地球温暖化による海水温の上昇により，巨大台風の襲来およびそれに伴う甚大な高潮災害の発生が危惧されている．高潮災害を未然に防ぐために，高潮推算の高精度化およびリアルタイム予測の重要性が増しつつある．本研究では，リアルタイム高精度高潮予測を目的に，非構造格子海洋流動モデルの1つであるFVCOM，メソ数値予報モデルMSMによる気象庁数値予報データ，海洋潮汐予測プログラムNAO.99Jbを用いた高潮推算システムを構築した．そして，本システムを適用した既往台風の高潮推算を実施することにより，結果の妥当性・適用性を検証した．推算の結果，台風の通過経路で最大高潮偏差の値および時間を良好に再現できることが認められた．また，大規模シミュレーションシステム上での並列計算により，本システムはリアルタイム高潮予測に適用可能であることが確認された．

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Translation speed and scale of tropical cyclone are important factor of storm surge at local bay. We have to estimate storm surge variation range from information of tropical cyclone parameter we can get before it approaches to local area. Synthetic TC data based on historical TC tracks were generated and they were used for input to numerical model for estimating the water level of storm surge at regional scale. The TC track of the worst-case scenario for Yatsushiro bay located in center of west Kyushu Island was selected numerically. Finally, it was shown that it is possible to estimate rough variation range of maximum surge height from simulation results.

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Based on shallow water wave hindcastings for a 65-year period of historical typhoons and a 100,000-year period of simulated typhoons, extremes of wave heights in the East China Sea are discussed. Main findings are 1)variation of the 100-year return wave height in the sea is less than ±5% for a 10-year extension of the data period, in cases where the maximum of the wave heights is around 16 m; 2)the location-dependent largest wave height generated by the historical typhoons ranges from 60 to 80 % of the probable maximum(pmx) wave height estimated for simulated typhoons; and 3)the 100-year return wave height in local areas around Kabashima close to the Goto Islands changes from 15 m at offshore points to 10 m at onshore points, which is more than 2 m greater than the previous estimate.

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衛星観測に基づく台風強度推定は、航空機観測が実施されていない北西太平洋において台風情報を即時的に発表するために必須である。気象庁では、TRMM/TMIマイクロ波放射計の10、19、21、37、85GHz帯の輝度温度分布に基づいて台風の最大風速の推定を行う方法を採用している。そこでは台風の構造を表現するために、台風中心から2度以内の領域の輝度温度を用いて同心円や円環の領域のパラメータを計算している。本研究ではその改良のため、台風の移動方向に相対的に、前方、後方、左、右の4象限に分割した領域も設定することで、台風の構造の非対称性を表した。これらのパラメータを1998－2008年の台風観測事例について計算し、k-means法によりクラスター分析を行うことにより台風の構造別に10種類のクラスターに分類した。そしてこれらのパラメータを説明変数、気象庁ベストトラックデータの最大風速を被説明変数として、回帰式をクラスターごとに作成した。
この2008年までの事例に基づく推定法を、2009－観測事例に適用して、最大風速の推定値の検証を行った。検証期間の全事例のRMSEは6.26 m s^-1であった。クラスター別に見ると、輝度温度の非対称性の強いクラスターは先行研究の方法と比較して推定精度が改善したが、軸対称性の強いクラスターに関しては先行研究の方法よりも推定精度が悪化したものがあった。推定精度の改善を阻む要因としては、回帰式の被説明変数がベストトラックデータすなわち推定値でありドボラック法等に起因する誤差を含むことや、台風中心の位置が6時間ごとのベストトラックデータの内挿であるために生じる位置ずれ等が影響していることが考えられる。

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Recently, due to global warming, there are growing concerns about possible tremendous storm surge disasters which might be caused by furious typhoons more than ever. Actually, however, even in the present climate conditions, there were some typhoons which might be able to cause severe disasters if it were in the worst case scenario, for example typhoon 1216. Fortunately, the typhoon 1216 didn't cause serious damage in the Ariake Sea since its track was away from Kyushu district. In this paper, we conducted several storm surge simulations with the parameters of the typhoon 1216 by assuming several different typhoon tracks including the worst track. The results show that the maximum storm tide would exceed the existing disaster prevention plan even in the present climate conditions if it had passed in the worst track.

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Three events of storm surge which yielded different tidal departures in the head of Mikawa Bay are compared and discussed from the viewpoint of response to the wind forcing. The mechanism of sudden sea level rise is investigated based on the data of wind, sea level and velocity obtained in the period of three different Typhoons which passed near the bay. The magnitude of preceding east wind which gives rise to the sea level in Ise Bay and quick change in wind direction from east to west are key factors to the development of large tidal departure in the head of Mikawa Bay. The propagation of surge waves as a free long wave is confirmed through the velocity profile data and also tested using a 2D simple numerical model.

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新潟市における台風時の降水において，トリチウム(T)濃度及び各種イオン（Na^＋，K^＋，Mg^2＋，Ca^2＋，Cl^－，NO₃^－，SO₄^2－）濃度を測定した。その結果，台風時の降水について以下のことが定量的に推定できた。(1)降水中のT濃度は，どの時間においてもその月の平均値より低い値を示す傾向にある。(2)降水中のT濃度は，採水日の直近日の降水の有無により，挙動が異なる。(3)降水中の各種イオン濃度は，NO₃^－を除いて，挙動が類似する。(4)降水中の各種イオンの組成比は，時間とともに海水の組成比に近づいていく。(5)本研究で定義した相対海水組成比を用いることで，降水への海水の影響を評価できる。

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In this study, for the Haruki River basin of the Fuji River system, we investigated motion initiation condition of sediment with high reproducibility using time series data of river bed fluctuation by sand surface gauge and river bed change calculation. Specifically, we confirmed the effects of calculation results by motion initiate evaluation methods and representative particle size for evaluating riverbed erosion, and discussed the reproducibility of floods accompanied by large-scale earth and sand production. Here, the method (A) is an evaluation for individual transport of gravel particles, Egiazaroff formula corrected by Ashida and Michiue (1972) was used in the evaluation formula. The method (B) is an evaluation for collective transportation of riverbed sediment with optional thickness and uses a formula to compare shear stress and shear strength in the river bed with the depth of representative particle diameter by Takahashi (1977). The conclusions obtained through the study are the following two points. First, in the method (A), which use the average particle size of the river bed, the motion initiation water depth of the mountain river was underestimated, and the erosion depth of the flow path and the amount of sediment discharged to the downstream area are overestimated. Secondly, in mountainous rivers, collective transport initiation due to sliding failure is dominant for riverbed erosion than individual transport initiation of gravel particles, by giving motion initiation condition of sediment assuming sliding of representative grain size (average grain size and d₆₀), reproducibility is improved for floods accompanied with large-scale earth and sand production in mountain rivers.

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In this study, an inflow prediction model was developed for Shiobara Dam in Tochigi Prefecture, Japan, which underwent an emergency discharge due to heavy rainfall in October 2019, using machine learning from past basin rainfall and dam inflow data.

A prototype system for predicting dam inflows up to 6 hours ahead was developed and applied to the October 2019 flood. The results confirm the possibility of estimating the time when rainfall in the upstream area begins to flow into the dam and reaches 250 m3/s as early as 6 hours before. Finally, we considered how to use this system, including during normal times, for efficient dam operation.

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　バルク法を組み込んだROMSをベースにした2段ネスト瀬戸内海高解像度海洋流動モデルを構築し，GPV-MSMおよびJCOPE2再解析値を境界条件に用いて，2012年，2013年の夏期から秋期にかけて同海域に接近・通過した5つの台風による広域水温低下現象について熱収支解析により詳細に検討した．瀬戸内海全体の水温変動に対する豊後水道－紀伊水道間の水平移流熱輸送の影響は大きくなく，海表面から入射する正味の熱フラックスの影響が卓越していた．顕著な海水冷却を惹起するのは主に潜熱損失であり，台風に伴う海上風が強いとき，盛夏時よりも初秋時に海上気温が海面水温を下回って海上接地境界層が不安定になったとき，乾燥した台風の影響を受けたときに負の潜熱が著しく強化されることなどを明らかにした．

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温帯気候に属する愛知県東三河南部におけるサトウキビ生産の可能性を探るため，農林8号（NiF8）の栽培試験を行い，収量特性および生育特性を調査・分析した．4年間の単収は春植5.0～5.5t・10a^-1，株出7.0～8.0 t・10a^-1，同甘蔗糖度は春植12.2～14.9％，株出13.2～15.9％を示した．甘蔗糖度は12月下旬まで上昇し，12月下旬～1月初旬の間に最大値を示し，その後，低温や霜の影響で低下する傾向が見られた．なお，収穫したサトウキビから黒糖を生産することができた．仮茎長の伸長速度は，7月中旬～9月上旬において顕著に高く，この期間は沖縄島より高い値を示した．植付け時期を変えた試験では，茎長は3月植が最も長くなり，4月植は僅差で，5月植以降は順次低下した．東三河では3月下旬～4月下旬が植付の適期と言える．収穫は糖度が低下する前の12月が適期と考える．天水栽培では仮茎長の伸長に降水量が影響し，7月末～9月における降雨後の伸長速度は一旦増加して30 mm d_^-1 以上の値を示す場合も見られた．その後，晴天が続くと日ごとに減少し，0～1 mm d^-1となる場合もあり，灌水の重要性を確認できた．作型による収量の比較から，2回株出までは春植より高い結果が得られ，株出栽培の有利性が示された．

本研究を通して，東三河南部におけるサトウキビの生育特性や植付および収穫の適期を明らかにした．東三河南部のサトウキビ生産は十分に可能であると判断する．

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The purpose of this research is to improve the evaluation accuracy of sediment transport phenomenon in period after large-scale sediment production by one-dimensional riverbed variation calculation. We carried out a reproduction calculation of sediment transport phenomenon over the three years after large scale sediment production for Harukigawa of the Fujikawa river basin. Hirano's model which can express coarse grain formation of riverbed surface layer was applied to the study model, and, regime theory was applied for flow width evaluation. Furthermore, we considered increase or decrease of α value of the regime theory by due to the occurrence of double-row bar and influence of the stenosed terrain. By comparing calculated value and actual value estimated by differential analysis of elevation values at two time periods, according to the proposed method of setting the α value, it is found that accuracy to reproducibility improves with respect to the river bed variation height and the passing sediment volume. In addition, from the past research, three features of sediment dynamics after large-scale sediment production have been clarified. (1) A period in which sediment discharge is active continues for several years to several ten years after large-scale sediment production. (2) Deposit sediment at the time of large-scale sediment production remains in the basin even after the active sediment discharge period. (3) Deposited sediment coarsen with time, by the time the active sediment discharge is over, it is approaching the average particle size at time before large-scale sediment production. By the proposed method, the features of (1) and (2) were reproduced. Moreover, by this method, we could express the tendency of river bed to coarsen.

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To clarify sediment dynamics in mountain rivers during the heaviest rainstorms, we observed river water levels and riverbed level at Harukigawa, Yamanashi prefecture. Due the large-scale landslide occurred in more than a hundred years ago, large steep devastated area is located in the upper end of Harukigawa watershed. Here we successfully described detailed sediment dynamics in three large rainstorms due to typhoons in 2011, and, several results were found. About sediment movement of mountain stream with a landslide, we found the following things. At steep mountain river, whether or not to occur riverbed variations is determined by the water level conditions. In addition, when the continuous rainfall exceeds the number 100 mm, sediment discharge will be frequent. After that, the high concentration sediment discharge with riverbed rise occurs more than once, and the more the water level is high, a large erosion and deposition occurs. During floods, the duration of the high concentration sediment discharge with riverbed rise was about up to about one hour. Therefore, temporal change of sediment discharge and river bed variation has been found that not determined by only the hydraulic conditions. The timing of the riverbed change to 800 m downstream from the confluence of the tributary is affected by the sediment discharge waveform from the tributary. If the scale of the sediment discharge is small, the impact distance will be smaller.

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琉球列島の海浜堆積物は主に石灰化生物の骨格片や殻で構成される。しかし，海浜堆積物の生産年代，生産場から海浜への運搬時間や堆積年代についてはよく分かっていない。本研究では，沖縄県瀬底島の海浜・サンゴ礁で採取した表層堆積物試料を用いて，有孔虫Baculogypsina sphaerulata（ホシスナ）の遺骸殻（以下，星砂と表記する）の磨耗度と放射性炭素（¹⁴C）年代から，海浜堆積物の生産年代や運搬・堆積過程を明らかにすることを目的とした。星砂の磨耗度分析の結果，礁原から海浜に向かって棘がある星砂の比率が低くなり，海浜では棘がない摩耗した星砂が多くみられる。¹⁴C年代測定の結果，サンゴ礁・海浜堆積物中の星砂の¹⁴C年代は全て約700cal yr BP（西暦1950年を基準とする暦年代）以降を示す。星砂の¹⁴C年代は礁原から海浜へ古くなる傾向がみられるが，礁池や礁原にも比較的古い摩耗した星砂がみられる。海浜堆積物の星砂の¹⁴C年代は，北端でより新しく，屈曲した中央部でより古い。一方，海浜堆積物中のサンゴ片・貝殻の¹⁴C年代の多くは西暦1950年以降の年代を示す。これらの結果から，星砂の生産は約700cal yr BP以降に増加したと考えられる。これは，後期完新世の相対的な海水準の低下に伴う礁原の発達によってホシスナの生息場が増加したことが関連すると考えられる。また，星砂は死後の数十年～数百年で波浪により礁原から海浜へ運ばれた後，沿岸流（潮汐流）により主に海浜の北側から中央部へ徐々に集積し，再びサンゴ礁へ戻されると推測される。さらに海浜の前進は現在も続いていることが示唆される。

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The Fukushima Dai-ichi Nuclear Power Plant accident led to the release of various and huge amount of radionuclides into the environment, and contamination of wide area of eastern Japan, mainly Fukushima prefecture. More than 70% of radioactive cesium, which dominates the exposure dose, was deposited in forest far from our living sphere and is considered to be remobilized with time by water flow and strong wind caused by natural events such as typhoons. Numerous researches on the behavior of radionuclides in the environment have been performed not only by observation in the contaminated regions but also by model analysis so far. This paper overviewed results of understanding and modeling of transport behavior of radiocesium from forests through river systems.

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