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H. Araki
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LONG-TERM CHANGE OF WATER QUALITY IN THE RESERVOIR OF THE ISAHAYA BAY RECLAMATION PROJECT Y. Mitsugi; N. Vongthanasunthorn; Y. Mishima; K. Koga; H. Araki; P. Ittisukananth
Lowland Technology International Vol 15 No 1, June (2013)
Publisher : International Association of Lowland Technology

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Abstract

In 1997, the Isahaya Reservoir was constructed at the innermost part of Isahaya Bay, Japan to prevent natural disasters and to develop water resources for large-scale farm lands. The main purposes of this study were to analyze the mechanisms underlying the water quality changes observed and to collect significant information for water quality management at the reservoir. Observed water quality parameters on chlorophyll-a, suspended solids, total nitrogen, dissolved inorganic nitrogen, total phosporus, dissolved inorganic phosphorus and chloride ion were analyzed by using a water quality model. It was found taht the results obtained from the developed water quality model agreed with the observed data. After calibrating the observed data, a simple sensitivity analysis was conducted to demonstrate the mechanisms of the water quality changes. The major water quality problems were suspended solids that had been resuspended by strong wind and eutrophication due to the enrichment of nutrients. The major mechanisms of water quality changes in the Isahaya reservoir were a coagulation and flocculation by brackish water and the transformation process of phosphorus. The coagulation affected the settling velocity of suspended solids and dissolved phosphorus. It was also revealed that the resolution process of dissolved phosphorus from suspended solids was controlled by the salinity.
DEVELOPMENT OF AN EVALUATION METHOD FOR RIVER ENVIRONMENT H. Araki; K. Koga; Y. Nishi; Y. Kajiya; S. Imae; S. Kimura; K. Hirano; M. Sakanashi; S. Toyosaki; H. Fukuyama
Lowland Technology International Vol 1 No 2, Dec (1999)
Publisher : International Association of Lowland Technology

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Assessment in planning and designing process is necessary especially for nature-oriented river. The main purpose of this study is to develop an assessment method for river environment. At a workshop composed of experts on river environment, a viewpoint to identify characteristics of watershed and/or river environment was added to viewpoints of the River Council in Japan. Furthermore, the new concept of "intermediate nature" is proposed to develop a goal-oriented assessment method. In this study, the prototype of a new assessment method "EMOREK" is proposed, somewhat similar to the AMOEBA method developed in the Netherlands. A case study on the T-river in Japan was carried out to realize the capability of the assessment method through problem analysis on the river environment.
PREDICTION MODEL OF INUNDATION IN PUMPED-FIELD LOWLANDS AND SCENARIOS FOR IMPROVING ITS PERFOMANCE N. Cao Don; H. Araki; H. Yamanishi; K. Koga
Lowland Technology International Vol 5 No 1, June (2003)
Publisher : International Association of Lowland Technology

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During rainy season, frequent flooding by strom water is one of the most serious problems in lowland areas, causing heavy effect on transportation, agriculture, industry, and economic activities. As a result, the required drainage water levels in this area are generally lower than the water levels of boundary rivers. Under such circumstances, pumping system should be designed from a viewpoint of integrated control floods. The Nam Ha lowland, in Vietnam, bounded by four surrounding rivers, is selected as a case study. The operation scheme in this area is a key factor for drainage and flood protection. This developed mathematical model can be used as a tool to evaluate the present drainage system as well as flooding processes in the field as well as inundation areas and water levels along drainage channels. It is found that the proposed model can be applied to evaluate integrated flood control system for pumped-field lowland. Such an operating system provides an effective tool by means of which the drainage system can be operated appropriately taking into account of tidal effects, rainfall intensity, and reaching time of the rainwater.
HYDRAULICS OF GROUNDWATER FLOW AND MECHANICAL PROPERTIES AFFECTING AQUIFER SYSTEM COMPRESSION IN SHIROISHI, SAGA PLAIN N. Cao Don; H. Araki; H. Yamanishi; K. Koga
Lowland Technology International Vol 5 No 2, Dec (2003)
Publisher : International Association of Lowland Technology

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Land subsidence in Shiroishi area in the Saga plain, Japan, has become noticeable since 1960s. Water supplied to agriculture has traditionally been a high priority for water managers in this region. Intense withdrawals of groundwater in excess of natural recharge have resulted in land subsidence in this region. Land subsidence can have several negative economic and social implications. Many problems associated with land subsidence can be observed in this area. In this paper, a numerical model that incorporated 3-D groundwater flow and I-D ground consolidation was applied to simulate groundwater level and ground consolidation. It is found that subsidence rapidly occurs throughout the area with the central prone in Shiroishi basin. Certain hydrogeologic parameters such as inelastic storage coefficient, elastic storage coefficient, and hydraulic conductivity of soil layers contribute significantly effects to both the rate and magnitude of consolidation. Moreover, a considerable reduction in discharge is supposed necessary for future development of the region to alleviate the effects of groundwater overdraft.
ESTIMATING THE POTENTIAL FOR CONJUNCTIVE WATER MANAGEMENT IN COASTAL PLAINS N. Cao Don; H. Araki; N. T. Minh Hang; H. Yamanishi; K. Koga
Lowland Technology International Vol 8 No 1, June (2006)
Publisher : International Association of Lowland Technology

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This paper presents the development and application of a conjunctive water management model for lowland catchments. The model incorporates a simulation model and a management model to simulate groundwater movement, ground consolidation and to search for the potential pumping amount of groundwater without violating physical and environmental constraints. The results reveal that groundwater levels in a coastal aquifer greatly vary in response to pumping. Consequently subsidence rapidly occurs throughout the area. The study also suggests that conjunctive water management can be used to improve water supply reliability, to reduce groundwater overdraft and land subsidence and to improve environmental conditions.
LOWLAND TECHNOLOGY INTERNATIONAL SPECIAL ISSUE – FOREWORD – H. Araki; S. Hayashi
Lowland Technology International Vol 9 No 2, Dec (2007)
Publisher : International Association of Lowland Technology

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Abstract

Lowlands imply regions having low elevation, which are particularly susceptible to climatic, sea water level and environmental changes. For example, global warming, which appears to be causing a rise in sea level, must ultimately affect the safety of coastal dikes and other coastal infrastructures, as well as threaten the water and ecological systems in lowland areas. Lowland regions are also particularly vulnerable to natural disasters. In 2004, several large earthquakes and Tsunami in the Asian region caused major damage in lowland areas. The importance of exploration of problems in lowlands has been recognized by researchers, planners, engineers and administrators all over the world.
SEGREGATION OF MICROPHYTOBENTHIC CHLOROPHYLL-A FROM SUSPENDED PARTICLES DURING TIDAL CYCLE IN NANAURA MUDFLAT, ARIAKE SEA, JAPAN C.-H. Koh; J. S. Khim; H. Araki; H. Yamanishi; K. Koga
Lowland Technology International Vol 9 No 2, Dec (2007)
Publisher : International Association of Lowland Technology

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The fluxes of microphytobenthic chlorophyll a (Chl-a) and suspended particulate matter (SPM) in water column and their relationship against tidal current have been examined during 15-days of full spring-neap tidal periods in the upper intertidal flat of Nanaura, Saga, Ariake Sea, Japan. The flood-ebb and spring-neap tidal conditions influenced within-day and daily variability in the fluxes of Chl-a and SPM, in terms of tidal energy. The Chl-a flux decreased relatively at slower pace than corresponding SPM flux at stage of decelerating incoming tide, which indicated the segregation of Chl-a from SPM followed by the slower settlement at depositional period. This ‘decoupling’ trend was consistently observed during the high tidal energy period of spring, particularly during the lower wind period (0-1 m s-1), but this was no more prevalent during the low tidal energy of neap and/or higher wind period (3-5 m s-1).
HYDROGEOCHEMICAL DESCRIPTION OF GROUNDWATER IN A COASTAL LOWLAND PLAIN NEAR THE ARIAKE SEA OF JAPAN N. Cao Don; Mohan S. Kumar; H. Araki; H. Yamanishi
Lowland Technology International Vol 10 No 1, June (2008)
Publisher : International Association of Lowland Technology

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Abstract

In the management of water resources, quality of water is just as important as its quantity. In this paper, an investigation was undertaken to better understand the hydrogeochemistry and hydrologic framework of the Shiroishi plain in Saga, Kyushu, Japan. A network of production boreholes and wells distributed over the studied region were sampled and the waters were analyzed for major ions. The results reveal that, in areas near the shore, salinization is more serious at deeper layers. Geochemical analyses showed that the Shiroishi aquifer has bicarbonate sodium water, with an increase of electrical conductivity, sodium and bicarbonates contents.
ENVIRONMENTAL IMPACTS CAUSED BY PADDY FIELD MANAGEMENT V. V. N. Murty; N. Cao Don; H. Araki
Lowland Technology International Vol 11 No 1, June (2009)
Publisher : International Association of Lowland Technology

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Paddy fields occupy large areas and are an important component of the cropped areas in the Asian Region. In this study, the environmental impacts caused by paddy field management are investigated and studied. It is observed that paddy fields cause both beneficial and adverse effects on the environment. The beneficial effects consist of flood retardation, sediment retention and recharge to groundwater. Important adverse effects are contamination to water resources, effect on human health and methane emissions. Steps needed to mitigate the adverse effects from paddy fields are also considered. These include understanding the water balance components for efficient water management, provision of surface and subsurface drainage systems and recirculation of drainage water. Water quality aspects, which need to be considered while recirculation drainage water and final disposal of the drainage water, are also studied. While all aspects of water quality are important, in general water quality aspects, which need attention, appear to be the total nitrogen and pesticide residues. Further studies are needed to manage both these constituents of the drainage water.
PHOSPHORUS RECOVERY FROM WASTEWATER BY HYDROTALCITE AND ZEOLITE Y. Mishima; H. Araki
Lowland Technology International Vol 12 No 2, Dec (2010)
Publisher : International Association of Lowland Technology

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A system using hydrotalcite and zeolite is developed for the recovery of phosphorus from wastewater having low phospate concetrations. As HT and Ze is independently used, redundant ion species are produced in a desorbing solution. As HT and Ze are used in combination, however, the opposite redundant ion species can be used to desorb PO43- and NH4+, respectively. Simply alkaline NaCl solution is used to desorb/regenerate HT/Ze. Moreover, desorbed substances can be recovered as magnesium ammonium phosphate (MAP) by the addition of Mg. In this paper, the desorption of PO43- and NH4+ from HT and Ze into a single desorbing solution and phosphorus recovery from the desorbing solutions as MAP are experimentally investigated. It is verified that the single desorbing solution can simultaneously desorb HT and Ze. Whereas 95% of phosphate was recovered from the desorbing soluition in which PO43- and NH4+ were accumulated, most of the recovered phosphorus was not MAP but Mg3(PO4)2 (MP). However, when the initial concentrations of PO43- and NH4+ in the desorbing solution increased, MAP was procuded rather easily and more than 90% of P was recovered. Further investigation into application for the practical plant is necessary.
Co-Authors C.-H. Koh H. Fukuyama H. Suhara H. Yamanishi J. S. Khim K. Hirano K. Koga M. Ohno M. Sakanashi Mohan S. Kumar N. Cao Don N. T. Minh Hang N. Vongthanasunthorn P. Ittisukananth S. Hayashi S. Imae S. Juengjarernnirathorn S. Kimura S. Toyosaki V. V. N. Murty Y. Kajiya Y. Mishima Y. Mitsugi Y. Nishi