• Journal of Korean Society of Water and Wastewater
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• v.34 no.1
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• pp.45-52
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• 2020

Even though sewers have been conventionally designed to prevent from sediment deposition using a specified minimum velocity or shear stress at a particular depth of flow or with a particular frequency of occurrence, it was appreciated that these methods do not consider the characteristics and concentration of the sediment and the specific hydraulic conditions of the sewer with sediment. In this study, a densimetric Froude number formula was suggested considering particle diameter and volumetric concentration of the sediment as well as flow depth and flowrate, based on several domestic field inspections, which was compared with other formulas proposed by previous investigators. When the sediment concentration was not considered, the calibration coefficient of 0.125-1.5 to the densimetric Froude numbers of this study was needed to obtain the similar ones with previous investigators'. For the densimetric Froude number formula obtained with consideration of sediment concentration, the exponent value of term C_v was almost the same as that of previous results and that of d₅₀/R_h was similar for F_r < 2.2.

• Journal of Korean Society of Water and Wastewater
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• v.33 no.2
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• pp.121-129
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• 2019

If sewage flows for an extended time at low velocities, solids may be deposited in the sewer. Sufficient velocity or tractive force should be developed regularly to flush out any solids that may have been deposited during low flow periods. This study aims to evaluate the periods (T) during which sewage flow greater than the minimum tractive force maintains on a spot in sewer pipe system with lower tractive force or lower velocity than expected in the design step, when a storage tank installed in a place upsteam pours water into the sewer. The effect to T of design factors of storage tank and sewer pipes was evaluated assuming the uniform flow in sewers. When the area of orifice in the storage tank is $0.062m^2$(or 0.28 m diameter), the maximum T of 31sec was maintained using the usually used preset range of values of several design factors. As the horizontal cross section of storage tank and water depth of storage tank and roughness in sewers increase, T linearly increases. Also, T linearly decreases as the diameter of a sewer pipe increases. Although T gradually decreases as the sewer pipe slope decreases to around 0.005, T decreases sharply when the slope is less than 0.003.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.4
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• pp.421-431
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• 2023

Sewer deterioration models can offer important information on prediction of future condition of the asset to decision makers in their implementing sewer pipe networks management program. In this study, Markov chain model was used to estimate sewer deterioration trend based on the historical structural condition assessment data obtained by CCTV inspection. The data used in this study were limited to Hume pipe with diameter of 450 mm and 600 mm in three sub-catchment areas in city A, which were collected by CCTV inspection projects performed in 1998-1999 and 2010-2011. As a result, it was found that sewers in sub-catchment area EM have deteriorated faster than those in other two sub-catchments. Various main defects were to generate in 29% of 450 mm sewers and 38% of 600 mm in 35 years after the installation, while serious failure in 62% of 450 mm sewers and 74% of 600 mm in 100 years after the installation in sub-catchment area EM. In sub-catchment area SN, main defects were to generate in 26% of 450 mm sewers and 35% of 600 mm in 35 years after the installation, while in sub-catchment area HK main defects were to generate in 27% of 450 mm sewers and 37% of 600 mm in 35 years after the installation. Larger sewer pipes of 600 mm were found to deteriorate faster than smaller sewer pipes of 450 mm by about 12 years. Assuming that the percentage of main defects generation could be set as 40% to estimate the life expectancy of the sewers, it was estimated as 60 years in sub-catchment area SN, 42 years in sub-catchment area EM, 59 years in sub-catchment area HK for 450 mm sewer pipes, respectively. For 600 mm sewer pipes, on the other hand, it was estimated as 43 years, 34 years, 39 years in sub-catchment areas SN, EM, and HK, respectively.

• Journal of Korean Society of Water and Wastewater
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• v.29 no.4
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• pp.503-510
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• 2015

The objective of this study is to analyze the investment adequacy of the projects implemented according to the master plan on sewerage rehabilitation at Seoul. The planned and actually implemented ratio of invested money on sewage treatment plants (STPs) to sewers were compared in two temporal periods. Though the planned ratio of investment on STPs to sewers was 50:50 (in 2009-2020), the actual implemented ratio in 2009-2013 was 34:66. Until 2020, the greater investment ratio on STPs to sewers should be made considering the necessity of coping with stricter legal compliance on advanced treatment, stormwater treatment and so on. The priority of the planned and partially implemented projects among four STPs and at each STP was evaluated. Considering only the performance indicator of reduced load of BOD, T-N, T-P per the capacity of each STP facility, the performance among four STPs was shown as Jung-Rang>Tan-Cheon>Seo-Nam>Nan-Ji. The reverse order of the performance results in the past may be considered for future investment priority, but the efficiency of operation implemented at each STP, deteriorated status of each STP, investment in the past and so forth should also be considered. As for the priority of projects conducted within each STP, projects related to legal compliance (such as advanced tertiary treatment, stormwater treatment, etc.) have highest priority. Odor-related project and inhabitant-friendly facility related projects (such as building park on STPs, etc.) has lower priority than water quality related projects but interactivity with end-users of sewerage should also be important.

• Journal of Convergence for Information Technology
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• v.10 no.7
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• pp.153-159
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• 2020

In order to find out the condition of flow in sewer pipes, this study investigated the characteristics of tractive force of sewage flow estimated using actual measured values of water level, velocity, and flowrate in sewers located at uppermost portion in a treatment area during dry weather periods. When the scene of sewage flow was taken by CCTV after cohesive and non-cohesive solids (tofu and sand) were put on the sewer invert, it was found that the solids could be flushed without significant interruption. In sewer with slope of 0.00319, the frequency exceeding the minimum tractive force of sewage during a weekday was zero, while it was 10 per day with slope of 0.00603. During the week of the field observation, the event to exceed the minimum tractive force occurred once, suggesting that sewer odor would potentially increase. Maximum tractive force in sewer with steep slope was 2.9-3.1 N/㎡, but with gentle slope it decreased to 1.6-1.7N/㎡. It was also observed that the interval of time maintained below the criterion of minimum tractive force increased, during weekends compared to weekdays and for the sewage including non-cohesive particles which could enter combined sewers during a storm period. This study found that the sewer sediments formed by direct feces input into sewers, through sewer pipes which were designed meeting the standard sewer design criteria, could be flushed without staying as deposited solids state for a long time.

• Magazine of the Korea Concrete Institute
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• v.15 no.4
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• pp.41-47
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• 2003

• Magazine of the Korea Concrete Institute
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• v.15 no.5
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• pp.52-60
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• 2003

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.159-162
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• 2005

Urban flooding is usually caused by the surcharge of storm sewers. For that reason, domestic studies about urban flooding are concentrated on the simulation of urban drainage system. However these approaches that find the pipes which have insufficient drainage capacity are very approximate and unreasonable ways. In this study, an accurate mathematical modeling is developed to analyze the impacts of an urban inundation for both flood prevention and flood-loss reduction planning and it is verified by using the simulation of July 2001 flooding in Seoul. The result of this study can be used to construct fundamental data for a flood control plan and establish a urban flood forecasting/warning system.

• Journal of Korean Society of Water and Wastewater
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• v.21 no.5
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• pp.631-639
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• 2007

This study investigated the construction and operation status of sewer pipes and water-purifier tanks near densely populated areas like large apartment complexes, in order to find out cause for offensive orders. The study results revealed that the main cause arose from the water-purifier tank and public sewer pipes near ordinary residential areas. First, in case of independent water-purifier tanks, the air is forced into the rotten part of large tanks nearby which should be operated in an anaerobic state, so that the tank changes into an aerobic state, or dirty water, which is returned during the sludge return process, falls on the top of the rotten tank, preventing scum from forming within the tank. Such problems cause incompletely purified water in the purifier tank to be discharged, which in turn results in filthy water. Second, in case of public sewer pipes, deteriorated or aging pipes, or the mixture of rain water and dirty water by mixing up combined and separated sewers system can cause foul odors in residential areas. Therefore, offensive odors in residential areas can be radically reduced through the appropriate construction and management of facilities including water-purifier tanks. As well, if more separate sewers are installed as part of an improvement project for public sewer pipes, complaints about foul smell can be minimized.

• Journal of Korean Society of Water and Wastewater
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• v.23 no.1
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• pp.47-55
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• 2009

Sewers are important national infrastructure and play an essential part by handling both wastewater and stormwater to minimise problems caused to human life and the environment. However, they can cause urban flooding when rainfall exceeds the system capacity. Sewer flooding is an unwelcome and increasingly frequent problem in many urban areas, and its frequency will increase over time with urbanisation and climate change. Under current standards, sewers are designed to drain stormwater generated by up to 10 year return period storms, but data suggests that many in practice have been experienced flooding with exceeding system capacity under increased storm events. A large number of studies has considered upgrading or increasing the design standard but there are still lack of information to propose a suitable return period with the corresponding system quantity to achieve. A methodology is required to suggest a proper level of standard within a suitable sewerage rehabilitation planning that can avoid the exceedance problem. This study aimed to develop a methodology to support effective sewer rehabilitation that could prevent urban flooding mainly resulted from the exceedance of existing storm sewer system capacity. Selected sewerage rehabilitation methods were examined under different storm return periods and compared to achieve the best value for money.