• Journal of Korea Water Resources Association
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• v.45 no.5
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• pp.445-454
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• 2012

The present study aims to investigate the long-term channel morphological changes derived from channelization, embankment and levee construction works in unregulated fluvial channel of the Jiseock River. Analyses of aerial photographs taken past (Year 1966) and recent (Year 2002) showed the temporally remarkable changes in channel planform such as channel shape, bar migration, vegetation encroachment in bar. During the period, the natural single threading changed into braided types together with decreasing sinuosity by 9.2%, increasing vegetation occupied bar ranged 97% of total bars area. Because such channel morphological changes are closely similar to those in dam downstream channels, we assume that both/either flow regime alteration and/or sediment transport discontinuity may be critical for the fixed channel and spread of vegetated bars even in unregulated river without dam reservoir upstream. We found more reduced frequency and magnitude of flooding water level comparing with past, but no significant alteration of inter annual water level variation. Bed material has been coarsened by 4~5 times and the riverbed has been degraded in overall channel but aggraded locally in conjunction reach of tributaries. The results indicates that reduced sediment dynamics in fluvial channel which derived by bed material coarsening, river bed degradation and unbalanced sediment transport capacity between tributary and mainstem can be a causal factor to trigger channel morphological changes even in unregulated rivers.

• ALGAE
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• v.18 no.2
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• pp.169-176
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• 2003

Algal growth potential test (AGPT) bioassay were conducted to evaluate the stream and reservoir water in the Okchon Stream Watershed during May to September 2002. The water quality of the stream water was clean in the upstream, deteriorating toward the downstream. In particular, SRP and $NH_4$ significantly increased due to treated wastewater. The average AGPT value of the Okchon Stream watershed was 22.4 mg dw ${\cdot}l^{-1}$, with the range of 0- 195.7 mg dw ${\cdot}l^{-1}$. AGPT value was the highest immediately after inflow of treated wastewater, averaging 91.3 mg dw${\cdot}l^{-1}$. AGPT was highly correlated with SRP, $NH_4$ and TIN factors, with P having the greatest effect on the growth of algae. Among N components, $NH_4$ was preferred to $NO_3$ for the growth of algae. Likewise, AGPT was closely linked to meteological and hydrological effects and development of natural phytoplankton. In survey stations, mesotrophic, eutrophic and hypertrophic conditions accounted for 43%, 21% and 36%, respectively. On the other hand, hypertrophic condition focused on the downstream reaches. AGPT was useful in determining not only the limiting nutrients but also the water fertility for the growth of algae. Based on the AGPT results, the management of point sources for water pollution in treated wastewater was important in the protection of aquatic environment in the stream and embayment.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.4
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• pp.25-36
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• 2021

This study analyzed the causes of flood accidents, such as isolation and lost footing accidents in Dorimcheon, to provide legal and institutional improvements. For cause analysis, Field Investigation, Stakeholder Interview, Report, manual, Law et al. Review, Analysis of water level change characteristics, automatic alarm issuance standard level analysis, and evacuation time according to river control were evaluated. Dorimcheon has the characteristics of a typical urban river, which is disadvantageous in terms of water control. In addition, the risk of flood accidents is high because the section where fatal accidents occur forms sharply curved channels. Tripping and isolation accidents occur in the floodplain watch and evacuation stage, which is the stage before the flood watch and warning is issued. Because floodplain evacuation is issued only when the water level rises to the floodplain, an immediate response according to the rainfall forecast is essential. Furthermore, considering that the rate of water level rise is up to 2.62 cm/min in Sillimgyo 3 and Gwanakdorimgyo, sufficient evacuation time is not secured after the floodplain watch is issued. Considering that fatal accidents occurred 0.46 m below the standard water level for the flood watch, complete control is very important, such as blocking the entry of rivers to prevent accidents. Based on these results, four improvement measures were suggested, and it is expected to contribute to the prevention of Tripping and Isolation Accidents occurring in rivers.

• Journal of Korea Water Resources Association
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• v.49 no.8
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• pp.693-705
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• 2016

In this study, the effects of sediment supply on the downstream of a large dam are investigated using a numerical model. The model simulation shows a good agreement with laboratory experiment results of sediment transport and diffusion from sediment pulses. The water surface changes from the various sediment bed elevations are also simulated using the model. The site which has a relatively stiff bed slope and meandering of a channel is selected as an appropriate location for sediment supply because of its shear stress enough to supply the sediment downstream. The model simulation shows the decrease of channel bed elevation through the simulation period with time. The well-deposition of sediment supplied from the downstream of dam is found in the location where the flow rate is relatively low. A bed relief index is increased with time and it is relatively greater in downstream compared to upstream. The channel bed variability increases as flow rate increases with a greater bed relief index. The results of this study demonstrate the importance of increasing water discharge of a large dam to increase the dynamic of channel bed and thus to enhance the efficiency of channel bed restoration by sediment supply.

• Journal of Korean Society for Geospatial Information Science
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• v.5 no.2 s.10
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• pp.145-152
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• 1997

A coupling of two-dimensional model and GIS technique is applied to simulate sediment transport analysis. Accurate transformations are performed for the data which have various reduced scales. Basic maps are discretized the mesh of true scale for the finite element model by using the digital map and the Traverse Mercator coordinate. Under $200m^3/s$ flow rate condition, velocity vectors, depth contours, velocity contours and deposition contours are Presented for the 5km reach of midstream of Keum River from confluence of Ji-chun to Baekche Bridge. The simulation results of the study agree well with those of one-dimensional varied flow analysis and observed data. The flow and deposition pattern revealed a meandering characteristics of the river qualitatively.

• Journal of the Korean Institute of Traditional Landscape Architecture
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• v.28 no.2
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• pp.37-44
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• 2010

Our country traditionally employed a defensive system against the aggression by foreign powers by using a town castle and mountain castle. The moat was one of such a defensive system; however, there is few research work on a moat in comparison with its long history. This study was carried out to see the process of the changes of the Wolseong Fortress at Gyuongju, focused on the moat of the scale and nature of the construction methods to analyze such a Wolseong Fortress at Gyuongju as a result of consideration through bibliographical study, on-site investigation, and interviews, etc. This research discovered some facts as follows: the moats of Wolseong fortress at Gyeongju are roughly divided into three types; the first one is a natural moat flowing curved by the south side of Wolseong using the natural stream[Namcheon]as it is; the second one is a pond-type moat made by digging up plane non-rectangular pond along stereobate of castle wall with lakefront built with stream pebbles, and the last one is masonry moat at the east side of Wolseong with chisel-trimmed granites orderly piled in a plane triangular form. Among these, the pond-type moat was identified at the east-north-west side of Wolseong and the pond slopes from east to west as a separate one constructed with the terraces.

• Magazine of the Korean Society of Agricultural Engineers
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• v.13 no.1
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• pp.2206-2217
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• 1971

Spillway and discharge channel of reservoirs require the Control of Large volume of water under high pressure. The energies at the downstream end of spillway or discharge channel are tremendous. Therefore, Some means of expending the energy of the high-velocity flow is required to prevent scour of the riverbed, minimize erosion, and prevent undermining structures or dam it self. This may be accomplished by Constructing an energy dissipator at the downstream end of spillway or discharge channel disigned to dissipated the excessive energy and establish safe flow Condition in the outlet channel. There are many types of energy dissipators, stilling basins are the most familar energy dissipator. In the stilling basin, most energies are dissipated by hydraulic jump. stilling basins have some length to cover hydraulic jump length. So stilling basins require much concrete works and high construction cost. Flip bucket type energy dissipators require less construction cost. If the streambed is composed of firm rock and it is certain that the scour will not progress upstream to the extent that the safety of the structure might be endangered, flip backet type energy dissipators are the most recommendable one. Following items are tested and studied with bucket radius, $R=7h_2$,(medium of $4h_2{\geqq}R{\geqq}10h_2$). 1. Allowable upstream channel slop of bucket. 2. Adequate bucket lip angle for good performance of flip bucket. Also followings are reviwed. 1. Scour by jet flow. 2. Negative pressure distribution and air movement below nappe flow. From the test and study, following results were obtained. 1. Upstream channel slope of bucket (S=H/L) should be 0.25<H/L<0.75 for good performance of flip bucket. 2. Adequated lip angle $30^{\circ}{\sim}40^{\circ}$ are more reliable than $20^{\circ}{\sim}30^{\circ}$ for the safety of structures.