• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.27 no.4
• /
• pp.247-254
• /
• 1991

Mackerel purse seine fishery is one of the most important fisheries in Korea and its annual mean catch from 1982 to 1988 is 350 thousand tons. Between 1982 and 1988, the characteristics of catch at 5 sectors of the sea area was analyzed according to operating sea block and the catch by fishes based on the data obtained from daily report of fishing condition that had been made out by 48 Korean fishing boats engaged in the fishery of purse seine. In these 5 sectors of the sea area, catch per net hauling in the coastal area of Cheju Island is less than that in the other sectors. Accordingly, the shape of fishing gear during operation has been measured to analyzed the deformation of net shape caused by the bottom current. (The lunar calender is used in the paper) The results obtained are as follows; The average CPUE of purse seines is 31.6 tons and it is higher from October to April than that from May to September. In the 5 purse seine fishing grounds, the ratio of net haul in the coastal sea area of cheju Island is 42.4% and it is the highest level, but the CPUE is 25.7 tons which is relatively low level. Each CPUE in the sea areas is significant differences with 1% level. Index of seasonal variation of mackerel CPUE from May to October is lower than the standard value, whereas index from November to January is higher. The diameter of circle by net shooting becomes shorter to the minimum caused by the bottom current during loose set, becomes narrower and the efficiency of fish encirclement becomes lower. The shape of leadline by bottom current becomes long oval type along with current direction in the tight set, while it becomes long oval type in the direction of a right angle to the current direction and the enclosed area is reduced hurriedly, and the deformation of net is most serious in the loose set.

• Korean Journal of Environment and Ecology
• /
• v.24 no.2
• /
• pp.186-193
• /
• 2010

In order to examine the traits of sluice gate water control, halophyte community formation and their inter-relations in Saemangeum, both water level condition and halophyte community formation were analyzed periodically and spatially on the topographic map with Surfer, Saemageum Spatial Analysis System, and related field reports. The traits of water level condition are that average water level in the growing period of halophytes was similar to annual average water level, annual low level and high level appeared in the growing period, and water level was usually maintained within a range of -1.0m~0.5m above mean sea level, but it has changed more frequently year by year. Routine water level control, natural disaster prevention, construction, and civil appeal took major percentages of the reasons for sluice gate's opening and shutting. Since 2007, not only the overall control frequency of sluice gate but also its control frequency for construction and natural disaster prevention have increased outstandingly. Halophyte community had formed at a rate of 1,209ha/year in the 4,315 ha land in 2008, 6.3 times larger than in 2005, and 2,382 ha above around 1.0m was estimated to be artificially vegetated, 89.1 % of the 2,673ha-size sown area. High water level was found to be a more possible determinant than average water level or low water level in halophyte community formation and it was thought to be secondary factors whether tillage was conducted or/and whether surface sealing formed.

• Korean Journal of Agricultural Science
• /
• v.17 no.2
• /
• pp.102-114
• /
• 1990

This study was carried out to analyze the operation of the sluice gates by taking Sabkyo Reservoir as the model, and to examine the formulae of the design criteria for the Agricultural Land Improvement Project by hydraulic model experiments. The results were summarized as follows ; 1. According to the records of gate operation for 9 years, the mean height of the opened gates was 4.13 m, the mean number of operated gates were 4.04, the average annual number of operation were 67 times, the average annual operating time were 192.5 hours, and the average operating time were 2.88 hours. 2. The water supplied through Sabkyo Reservoir was 88.15 megatons per year, which was about 1.4 times the effective storage capacity. And the annual volume of pumping in May, which is the most water demanding season, was 29.56 megatons in average. 3. As the submerged orifice was transformed into the surface orifice, the suggested formulae for the orifice flow on the design criteria for the Agricultural Land Improvement Project showed a discontinuous line on the transition zone. It should be improved, because it is different from the real hydraulic phenomena. 4. The formulae for the orifice flow which are divided into the submerged and surface orifices are being used. However, these formulae could be substituted for the formular, $q=C{\cdot}W\sqrt{2gH_1}$, if the discharge coefficient considering the reservoir water level, the sea water level, and the gate opening height is used.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.3 no.4
• /
• pp.3-22
• /
• 2000

To know characteristics of water quality in coastal sea around the Keum river estuary in summer, we studied the water quality of surface, middle and bottom level during Jun e～september, 1998. The mean concentrations of COD, DIN, DIP & chlorophyll-a were 1.36mg/L, 28.60㎍-at/L, 0.48㎍-at/L and 4.14㎍/L, respectively, which were over eutrophication criteria in sea water. After the Keum river dyke was constructed, seasonal freshwater discharge was largely changed. About 80% of total annual freshwater discharge was concentrated in summer as rainy season from July to September. The correlation coefficient of DIN versus salinity was shown to be high, and thus the concentration of DIN was closely related to freshwater discharge. Maximum Chlorophyll-a concentration was occurred in September, due to increased DIP concentration, high water temperature and low salinity after heavy rainfall in August. The results of Principal Component Analysis showed that the first factor represented a series of eutrophication factors, the second factor w3s a valiance of seasonal fluctuation, and the third was a variance of progress of mass change.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.18 no.2
• /
• pp.65-69
• /
• 2013

In situ measurement of a primary production in East Sea, a marginal sea with a fair accessibility, is nonetheless an arduous task because of dynamic variability. In this study, we estimated the mean value of background (gross) primary production over the warm region of the East Sea based on a biogeochemical hypothesis. We propose an immiscible-shoaling hypothesis for the estimation of primary production, which assumes that primary production in the warm region occurred only by the nutrient supply through the Korea Strait. Annual primary production thus estimated is $209\;gC\;m^{-2}\;y^{-1}$, which is comparable to the satellite-based estimates of net primary production in the region. However, since this hypothesis assumes that primary production is based on only the new nutrients supplied to the system, primary production would increase by 40% if we release the assumption, and assume f = 0.6. This suggests that nutrient influx through the Korea Strait alone is more than enough to support primary production previously reported. Primary production may increase as much as two times if we considered other external perturbations excluded intentionally to estimate the background level of primary production, such as coastal upwelling, submerged ground water discharge, aeolian input, ocean dumping, and mixing by typhoons as well as the contribution of cyanobacteria that has not been quantified in the region. This implies the primary production in the warm region of the East Sea would be comparable to that of the Peru upwelling region with f = 0.6.

• Proceedings of the KSRS Conference
• /
• 2002.10a
• /
• pp.3-6
• /
• 2002

In this study, we investigate the atmospheric environment changes in the aspect of optical remote sensing using surface observation data from 1971 to 2000 of Korea Meteorological Administration. Visibility, spatially averaged over Korean peninsula, is systematically reduced from about 28km to 18km during the last 30 years. It means that atmospheric conditions for the optical remote sensing over Korean peninsula are growing worse and worse due to the degradation of air quality. The 30-year average of cloud amount shows a strong seasonal variation, maximum(75%) in summer and minimum (35%) in autumn. Precipitation also shows a very similar variation pattern with cloud. The temperature and sea level pressure show a opposite seasonal change pattern, maximum(minimum in SLP) in summer and minimum(maximum in SLP) in winter, respectively. Relative humidiy(RH) is one of the variables mostly affected by urbanization or urban heat island. As a results, annual mean RH is decreased from 73% to 68% during last 30 years. When we take into account the favorable and unfavorable factors all together, summer and autumn are the worst and the best season for optical remote sensing in Korea.

• 한국해양학회지
• /
• v.7 no.2
• /
• pp.86-97
• /
• 1972

The tides, tidal currents and tidal prisms at Inchon Harbor are studied with recent data. The tides at Inchon Harbor is of semi-diurnal type having a spring range of 798cm and a phase age of 2 days. The monthly mean sea level at Inchon has a maximum at August and a minimum at January with a annual range of about 40cm. the tidal currents at Inchon Outer Harbor are of semi-diurnal type same as tides and nearly reversing type. The flood and ebb currents set north and south with a velocity of about 90-175 cm/sec and 120-225 cm/sec at spring tide and begin 0.2 hours after L.W. and 0.7 hours after H. W., respectively. Non-tidal currents flow southward with 10-20 cm/sec at west side of the stream and northward with 15-20 cm/sec at east side of the stream at Inchon Outer Harbor. The flood volume through the Inchon Outer Harbor fluctuates fortnightly from 590 10$\^$6/㎥ spring tide to 260 $10^6/m^3$ at neap tide and ebb volume changes from 470 $10^6/m^3$ at spring tide to 200 $10^6/m^3$ at neap tide, respectively. The flow area along the channel to the Estuary of Yeomha is controlled by the tidal prism as expressed by $A=1.14{\times}10^{-4}P^{0.966}$

• Journal of Korean Society for Atmospheric Environment
• /
• v.18 no.4
• /
• pp.253-264
• /
• 2002

Surface ozone concentrations measured at 40 monitoring sites in three major cities (Seoul, Busan, and Daegu) of Korea during 1993~2000 were analyzed to understand the characteristics of temporal and spatial distributions. Trends were analyzed for annual mean, 95th percentiles of daily 8-hour maximum and days exceeding 8-h ozone standard of 60 ppb. Three indicators exhibited increasing trends (+0.75 ppb yr$^{-1}$ , +2.20 ppb yr$_{-1}$ , and +5.35 days yr$_{-1}$ on average) throughout the study period at all cities. Diurnal and seasonal variations were the largest in Seoul followed by Daegue and Busan, due to the high photochemical production and titration of ozone (Seoul), strong wind and constant supply of background ozone from the ocean (Busan). In the urban centers and industrial areas at all cities, scavenging of ozone by NO reduces the daily 8-hour maximum ozone by 10 ppb on average. High concentrations of ozone have frequently occurred in downwind eastern (Seoul and Daegu) or northern (Busan) sides of the territory. In particular, the coastal area of Busan had relatively high ozone level due to the local sea land breeze circulation. The results indicated that the temporal and spatial variations of ozone concentration were non -uniform and were closely related to the local environments; emission levels, climates, and geographic locations.

• Journal of Ecology and Environment
• /
• v.42 no.1
• /
• pp.12-19
• /
• 2018

Background: The objective of this study was to determine the relationship between soil environmental factors and halophyte distribution in the west coast of South Korea. Soils of our study sites were categorized into two groups: salt marsh and estuary marsh. Results: Salinity was higher in the salt marsh group than that in the estuary marsh group. However, total nitrogen, silt, and clay contents were higher in the estuary marsh group than those in the salt marsh group. Although altitude had a wider range in the salt marsh group, the mean altitude was higher in the estuary marsh group than that in the salt marsh group. Annual halophytes of seed propagation species were distributed parallel to the coast line on salt marsh. Higher coverage of vegetation was found in the area closer to the coast line. Plant density was higher near dead parental plants in estuary marsh, showing less difference in area that was more distant from the coast line. Conclusions: Results of canonical correspondence analysis (CCA) for vegetation distribution and sediment environmental factors and germination analysis in the coast line showed significant relationship with halophyte distribution. Therefore, they can be used as an indicator of coastal plant movement due to sea level rise.

• Journal of Korean Society on Water Environment
• /
• v.35 no.6
• /
• pp.580-588
• /
• 2019

The flow of the middle and downstream of the Yeongsan River is stagnant by two weirs of Seungchon and Juksan and the estuary dam and maintained in freshwater. In this study, the Environmental Fluid Dynamics Code-National Institute of Environment Research(EFDC-NIER) model was applied to the Yeongsan River to simulate water flow, temperature, and salinity stratification. The EFDC-NIER model is an improved model which can simulate multi-functional weirs operation, multiple algal species, and the vertical movement mechanism of algal based on the EFDC model. The simulation results for the water level, water temperature, velocity, and salinity reproduced the observed values well. The mean absolute error(MAE) of the model calibration in the annual variations of the water level was 0.1-0.3 m, water temperature was 0.8-1.7 ℃, velocity was 4.5-7.1 cm/sec, and salinity was 1.5 psu, respectively. In the case of scenario simulation for the full opening of the estuary dam, the water level of the estuary dam was directly impacted by the tide so it was predicted to rise - 1.35 m to 0.2 m on average sea level. The velocity was also predicted to increase from 2.7 cm/sec to 50.8 cm/sec, and the flow rate to increase from 53 ㎥/sec to 5,322 ㎥/sec.