ABSTRACT This article presents comparison of Artificial Neural Networks (ANNs) and Hydrologic Engineering Centre-Hydrologic Modelling System (HEC-HMS) model for rainfall-runoff (R-R) process. Aim of the present work is to forecast runoff one day ahead at Shivade station of Upper Krishna Basin, India, using 17 years of daily rainfall and discharge data. The R-R modelling can be exercised using various traditional methods which generally require exogenous data in the form of basin parameters. Unavailability of such data becomes major impediment in applying these models at many basins. In such situations, soft computing techniques like ANNs have been extensively applied to model R-R process. Though ANN is now an established tool in hydrology, compared to HEC-HMS, its results are viewed with suspicion owing to its data-driven nature rather than a model-driven nature. In this study, ANN model performed reasonably well, with a higher correlation coefficient (0.87) and the lowest Root Mean Square Error (136.28 m3/s) when compared with HEC-HMS (0.76, 139.8 m3/s) respectively. Novelty of the present work lies in model development using restricted basin data. Both models showed less accuracy in predicting extreme events. Finally, it is concluded that ANN model can be used as a supplementary technique along with HEC-HMS for this phenomenon.

ABSTRACT The present review paper offers the learning of steep boulder beds, and other dynamic topographic conditions, for deep understanding of scour catastrophes and recognizing absolute measures to link this key research gap. Though many models exist for silt, sand, and small size coarser bed materials, but no certain model is available universally for scour estimation in bed material above this size. This review paper claims for amplified research into boulder beds, steep bed slopes and dynamic river and stream conditions. Also, the present work highlights the requirement for evolving absolute criteria for such geographical weaknesses. The importance of taking into account complex and dynamic environments in the study of scour failures is also emphasized. Besides, the instant review paper discusses the scientific advancement for more precise and safe predictive models for scour, to discover a guiding tool to a strategy that augments well for the health of hydraulic structures to synchronize with the fundamental philosophies of long-term safety, economy, and functionality.

ABSTRACT In this work, a desilting chamber of the Kholongchhu Hydroelectric Project, Bhutan, was used to test the settling efficiency using physical model and Flow-3D, a three-dimensional computational fluid dynamics (CFD) software. As sediment particles greater than a particular size can cause erosion and damage to underwater machinery, the estimation of settling efficiency is essential during the planning, designing and implementation phases of hydropower projects. These studies were carried out using 12 distinct particle sizes (0.25 mm, 0.24 mm, 0.23 mm, 0.22 mm, 0.21 mm, 0.2 mm, 0.19 mm, 0.18 mm, 0.17 mm, 0.16 mm, 0.15 mm and 0.1 mm). The settling efficiency for the particle size 0.2 mm obtained by physical model and CFD simulations were 92.2% and 93.6%, respectively.

ABSTRACT Hydraulic structures at river crossings, especially culverts in ephemeral streams, are susceptible to damage during floods due to culvert scour, caused by various factors. It is essential to implement preventive measures to ensure the longevity and safety of these structures. This paper aims to present a comprehensive review of the factors influencing local scour downstream of culverts, offering a thorough understanding of this phenomenon. Consequently, a thorough review of the experimental studies and their corresponding outcomes documented in the literature is conducted. The analysis is divided into two main sections. The first section discusses dimensional analysis, while the second section delves into the key parametric factors affecting scouring, including flow regime, scour time, and experimental studies documented in the literature. The methods used in the second section are categorized into three distinct categories: channel and culvert dimensions, flow conditions, and sediment characteristics. This article not only provides a platform for researchers to conduct laboratory research but also assists hydraulic engineers in identifying crucial factors in culvert design.

ABSTRACT The accurate prediction of scour depth in culverts is crucial to ensure public safety and due to the uncertainties in classical empirical/deterministic equations, it remains challenging. This study presents new ensemble multi-models to predict scour depth and quantify model bias and uncertainty. In this study, culvert scour was predicted by gene expression programming (GEP) and least square support vector machine (LSSVM), firstly based on dimensionless parameters. In the multi-model ensemble strategy, four ensemble approaches, namely SM, WM, LSSVM, and BMA were applied. The LSSVM showed overall best skill for the multi-model approach, that reduced the error by 61.3% and increased the coefficient of determination by 52.1%. The results showed the proposed approach can satisfy the requirements of simplicity, applicability, and accuracy at the same time. For application purposes, we provided a simple code to obtain scour depth with great accuracy using LSSVM. BMA and LSSVM were used to quantify the scour culvert uncertainty. The results of the uncertainty analysis showed that the LSSVM predicts scour depth quite well and generates high-quality prediction intervals. The results revealed that a multi-model ensemble strategy improved accuracy, certainty and reliability for culvert scour compared to empirical equations.

ABSTRACT Balancing between sediment removal discharge and dam reservoir storage loss considering river environmental impact is of major and practical concern. The paper presents indices for evaluating the sediment removal performance of a Vertical Multi-hole Hydrosuction System (VMHS) in view of environmental impacts. A new hole arrangement on the vertical pipe of VMHS was experimentally examined. The compiled data of the temporal variations of the sediment concentration and the cumulative volume of removed sediment demonstrated that the arrangement of the holes on the vertical pipe of VMHS has profound impact on the speed of sediment removal and on the reservoir water loss. The high concentration of the outflow from the reservoir, however, might affect the downstream water course environment. The proposed indices could be applied to determine the proper duration for terminating the hydrosuction process in order to obtain a balance between the storage capacity and the downstream water course environment.

ABSTRACT Mass transfer-based models are among the extensively applied reference evapotranspiration (ET o ) estimation approaches that have been proven to provide reliable estimates under certain climatic and geographical conditions. A major issue with such approaches is the high variations in wind speed time series, which is a governing meteorological parameter in mass transfer-based models. few studies have focused on applying wavelet transform as a robust pre-processing technique for ETo estimation. A major question with coupling wavelet transforms with soft computing methods would be the proper choice of the wavelet function, vanishing moments and the decomposition levels. The present study aims at assessing different wavelet functions coupled with boosted regression tree (BT) models, i.e. wavelet-BT (WBT), in estimating ET o values (through mass transfer parameters) in both coastal and island regions, where it is supposed that wind speed variations are affected by sea–inland interactions and so has the sharp variations (unlike ET o ). The obtained results showed that the coupled WBT model could improve the single BT model results to a great extent, and meanwhile, the Daubechies wavelet function with six vanishing moments provided the most accurate results in all the locations. Further, the best simulation outcomes with each wavelet function were obtained when the maximum possible decomposition level was used with each function.

ABSTRACT This research work proposes a combined method for mapping flood loss in catchment scale in which direct rainfall modelling and fuzzy approach are linked. The direct rainfall modelling was carried out using HEC-RAS 2D in which rainfall event hyetograph was defined as the boundary condition, and infiltration layer and roughness layer were other main inputs of the model. The fuzzy loss model was developed to assess direct-tangible damages of the flood in which expert opinions were applied to generate verbal fuzzy rules of flood loss. In this model, depth and velocity are inputs and normalized flood loss (between 0 and 1) is output. The results of the direct rainfall model and the fuzzy loss model were combined to generate loss map using python scripting in geographical information system. The output of direct rainfall model was verified based on recorded depths at downstream hydrometric station in which the Nash–Sutcliffe efficiency (NSE) and root mean square error (RMSE) were applied as the evaluation indices. Due to acceptability of indices (NSE = 0.75, RMSE = 0.83 m), the direct rainfall model was reliable. Maximum flood loss was 0.91 in the case study. Using the proposed approach is recommendable for to improve flood damage assessment in the catchments.

ABSTRACT Transitions are needed in hydraulic structures which are flumed. In expanding transitions, flow separates from the boundary if the angle of divergence exceeds about 5 degrees. The present paper gives an insight into the turbulence effect and energy loss in expanding transition with small angle of divergence. In wide angle expansion, flow separates from the boundary resulting in highly non-uniform velocity distribution at the exit of expansion resulting in erosion of down stream channel. Author performed experiments to control separation of flow in wide angle expansion. The paper discusses about the devices used by the author to control separation in wide angle expanding transition.

ABSTRACT Due to complex nature of the riverbank erosion and owing to action of wide variety of forces on the particles, it is an uphill task for the researchers to find a general approach to riverbank failure mechanism. Here, a planar failure-block of right-angled trapezoidal shape spanning to the tension crack has been considered. Transformation of inter-particle microscopic forces into macroscopic forces has been made to analyse the stability of the block. Stability of the failure block is a function of the bank erosion rate in terms of the escape velocity. Moreover, varying free surface water level has been investigated to study the dynamic behaviour of the bank. With the increasing number of base particles in the tension crack from 10 to 100, escape velocity increases by 8.47% as the water level rises and 10.74% as it falls. Similarly, the increase in escape velocity with free surface water level height from 0 to full height of the tension crack is 39.4% as the water level rises and is 48.4% as water level falls. Rising water level increases hydrostatic confining pressure force, which is a resistive force. This increases the escape velocity continuously leading to greater stability of the mass.