• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.237-237
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• 2015

The district of Marlborough has had more than its share of river management projects over the past 150 years, each one uniquely affecting the geomorphology and flood hazard of the Wairau Plains. A major early project was to block the Opawa distributary channel at Conders Bend. The Opawa distributary channel took a third and more of Wairau River floodwaters and was a major increasing threat to Blenheim. The blocking of the Opawa required the Wairau and Lower Wairau rivers to carry greater flood flows more often. Consequently the Lower Wairau River was breaking out of its stopbanks approximately every seven years. The idea of diverting flood waters at Tuamarina by providing a direct diversion to the sea through the beach ridges was conceptualised back around the 1920s however, limits on resources and machinery meant the mission of excavating this diversion didn't become feasible until the 1960s. In 1964 a 10 m wide pilot channel was cut from the sea to Tuamarina with an initial capacity of $700m^3/s$. It was expected that floods would eventually scour this 'Wairau Diversion' to its design channel width of 150 m. This did take many more years than initially thought but after approximately 50 years with a little mechanical assistance the Wairau Diversion reached an adequate capacity. Using the power of the river to erode the channel out to its design width and depth was a brilliant idea that saved many thousands of dollars in construction costs and it is somewhat ironic that it is that very same concept that is now being used to deal with the aggradation problem that the Wairau Diversion has caused. The introduction of the Wairau Diversion did provide some flood relief to the lower reaches of the river but unfortunately as the Diversion channel was eroding and enlarging the Lower Wairau River was aggrading and reducing in capacity due to its inability to pass its sediment load with reduced flood flows. It is estimated that approximately $2,000,000m^3$ of sediment was deposited on the bed of the Lower Wairau River in the time between the Diversion's introduction in 1964 and 2010, raising the Lower Wairau's bed upwards of 1.5m in some locations. A numerical morphological model (MIKE-11 ST) was used to assess a number of options which led to the decision and resource consent to construct an erodible (fuse plug) bank at the head of the Wairau Diversion to divert more frequent scouring-flows ($+400m^3/s$)down the Lower Wairau River. Full control gates were ruled out on the grounds of expense. The initial construction of the erodible bank followed in late 2009 with the bank's level at the fuse location set to overtop and begin washing out at a combined Wairau flow of $1,400m^3/s$ which avoids berm flooding in the Lower Wairau. In the three years since the erodible bank was first constructed the Wairau River has sustained 14 events with recorded flows at Tuamarina above $1,000m^3/s$ and three of events in excess of $2,500m^3/s$. These freshes and floods have resulted in washout and rebuild of the erodible bank eight times with a combined rebuild expenditure of $80,000. Marlborough District Council's Rivers & Drainage Department maintains a regular monitoring program for the bed of the Lower Wairau River, which consists of recurrently surveying a series of standard cross sections and estimating the mean bed level (MBL) at each section as well as an overall MBL change over time. A survey was carried out just prior to the installation of the erodible bank and another survey was carried out earlier this year. The results from this latest survey show for the first time since construction of the Wairau Diversion the Lower Wairau River is enlarging. It is estimated that the entire bed of the Lower Wairau has eroded down by an overall average of 60 mm since the introduction of the erodible bank which equates to a total volume of $260,000m^3$. At a cost of $$0.30/m^3$ this represents excellent value compared to mechanical dredging which would likely be in excess of $$10/m^3$. This confirms that the idea of using the river to enlarge the channel is again working for the Wairau River system and that in time nature's "excavator" will provide a channel capacity that will continue to meet design requirements.

• Journal of Soil and Groundwater Environment
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• v.14 no.4
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• pp.33-44
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• 2009

Water curtain of an underground LPG storage cavern is a facility to prevent leakage of high pressure gases, for which groundwater should flow freely towards the cavern and groundwater level also must be stably maintained. In this study, in order to evaluate qualities of seepage water and surrounding groundwater of an underground LPG storage cavern in Yeosu, 4 rounds of samplings, field measurements and laboratory analyses (February, May, August, October of 2007) were conducted. According to field measurements, pH was weak acidic to neutral but it gradually increased with time. Electrical conductivity (EC) of groundwater near a salt stack showed very high values between 10.47 and 38.50 mS/cm. Dissolved oxygen (DO) showed a very wide range of 0.20~8.74 mg/L and a mean of oxidation-reduction potential (ORP) was 159 mV, which indicated an oxidized condition. Levels of $Fe^{2+}$ and $Mn^{2+}$ were mostly less than 3 mg/L. All of seepage waters showed a Na-Cl type while only groundwater near the salt stack showed a Na-Cl type with a high total dissolved solid. The other groundwaters exhibited typical $Ca-HCO_3$ types. Levels of aerobic bacteria were mostly very high (573-39,520 CFU/mL). Based on the analyses of these hydrochemistry and biological characteristics, it is concluded that there are no particular problems in groundwater and seepage water, which not causing a trouble in the cavern operation. However, both for control of bio-clogging and for sustainable operation of the water curtain system, a regular hydrochemical and microbiological monitoring is required for the seepage water and surrounding groundwater.

• Journal of Korea Water Resources Association
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• v.56 no.4
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• pp.235-243
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• 2023

Due to the revision of the River Act and the enactment of the Act on the Investigation, Planning, and Management of Water Resources, a regular bed change survey has become mandatory and a system is being prepared such that local governments can manage water resources in a planned manner. Since the topography of a bed cannot be measured directly, it is indirectly measured via contact-type depth measurements such as level survey or using an echo sounder, which features a low spatial resolution and does not allow continuous surveying owing to constraints in data acquisition. Therefore, a depth measurement method using remote sensing-LiDAR or hyperspectral imaging-has recently been developed, which allows a wider area survey than the contact-type method as it acquires hyperspectral images from a lightweight hyperspectral sensor mounted on a frequently operating drone and by applying the optimal bandwidth ratio search algorithm to estimate the depth. In the existing hyperspectral remote sensing technique, specific physical quantities are analyzed after matching the hyperspectral image acquired by the drone's path to the image of a surface unit. Previous studies focus primarily on the application of this technology to measure the bathymetry of sandy rivers, whereas bed materials are rarely evaluated. In this study, the existing hyperspectral image-based water depth estimation technique is applied to rivers with vegetation, whereas spatio-temporal hyperspectral imaging and cross-sectional hyperspectral imaging are performed for two cases in the same area before and after vegetation is removed. The result shows that the water depth estimation in the absence of vegetation is more accurate, and in the presence of vegetation, the water depth is estimated by recognizing the height of vegetation as the bottom. In addition, highly accurate water depth estimation is achieved not only in conventional cross-sectional hyperspectral imaging, but also in spatio-temporal hyperspectral imaging. As such, the possibility of monitoring bed fluctuations (water depth fluctuation) using spatio-temporal hyperspectral imaging is confirmed.

• Journal of the Korean Institute of Traditional Landscape Architecture
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• v.32 no.1
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• pp.107-119
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• 2014

The purpose of this study is to examine the current status of vascular plants and naturalized plants growing in the Seongeup Folk Village in Jeju and to consider and compare their distribution patterns and the characteristics of emergence of naturalized plants in other folk villages and all parts of Jeju, thereby exploring measures to well manage naturalized plants. The result of this study is as follows.11) The total number of vascular plants growing in Seongeup Folk Village is identified to be 354 taxa which include 93 families, 260 genus, 298 species, 44 varieties and 12 breeds. Among them, the number of naturalized plants is 55 taxa in total including 22 families, 46 genus, 53 species, and 2 varieties, which accounts for 21.7% of the total of 254 taxa identified all over the region of Jeju. The rate of naturalization in Seongeup Folk Village is 15.5%, which is far higher than the rates of plant naturalization in Hahoi Village in Andong, Yangdong Village in Gyeongju, Hangae Village in Seongju, Wanggok Village in Goseong, and Oeam Village in Asan. Among the naturalized plants identified within the targeted villages, the number of those growing in Jeju is 9 taxa including Silene gallica, Modiola caroliniana, Oenothera laciniata, Oenothera stricta, Apium leptophyllum, Gnaphalium purpureum, Gnaphalium calviceps, Paspalum dilatatum and Sisyrinchium angustifolium. It is suggested that appropriate management measures that consider the characteristics of the gateway to import and the birthplace of the naturalized plants are necessary. In the meantime, 3 more taxa that have not been included in the reference list of Jeju have been identified for the first time in Seongeup Folk Village, which include Bromus sterilis, Cannabis sativa and Veronica hederaefolia. The number of naturalized plants identified within the gardens of unit-based cultural properties is 20 taxa, among which the rate of prevalence of Cerastium glomeratum is the highest at 62.5%. On the other hand, the communities of plants that require landscape management are Brassica napus and other naturalized plants, including Cosmos bipinnatus, Trifolium repens, Medicago lupulina, Oenothera stricta, O. laciniata, Lotus corniculatus, Lolium perenne, Silene gallica, Hypochaeris radicata, Plantago virginica, Bromus catharticus and Cerastium glomeratum. As a short-term measure to manage naturalized plants growing in Seongeup Folk Village, it is important to identify the current status of Cosmos bipinnatus and Brassica napus that have been planted for landscape agriculture, and explore how to use flowers during the blooming season. It is suggested that Ambrosia artemisiifolia and Hypochaeris radicata, designated as invasive alien plants by the Ministry of Health and Welfare, should be eradicated initially, followed by regular monitoring in case of further invasion, spread or expansion. As for Hypochaeris radicata, in particular, some physical prevention measures need to be explored, such as for example, identifying the habitat density and eradication of the plant. In addition, it is urgent to remove plants, such as Sonchus oleraceus, Houttuynia cordata, Crassocephalum crepidioides, Erigeron annuus and Lamium purpureum with high index of greenness visually, growing wild at around high Jeongyi town walls. At the same time, as the distribution and dominance value of the naturalized plants growing in deserted or empty houses are high, it is necessary to find measures to preserve and manage them and to use the houses as lodging places.

• Journal of the Korean Institute of Traditional Landscape Architecture
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• v.32 no.2
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• pp.68-81
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• 2014

This study was conducted to identify the spacialty, to illuminate the existence and values of Myeongwoldae(明月臺) and Forest Myeongwol, and to suggest the sustainable usage, preservation and management plans with the purpose of ecological and cultural landscaping characteristic and value identification. The result of the study is as follows. Castle Myeongwol and Port Myeongwol shows the status of Hallim-eup Myeongwol District which is the administrative center of western Jeju as well as is the fortress. Building Wolgyejeongsa and School Woohakdang, the head temple of education and culture, located in Myeongwol District represents the spaciality of Myeonwol-ri which was the center of education. Stand Myeongwol is one of the most representative Confucian cultural landscapes in Jeju Island and the field of communion with nature where scholars enjoy poetries, nature, changgi(Korean chess), and go in the Joseon Dynasty period. It was found that the current relics of Myeongwoldae was recovered through the maintenance project conducted by Youth Group Myeongwol composed with Hongjong-si(洪鍾時) as the center during the Japanese colonial era in 1931. It seems that the stonework of Myeongwoldae composed of three levels in the order of square, octagon, and circle based on the heaven-man unity theory of Confucianism and the octagon in the middle is the messenger of Cheonwonjibang(天圓地方), in other words, between the square-shaped earth and the circle-shaped sky. It is assumed that both Grand Bridge Myeongwol and Bridge Myeongwol were constructed as arched bridges in early days. Bridge Myeongwol is the only arched bridge remaining in Jeju Island now, which has the modern cultural heritage value. In Forest Myeongwol, 97 taxa of plants were confirmed and in accordance with 'Taxonomic Group and Class Criteria of Floristic Specific Plants', eight taxa were found; Arachniodes aristata of FD IV and Ilex cornuta, Piper kadsura, Litsea japonica, Melia azedarach, Xylosma congestum, Richosanthes kirilowii var. japonica, Dichondra repens, Viburnum odoratissimum var. awabuki of FD III. Otherwise, 14 taxa of naturalized plants including Apium leptophylihum which is imported to Jeju Island only were confirmed. In Forest Myeongwol, 77 trees including 41 Celtis sinensis, 30 Aphananthe aspera, two Wylosma congestum, a Pinus densiflora, a Camellia japonica, a Melia azedarach, and an Ilex cornuta form a colony. Based on the researched data, the preservation and plans of Myeongwoldae and Forest Myeongwol is suggested as follows. Myeongwoldae, Bridge Myeongwol, and Forest Myeongwol should be managed as one integrated division. Bridge Myeongwol, an arched bridge which is hard to be found in Jeju Island is a high-standard stonework requiring long-term preservation plans. Otherwise, Grand Bridge Myeongwol that is exposed to accident risks because of deterioration and needs safety diagnosis requires measures according to the result of precise safety diagnosis. It is desirable to restore it to a two-sluice arched bridge as its initial shape and to preserve and use it as a representative local landmark with Stand Myeongwol. In addition, considering the topophsis based on the analysis result, the current name of Jeju Special Self-Governing Province Monument No. 19 'Myoengwol Hackberry Colony' should change to 'Myeongwol Hackberry-Muku Tree Colony'. In addition, the serial number system which is composed without distinction of hackberry and muku tree should be improved and the regular monitoring of big and old trees, specific plants, and naturalized species is required.