Vertical slot fishways are critical for enhancing river connectivity and facilitating the upstream migration of fish. Of particular significance are resting pools – these are essential components where fish can recuperate and restore energy during their journey. Despite their importance, research regarding the impact of resting pool gradients (RPGs) on the overall performance of fishways remains limited. In this study, three-dimensional simulations were used to analyse a 96-stage vertical slot fishway and comparative analyses of flow field distributions were conducted across three different RPGs under typical operational water conditions (backwater profile, drawdown profile and uniform flow). The findings indicate that the RPG significantly influences the overall water surface profile in the fishway. A RPG of J3 = 0% minimises both overall and localised flow velocities and turbulent kinetic energy throughout the fishway. This configuration allows higher conventional pool gradients, thereby reducing the structural requirements of the fishway system.

The increase of impermeable surface is inversely proportional to infiltration, thereby increasing flooding. The lack of study on the role of green open space (GOS) in Jakarta’s urban hydrology was identified as a critical factor that discounted the role, and the target of GOS in supporting urban sustainability has not been achieved in Jakarta. The aim of this study was to fill this research gap by analysing the potential of GOS in minimising runoff through optimisation of its function as a storage area for water reserves. Data analysis was done quantitatively using Horton, Thornthwaite–Mather and Ffolliot equations. Results showed that recharge and discharge areas play a critical role in determining optimal water reserve locations, and soil texture is an important indicator that affects runoff. In addition, the proportion of GOS (as indicated by its fulfilment target in urban planning) affected an area’s chances of inundation and flooding. This study concluded that the hydrological function of GOS could be optimised through the sponge city system with GOS and blue open space integration using bioretention.

Accurately predicting flood-induced local scour around complex reinforced concrete (RC) piers remains challenging, as many existing studies rely on simplified single-column assumptions. Although recent models have sought to address complex pier geometries, they frequently fail to incorporate sufficiently influential parameters, thereby limiting their predictive accuracy and applicability. In this study, three advanced machine learning (ML) techniques – Gaussian process regression, ensemble learning and an artificial neural network (ANN) – integrated with Bayesian optimisation for hyperparameter tuning were employed. A dataset of 336 clear-water experiments, encompassing a wide range of hydraulic and structural conditions, was compiled for model training and validation. Model performance was evaluated using ten-fold cross-validation and a test set. Among the models, the ANN demonstrated the highest performance on the test set, achieving a root mean square error of 0.134, mean absolute error of 0.093, mean absolute percentage error of 17.3% and a coefficient of determination of 0.871, significantly outperforming existing empirical formulas and previously established ML approaches. Additionally, Shapley additive explanations were used to interpret feature contributions, revealing that flow-related parameters had the greatest influence, followed by sediment characteristics and structural geometry. These findings provide both accurate predictive tools and physical insight into the scour process around complex RC piers.

The problems of artificial groundwater recharge in desert areas include low rainfall and limited water resources, deposition of large amounts of sediment and high evaporation rates. In this study, an attempt has been made to mitigate these issues by introducing a new method of artificial recharge specifically designed for desert areas. For this purpose, a physical model was constructed. Through multiple experiments, which involved varying parameters such as input flow rate, materials used to construct the unsaturated environment, and changes in the depth and width of the infiltration trench, a new artificial feeding method was presented. An empirical equation was also proposed, aiming to estimate the infiltration capacity from the trench. Examination of nine earthen channels showed that the Davis and Wilson, Molesworth, Moritz and Ingham equations are not accurate for estimating water leakage in different areas. To solve this problem, the researchers adjusted the equations with regional correction coefficients. The results showed that the equation presented with the features considered in it has a significant accuracy in estimating the amount of leakage compared to real data and can also be used in different areas.

When constructing underground engineering projects within water-rich strata, the adverse effects of high ground stress, high water pressure and excavation disturbance are significant, and can easily lead to disasters such as instability of the surrounding rock. There is an urgent need to study the stability of surrounding rock in deep underground engineering works under fluid–solid coupling. This study develops a three-dimensional finite-difference-based fluid–solid coupled non-linear model incorporating initial pore water pressure and excavation progress. The evolution of the multi-field response of surrounding rock during excavation under diverse pressure conditions is studied. The findings demonstrate that as initial pore water pressure rises, the plastic zone progressively extends deeper into the surrounding rock, while the deformation of the surrounding rock, the seepage velocity and the influence range of groundwater seepage all increase. The maximum seepage velocity of groundwater reaches 5.1 × 10−6 m/s. When excavation advances to 2 m, the stress concentration area is mainly concentrated in the corner area where the sidewall and the vault intersect and the corner area where the sidewall and the arch bottom intersect. When the footage is 4 m, the deformation of surrounding rock increases significantly. The vault displacement surges abruptly from 1.7 to 8.0 cm, while the arch bottom displacement rises linearly from 2 to 7 cm. The research results can provide some reference and guidance for similar underground engineering.

Seepage around river structures increases the risk of sediment removal and deeper scour, potentially compromising the stability of structures such as spur dykes. These spur dykes are installed along riverbanks to redirect water flow, control erosion and stabilise riverbeds. This study aimed to investigate the effects of three different combinations of permeable and impermeable spur dykes on bed morphology and scour progression around T-shaped spur dykes with seepage and no seepage conditions. Set A comprises three impermeable spur dykes in series, while set B (60%, 0%, 0%) and set C (60%, 30%, 0%) feature combinations of permeable and impermeable spur dykes with different percentages allocated to each spur. The results revealed significant reductions in the maximum scour depth at the initial spur dyke under conditions without seepage when permeable sets B and C were used; the values were 37.6% and 55.2%, respectively, lower than those for impermeable set A. When considering VS1, applying permeability set B leads to a reduction of 38.5%, and using permeability set C results in a reduction of 42.4% compared to impermeable spur dykes (set A). The findings indicated that the most effective combination for determining spur dyke permeability was set C, while the most substantial scour depth was produced in spur dyke set A.

The local scour around bridge piers poses a significant threat to the stability of coastal and fluvial structures. Although extensive research has been conducted on scour under unidirectional currents or waves, studies on bidirectional tidal flow remain limited. In this study physical modelling is employed to investigate scour around a complex pier (column, pile cap and pile group) under bidirectional tidal and unidirectional flow in a flume. A terrain scanner is used to obtain bed elevations around the pier. Local scour holes and sand ripples induced by bidirectional and unidirectional flows are discussed. The results reveal that bidirectional flow produces symmetrical scour holes with reduced maximum depths owing to periodic sediment backfilling. The scour depth and morphology are highly sensitive to the flow attack angle, with 45° causing the most severe erosion. These findings underscore the importance of incorporating tidal directionality and pier geometry in scour prediction models for safer design in tidal environments.

Rock weirs are low-head hydraulic structures commonly used in river training. The flow over rock weirs can dislodge rocks to cause structural failure, but studies investigating the scale effects in this phenomenon are limited. Two flume tests (i.e. large-scale and small-scale flume tests) with fixed bed were conducted and combined as a scale series to investigate this topic. The process and limit of rock dislodgement from the rock weir in each flume are compared, and the causes for the scale effect are discussed. The results show that: (a) for partially submerged conditions, the over-flow regime corresponding to the incipient rock dislodgement varies with flume scale, leading to different rock dislodgement processes; (b) the limit representing the incipient or a few amounts of rock dislodgement agrees well for different flume scales, while the limit related to weir failure in a large-scale flume is lower than that in a small-scale flume; (c) the scale effect of rock dislodgement from rock weirs is attributed to the fact that geometrically similar rock weirs often exhibit dissimilar void ratios. To minimise the scale effect in flow-induced rock dislodgement of rock weirs, effective control of the similarity in weir void ratio needs to be considered.