Self-Cleansing Urban Drain Using Sediment Flushing Gate Based On Incipient Motion

Sediment deposition in urban open concrete storm drain has caused many adverse effects to the drainage system such as flash flood and environmental pollution. This study aimed to provide recommendations for the purpose of sedimentation mitigation in urban open concrete storm drain. To understand the physical characteristics of sediment deposition; sampling was taken from 57 locations in Kuching city, surrounding towns outside Kuching city and Penang consisting of residential, commercial and industrial areas and subjected to sieve analysis. Results showed that the samples were mainly inorganic and noncohesive with sand as the major component followed by gravel and silt and clay for most of the samples. To improve the design criteria, incipient motion experiments were conducted in a 0.6 m wide flume for sediment with 50 d sizes of 0.81 mm, 1.53 mm 4.78 mm. Combining the results from the current incipient motion experiments with the results from an earlier researcher for a 0.3 m wide flume, multiple linear regression were performed and the best equations for each of the critical shear stress and critical velocity approach were developed. A design chart relating the self-cleansing design relationship between drain minimum slope with the design minimum flow rate and the respective standard drain size was also developed. To further improve the self-cleansing capability of open concrete storm drain, a tipping flush gate was designed and installed on site at Taman Pekaka, Nibong Tebal, Penang and subjected to monitoring for four months between 14th November 2012 and 15th March 2013

Drought and climate change assessment using Standardized Precipitation Index (SPI) for Sarawak River Basin

Severe droughts in the year 1998 and 2014 in Sarawak due to the strong El Nino has impacted the water supply and irrigated agriculture. In this study, the Standardized Precipitation Index (SPI) was used for drought identification and monitoring in Sarawak River Basin. Using monthly precipitation data between the year 1975 and 2016 for 15 rainfall stations in the basin, the drought index values were obtained for the time scale of three, six and nine months. Rainfall trend for the years in study was also assessed using the Mann–Kendall test and Sen’s slope estimator and compared with the drought index. Findings showed that generally there was a decreasing trend for the SPI values for the three time scales, indicating a higher tendency of increased drought event throughout the basin. Furthermore, it was observed that there was an increase in the numbers of dry months in the recent decade for most of the rainfall stations as compared to the previous 30 to 40 years, which could be due to climate change. Findings from this study are valuable for the planning and formulating of drought strategies to reduce and mitigate the adverse effects of drought

Monitoring Drought Using the Standardized Precipitation Index (SPI) in Sarawak River Basin

Drought is hard to be detected and monitored. Severe droughts in the year 1998 and 2014 in Sarawak due to strong El-Nino has impacted the water supply and irrigated agriculture, In this study, the Standardized Precipitation Index (SPI) was used for drought identification and monitoring in Sarawak River Basin. Using monthly precipitation data between the year 1875 to 2016 for 15 rainfall stations in the basin, the drought index values were obtained for the time scale of 3, 6 and 9 months. The findings show that generally there were a decreasing trend for the SPI values for the there time scales, indicating a higher tendency of increased drought event throughout the basin. Findings from this study are valuable for the planning and formulating of drought strategies to reduce and mitigate the adverse effect of drought

Sediment deposition characteristics of urban concrete drains in Kuching City, Sarawak, Malaysia

Sediment deposition in drains has been found to be one of the major causes of flooding in urban areas. In order to design an effective removal mechanism, an understanding of the characteristics of the sediment deposition is needed. This paper highlights the results of sediment size characteristics analysis done on sediment samples collected from concrete drains in Kuching city, Sarawak, Malaysia. A total of 30 sediment samples from 10 urban locations (4 residential areas, 5 commercial areas and 1 industrial area) were collected and subjected to sieve analysis. Results from sieve analysis had shown that the major component of the sediment is sand with an average percentage of 68.8%, followed by gravel with average percentage of 30.4% and silt and clay as the minor component with an average percentage of 0.8%. Of the 30 samples, 7 samples show bimodal characteristics while 23 samples show unimodal characteristics. 14 out of the 23 unimodal samples had shown a non uniform distribution with the tendency to skew to the coarser grain size. Due to this, the conventional use of median grain size d50 as the effective size for the sediment samples might not be a good representation for the sediment distribution. Further statistical analysis in this paper had suggested that the mode grain size is a much better representative grain size due to its stability when compared to median and mean size. Thus, a much better representative size for the sediment samples from Kuching urban areas would be the mode size (in this case is d45). An analysis on drain characteristics had shown that trapezoidal shape drain tends to have higher blockage percentage due to sediment deposition when compared to rectangular shape drain

A Hydrology and Hydraulic Case Study on January 2015 Flash Flood in UniGarden, Kota Samarahan, Sarawak

This study investigated the possible causes for occurrence of flash flood in UniGarden by looking into the hydrologic and hydraulic factors. This study consists of the assessment of water balance (precipitation, surface runoff, and infiltration) as well as the suitability of the hydraulic capacity of the existing earth drain based on MSMA guidelines. The site works involved analysis on precipitation, measurements of size of the earth drain and the corresponding flow velocity, and water quality testing. The consistency in annual rainfall and comparison between storm in year 2007 and 2015 indicated that precipitation was not the main cause of the flash flood. The infiltration of both storm events were limited due to precipitation few days prior to the extreme storm event that partially saturated the previous ground. There was a 45% increase in the average peak flow in 2015 than that in 2007. The TSS in both low flow and high flow were relatively low, providing estimated sediment loading up to 84.81 g d-1, which is not likely to have a direct effect on reducing the earth drain size. Rapid vegetation growth slow down flow, reduced free flow area of the earth drain, thus decreased its hydraulic capacity. Lowest invert level point of the drain was found to be located some distance away from the outlet, indicating potential backflow of water. These findings suggests that the increase in runoff, decrease in hydraulic capacity, and the improper invert level of the earth drain contributed to the flash flood in UniGarden on 18 January 2015. This finding is essential in providing insight to the incident as well as call for consistency review of drainage network in land development policy and decision making

TREND AND STATISTICAL ANALYSIS OF ANNUAL MAXIMUM DAILY RAINFALL (AMDR) FOR SARAWAK RIVER BASIN, SARAWAK, MALAYSIA

The Sarawak River Basin is one of the major river basins located in the southern part of Sarawak, Malaysia, and has experienced frequent extreme rainfall resulting in flash floods in recent years. This study aims to carry out trend and statistical analysis of annual maximum daily rainfall (AMDR) for 10 rainfall stations distributed evenly in the basin from 1975 to 2020. From the analysis, the AMDR records high variability for most of the rainfall stations, with the month of January having the highest occurrence of AMDR events. The linear regression plot of the mean AMDR showed a slight decreasing trend over the past four decades. The threshold rainfall value of 180 mm was used to perform frequency analysis, and the result shows that the return period for daily rainfall exceeding 180 mm was 2.71 years. The occurrence probability of the flood event at least once in 1, 2, 3, 4 and 5 years was 0.37, 0.60, 0.75, 0.84 and 0.90, respectively. A frequency curve based on the mean AMDR data with Gumbel distribution fitting was also developed from the current study and can be applied to the planning and design of flood infrastructures in the basin

Site specific Rainfall Temporal Pattern (RTP) for sustainable development of Kuching City, Sarawak, Malaysia

An understanding of rainfall temporal patterns is important for flood estimation and planning for sustainable flood designs and management. However, current published rainfall temporal patterns in design manuals are mostly generalised for a region which covers large areas. This raises doubts regarding its accuracy, especially for sensitive urban areas which are prone to flash floods. In the current study, a site-specific rainfall temporal pattern has been developed for Kuching using the Average Variability Method. The data of 5 minutes interval from year 2010 to 2018 for Kuching Airport rainfall station was used in the current study. Both the normalized and non-normalised rainfall temporal patterns were developed for 10 minutes, 15 minutes, 30 minutes, 60 minutes, 120 minutes, 180 minutes and 360 minutes. The developed rainfall temporal patterns were then compared with the recommendations from two other published design manuals. Results showed that most of the fractions in the published rainfall temporal patterns have more than 20% differences when compared with the current study. The developed rainfall temporal patterns from the current study can be adopted for flood design purposes in the city of Kuching in Sarawak. This fulfils Sustainable Development Goal 11 by reducing the adverse effects of flood in the city

Duration of Hydraulic Flushing and its Effect on Sediment Bed Movement

Hydraulic flushing is the most widely used method for sediment removal in sewer. However, open storm sewer tend to have longer flushing duration as compared to closed conduit sewer. This is due to storm water could enter more directly and rapidly into open storm sewer especially during rain events. The current study aims to determine the effect of flushing duration on the efficiency of sediment removal which is lacking in the literature. Flushing experiment was conducted in a rectangular flume for varying flushing durations namely approximately 3 seconds, 30 minutes and 60 minutes. Changes of the sediment bed profile were observed after each flush. Findings from the experiment has shown that short duration flushing is more efficient in terms of more sediment volume being removed as compared to long flushing duration. In terms of mean sediment bed front advancement, long flushing duration will moved the sediment bed front further than short duration flushing. The knowledge from the current study can be used to design a more efficient flushing devices for the management and active control of sediment in sewer system

Duration of Hydraulic Flushing and its Effect on Sediment Bed Movement

Hydraulic flushing is the most widely used method for sediment removal in sewer. However, open storm sewer tend to have longer flushing duration as compared to closed conduit sewer. This is due to storm water could enter more directly and rapidly into open storm sewer especially during rain events. The current study aims to determine the effect of flushing duration on the efficiency of sediment removal which is lacking in the literature. Flushing experiment was conducted in a rectangular flume for varying flushing durations namely approximately 3 seconds, 30 minutes and 60 minutes. Changes of the sediment bed profile were observed after each flush. Findings from the experiment has shown that short duration flushing is more efficient in terms of more sediment volume being removed as compared to long flushing duration. In terms of mean sediment bed front advancement, long flushing duration will moved the sediment bed front further than short duration flushing. The knowledge from the current study can be used to design a more efficient flushing devices for the management and active control of sediment in sewer system

SWMM Modelling of Automated Hydraulic Flushing Gate as a Flow Control Structure

This study explores the concept of hydraulic flushing gate with an automated control system as a flow control structure of the urban stormwater system. The research team has implemented a flush gate with the automated control system to the flow of the water in a drainage channel. The flow control structure was used to determine the effectiveness of such design by applying the concept of virtually on a real-world drainage system at Jalan Astana, Kuching. Computer representations of the existing drainage system and flow control structure were built using EPA SWMM 5.0 model. The series of flow control structure was proven to hold the runoff from 10-year storm. The modelling result shows that there is 25.9 % of flow reduction at outlet node. As a modification of the existing drainage system in the urban area involves high construction cost; by installing a flow control structure in the drainage system is an innovative way to control the flow of the water