Flow structures in dividing open channels: a review

The supply of water for human consumption starts with the abstraction of ‘raw’ water from various sources. Most of these facilities convey raw water by pumping it directly from rivers via lateral channels to nearby water treatment plants, but this is badly affected by debris and sediment clogging at the intake structures. Lateral intakes are actually special cases of river bifurcations, where the channel naturally divides into two different branches, each carrying part of the flow and sediment. Many researchers have completed studies on bifurcations/diversions to understand the behaviour of water flow and sediment transport. However, a complete understanding of the phenomenon, especially in relation to secondary flows and vortices, is lacking up to this day. In fact, if this can be overcome, it will greatly contribute to the fundamental study of hydrodynamics at asymmetric fluvial bifurcations as well as in optimal design of diversions. Thus, the distribution of water flow in both main and lateral channels requires further detailed investigation. A review of the current state of research is discussed in this paper, with the objective of identifying the grey areas and gaps specifically in the investigation of complex turbulent behaviour of flow structures in open channels with lateral diversions

Hybrid social force-fuzzy logic evacuation simulation model for multiple exits

One of the most important aspect of evacuation management system, when it comes to organizing a safer large- scale gathering is crowd dynamics. Utilizing evacuation simulation of crowd dynamics during egress, for planning efficient crowd control can minimize crowd disaster to a great extent. Most of the previous studies on evacuation models have been done over a discrete space which have neglected the uncertainty aspect of an agent’s decision making, especially when it comes to panic situations. This study proposes a model for evacuation simulation under uncertainty conditions in a continuous space via computer simulations. It will focus on developing an intelligent simulation model utilizing one of the artificial intelligence techniques which is fuzzy logic. Social Force Model will be taken as the base for basic agent motion. Membership functions such as distance from the exit, familiarity and visibility of the exit, density of crowd around the exit are incorporated in the fuzzy logic system to model the system. From our findings, it can be deduced that factors such as density, distance, and familiarity all considerably affect the time of evacuation of agents from the threat place. Indeed, uncertainty aspect influences agents’ decision making, thus affecting the result of evacuation time

Flow-3D CFD model of bifurcated open channel flow: setup and validation

Bifurcation is a morphological feature present in most of fluvial systems; where a river splits into two channels, each bearing a portion of the flow and sediments. Extensive theoretical studies of river bifurcations were performed to understand the nature of flow patterns at such diversions. Nevertheless, the complexity of the flow structure in the bifurcated channel has resulted in various constraints on physical experimentation, so computational modelling is required to investigate the phenomenon. The advantages of computational modelling compared with experimental research (e.g. simple variable control, reduced cost, optimize design condition etc.) are widely known. The great advancement of computer technologies and the exponential increase in power, memory storage and affordability of high-speed machines in the early 20th century led to evolution and wide application of numerical fluid flow simulations, generally referred to as Computational Fluid Dynamics {CFD). In this study, the open-channel flume with a lateral channel established by Momplot et al (2017) is modelled in Flow-3D. The original investigation on divided flow of equal widths as simulated in ANSYS Fluent and validated with velocity measurements

Discharge distribution in open-channel T-shape bifurcations: effect of a reduced side branch width

The primary challenge for river managers in handling open-channel bifurcations is the prediction of the discharge distribution to downstream branches. In this study, we aimed to summarize and complete the available database and empirical correlations for T-shape bifurcations at 90°, both in subcritical and transcritical flow regimes, in equal and reduced side branch width geometries. An experimental campaign generated a database of 668 new configurations in addition to 299 sets collected from the literature. The existing correlation for predicting the discharge distribution in the subcritical regime appears to be of limited agreement with these data, whereas a new empirical relationship significantly increases the accuracy and is useful for a side branch as narrow as a third of the main branch width. Regarding the free-recirculation transcritical regime, the present data validate the correlation proposed in 1967 for downstream branch ratios not tested by the authors. An approach was proposed to predict the flow discharge distribution for configurations without a priori knowledge of the flow regime

Temporal distribution of heavy rainfall for upper Klang catchment

Data from 4 pluviograph stations in the upper Klang basin were used to derive time distributions of heavy rainfall using the NOAA method. Rainfall cases for the temporal distribution analysis were selected from the annual maximum series usually used in the rainfall frequency analysis. Each case (i.e., maxima) was the total accumulation over a selected duration (1,6 ,12, 24 hour for this study). For each rainfall case, cumulative rainfall amounts were converted into percentages of the total rainfall amount at specified time increments. All cases for a specific duration were then combined and these rainfall cases were analysed separately, determining the percentage accumulated to 10, 20,30,40,50,60,70,80,90 and 100% of its total duration. For each duration, the percentage was determined by a percentage series of total rainfall, and the probabilities calculated. In order to obtain the values of rainfall based on above definition, linear interpolations were carried out between the probabilities and the immediately previous and subsequent probabilities. The temporal distribution curves for nine deciles (10% to 90%) were plotted in the same graph. Results show that first-quartile and second-quartile storms occurred most frequently with durations less than or equal to 12 hours; and first-quartile and fourth quartile storms most often had durations of 24 hours. Following the principles of Huff (1990), the temporal distribution curves derived in this study are recommended to be used for normal design as follows: • For 1 hour duration, it is recommended that second quartile relations be used to establish typical time distributions. • Time distributions for storms lasting 6 hours ,12 hours and 24 hours are most likely to conform to a first-quartile distribution. For most purposes, the median curves are probably most applicable to design. These curves are more firmly established than the more extreme curves, such as those for the 10% and 90% probability levels, which are determined from a relatively small portion of each quartile’s sample. However, the extreme curves should be useful when runoff estimates are needed for the occurrence of unusual storm conditions, such as typified by the 10% curves

Infilling streamflow data using HEC_HMS

A set of quality control streamflow data is always required in the planning, design and management of water resources projects. Although every effort has been made by the authority in the collection of complete and continuous hydrological data such as rainfall and streamflow, gaps and incomplete data sets with inadequate length are always encountered, as is always the case. These can be due to faulty field instruments, the occurrence of natural disasters and other reasons. Over the years, various techniques have been developed to infill the missing data, especially the streamflow data. These techniques include regression analysis ,rainfall runoff modelling and the use of artificial neural networks(ANN) data driven models. In this study, the HEC-HMS model is used to simulate long term daily streamflow of Sg Melaka. The process involved using recorded flow and rainfall data of 1989-1992 to calibrate the model and the model validation using records of 1985-1986. Results show that the model can be used to estimate the flows of Sg Melaka once properly calibrated. This is also shown in the results of flow duration curves. From this study, it can be concluded that missing flows of Sg Melaka can be infilled using the HEC-HMS moel and daily rainfall records in the basin. Streamflow records can be extended if complete rainfall records are available for periods where no streamflow records are available

Design rainfall temporal patterns for upper Klang catchment

Rainfall temporal patterns are needed as inputs for hydrologic models such as unit hydrograph or runoff routing method used in the derivation of flood hydrographs. The patterns adopted can have a major effect on the resulting flood computed. Short and long duration rainfall data are both required for different sizes of catchments to determine and locate the flood producing critical storms in flood estimation. Design temporal patterns with different durations are therefore also required for distributing the storm rainfall in flood calculations. Patterns for a large number of durations with reasonably short time intervals are needed by designers to reduce the need for interpolation and to maintain the accuracy in obtaining the peak of the hydrograph. In this study, pluviograph data for the Upper Klang Catchment with records of over 30 years are used to derive temporal patterns for 20 standard durations as per ARR87. Rainfall temporal patterns for the upper Klang were derived for rainfall durations from 10 minutes to 72 hours and for time intervals from 5 minutes to 4 hours. The patterns presented in this study demonstrate the use of Average Variability Method in deriving design rainfall temporal patterns for data of the Klang Catchment and the patterns derived can be used for design flood estimations for catchments in the same general region

Post COVID-19 river quality: challenges ahead!

MCO has been keeping humans locked in their homes-- which also means away from the nature. As the air quality improving due to less pollution caused by vehicles and factories; we might wonder does the situation goes the same for our river? What are the challenges in improving the quality of our river pre- and post-MCO? Lets find out and join us in this special webinar