Ryoichi Yamanaka

THE MONITORING METHOD USING UAV OF THE HABITAT FOR AN ENDANGERED TIGER BEETLE IN A CREATED SANDY SHORE

徳島県沖洲海浜(図-1)では,希少種ルイスハンミョ ウ(Cicindela lewisi ;写真-1)の生息地埋め立ての代償と して人工海浜が2007年に造成され,生息環境の保全が 進められている.しかし,2016年以降ルイスハンミョウ の幼虫は確認されておらず,生息環境条件の再検討や 海浜の再整備が急務となっている.本種は春から夏にか けて産卵し,半年から1年間幼虫として土壌に巣孔を作っ て生活する.生息する土壌深度は成長に伴い変化するた め,それぞれの時期における地形変動を把握することが 本種の保護や生息環境の保全を進めるうえで重要である. 特に,産卵時期である7月~8月は台風襲来期と重なるた め,月に数回の測量が必要となる.しかし現行の RTK-GPS(VRS方式;以降「VRS」)方式による測量では1 回の測量に3日間の時間を要し,高頻度での測量が難しい. 近年,無人航空機(Unmanned Aerial Vehicle;以降「UAV」 と称する)を使い,低コストで行える地形測量技術が開 発されつつある. そこで本研究では,現行の方法より簡便なルイスハン 図-1 沖洲人工海浜の位置図

DIN Fixation by Macroalgae and Release from Sediment by the Burrowing Macrophthalmus japonicus

(1)底質の栄養塩の溶出量および同化量 調査は徳島県勝浦川河口干潟(図-1)の泥質域(約 5000m)において2007年3月から12月に行った.本調査 域はヨシ原に囲まれており,波浪は数 cm程度,潮流は 小さい地点であった.また,当調査域の底質環境につい てシルト・クレイ率は約40%,含水率は約28%,D.L.は0.90mであった.試料はコアサンプラー(Φ8cm)を用 いて深さ10cmまでの底質を採取し,実験室に持ち帰っ て底質の栄養塩の溶出量および同化量の測定を行った. 調査は現場において毎月2~3回の底質試料(n=3)を採取 し,実験に供した.実験にあたっては,底質試料の入っ たコアサンプラーの周りにアルミホイルを巻き,横から の光を遮断した後,作成したチャンバー容器にセットし た.底質が巻き上がらないように滅菌ろ過海水を注入し, 密封した.その後,恒温水槽(TAITAC製:CL-150F) にチャンバー容器を移し,実験中は底質に影響を与えな いよう撹拌を行って,現地で測定した水温に恒温水槽を 設定した.また,ハロゲンランプ(Dupla製:Electra) ヤマトオサガニの造巣活動に伴う底質から水中へのDIN回帰と 藻類による固定 DIN Fixation by Macroalgae and Release from Sediment by the Burrowing Macrophthalmus japonicus

Study on Generation Mechanisms of Tsunami Resistance of Gentle Slope Revetment

Many coastal structures, especially embankment and revetment, were damaged seriously by Tsunami of Tohoku Earthquake occurred at March 11, 2011. However, many Gentle Slope-type Revetments were not broken and remain the function of disaster prevention. In this study, we focused generation mechanism of robustness of Gentle Slope-type Revetments to overflowing tsunami on the basis of field observation in Miyagi Prefecture and numerical analysis.The field observation revealed that almost no Gentle Slope-type Revetments were broken. Numerical results suggest that the robustness of the Gentle Slope Revetments is due to the decrease in the water surface elevation of the overflow and the landside scour depth.

Analysis of Tsunami Resonance and Impact in Coastal Waters

Recently, extreme tsunami waves generated by submarine earthquake have caused tremendous damages to the coastal cities and ports. Strong seiche oscillations and runups are observed in specific sea areas around the world. Although no frequent impacts to the coast of Korean peninsula, there exist some important events in the east of Korea in the past. This study focuses on two historical events and recalculate with different fault and rupture mechanism for prediction considering the recent trend of submarine earthquake. The present study of the 1983 Akita tsunamis demonstrates the multi-scale resonance along continental coasts. Together with the Nankai tsunami for inland sea, we have confirmed the inland sea resonance surrounded by islands in defining the impact along the coast. Coherence and wavelet analyses for deducing a predominant period and time frequency are useful in reasoning the inundation. The resonance modes, which are largely independent of the tsunami source, allow identification of at-risk communities and infrastructure for mitigation of tsunami hazards. Furthermore, understanding of the resonance and the predicted runups for the site of power plant and industrial complex in the east coast of Korea would allow better preparation for the future disasters.

Impact of river discharge on surface water variability in Amagasaki port, Japan

Amagasaki port is located closed-off section of the Osaka bay, Japan. On the side of the vertical seawalls in the port, a large amount of mussel attached to the objects and drop off to the sea bottom every summer and the mussel drop-off is a pollution load for sea bottom environment. The mussel drop-off is often occurred at the time of sudden water quality change, especially temperature and salinity. Therefore, this study focuses on the period characteristic of surfer salinity in Amagasaki port, wavelet analysis attempt for observed salinity to clarify the occurrence time of the sudden water quality change. Hydrodynamics at the time of river runoff are analyzed by a three-dimensional baroclinic flow model. This study clarified that the occurrence of river runoff was indicated by wavelet analysis at Amagasaki port and the river discharge from Yodo River mainly affected to the sudden change of surface salinity at the sea area, which is a semi-enclosed area and surrounded by reclaimed land.

Seasonal Changes of Baroclinic Circulation and Water Exchange in the Bohai Sea

In four principal sea areas in China, accelerated water pollution has recently become more widespread and severe with rapid economic growth. In enclosed areas such as the Bohai Sea, red tides are occurring with greater frequency, degrading ecosystems and causing eutrophication. As the first step in clarifying the mechanisms of ecosystem and coastal eutrophication and for considering concrete enforcement measures to reduce the damage, the present study focuses on physical phenomena such as hydrodynamics and transport processes. First, the flow structure and density field in the Bohai Sea are examined using a three-dimensional baroclinic flow model. Second, the seasonal change of wind and surface heat transfer on the residual current system and the water exchange through the Bohai Strait are examined using a Lagrangian particle tracking method. This computation makes clear that the residual currents in the majority of the Bohai Sea are very weak, less than 0.05m/s. The effect of seasonal winds on hydrodynamics such as residual currents in the Bohai Sea, water exchange between the Bohai Sea and the Yellow Sea, and stratification induced by heat transfer at the sea/water surface are studied.