study consists of large variation in time and spatial scales. Timescale of river varies from years to second, and, similarly, the variation of spatial scales is from kilometre to millimetre. Spatial scales can be divided into river basin scale and hydraulic scale, and temporal scale can be divided into hydrological, hydraulic and turbulence. Each spatio-temporal scale has fixed contextual uses. In general, turbulence plays the most key role with respect to the influences that rivers have on their channels and beds. Turbulent flows are characterized by asymmetrical patterns, irregular behaviour and the existence of various spatio-temporal scales. To extract better turbulence events and flow structure using point velocity measurements (Eulerian approach) in river, we are proposing generalized three-dimensional octant events instead of conventional two-dimensional quadrant events. Beyond that, we characterize the transitional probability of octant event occurrence in the case of unsteady flow condition. In the field, there is the assumption of steadiness of the flow under high unsteady conditions. Basically, river discharges and all the associated processes are physically unsteady, and river channel flows are typically non-uniform. In this chapter we are mainly discussing the new emerging methodological aspects to characterize the river turbulence using state-of-the-art technology. In this chapter, some of the major issues and developments linked with river dynamics and turbulence study have also been discussed with two case studies. The case studies have been presented and discussed using experimental data and their interpretation in light of river dynamics. The study has significant importance because the turbulent motion is the natural state of river engineering problems.

Noise in the velocity measurements and boundaries effect in an open channel with Piano Key Weir

Abstract An Acoustic Doppler Velocimeter (ADV) system, with digital signal processing has been used to measure the longitudinal, transverse, and vertical velocity components in three‐dimensional, fully developed open‐channel flow with transversely placed Piano Key Weir (PKW). Simple experiments were conducted to deduce the influence of boundaries on noise occurrence. Both the longitudinal boundary (PKW) and vertical boundary (channel bed) affect noise. Magnitude of noise has been found to be increasing near both the boundaries. Consequences of noise on the first- and second-order velocity parameters have also been estimated. Results show that there is existence of higher correlation between noise and second-order velocity (turbulence) than first-order velocity. After the noise removal from the data-sets, the reduction in the magnitude for the second-order velocity is found up to 80%. Magnitude of reduction is also dependent on the distance from the hydraulic structure. Analyses of data-sets in the horizontal plane indicate presence of noise (i.e. higher uncertainty) below the relative depth 0.3. Where, relative depth is defined as the ratio of point depth of measurement to total flow depth.

Hydropolitics in Transboundary Water Conflict and Cooperation

Water is a fundamental human need and key to economic development. Since the beginning of civilization, people have faced problems associated with river and freshwater sharing. To add on to the precarious situation, most of the freshwater rivers are transboundary rivers, i.e. they cross at least one political border, either a border within a nation or an international boundary. Water politics, commonly known as hydropolitics, are politics affected by the availability of water and water resources, which play an important role in transboundary water management. Hydropolitics relate to the ability of geopolitical institutions to manage shared water resources in a politically sustainable manner, i.e. without tensions or conflict between political entities. As the pressures of population and economic growth increase, water resources are under increasing stress. As the stress on water resources increases, the risks associated with the management of transboundary rivers increase exponentially given the hegemonic disparities of the riparians. This gives rise to risks of conflict while generating opportunities of cooperation which can be analysed with the help of risk-opportunity index developed using fuzzy synthetic evaluation technique proposed by Rai et al. (J Hydrol 519:1551–1559, 2014). It has been proposed to formulate a hydropolitical sustainability index (HypSI) keeping in view the circles of blue sustainability (blue indicates water in this chapter) which considers the social desirability, political legitimacy, economical viability, environmental sustainability and technical feasibility aspects of shared water resources.

Empirical and Mathematical Modeling of Head and Discharge Over Piano Key Weir

Increasing demand of energy and limited conventional energy sources (coal, petroleum, natural gas, etc.) initiated the alternative thinking of hydropower projects. Due to easy and high head availability in mountainous regions, India has immense potential of hydropower. Spillways are the one of the important elements of hydropower projects. Spillways are generally used in the hydropower to spill the excess amount of water. Piano Key Weir is the ungated spillway structure generally used to get high discharge intensity under limited width. This study formulates the empirical relationship between the head and discharge over Piano Key Weir. This study also evaluates the weir coefficient values of Piano Key Weir through HEC-RAS modeling.