本研究では，大分県佐伯市を対象として津波防災について検討を行うとともに，番匠川河川環境の津波による被害想定を行った．佐伯市は，南海トラフ地震発生時には県内で最も早く津波が到達するとともに，場所によっては予想される津波高は10ｍを超える．検討にあたっては，中央防災会議が実施した津波の佐伯市街地への津波到達時間，浸水深，および氾濫流速を基に，現況での津波防災と番匠川河川環境や生態系への影響を考察した．

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In the Banjo River (Saiki, Oita), the population of clam drastically decreased after 1994 and has not been recovered yet. In order to make the reason clear some field surveys on water quality (: DO, salinity, water temperature, etc.), sediment quality and flow patterns were carried out from 2003 to 2004 in the Banjo estuary and Saiki Bay. Measurement results by ADCP showed the dominant flood current through the shorter navigation channel and the dominant ebb current through the longer one. In addition, water body tended to be stagnant in a neap tide and oxygen deficiency was measured in the longer channel. It was confirmed that temporal variation of DO concentration in the Banjo estuary depended on both flow patterns of tidal current and a redox conditions in the sediment.

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The author proposed the general formula for the fatigue strength as follows: σ_nW=σ_n-k_1τ, \labeleq1where σ_nW and σ_n mean the fatigue strength,respectively,with or without diminishing the effect caused by repeated load having the stress difference τ in shearing,and k₁ is a coefficient depending on micro-slip-path besides τ. In other words, σ_n correspends to the separating strength discussed Previously.
For steel,k₁ is about 2.8∼3.3 and σ_t is equal to (2.3∼2.7)σ_u,where σ_u indicates the fatigue limit in single blow tension. Furthermore,the following expressions were derived, respectively: σ_W,fatigue limit in tension and compression=(0.53∼0.68)σ_u, σ_W′, fatigue limit in bending\doteqdot(1.1∼1.3)σ_W, τ_u, fatigue limit in single flow torsion\doteqdotσ_W, and τ_W, fatigue limit in double blow torsion=(0.3∼0.4)σ_u. With the same conception, for cast iron, σ_u′, σ_W′, σ_W″, τ_u′ and τ_W′ which correspond to σ_u, σ_W, σ_W′, τ_u and τ_W respectively, for steel, were expressed using stress concentration factor α_kt (in tension) or α_kt (in shearing), correcting factor k₂ against k₁ and factor δ in bending. For an example, for σ_W′ the following formula was derived : α_ktσ_W’=σ_t-k_1k_2(σ_kt/2+α_ks/2)σ_W’ \labeleq2
For steel containing x% of carbon, an approximation was put forward empirically as follows: σ_Wx’=(0.6 ∼0.9){σ_fs+(σ_ps-σ_fs)(x/0.9)^2/3}\labeleq3
where σ_fs and σ_ps indicate the yceld point of firrite and pearlite, respectively. This idea could be applied also to the carburized steel, which is considered to be composed of harder outer case and softer inner part. Furthermore, the author discussed the outer notch effect on fatigue.

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This study attempts to evaluate the potential risk of tsunami driven by Nankai trough earthquake with investigation of land price based on the hedonic approach in Saiki, Oita. Simulations have been conducted by the cabinet office, government of Japan and Oita local government, and results, e.g. the estimated inundation height and travelling time of tsunami, have been published. The land prices are assumed to be a good descriptor of the potential risk of tsunami as well as convenience and comfort of the life. The land prices were taken to be a function of accessibility to the Saiki train station, schools, and parks, and of risk factors, e.g. elevation, the predicted flood depth due to tsunami and so on. The multiple regression analyses show that the land prices decrease with increased distance from the Saiki station. The effect of the potential risk of tsunami is also described by the land prices, i.e. the land prices decrease as the estimated flood depth increases.

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River flow regime is important role in determining the river morphology, water use and biotic composition. In Japan, however, river management based on the concept of variation of flow regime is not taken. Because the knowledge of potential hydrological regime is lacking. In this study, we proposed the flow regime indicators which can explain seasonal change of stream flow at 52 watersheds in the Kyushu region. And, we investigated the relationship between flow regime indicators and factors that affect the hydrology (physiographic factors, geological factors and vegetation factors). Result of multiple regression analysis, flow regime indicators were well explained by the factors of physiography, geological and vegetation. The results indicated that geology of volcanic ejecta tends to stabilize the flow fluctuation, and urbanization and plantation tend to increase frequency of disturbance and drought.

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    本報告書では，大分県番匠川の河口干潟を対象水域として，河口干潟の環境変化がアサリ(Ruditapesphilippinarum）の成育に及ぼす影響と，それに対する河川整備および環境管理のあり方について考察を行 った．既往の報告から得られた知見を整理した結果，アサリ漁獲量急減以後において，番匠川河口域では，①樋門・樋管からの栄養塩の流入によって富栄養化の傾向にあること，②富栄養化によると考えられるアオサ（Ulva spp.）の異常増殖が認められることから，アオサの異常増殖後の枯死と腐敗によって生ずると考えられる底質直上水の嫌気化と硫化水素（H2S）の発生がアサリの成育阻害を引き起こしていると考えられた．アオサからのH2Sの発生量とアサリの成育に及ぼす影響について室内実験を行った結果，アナアオサ（Ulva pertusa）の腐敗によって発生するH2Sがアサリの生存に影響を及ぼすことが明らかになった．このことは，番匠川河口干潟においてもアナアオサから発生したH2Sがアサリの死亡を引き起こし，アサリ漁獲量低下の原因となる可能性を示唆するものであると考えられる．したがって，番匠川河口干潟においてアサリ漁獲量を回復させるためには，アナアオサの異常増殖の原因となると考えられる河口域の樋門・樋管からの栄養塩の流入負荷量を低下させるような流域の水質管理や底質の嫌気化を防ぐような河川流量管理等の対策が必要であると考えられる．

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The rainy season in 1732 persisted for some 50 days. In the intercalary month of May, it rained day after day. Around May 10th, there was heavy rainfall resulting in extensive flood damage. Fortunately however, as the rain fell comparatively early, it was possible to minimize the damage by replanting the seedlings and also by switching to dry field farming. Following the rainy season, rainfall was moderate but the weather was unstable with thunderstorms, mixed sunshine and rain, and drizzles frequently occurring, lowering temperatures. The presumption is that the unfavorable conditions which had continued since the planting of the rice plants resulted in their feeble growth.
There was an abnormal outbreak of planthoppers immediately following the end of the long rainy season and it was widely believed that this outbreak of planthoppers was related to the prolonged rains. However, recognition of the insect outbreak was based on theories of natural causes and the “In-yo-Gogyo-setsu” (Yin-yang and the Five Elements). Naturally, it was concluded that the extended rain had caused air borne planthoppers to arrive in great numbers. The presumption is now that the scant sunshine and high humidity prevailing during June and July, together with the growing conditions of rice plants, resulted in even heavier damage by the planthoppers.
In the Kyushu, Chugoku and Shikoku districts, all private and Shogunate domains sent in urgent warnings (notifications) concerning the outbreak of planthoppers to the Shogunate government. Even when we examine the detached territories, we find that it was only the Mimasaka domain of the Annaka Clan that failed to send in a notification. In the Kinki district, 21 private clan domains (out of 57) and 11 magistrates' offices of the Shogunate domains (out of 15) sent in urgent warnings. The majority of the private domains in Kyushu also sent in their notifications at an early date. With respect to the private domains in Chugoku and Shikoku, the periods when notifications were sent in differed between the western and eastern halves of the districts assuming that a line is drawn from north to south down the center of these two districts. Notifications from private domains in the eastern parts of the Chugoku and Shikoku districts were sent in a at a later date as was the case with the Kinki district. Their notifications were sent in late because it was after harvesting that they realized than the damage was far worse than first expected.
In Kyushu, abnormal insect damage caused by white-backed rice planthoppers occurred from the beginning of June. The Omura domain suffered severe damage in early June, and similar damage, the “Kabudae” phenomenon, struck the Isahaya and Saeki domains in mid-June with the result that these three domains resorted to switching to dry field farming. In Westen Japan, abnormal insect damage had occurred in almost all areas by mid-July. Particularly in villages in the Suo Hagi and Aki Hiroshima domains, rice crops were completely destroyed in a matter of a few days around July 15th. This date coincided with the period when late rice formed ears. The damage suffered during this period was that caused mainly by brown rice planthoppers. Shiinoki Village of the Chikuzen Akizuki domain experienced damage from both white-backed planthoppers and brown rice planthoppers. However, around July 11th the principal cause of rice plant damage changed from white-backed to brown rice planthoppers.
Discovery of the oiling method to exterminate planthoppers marks an epoch in the history of agriculutral techniques of the modern age, but there is as yet no established theory concerning this method. Information on the oiling method spread primarily around the Fukuoka domain, the Omura domain and the territory controlled by Hitadaikan. In the Fukuoka domain, the villages were notified to adopt the oiling method as a “divine message from the Tenman-sama.”

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