• Korean Journal of Environmental Biology
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• v.37 no.1
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• pp.48-59
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• 2019

This study analyzed the water quality characteristics and developed empirical models prior to and after the construction of Baekje Weir, in the Geum River watershed between 2004-2017. The comparative evaluation of the surface water chemistry before and after the four major river projects on the weirs indicated that total phosphorus (TP), based on annual data, rapidly decrease after the construction of the weir while the total nitrogen(TN) decreased. Conversely, chlorophyll-a (CHL) concentration, which is a good indicator of primary productivity, increased after the construction of the weir together with an increase in specific conductivity. Simply put, the construction of the weir led to the decrease in concentrations of N and P due to the increased water residence time (WRT), whereas the CHL :TP ratio greatly increased in magnitude. The regression analysis of the empirical model indicated that CHL had no significant relation (r=0.068, p=0.6102, n=58) with TP before the weir construction, but had a relation with TP after the weir construction (r=0.286, p<0.05, n=56). Therefore, such conditions resulted in an increase in primary productivity on a given unit of phosphorus, resulting in frequent algal blooms. In contrast, seasonal suspended solids (SS) and TP increased during the monsoon period, compared to the pre-monsoon, thereby showing positive correlations (r>0.40, p<0.01, n=163) with precipitation. If the government consistently discharges water from the weir, the phosphorus concentration will be increased due to its reversion to a lotic waterbody from a lentic waterbody hereby reducing algal blooms in the future.

• Journal of Korea Water Resources Association
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• v.43 no.6
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• pp.525-531
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• 2010

In this study, the effects of upstream Froude number ($Fr_1$), weir height (h), weir length (L), weir width (W) and main channel width (B) on the discharge coefficient of broad crested side-weirs in a relatively wide rectangular open channel were investigated experimentally. Furthermore the relationship between discharge coefficients of sharp crested side weir and broad crested side weir was studied using the concept of De Marchi discharge coefficient. The effect of $Fr_1$ on the relationship between discharge coefficients of sharp crested side weir and broad crested side weir is decreased in wide open channel and the relative importance of other influential parameters like h/$y_1$, L/B, and W/($y_1-h$) are increased. New estimated equations for the discharge coefficients of broad crested side weir are suggested from regression analysis with the experiment data sets.

• Magazine of the Korean Society of Agricultural Engineers
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• v.20 no.1
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• pp.4614-4625
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• 1978

The construction of the equipment of water utilization has been developed since the ancient Korea period, 1906 in order to develope and modernize the agriculture. As the results, 83% of total paddy field area, 1,268,949.8 ha has developed into the irrigated paddy field, and the rest of area, 17% has remained nonirrigated paddy field (due to the data of the statistics of 1975). The ratio of the irrigated paddy field area among the total weir was marked 13.14% (area, 137,926.3 ha) and the third grade of total irrigated paddy field in accordance with the facilities of water utilization. In case of Gangwon-Do, the 44.18 percentage of the total irrigated paddy field, 51,057.2ha has been and pointed out first grade. As the results, we found out the following articles : 1. The total weir, 1,641 that sumed concrete weir 647 and conventional weir 967 has been constructed and has irrigated the 44.l8% of total irrigated paddy field of Gangwon-Do. 2. These weirs have been public possession of those villages to be 96.1 percentage of total weir and was controled by them. 3. Those weirs that were constructed across tributary (first, secondary and third tributary) at vallies (elevation 100∼1,000m) have marked that 45 percentage of total number of catchment area has 100∼1,000 ha, and 70 percentage of total number of basin area has been below 10 ha and has constructed about 5 of step-shape. 4. The construction of most weirs has became generally about 50m length, about 1m height. 5. The 80 percentage of newly constructed concrete weir has aged below 10 years. It seemed that 79 percentage of conventional weir has aged over 20 years and 41% of contructed weir has needed to be improved quickly. 6. If privious weirs, 296 will constructed newly, they can irrigate 3,600.8 ha of paddy field and 45.8% of total irrigated paddy field will have been and will contribute to the production of much rice.

• Journal of Ecology and Environment
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• v.39 no.1
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• pp.99-110
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• 2016

The objective of this study was to analyze chemical water quality, ecological characteristics of fish compositions, and ecosystem health before- (B_wc; 2008-2009) and after-the weir construction (A_wc; 2011-2012) at Juksan Weir and Seungchon Weir of Yeongsan River watershed. Suspended solids (SS) and chlorophyll-a (Chl-a) in Juksan Weir increased, whereas nutrients such as total nitrogen (TN) and total phosphorus (TP) decreased in the epilimnetic water. In Juksan and Seungchon weirs, fish species distribution analysis in the periods of B_wc and A_wc showed that sensitive species were rare and tolerant species were dominant in the community. In the analysis of trophic guild, relative abundance of carnivore species are increased to 22% and 12%, respectively, after the constructions of Seungchon Weir and Juksan Weir. Mann-Whitney U-tests of nonparametric statistical analysis indicated that omnivore and carnivore species had significant differences (p < 0.05) between the B_wc and A_wc. The massive population growth of an exotic species, Micropterus salmoides, was evident in Seungchon Weir to influence on the structures of fish communities. The model values of mean Index of Biological Integrity (IBI), based on fish assemblages, were < 15, which indicates "poor" condition in the river health, and the significant difference of IBI values was not found between the B_wc and A_wc.

• Journal of Korea Water Resources Association
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• v.40 no.3
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• pp.277-286
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• 2007

In this study, we analyzed the flow characteristics in the wide-crested side weir of trapezoidal section by using a three dimensional numerical stimulation. From this study, as the Froude number increases in the main channel, the overflow discharge ratio and the discharge coefficient of lateral overflow tend to decrease. And it was also found that the increase of the lateral overflow reduces the channel discharge area in the downstream, and the size of recirculating zone is increasing in the opposite side of side weir. The stream-wise water surface on the side where the side weir is installed falls down rapidly in the weir starting point, gradually ascending, and rapidly rising at the end point. The reason why the water surface rapidly rises at the weir end point is because the weir end point hinders the flow.

• Journal of Environmental Science International
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• v.25 no.4
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• pp.491-504
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• 2016

This study, examines the flow characteristics of upstream channel depending on water gate operation of Nakdan Multi-fuctional weir. The specific purpose of this study are to simulate the variation of flow velocity depending on the operation of the weir using 1-dimensional hydraulic model, HEC-RAS, and compare it with observed velocity. For discharge conditions from $50m^3/s$ to $3,500m^3/s$, it is observed that the velocity of upstream channel is almost constant, whereas for probability flood discharge, the velocity and froude number are increased as the discharge values are increased. The velocity values for downstream boundary condition EL, 40.0 m are more decreased than those for EL. 40.5m. From comparison on the variation of water stage depending on water gate operation, it is observed that the stage values are almost constant for discharges below $300m^3/s$, whereas 5 cm to 20 cm for discharges over $700m^3/s$. Flow velocity at streamflow gauging station. Nakdong, is decreased by more than 875% after installing the weir. The results obtained from this study indicate that the velocity of upstream channel is decreased and the discharge and velocity of downstream channel are significantly varied after installing the weir.

• Journal of The Korean Society of Agricultural Engineers
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• v.57 no.2
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• pp.57-66
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• 2015

The purpose of this study was to improved the durability of a improved movable weir by replacing the improved movable weir's metal gate with a hybrid steel/glass fiber reinforced polymer composites panel gate. Because the metal gate of a improved movable weir is always in contact with water, its service life is shortened by corrosion. This study made four type of hybrid steel/glass fiber reinforced polymer composites panel gate with different steel gate surface deformation (control, sand blast, scratch and hole), flexural. Fracture properties tests were performed depending on the steel gate surface deformation. According to the test results, the flexural behavior, flexural strength and fracture properties of hybrid steel/glass fiber reinforced polymer composites panel gate was affected by the steel panel gate surface deformation. Also, the sand blast type hybrid steel/glass fiber reinforced polymer composites panel gate shows vastly superior flexural and fracture performance compared to other types.

• Journal of Wetlands Research
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• v.13 no.3
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• pp.677-686
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• 2011

This study proposes a formula to calculate length of river bed protection through experimental research and an experimental plant has been installed to investigate the parameters which influence the length of scouring in the river after overflowing the weir. Through hydraulic experiments, the critical velocity, difference of water level between upstream and downstream and height of weir have been selected as independent variables. And new formula to calculate a length of river bed protection is suggested as the result of this study in the consideration of complex weir that consists of movable and fixed weir. The new formula is verified through additional experiments. Results of this study can be used for weir structures' construction and maintenance plans.

• Journal of Korean Society on Water Environment
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• v.35 no.1
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• pp.55-63
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• 2019

The Four Major Rivers Restoration Project started in 2009 and completed in early 2013 is a large-scale inter-ministry SOC project investing ₩22.2 $10^{12}$ and one of the Project's objectives was to enhance the water-quality grade through recovering the river eco-system and environment. The average concentration and probability distribution of water-quality constituents at given and selected sampling sites are very significant elements for analyzing and controlling the water-quality of rivers or reservoirs effectively. Average concentration can be estimated by point estimator, distribution function of water-quality constituents or Bootstrap method, in which the distribution function estimated with more data in case of insufficient dataset, is applied. Ipo and Gangcheon water-quality monitoring stations in South Han River were selected to compare and analyze the variation of concentration before and after Ipo and Gangcheon Weirs construction, using the whole 4-year's data, from 2005 to 2008 and from 2014 to 2017. Water-quality constituents such as BOD and COD relating to oxygen demanding wastes and TP and Chlorophyll-a relating to the process of nutrient enrichment called eutrophication were also selected. The guidelines for water-quality control and management after weir construction including evaluation of water-quality constituents' variations can be presented by this paper.

• Ecology and Resilient Infrastructure
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• v.3 no.4
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• pp.294-301
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• 2016

The underflow type movable weirs were arranged in a multi-stage way at a section of the Chiseong River, a tributary of Geum River, where flooding is observed frequently. The flood control and the movable weir management levels were compared with the occasions of installing the existing weir for analysis. The peak discharge decreased by a maximum of 97% for the underflow type movable weir, and the downstream flood elevation decreased by a maximum of 82%. The amount of storage also increased by a maximum of 463% by the distribution and storage functions of the multi-stage arrangement of the underflow type movable weirs. It is possible to suggest that the management level of each movable weir for the target storage of the reach and the flood reduction level through the relationship among this storage, downstream peak flood elevation, and peak flow.