An estimation of discharge using mean velocity derived through Chiu’s velocity equation

To estimate discharge through the year (dry season and flood season), a stage–discharge curve derived through monitoring discharge in about 20 rivers or channels every year has been generally used. As revealed in many studies, however, the stage–discharge curve is inevitably affected by their hydraulic characteristics. This suggests that the use of a stage–discharge curve derived without considering hydraulic characteristics unique to a river or channel may produce significant errors in estimating discharge at not only low stage (during dry seasons) but also high stage (during flood seasons). In this study, the authors proposed a method to calculate the mean velocity and to estimate the discharge considering the hydraulic characteristics of a river or channel (e.g. the bed slope, wetted perimeter, width, kinematic viscosity, etc.); the method was developed using Chiu’s velocity equation. With the proposed method, it is possible to calculate a maximum velocity that is difficult to measure in an open channel, derive an entropy function representing the equilibrium of the channel, and thereby, estimate reliable discharge even in a flood season. To comparatively verify the utility of the proposed method, relations between the results of analysis using Manning’s and Chezy’s mean velocity equations and the values of measured discharge were addressed together. The results of analysis using lab data sets and measured data sets revealed that the proposed method was significantly more accurate in estimating discharge, even in flood seasons, when compared with the conventional method.     

Detection of mean-field bias of the radar rain rate using rain gauges available within a small portion of radar umbrella: a case study of the Donghae (East Sea) radar in Korea

Observation of a storm approaching from the ocean to the in-land area is very important for the flood forecasting. Radar is generally used for this purpose. However, as rain gauges are mostly located within the in-land area, detection of the mean-field bias of radar rain rate cannot be easily made. This problem is obviously different from that with evenly-spaced rain gauges over the radar umbrella. This study investigated the detection problem of mean-field bias of radar rain rate when rain gauges are available within a small portion of radar umbrella. To exactly determine the mean-field bias, i.e. the difference between the radar rain rate and the rain gauge rain rate, the variance of the difference between two observations must be small; thus, a sufficient number of observations are indispensable. Therefore, the problem becomes determining the number of rain gauges that will satisfy the given accuracy, that being the variance of the difference between two observations. The dimensionless error variance derived by dividing the expected value of the error variance by the variance of the areal average rain rate was introduced as a criteria to effectively detect the mean field bias. Here, the variance of the areal average rain rate was assumed to be the climatological one and the expectation for the error variance could be changed depending one the sampling characteristics. As an example, this study evaluated the rainfall observation over the East Sea by the Donghae radar. About 6.8 % of the entire radar umbrella covered in-land areas, where the rain gauges were available. It was found that, to limit the dimensionless error variance to 2 %, a total of 26 rain gauges are required for the entire radar umbrella; whereas, a total of 24 rain gauges would be required within the in-land area with available for the rain gauge data.     

Rainfall frequency analysis using a mixed GEV distribution: a case study for annual maximum rainfalls in South Korea

Extreme rainfalls in South Korea result mainly from convective storms and typhoon storms during the summer. A proper way for dealing with the extreme rainfalls in hydrologic design is to consider the statistical characteristics of the annual maximum rainfall from two different storms when determining design rainfalls. Therefore, this study introduced a mixed generalized extreme value (GEV) distribution to estimate the rainfall quantile for 57 gauge stations across South Korea and compared the rainfall quantiles with those from conventional rainfall frequency analysis using a single GEV distribution. Overall, these results show that the mixed GEV distribution allows probability behavior to be taken into account during rainfall frequency analysis through the process of parameter estimation. The resulting rainfall quantile estimates were found to be significantly smaller than those determined using a single GEV distribution. The difference of rainfall quantiles was found to be closely correlated with the occurrence probability of typhoon and the distribution parameters.     

A Study of the Improvement of Planning Systems for Land Use Control in Agricultural Heritage Sites

The number of GIAHS sites is increasing these days and will continue to do so gradually in East Asian countries including Korea, China and Japan. As a result, conservation of heritage sites is more and more important, especially in Korea. Dealing with issues surrounding land use conflicts are important for conservation of heritages in order to harmonize between conservation and development to prevent reckless development. This study aims to identify measures for land use management and control to allow for sustainable development around agricultural heritage system sites. The results point to the importance of public-private partnerships and local ordinance systems or comprehensive planning of land use controls for agricultural heritage system sites.     

Development and application of a novel miniature in situ microprofiler (NAFRI BelpI)

We have developed a novel miniature in situ microprofiler (NAFRI BelpI) for coastal and deep-sea studies. The BelpI can carry up to three oxygen microsensors, and it allows for simultaneous replicate measurements in a relatively small area. All functions can be controlled and programmed via a small magnetic bar and three reed switches; this feature facilitates the initial setup both onboard and underwater. The large LCD window shows basic information such as the movement intervals of the linear stage, number of replicate measurements, waiting time between measurements, and the pA from the microsensors. From high-resolution vertical profiles of oxygen in coastal sediment measured using the microsensors, the diffusivity boundary layer thicknesses was determined to be in the range 0.30–0.35 mm. In addition, the time-series measurement of oxygen profiles in permeable sandy sediment showed advective transport of oxygen into pore water by tidal agitation. Two examples of in situ measurement using a BelpI suggest that it can be widely applied to the study of the sediment-water interface.     

Comparison of primary productivity algorithms for Korean waters

This study compares five primary productivity algorithms for Korean waters. Five algorithms are in the form of vertical generalized production models: One algorithm is for gross primary production and four are for net primary production. The five algorithms were evaluated using 117 in situ primary production datasets observed by 20 cruises from 1994 to 2011 in Korean waters (East Sea, Yellow Sea, East China Sea, and Yeosu Bay). The results show that the regionally-tuned variants give better results than the original formulation. We recommend, among the tested algorithms, YSVGPM (Yellow Sea Vertically Generalized Productivity Model) for gross primary productivity algorithm and Kameda-Ishizaka algorithm for net primary productivity algorithm for estimating primary production in Korean waters.     

Impact of estuary barrage construction on fish assemblages in the lower part of a river and the role of fishways as a passage

The construction of an estuary barrage, an instream structure in the lower reaches of a river, causes significant physical changes in water flow patterns and river morphology, and results in altered environmental conditions. Here, we examined the impact of the Geum River estuary barrage, completed in 1990, on fish assemblages by using a literature search and fresh surveys of fishways in the barrage. We found that fish assemblages upstream and downstream of the barrage were altered following its completion. After construction, more species were found in the freshwater area, with a particularly great increase in freshwater species. Conversely, estuarine and marine species were only consistently caught in the downstream salt-water area, although the number of species increased. In total, 15,829 fish from 47 species and 20 families were identified at the three types (pool and weir, rubble type, and boat passage) of fishways in the barrage. The dominant species were Chelon haematocheilus, an estuarine species, Coilia nasus, a diadromous species, and Erythroculter erythropterus, a freshwater species. The mean total length of fish (101.9 ± 76.0 mm) in the boat passage fishway was approximately 100 mm lesser than those in the pool and weir (207.2 ± 112.8 mm) and rubble type (205.8 ± 112.7 mm) fishways. The boat passage fishway was the most efficient for fish movements. The current fishway system is not sufficient for fish migration, and thus additional ways are required to improve the system such as the boat passage. Few estuarine or diadromous species were found in both freshwater and salt-water areas, but freshwater fishes that accidently moved to salt-water area actively used fishways. Therefore, fishway management in the Geum River estuary barrage has to focus on freshwater fish; however, this may need to change to a focus on migratory fishes depending on ecological life cycles of migratory fish.     

Effect of different wavelengths of light on the antioxidant and immunity status of juvenile rock bream, <Emphasis Type="Italic">Oplegnathus fasciatus</Emphasis>, exposed to thermal stress

We investigated the effect of light wavelengths on antioxidant and immunity parameters in juvenile rock bream, Oplegnathus fasciatus, exposed to thermal stress (25 and 30°C). We exposed the fish to light emitting diodes (LEDs) emitting green (520 nm) and red light (630 nm) of 0.25 and 0.5 W/m² intensity, and measured the activity, and mRNA and protein expression levels of the antioxidant enzymes, superoxide dismutase, catalase, and glutathione peroxidase. We also determined the levels of plasma hydrogen peroxide (H₂O₂), melatonin, and lysozyme. Furthermore, the mRNA and protein levels of caspase-3 were measured and terminal transferase dUTP nick end labeling (TUNEL) assays were performed. We observed that mRNA expression and activities of antioxidant enzymes and plasma H₂O₂ levels were significantly higher after exposure to high temperatures. However, increases in these parameters were significantly lower after exposure to green LED light. The plasma melatonin and lysozyme levels were significantly lower in the different groups after exposure to high temperatures; however, in groups exposed to green LED light, their levels were significantly higher than those in the control group. The expression pattern of caspase-3 mRNA was similar to that of H₂O₂. The TUNEL assay showed that apoptosis was markedly higher at higher water temperatures than that at 20°C. These results indicate that high water temperatures induce oxidative stress and decrease the immunity in juvenile rock bream but green LED light inhibits the rise in oxidative stress and combats the decrease in immunity and should, thus, be useful in the culture of rock bream.     

Modeling of marine litter drift and beaching in the Japan Sea

Characteristics of drift and beaching of floating marine litter in the Japan Sea are examined numerically using the reanalysis data of the Japan Sea Forecasting System of Kyushu University. The residence time of model marine litter deployed uniformly over the surface of the Japan Sea strongly depends on the buoyancy ratio. However, almost all litter beaches or flows out through straits within 3 years. Experiments with inputs of litter imposed at large cities and the Tsushima Straits as well as river basins of the Japan Sea exhibit a good agreement with beach surveys with regard to country ratios of beached litter along the Japanese coast in cases of lighters. In a case of lighter, almost all lighters originating from Japan beach along the Japanese coast, while almost all lighters originating from a country surrounding the Japan Sea except Japan beach along the coast of that country and the Japanese coast.