Prediction of local scour around wide bridge piers under clear-water conditions

Local scour is the removal of sediment from around bridge piers due to flowing of water. A large amount of local scour is dangerous to the bridge piers and causes the structure tend to collapse and loss of life without any warning. Many researchers have already investigated the phenomenon of local scour around bridge piers. The literature search revealed that there is very little information on predictive equations or data on scour around wide piers. Most of the predictive equations in the literature are intended to apply equally well to large and small piers. Hence, this leads to a situation in which design is prioritised over prediction, which thus proves costly and economically inefficient. This study attempted to fill this gap where new experimental data from a physical model of scouring around a cylindrical and rectangular wide pier embedded in two types of uniform sediment beds are presented. The effects of sediment sizes and various pier widths on equilibrium scour depth of wide bridge piers are described. New empirical relation for the estimation of non-dimensional maximum scour depth for a wide pier were proposed as functions of the sediment coarseness. The experimental data obtained in this study and data available from the literature are used to validate the predictions of existing methods and the accuracy of the proposed method. The proposed method gives reasonable scour depth predictions and was verified with statistical methods where the root mean square error was reduced from 71% to 26%. The new empirical relation agrees satisfactorily with the experimental data

SUSPENDED SEDIMENT DYNAMICS CHANGES IN MEKONG RIVER BASIN: POSSIBLE IMPACTS OF DAMS AND CLIMATE CHANGE

ABSTRACT: This paper evaluates the potential impact of climate change and dams on suspended sediment (SS) dynamics in the Mekong River Basin (MRB). To this end, a distributed process-based sediment transport model was used to examine the potential impact of future climate and dams on suspended sediment dynamics changes in the MRB. Climate scenarios from two GCMs outputs together with effects of 3 existing, 5 under construction and 11 planned dams were considered in the scenario analysis. The simulation results show that the reductions in annual suspended sediment load (SSL) are likely to range from a 20 to 33%, 41 to 62%, and 71 to 81% for existing, under construction, and planned dams respectively in case of no climate change for baseline scenario (1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000). Moreover, the reductions on sediment concentration (SSC) are even greater (23% to 78%) due to the potential impact of dams. In contrast, the SSL and SSC shows 40% to 92% increase in the near future (2041-2050) and 28% to 90% in the far future (2090)(2091)(2092)(2093)(2094)(2095)(2096)(2097)(2098)(2099). As the projected climate change impact of sediment varies remarkably between the different climate models, the uncertainty should be taken into account in sediment management. Overall, the changes in SSL and SSC can have a great implication for planned reservoirs and related sediment management

Performance of prefabricated sewage treatment plants at a military academy

This paper presents the results of performance monitoring of wastewater treatment systems installed at Universiti Pertahanan Nasional Malaysia (UPNM). UPNM is a military-based university located in Sungai Besi Camp, Kuala Lumpur, Malaysia. As the university expands, new buildings were constructed and new prefabricated sewage treatment plants (STPs) were installed. Effluent of these STPs were monitored and compared with required standards. Effluent samples were collected from three STPs for three months and tested for parameters of pH, temperature, biochemical oxygen demand (BOD), chemical oxygen demand (COD), ammoniacal nitrogen, nitrate, and phosphorus. The results were then compared with the standard B of the Environmental Quality (Sewage) Regulations 2009. Diurnal fluctuation of the effluent quality was also studied. From the data observed, it shows that the performance of the wastewater treatment plant is good. The effluent quality also achieved the allowable standards set by the authority. Maximum diurnal fluctuation was observed for COD which fluctuated between 18 and 52 mg/L which is still lower than standard B for COD effluent limit of 200 mg/L

Effect of different types of soil covers on sediment concentration and hydraulic parameters

Soil erosion issue is common among construction sites. The phenomena usually takes place on sloped areas with no soil cover. The main objectives of the research are to determine the sediment concentration of rain induced on different types of covers and also to determine the hydraulic parameters. Besides that, the research also has to investigate the relation of the sediment concentration with hydraulic parameters. This research will take place in rainfall simulator using soil sample collected from sloped areas. The hydraulic parameters of this experiment consist of flow velocity, flow depth, shear stress, and unit stream power. Soil sample will be placed on four trays with different types of covers and properly arranged in the rainfall simulator with slope of 20 ᵒ. The sample will undergo rainfall event for two hours. The surface runoff collected and the sediment concentration measured using Total Suspended Solid (TSS) testing. The result shows the stream power of dry leaves is higher among those four covers with 0.0046 msˉ¹ followed by grass cover with 0.0033 msˉ¹ than gravel with 0.0023 msˉ¹, and lastly bare soil cover with 0.0008 msˉ¹. However, sediment concentration and surface runoff that were produced by bare soil is the highest followed by gravel, then leaves, and lastly grass. Generally, the sediment production in descending order started with the bare soil, gravel, dry leaves, and grass. From the research shown, rain induced on vegetation cover can be used as a low-cost initiative to control the soil erosion on construction slope area

Preliminary experimental study on effectiveness of aquatic vegetation on sediment transport capacity

Vegetation affects sediment transport by obstructing the flow and changing the turbulence characteristics. Common sediment transport equations are not applicable to situations with submerged vegetation. A laboratory experiment was carried out in which flow, vegetation, and sediment transport were measured in an open channel model with a 240 cm long section of 50 cm high x 50cm width with submerged vege-tation in a sand bed. Measured data from various vegetation density and height were analyzed to obtain estimates of the trapping efficiency. Results show an increment of the trapping efficiency with 86.7% and 94.2% reduction in sediment concentration compared to a case without vegetation

Risk based analysis for detention pond overflow at Iskandar Malaysia (Nusajaya), Johor

Overflow risk of detention pond is defined as the probability of having a rainfall event that produces a runoff volume more than the available storage capacity of detention pond. Overflow risk analysis depends on the waiting period (elapse time) and draining time. This study dealt with risk analysis of detention pond overflow at Ledang Heights, Nusajaya, Johor Bahru. Monte Carlo simulation the simplest application to estimate the probability of occurrence of the 10 year rainfall interevent timeswas applied during this study. The maximum value for interevent time was 8 hr and 6 hr occurred with probability 24.18% and 28.39% after 5000 and 10000 trials respectively using Gamma distribution. The most likely range for interevent time were 2 to 18 hr (1.34%-1%) and 2 to 22 hr (3.84%-0.05%). The equation by Guo (2002) was applied during this study. The highest overflow risk obtained was 0.425 for the longest drain time of 71.75 minutes and for shortest elapse time. The overflow risk increases as the drain time increases and the elapse time decreases. Therefore, the selection of a proper drain time (recession time) is very important for reducing risk of overflow. Size of detention pond at the site is 70 m length x 70 m width x 3 m depth. The new size suggested was 82 m length x 70 m width x 3 m depth. The storage capacity of detention pond was larger than the volume of maximum rainfall data. The new size of detention pond is appropriate at the area because it could collect the maximum volume of runoff over a longer time period at the lowest overflow risk. It is suggested to design at lower elapse and drain time to minimize the overflow risk