Search

鞠智城の貯水池と韓国の古代山城の集水遺構を、立地、構造、機能的側面に分けて比較、分析した。鞠智城の貯水池は、韓国古代山城の集水遺構と立地＋構造＋機能的な面で親縁性が高いことが確認された。そして、築造技術的には百済、立地と構造的には百済・高句麗と類似しているといえる。

The purpose of this study is to develop and apply the carbon dioxide (CO2) measurement technique and to elucidate the CO2 concentration dynamics in the reservoir of freshwater regions, where the photosynthetic rate is high and the short-term changes are affected by the inflowing river. To clarify the CO2 concentration dynamics in the surface water, pH, dissolved oxygen (DO) and electric conductivity (EC) has been continuously and monthly measured in Sengari reservoir from 2016 to 2018.The total alkalinity (TA) highly correlated with the electric conductivity, and a linear equation that converts EC to TA was obtained for Sengari reservoir. The values of CO2 partial pressure (pCO2) were calculated using the “CO2SYS” by CDIAC that uses pH and TA. DO and pCO2 fluctuated with high correlation (R2= 0.90). This suggests that CO2 dynamics can be measured in freshwater using this method. DO and pCO2 records at the Sengari reservoir during the summer stratification period, when the photosynthetic rate was high, indicated prominent diurnal variations corresponding to the changes in solar radiation. In summer, surface water CO2 fluctuation had large diurnal change by photosynthesis, and atmospheric CO2 is absorbed to surface water. In the autumn, CO2 in surface water is released to the atmosphere.

長年，国内外の様々な地域で水環境の調査・研究を続けてきたが，最近は，年に1～2回，海外で調査する機会を作るように努め，その結果を継続して報告してきた。特に，アジア地域に力を入れ，マレーシア，インドネシア，中国，韓国と調査してきたが，2019年7月にAOGSがシンガポールで開催された際，シンガポール島全域の調査を行う機会を得たので，その概要を報告する。調査を行ったシンガポール島は，63の島からなるシンガポール共和国最大（東京23区程度）の島で，高度に都市化され，人口密度も高い（世界第2位）。高低差のない国土であるため水資源に乏しく，多数の貯水池と隣国マレーシアから購入した水に頼っている。河川は，勾配がなく緩やかなため，停滞しているところが多く濁っていて水質が悪いと思われたが，実際にサンプリングして分析したところ，水質が悪いのは汽水域など特別な場所に限られ，予想以上に良好な地点が多かった。汚水処理施設の充実と考えられる。人口密度が高く都市化はしているものの，居住空間としては，高層住宅を活かすことで公園や緑地が広くとられており，水辺空間も整備されていて，貴重な自然環境を保全する努力が見られ，学ぶ点が多かった。, Singapore Island, which was surveyed, is the largest island in the Republic of Singapore （about 23 wards in Tokyo） consisting of 63 islands, highly urbanized, and has a high population density （the second largest in the world）. Since it is a land with no difference in elevation, it lacks water resources and relies on many reservoirs and water purchased from neighboring Malaysia. Since the river has no slope and is gradual, it seems that there are many stagnant places and it is cloudy and the water quality is poor, but when actually sampled and analyzed, the poor water quality is found in special places such as brackish water areas. It was limited, and there were many better points than expected.Although the city is densely populated and urbanized, by utilizing high-rise housing as a residential area, there are many green spaces and a waterside space, and efforts to preserve the precious natural environment were seen, and there were many points to learn.

By the heavy rain in the northern part of Kyushu in July 2017, many rivers in the Chikugo River sys-tem were flooded and caused serious damage. In the Sata River located in the middle basin of the Chikugo River system, a large amount of driftwood flowed into the Terauchi dam due to the intensive flood. If driftwood had flowed into the downstream and had been clogged by the bridge piers, the Sata River might have overflowed in wide area near the bridges. Actually, there was little damage in the down-stream area because Terauchi dam had effects of flood control and driftwood trapping. In this study, the quantitative estimating method was developed by using the image processing software, Image J, to esti-mate driftwood volume and sizes over the reservoir area. In addition, the influence of driftwood trapping by the Terauchi dam on the downstream flood damage reduction was estimated by using two-dimensional hydraulic TELEMAC-2D model.

Reservoir sedimentation is one of the most important problems for securing long term achievement of hydropower plant operation in the future. We have already classified the sedimentation problems regarding the reservoir types and proposed effective sediment control measures for regulating reservoirs. On the other hand, sedimentation problems in storage reservoirs need to be more studied. In this paper, we have evaluated the influence of sedimentation progress in storage reservoirs on power generation by analyzing long-term operation record. Finally, future influence of reservoir sedimentation was predicted from the viewpoints of changing active storage capacity, inflow water regime and the maximum hydropower discharge.

広島湾に注ぐ太田川と八幡川において, それぞれの河川に設けられた4つの貯水池(魚切貯水池, 樽床貯水池, 立岩貯水池, 王泊貯水池)の前後および貯水池内上下層における約20年間の水質データを集計して統計処理し, それらの長期的変動を明らかにした。すべての貯水池で共通した現象として, 貯水池のTN/TP が経年的に上昇する傾向が見受けられた。魚切貯水池では貯水池前後のデータが揃い, 貯水池で窒素・リンともトラップされ, 下流で再び人間活動によって添加されていることが理解された。貯水池でトラップされる溶存態無機窒素(DIN)と溶存態無機リン(DIP)の量を平均河川水流量とそれらの貯水池前後での平均濃度差から計算したところ, DINで6.9tNy-1, DIPで0.63tPy-1となった。仮に同様のことが太田川水系に設置された15の貯水池で起こっていると仮定すると, 広島湾に本来流入するはずだったDINとDIPをそれぞれ約30%および35%をこれらの貯水池がトラップしていると見積もられる。, Long-term changes in water quality in and upstream/downstream of four reservoirs (Uokiri, Tarutoko, Tateiwa and Ohdomari reservoirs) were statistically investigated using an approximately 20 years monitoring data. Increasing trend of TN/TP in the reservoir water was commonly found in the four reservoirs. At Uokiri Reservoir where complete data set was available, it was clear that both nitrogen and phosphorus were significantly trapped in the reservoir. Furthermore, addition of nitrogen and phosphorus in the downstream due to human activity was also obvious. The amounts of trapped dissolved inorganic nitrogen (DIN) and phosphorus (DIP) at the Uokiri Reservoir were estimated to be 6.9 tNy-1 and 0.63 tPy-1. Assuming the same trapping mechanism is working at 15 reservoirs on the Ohta River, it is estimated that 30 % of DIN and 35 % of DIP which should be loaded to the estuary could be reduced by their trapping mechanisms.

中国三峡地域では、ダム貯水による斜面変動が活発になっている。本研究では，貯水による斜面安定性への影響を解明するために，活発的に変動している樹坪地すべりにおいて，伸縮計を用いて斜面変動の連続観測を行なった。地下水存在状態を解明するために，1m深地温探査を行った。その結果、斜面内部の地下水の分布は斜面変位に直接関係していることは分かり、また、計13台の伸縮計の観測結果より，斜面変動の様子が概ね把握できた。, The Three Gorges Dam construction on the Yangtze River in China is the largest hydro-electricity project in the world. After the first impoundment in June 2003, many landslides occurred or reactivated. Shuping landslide is one of the most active landslides among them. In this paper, the deformation of the Shuping landslide monitored by GPS, extensometers, and crack measurements are summarized. Also, for the investigation of the groundwater situation, 1m-depth ground temperature measurement was conducted, and the groundwater veins were estimated. Based on the monitoring data and exploration results, a deformation model of the landslide caused by impoundment of reservoir was proposed.

三方湖の湖水の取水量検討のため, 多段貯水池水収支モデルを用いて, 三方湖群の水収支の数値解析を行った。湖群や海は, 短い水路でつながっているため, 水路の流れをマニング式で近似し, 良好な解析結果を得た。この結果から, 下流からの逆流水量が, 平均潮位・潮汐の振幅・降水量および河川流入量に影響されていることがわかり, 三方湖群の水収支特性が明らかとなった。, To examine the amount of intake water from Lake Mikata, water balance of the Mikata Lakes is analyzed numerically using a water balance model with plural tanks. As the lakes and sea are connected by short channels, the flows through the channels are approximated using the Manning formula. The numerical solution showed good agreement with observed values. The results showed that the inflow rate from downstream is affected by mean tide level, tide amplitude, precipitation and river flow. The results also showed the characteristics of the water balance in the Mikata Lakes. That is, the inflow rate from downstream becomes larger in summer due to less precipitation, less river flow and higher mean tide level in summer, and the influence of the annual change of precipitation on the water balance is larger than that of the tide level.