Jazuri Abdullah

Flood flow simulations and return period calculation for the Kota Tinggi watershed, Malaysia

The City of Kota Tinggi in Malaysia was under more than 5 m of water during the floods in December 2006 and January 2007. The watershed received between 280 and 530 mm of rain in 4 days. These extreme events occurred 3 weeks apart and caused extensive damages. The application of the fully distributed twodimensional model two-dimensional runoff, erosion and export (TREX) to simulate these events and the estimation of the return period of such extreme events are the main objectives of this study. The model performance was very good based on the relative percentage different (3.7%), percent BIAS (overestimated the volume by 1.5%) and Nash–Sutcliffe efficiency coefficient (0.8). The TREX model is successful in simulating extreme flood events. The December 2006 rainstorm event at Kota Tinggi is extremely rare, and this multiday rainstorm had an estimated return period greater than 2000 years. The analysis of the return period shows that multiday rainstorms occur more frequently than single-day events. In addition, we produce a flood threshold graph by integrating both the hydrological modelling process using TREX and the theoretical formulation of return period. The proposed flood threshold graph is useful in the estimation of the amount of accumulated rainfall from multiday rainfall that can cause flooding on a large watershed like Kota Tinggi.

Establishment of jet index ji for soil erodibility coefficients using jet erosion device (JEd)

Soil erodibility has been identified as one of the major factors that govern threshold of resistance to erosion. Accurate measurement of soil erodibility in the field is indeed important for the determination of critical shear stresses. Critical shear stress is the stress that initiates particle movement that promotes shifting of the bankline. An attempt to establish soil erodibility parameters was successfully carried out using a newly fabricated Jet Erosion Device (JEd) based on soil properties. Soil erodibility coefficients are introduced to represent the erodibility of the soils under study. Statistical test is used to confirm the validity and accuracy of the proposed technique. Field data measurements were carried out on 3 rivers. Empirical models were developed using data from Selangor River and validated using data from Bernam and Lui rivers and other secondary river data. Analyses have shown high correlations and the parameters were further examined and analysed for the development of a predictive relationship for Ji. The most accurate model was selected based on the adjusted R 2 , standard error of the estimate and discrepancy ratio to illustrate its significance. Selection of the predictive variables was based on their ability to explain the variation of J i. The models established could significantly reduce the cost, time and usage of water supply for field data collection using JEd.

Salinity Velocity Pattern in Estuary Using PIV

Estuaries are bodies of water along the coasts that are formed when freshwater from rivers flows and mixes with saltwater from the ocean. The mixing process in estuary is due to the forces that forced the freshwater from river to interact with saltwater at the ocean. Thus, it will give effect to the mixing properties of the estuary. The objective of this research is to analyze the salinity mixing pattern using Particle Imaging Velocimetry (PIV). A laboratory investigation was conducted in a Perspex channel to observe the mixing process in estuary. The images of the mixing process had been captured using the PIV system. Five parameters had been analyzed: Reynolds Stress, Turbulence Intensity, U for speed, V for velocity, and Vorticity using Matlab. The results show that two layers of water had been established inside the Perspex channel where saltwater had been observed to be at the bottom of the channel due to difference in density between freshwater and saltwater. This showed typical salt-wedge estuary characteristics.

Detection and Transportation of Nutrients and Pathogenic Bacteria in Kerayong River Water

Water is one of the most important sources of human life. Rainfall is abundant source that can provide water for human consumption. However, the clean water source cannot be relished, as a result of pollution caused by humans. Development and modernization cause water to become filthy and not suitable to be used directly and require rigorous treatment. Kerayong River that passes through residential and industrial area in Kuala Lumpur also became a victim of water pollution. 6 sampling points along the Kerayong River in this study showed the high rate of ammoniacal nitrogen and phosphorus in the river water, which is 6.92–10.83 mg/L and 2.22–3.53 mg/L, respectively. The presence of nitrate and nitrite concentration can also be detected from 0.09–0.22 mg/L to 0.05–0.17 mg/L, respectively. Pathogenic bacteria such as Salmonella, Shigella, E.coli, and Pseudomonas aeruginosa were detected in concentrations up to 173 cfu/ml in the river water, overcoming the limits. Although only in sampling points 1–4 could detect Vibrio spp. with low concentration, but it still needs to be concerned. Overall, the river water is not suitable for use directly without going through the proper water treatment process.

Estimation of Peak Discharges Using Flood Frequency Analysis and Hydrological Modeling System

This study presents the methodology to estimate peak discharges using flood frequency analysis (FFA) and hydrological modeling system (HMS). FFA method was performed using two distribution functions, i.e., Gumbel’s extreme value distribution (Gumbel’s) and lognormal (LN) distribution, while HMS was carried out using the Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS) software. Long and reliable daily streamflow and rainfall data (i.e., 50 years) recorded at Sungai Rinching, Selangor, were used. Goodness-of-fit test indicates that the chi-square (χ2) values for Gumbel’s and lognormal distributions are 1.952 and 7.976, respectively, which are significantly less than the \({\upchi}_{\alpha ,v}^{2}\) value of 9.488. However, Gumbel’s is chosen to represent the distribution of annual maximum daily streamflow because the χ2 test value was much lesser as compared to lognormal distribution. The calibration and validation processes were carried out to test the suitability of HEC-HMS software to simulate the streamflow of Sungai Rinching. The relative percentage difference (RPD) estimated for peak discharges from these processes was between 3 and 6 %, and maximum lag times were only 1 h. These results indicate that the model performance is very good. The peak discharges for several average recurrence intervals (ARIs), i.e., 2, 5, 10, 20, 50, and 100 years estimated using FFA and HMS, were also compared. Results show that the peak discharges estimated using HMS for all ARIs (except 2 years) are comparable to the values given by FFA, and the given percentage differences are between 2.7 and 12.2 %. This finding indicates that HEC-HMS may be used as a tool in simulating the daily streamflow and estimate the annual daily maximum streamflow of several ARIs at Sungai Rinching.

Centerline Bed Elevation Profile of Sand Bed Channel due to Bar Formation

Numerous data on bar formation have been accumulated yet the methods to predict bar geometry especially bar height are still insufficient. Objectives of this study to determine the trend in term of a significant difference of centreline bed elevation profile along the longitudinal distance. This can be investigate by carried out an experimental work in an erodible sand bed channel using a large-scale physical river model. The study included the various hydraulic characteristics with steady flow rates and sediment supply. An experimental work consists of four matrices of flow rate and channel width with other variables namely grains size and bed slope were kept constant. Analysis have included the discussion on a significant difference of centreline bed elevation profile along the longitudinal distance. As a conclusion the higher velocity in the smaller channel width have induced erosion of the banks that resulted in elevation increase while the larger flow rates have contributed to higher elevation.

Keynote: Analysis of Extreme Floods in Malaysia

This article reviews some of the recent advances in the analysis of extreme flood events in Malaysia. First, a detailed analysis of daily rainfall precipitation measurements leads to new understanding regarding Malaysian monsoons: the conditional probability of rainfall steadily increases as a function of the number of successive rainy days. The probability of multiday rainfall events has also been analyzed using stochastic models like DARMA(1,1) to demonstrate lower periods of returns of large precipitation amounts for rainfall events between 4 and 12 days. Advances in numerical modeling of surface runoff using the TREX model allowed improved simulations of large floods when considering rainfall amounts between the 2- and 100-year events and the PMP for extreme floods on both small to large watersheds in Malaysia. Examples on Lui, Semenyih, and Kota Tinggi have also been possible with GIS data at 30–90 m resolution. The recent floods of the Kota Tinggi and Muda River are also briefly discussed. Finally, a brief overview of the DID River Management Manual is also presented.

Hydrological Modeling in Malaysia

Hydrological modeling in Malaysia using two-dimensional fully distributed and physically based model is relatively new. Basic guidelines in choosing model dimensions (i.e., 1D, 1D–2D, 2D, and 3D) are discussed. The application of 3D model will give more accurate results if the groundwater movement is considered but requires more time to simulate and prepare input data. However, the 1D model is less accurate in representing the real topography of the study area, even though requires short time to simulate. This chapter also gives an overview about the hydrological modeling in Malaysia which ranges from 1D to 3D. Several researches on hydrology using different model were reviewed. The success of each model will be highlighted.