• Journal of Sensor Science and Technology
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• v.30 no.1
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• pp.25-29
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• 2021

In this study, we successfully developed a highly reliable ultrasonic sediment sensor to detect the sediment levels in sewer pipes in harsh environments. The ultrasonic transducer employed in the ultrasonic sediment sensor was designed so as to possess a simple structure. The developed sensor was carefully optimized by simulating the electromechanical characteristics, radiated sound wave pressures, and directivity via finite element analysis. It was also designed to possess a simple mounting structure minimizing the flow disturbance in a 400-mm sewer pipe; additionally, eight ultrasonic transducers were arranged in a four-channel mode, allowing for measurement of the sediment height in five easy steps. Through experimental evaluations, we verified the performance of the ultrasonic sediment-level sensor and its industrial applicability. The results suggested that although the precision value was notably low at 15 mm, the sediment detection performance was adequate; therefore, the developed sensor can potentially be used in industrial applications.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.11 no.3
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• pp.74-86
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• 2008

To assessment the disturbances of the Namgang caused by dam construction, upstream area was selected for the reference reach and downstream area was selected for the comparison reach. And these reaches were surveyed and analyzed according to the assessment criteria of the river disturbances.The artificial factors of river disturbances were classified as river improvement works, dam construction and aggregate dredging. The indexes were physical factors as like epifaunal (bottom), embeddedness, velocity/depth regime, sediment deposition, channel flow status, channel alteration, frequency of riffles, bank stability, vegetative protection, riparian zone etc.The assessment results showed 46% of the assessment criteria which was serious status in dam downstream area and 89.5% of it which was excellent status in dam upstream.Finally, the results showed that physical river environment in downstream area was disturbed by the discharge control and the interception of sediment discharge by dam, consequently this disturbance give rise to impact of ecosystem in river.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.12 no.3
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• pp.83-97
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• 2009

The objects of study is to propose criteria for physical river disturbance assessment and as case study to show the application results for river improvement. For this purpose, the river disturbance assessment method for past disturbance process and the present-day potential natural state of stream is proposed. To assess the disturbance of the Youngcheon River caused by river improvement, One ares of Nam River was selected for the reference reach and two areas of Youngcheon River were selected for the comparison reach. And these reaches were surveyed and analyzed according to applying criteria of the river disturbances assessment. The assessment indices were physical factors as like epifaunal (bottom), embededness, velocity/depth regime, sediment deposition, channel flow status, channel alteration, frequency of riffles, bank stability, vegetative protection and riparian zone etc. The results showed that physical river environment in Youngcheon River area was disturbed by artificial revetment and bed excavation, consequently this disturbance give rise to impact of ecosystem in river. Hereafter, the criteria for river disturbance assessment are needed to consider various river characters as bed materials and bed slop etc.

• Journal of Korean Society of Forest Science
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• v.105 no.3
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• pp.321-329
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• 2016

To estimate the sediment discharge controlled by sediment-filled check-dam and thereby enhancing factor for check-dam design and dredging criteria, we surveyed slope failures and stream-bed fluctuation caused by geomorphic disturbances (i.e., landslides and debris flows) in Inje, Gangwondo. In general, check-dams play roles for restraining and controlling sediment discharge within a section under the design equilibrium gradient and a section under the design flood gradient, respectively. The results in this study showed same pattern: that is, the closed type check-dam, which has a design restraint sediment discharge of $2,111m^3$, estimated to control a sediment discharge of $3,996m^3$ in the stream section within 250 m right upper area immediately after the disturbances occurred in 2006. As a result, a design control sediment discharge of the check-dam was larger than its design restraint sediment discharge. This represents that the check-dam is still having an own function for controlling sediment discharge although it exceeded the designed capacity by the sediment discharged from upstream during the disturbances. Our finding suggests that the sediment discharge controlling of check-dam may need to be evaluated separately from its sediment discharge restraint. Currently, the country, however, does not consider the design control (or restraint) sediment discharges, based on the actual field survey, as criteria for check-dam design and/or dredging work. Therefore, the accumulation of the quantitative data is required to support that check-dam has functions for both restraining and controlling sediment discharge. This would be a way to develop our erosion control technology to the scientific technology equipped with a more objective and systematic aspects.

• The Journal of the Acoustical Society of Korea
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• v.22 no.4E
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• pp.167-175
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• 2003

Shear wave velocity was measured and grain size analysis was conducted on two core samples obtained in unconsolidated marine sediments of the western continental margin, the East Sea. A pulse transmission technique based on the Hamilton frame was used to measure shear wave velocity. Duomorph ceramic bender transducer-receiver elements were used to generate and detect shear waves in sediment samples. Time delay was calculated by changing the sample length from the transducer-receiver element. Time delay is 43.18 μs and shear wave velocity (22.49 m/s) is calculated from the slope of regression line. Shear wave velocities of station 1 and 2 range from 8.9 to 19.0 m/s and from 8.8 to 22 mis, respectively. Shear wave velocities with depth in both cores are qualitatively in agreement with the compared model〔1〕, although the absolute value is different. The sediment type of two core samples is mud (mean grain size, 8-9Φ). Shear wave velocity generally increases with sediment depth, which is suggesting normally consolidated sediments. The complicated variation of velocity anisotropy with depth at station 2 is probably responsible for sediment disturbance by possible gas effect.

• Korean Journal of Ecology and Environment
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• v.43 no.2
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• pp.212-220
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• 2010

Effects of sediment and toxic cyanobacterium Microcystis aeruginosa on feeding behaviors of an omnivorous fish, gold fish (Carassius auratus) were examined in laboratory and in situ mesocosm. Laboratory feeding experiments were performed in small aquaria (7 L) with cyanobacterial blooms (mainly M. aeruginosa) under the condition of sediments and no-sediments, and toxic (NIES-298) and non-toxic M. aeruginosa (NIES-101). In situ feeding experiments were conducted at the shore of eutrophic lake (Lake Ilgam, Seoul) in the mid-July, 2005. Results showed that fish introduction decreased the concentration of Chlorophyll-a (Chl-a) at higher rate in no sediment-containing aquaria. In contrast, there was a drastic increase of Chl-a in the sedimentcontaining aquaria. Fish effectively removed the M. aeruginosa cells without algal toxin (microcystin). Fish also selectively removed the large size Chl-a (>$50{\mu}m$), although all kinds of nutrients were increased after fish introduction, especially ammonia. Our results indicate that the strategic introduction of domestic omnivores Carassius auratus, to control cyanobacterial bloom in eutrophic lake will negatively play in the water quality improvement via a sediment disturbance and a density-dependent digestion.

• Journal of the korean society of oceanography
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• v.38 no.4
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• pp.166-172
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• 2003

Multi­Sensor Core Logger (MSCL) is a useful system for logging the physical properties (compressional wave velocity, wet bulk density, fractional porosity, magnetic susceptibility and/or natural gamma radiation) of marine sediments through scanning of whole cores in a nondestructive fashion. But MSCL has a number of problems that can lead to spurious results depending on the various factors such as core slumping, gas expansion, mechanical stretching, and the thickness variation of core liner and sediment. For the verification of MSCL data, compressional wave velocity, wet bulk density, and porosity were measured on discrete samples by Hamilton Frame and Gravimetric method, respectively. Acoustic impedance was also calculated. Physical property data (velocity, wet bulk density, and impedance) logged by MSCL were slightly larger than those of discrete sample, and porosity is reverse. Average difference between MSCL and discrete sample at both sites is relatively small such as 22­24 m/s in velocity, $0.02­-0.08\;g/\textrm{cm}^3$ in wet bulk density, and 2.5­2.7% in porosity. The values also show systematic variation with sediment depth. A variety of factors are probably responsible for the differences including instrument error, various measurement method, sediment disturbance, and accuracy of calibration. Therefore, MSCL can be effectively used to collect physical property data with high resolution and quality, if the calibration is accurately completed.

• Ecology and Resilient Infrastructure
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• v.1 no.2
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• pp.49-60
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• 2014

Fish assemblages play an integral role in stream ecosystem and are influenced by stream environmental conditions and habitat disturbances. Fish community structures and habitat parameters of U.S. EPA rapid bio-assessment protocol were surveyed to investigate the effect of stream environment and habitat disturbance on fish communities at 13 study sites in the Gapyeong Stream, a typical gravel-bed stream. Principal component analysis (PCA) based on data from habitat assessment at each study site indicated that the study sites were differentiated by habitat parameters such as embeddedness, velocity/depth regime and sediment deposition, which were related with bed slope. A total of 46 species belonging to 12 families were collected in the Gapyeong Stream. A dominant species was Zacco koreanus, subdominant species was Z. platypus. Hierarchical cluster analysis based on species abundance classified fish communities into the three main groups along the stream longitudinal change. Non-metric multidimensional scaling (NMDS) portrayed that fish community structures were related to major habitat parameters, i.e., epifaunal substrate/available cover, embeddedness, velocity/depth regime, sediment deposition, channel alternation and frequency of riffles. These results suggested that fish community structures were primary affected by the longitudinal environmental changes, and those were modified by habitat disturbance in the Gapyeong Stream, a gravel-bed stream.

• Korean Journal of Ecology and Environment
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• v.41 no.4
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• pp.431-440
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• 2008

Turbid water or suspended sediment is associated with negative effects on aquatic organisms; fish, aquatic invertebrate, and periphyton. Effects of turbid water on fish differ depending on their developmental stage and a level of turbidity. Low turbid water may cause feeding and predation rates, reaction distance, and avoidance in fish, and it could make fish to die under high turbidity and long period. Therefore, it is very important to find out how turbid water or suspended sediment can affect fish in domestic watersheds. The objectives of this study were 1) to introduce international case studies and their standards to deal with suspended sediment, 2) to determine acute toxicity in 4 major freshwater fishes, and 3) to determine in relation to adverse effect of macroinvertebrates and fish. Impacts of turbid water on fish can be categorized into direct and indirect effects, and some factors such as duration and frequency of exposure, toxicity, temperature, life stage of fish, size of particle, time of occurrence, availability of and access to refugia, etc, play important role to decide magnitude of effect. A review of turbidity standard in USA, Canada, and Europe indicated that each standard varied with natural condition, and Alaska allowed liberal increase of turbidity over natural conditions in streams. Even though acute toxicity with four different species did not show any fatal effect, it should be considered to conduct a chronic test (long-term) for more detailed assessment. Compared to the control, dominance index of macroinvertebrates was greater in the turbid site, whereas biotic index, species diversity index, species richness index, and ecological score were smaller in the turbid site. According to histopathological analysis with gills of macroinvertebrate and fishes, morphological and physiological modification of gills due to suspended sediments can cause disturbance of respiration, excretion and secretion. In conclusion, in order to maintain good and healthy aquatic ecosystem, it is the best to minimize or prevent impact by occurrence of turbid water in stream and reservoir. We must make every effort to maintain and manage healthy aquatic ecosystem with additional investigation using various assessment tools and periodic biomonitoring of fish.

• Ecology and Resilient Infrastructure
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• v.3 no.1
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• pp.14-21
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• 2016

This study investigated the behavior of sediment bars in a compound channel with a drop structure. Flow was separated into side banks by alternate bars, and flow was concentrated into the downstream of bar fronts. The bed downstream of a drop structure degradated due to the concentrated flow from it. Bar shapes were kept by the influence of their shapes upstream. Alternate bars, central bars, and multiple bars were developed as the width to depth ratio increased, and the number of bars increased. The bar in the downstream of a drop structure decreased in length due to the concentration of flow and its disturbance.