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Both sounding and sediment sampling on the sea bottom have been carried out by the same method as the last time in Yotsuyahama coast on July.27 2011, July.24 2012, Sept.30 2014, and Oct.2 2014. Several sedimentary samples on the sea bottom have been tried to analyze into the grain size with precise accuracy. Also, these datas were attempted to analyze surely. Double crescent-shaped bars were found out on those two measuring lines of the sea bottom. It was shown clearly that the existence of submerged breakwater has given the full influence to the sedimentation of the sea bottom. The results of data analyses on both the bottom profile and the grain size composition of the sediment on the sea bottom provide some ideas to understand the reasons for the coastal erosion.

Both sounding and sediment sampling on the sea bottom have been carried out by the same method as the last time in Yotsuyahama coast on July.27 2011, July.24 2012, Sept.30 2014, and Oct.2 2014. Several sedimentary samples on the sea bottom have been tried to analyze into the grain size with precise accuracy. Also, these datas were attempted to analyze surely. Double crescent-shaped bars were found out on those two measuring lines of the sea bottom. It was shown clearly that the existence of submerged breakwater has given the full influence to the sedimentation of the sea bottom. The results of data analyses on both the bottom profile and the grain size composition of the sediment on the sea bottom provide some ideas to understand the reasons for the coastal erosion.

Ogata Wave Observatory is located in Yotsuyahama coast, Niigata Pref., Japan. Yotsuyahama coast is in the center of Joetsu-Ogata coast. In this region, Katamachi sand dune develops very much, and the sediment in Joetsu-Ogata coast is composed of both sand and gravel. There are several artificial structures like submerged breakwater in Yotsuyahama coast. The coastal area between Naoetsu harbor and Yotsuyahama coast has been suffered from severe beach erosion. Both sounding and sediment sampling on the sea bottom have been carried out in Yotsuyahama coast on June.28 2008, Oct.15 2009, Mar.1, 6 2010, and Aug.17 2010, and Nov.7 2010. The longshore measurement section is about 200m offshore from shoreline, and the cross-shore measurement sections are at the central region and the joint region of a crescent-shaped bar. The sediment sampling has been conducted in the cross-shore measurement sections at interval of 1.0m deep. It was shown clearly that the existence of Observatory Pier has given the full influence to the sedimentation on the sea bottom. The results of data analyses on both the bottom profile and the grain size composition of the sediment on the sea bottom provide some ideas to understand the reasons for the coastal erosion.

Ogata Wave Observatory, Kyoto University is located in Yotsuyahama coast, Niigata Pref., Japan. Yotsuyahama coast is in the center of Joetsu-Ogata Coast. In this region, Katamachi sand dune develops very much, and the sediment in Joetsu-Ogata Coast is composed of both sand and gravel. Jogehama coast is another coast in Joetsu-Ogata Coast and is in a natural state. The distance between Yotsuyahama and Jogehama coast is about 3.0km long. The seashore between Yotsuyahama and Jogehama coast has been suffered from severe beach erosion. Both sounding and sediment sampling on the sea bottom have been carried out in Jogehama coast on Nov.7 2010, July.27 2011, July.24 2012. The longshore measurement section is about 200m offshore from shoreline, and the cross-shore measurement sections are at the joint region and the central region of a crescent-shaped bar. The sediment sampling has been conducted in the cross-shore measurement sections at intervals of 1.0m deep. The results of data analyses on both the bottom profile and the grain size composition of the sediment on the sea bottom provide some ideas to understand the reasons for the coastal erosion.

Ogata Wave Observatory is located in Yotsuyahama coast, Niigata Pref., Japan. Yotsuyahama coast is in the center of Joetsu-Ogata coast. In this region, Katamachi sand dune develops very much, and the sediment in Joetsu-Ogata coast is composed of both sand and gravel. There are several artificial structures like submerged breakwater in Yotsuyahama coast. The coastal area between Naoetsu harbor and Yotsuyahama coast has been suffered from severe beach erosion. Both sounding and sediment sampling on the sea bottom have been carried out in Yotsuyahama coast on June.28 2008, Oct.15 2009, Mar.1, 6 2010, and Aug.17 2010, and Nov.7 2010. The longshore measurement section is about 200m offshore from shoreline, and the cross-shore measurement sections are at the central region and the joint region of a crescent-shaped bar. The sediment sampling has been conducted in the cross-shore measurement sections at interval of 1.0m deep. It was shown clearly that the existence of Observatory Pier has given the full influence to the sedimentation on the sea bottom. The results of data analyses on both the bottom profile and the grain size composition of the sediment on the sea bottom provide some ideas to understand the reasons for the coastal erosion.

砂・礫海岸である大潟海岸の中央部より, 3km程, 北東寄りの上下浜で海浜の調査を行った。2009年10月30日と2010年10月8日の2回, 海浜の前浜に形成されるビーチカスプのうちの小カスプにおいて, 断面を得るために地形測量を行う, とともに, 極高点と極低点というように, 交互に, 数十個の底質を採取した。形成状態の変異差を調べるために, 大カスプの突出部と湾入部で, それぞれ, それらの行為を行った。また, 2010年10月8日に, 大カスプの突出部と湾入部において, 汀線から小カスプの極高点, あるいは極低点を通って, 後浜, あるいは前浜のみ(湾入部), まで, 地形測量と５m間隔の底質採取をそれぞれ行った。これらを分析, 解析して, 熟考する事こそが, 海岸侵食の原因解明に至る糸口となるのではないか。, Ogata Wave Observatory, Kyoto University is located in Yotsuyahama coast, Niigata Pref., Japan. Yotsuyahama coast is in the center of Joetsu-Ogata Coast. In this region, Katamachi dune develops very much, and the sediment in Joetsu-Ogata Coast is composed of both sand and gravel. Jogehama coast is another coast in Joetsu-Ogata Coast. The distance between Yotsuyahama and Jogehama coast is about 3km long. The seashore between Yotsuyahama and Jogehama coast has been suffered from severe beach erosion. Sediment samples have been taken on each crest and trough of the small cusps in Jogehama beach on October 30th in 2009 and October 8th in 2010. Another samplings of beach sediment have been carried out in Jogehama beach on October 8th in 2010. The beach sediment from the shoreline to the backshore at 5m interval has been collected on each projection and embayment of the large cusps. Also, beach profiles have been measured in the beach at the same date. Consequently, the analysis results on both the beach profile and the grain size composition of the beach sediment provide some ideas to solve the source of the coastal erosion.

本報告は, 2008年夏の大潟波浪観測所・観測桟橋撤去後に行われている海底地形計測および海底底質の調査結果を示すものである。今回の観測は, 大潟波浪観測所の旧観測桟橋周辺において2010年8月に行われた。調査項目は, GPS機能付き測深器による海底面形状の計測, 海底表層の底質採取, および海底底質のコアサンプリング調査である。海底面形状の計測では, 2009年に計測された結果とほぼ同様の海底面形状となっていることが確認された。海底底質のコアサンプリング調査からは, 沿岸砂州をはさんで岸側と沖側で粒径分布が大きくことなり, 沖側では淘汰が進み深さ方向にほぼ一様の粒径分布となっていることが確認された。, This paper shows some results of a field observation carried out in Aug. 2010 in Joetsu-Ogata coast. In this field observation, three measurements have been conducted; (1) bottom profile measurement with depth sounder and (2) collection of the samples of bottom sediment, and (3) sampling of boring cores. The observation site is near the location of old observation pier, and the size of the measurement area in longshore and cross-shore directions are about 900m and 800m, respectively. The bottom profile in the observation site is measured by the depth sounder with GPS locator. It is found in the 2D bottom profile that a crescent-shaped sandbar and shoreline retreat exist. From the results of core sampling, the sorting of grain size in cross-shore direction and the deposition in alternate layers are observed.

大潟海岸の中央部に位置している京大観測用桟橋の沖側に，弧状沿岸砂州が形成されている。この弧状沿岸砂州の変異を考察するために，深浅測量と海底底質採取を，2005年3月6日と2005年9月28日に行った。深浅測量は，汀線から約200m沖の沿岸方向の1測線と，弧状沿岸砂州中心部と接合部の2測線を通る岸沖方向の測線で行った。また，海底底質採取は水深約1mごとに，深浅測量と同じ岸沖方向の2測線上で行った。なお，弧状沿岸砂州中心部の測線は，桟橋の南西側の縁に合致しているため，桟橋の根元から先端にかけて採取した底質試料を採用した。それは，2005年3月6日と9月28日に一番近い時期である，2005年3月15日と9月16日の底質試料を採用した。海底地形の変形と海底底質の粒度組成の岸沖方向変異の考察から，変則的な動きをしていることがわかった。また，海底底質と海岸砂丘砂との相関関係も示された。, The observation pier which belongs to DPRI., Kyoto Univ. is located at the center of Ogata coast, Japan. A crescent-shaped bar exists off the observation pier, and its shape is like an arc of a half circle.In order to investigate the temporal change of the position of the bar, the author has carried out the field observations on March 6th and September 28th in 2005. The field observations include depth sounding and sediment collection.The depth sounding has been conducted on 3 measurement lines, and some sediment samples have been taken from the sea bottom at 1m deep interval on the same measurement sections of the depth sounding. As a result, it is found that the change of bottom profile and grain size composition in cross-shore direction have considerable magnitude during the observation period. The correlation between sediment of the sea bottom and adjacent coastal dune is also shown in this paper.

大潟波浪観測所では，桟橋沿いの海底地形計測を原則として月に1回実施され，桟橋周辺の底質採取も年数回実施されてきた。2008年夏に観測桟橋が撤去され，海上の船舶から測深器を使っての海底地形計測および底質採取を継続することとなった。 今回の観測は，大潟波浪観測所の旧観測桟橋周辺で，沿岸方向に約700m，岸沖方向に約600mの領域である。海底面形状の計測では，GPS機能付きの測深器を用いて，対象範囲内における緯度，経度，水深のデータを収集した。計測された結果を補間することにより，対象範囲内の海底面形状を面的に把握することができた。並行して海底底質の採取も行い，採取された底質の粒度分析結果より，底質の岸沖方向の分布特性に関する情報を得た。, This paper shows some results of a field observation carried out in Oct. 2009 in Joetsu-Ogata coast. In this field observation, two measurements have been conducted; (1) bottom profile measurement with depth sounder and (2) collection of the samples of bottom sediment. It is found in the 2D bottom profile that a crescent-shaped sandbar exists. As a result, the former observation can be confirmed at the pier near the bow spit, an extension of the old pier was to ensure that they are located near the crest of the spit arc. The grain size analyses of the observed samples of bottom sediment also have carried out. It is observed the differences in particle size distribution in cross-shore direction. Differences in particle size distribution in the offshore sandbar and the shore side, obtained information about the state of the direction distribution of the sediment off the coast.

上越･大潟海岸のほぼ中央に位置する大潟波浪観測所では，観測桟橋沿いの海底地形と海底底質の採取が継続的に行われている。本報では，これまでの計測結果の中で，特に断面地形の侵食傾向が顕著であった期間(2001年縲・004年)における2月時点での底質の粒度分析結果と，岸沖方向海底地形の計測結果について検討する。断面地形の侵食傾向が顕著な期間では，断面地形変化の規模は小さいものに留まり，汀線が後退した状況が継続されている。その一方で，断面形状に大きな変化が認められない状況下でも，底質の分布状況は経年的に変化している状況が確認された。, This report shows some comparison results on observed cross-shore profiles of the grain size composition and bottom topography around the observational pier at Ogata wave observatory (OWO). Observed results presented in this report were measured and taken in February (2001 - 2004). February is just the middle of winter season, and the coastal region facing Japan Sea is exposed to severe wave conditions. The bottom profiles from 2001 to 2003 have the characteristics of reflective beach, and they don't have so much difference among each profiles. However, the cross-shore distributions of grain size have annual variation. Considerable sediment transport is expected under quasi-equilibrium state of cross-shore bottom profile.

上越･大潟海岸のほぼ中央に位置する大潟波浪観測所では，観測桟橋沿いの海底地形と海底底質の採取が継続的に行われている。本報では，冬季季節風の影響を強く受けている2月時点での底質の粒度分析結果と，岸沖方向海底地形の計測結果から，桟橋沿いの地形変化ならびに底質の分布状況の経年的な変化について検討する。桟橋沿いの岸沖方向海底地形は2000年以降目立った地形の変動の無い状況が続いていたが，2005年以降に汀線が前進する様子が確認された。最近数年間の海底底質の分布状況の変化からは，2003年縲・004年頃に底質の分布に変化があり，相対的に粒径の小さな土砂の堆積が確認された。, This report shows observed results of cross-shore profiles of the grain size Composition and bottom topography around the observational pier at Ogata Wave Observatory (OWO). The measurements of cross-shore bottom profile have been carried out once a month, and the bottom profile change in recent 10 years is small except before 2000 and after 2005. After 2005, shoreline advance is observed even though Joetsu-Ogata coast have been suffered from severe beach erosion for long time. From the results of grain size analysis, it is found that relative fine sand accumulates around the observational pier after 2005.

大潟波浪観測所では観測専用桟橋に沿って，月に1回測深と海底底質採取を行っている。現在，観測桟橋近傍海域は侵食性の海岸であり，弧状沿岸砂州の中央部に位置している．この海域において，2003年8月23日，10月7日，2004年10月7日，11月10日に行った深浅測量と海底底質採取データを解析した。深浅測量は，汀線から沖へ約200ｍの地点を汀線に沿った1測線と，岸沖方向の2測線を行った。また，海底底質採取は，岸から沖へ水深1ｍごとに，桟橋沿いの1側線，弧状沿岸砂州接合部の岸沖方向の1側線で実施した．海底地形の変形と海底底質の粒度組成の岸沖方向変化の考察から，この海域の地形，底質の特性は，自然海浜である上下浜海岸とは異なり，年間を通して変動が急激で不規則であることがわかった。, Monthly beach profile sounding has been carrying out since 1972 along the Observation Pier, Ogata Wave Observatory, DPRI, Kyoto University by the author. Sediment sampling from the sea bottom has also been conducted. This paper reports the analyzed results of profile and sediment sampling data measured on days of Aug.23, Oct.7, 2003, Oct.7, and Nov.10, 2004. Beach profiles of alongshore sounding line 200m offshore and two cross-shore measuring lines are analyzed in this paper. Sediment sampling was conducted with 1m-pich on two cross-shore measuring lines which locate on the center and jointed lines of the crescent-shaped bar surrounding the Pier, respectively. It was made clear that both the sea bottom profiles and the grain size composition of the sea bottom sediment have changed dramatically and irregularly in all seasons in this erosion coast.

大潟海岸において，自然海岸である上下浜で，深浅測量と海底底質採取を，2001年8月6日，2002年9月20日，2003年8月23日，2003年10月7日に行った。深浅測量は，1日に，汀線から沖へ約200mの地点を汀線に沿った1測線と岸沖方向の2測線を行った。また，海底底質採取は，岸から沖へ水深1mごとに，2測線の弧状沿岸砂州中心部，接合部(深浅測量も同様)で行った。海底地形の変形と海底底質の粒度組成の岸沖方向変異の考察から，冬季にそれぞれ最も顕著であることが示された。また，海底底質と海岸砂丘砂との相関関係も示された。, This author has considered the grain size composition of the sediment of the sea bottom, which movedalong a natural providence, at Jogehama's coast. This author has carried out the sounding and thegathering of sediment off of the sea bottom, here, on Aug.6.2001, Sept.20.2002, Aug.23.2003, andOct.7.2003. This author has carried out sounding, from south west to north east 200m offshore on ameasuring line, along the shoreline, and from shoreline to offshore on two measuring lines, each day. Also, this author has carried out the gathering of sediment off of the sea bottom, from the shoreline to offshore, every 1m in depth, at both the central measuring line on the crescent-shaped bar and the jointed measuringline on the crescent-shaped bar, each day. In doing this, this author has considered the changes in the seabottom profile, and variation from the shoreline to offshore, in the grain size composition of the sedimentof the sea bottom. Also, this author has been able to show by means of evidence, that both the sea bottomprofiles and the grain size composition of the sediment of the sea bottom, have changed dramatically inthe winter season. Furthermore, this author has examined the correlation between the sediment of the seabottom and the recent coastal sand dune.

上下浜海岸で，自然の節理にそって動作する，海浜底質の粒度組成を考察した。2001年8月6日と2002年8月31日に，南西から北東へ向って，汀線に沿って，200m沖の深浅測量による海底地形と大カスプの，互いに対応して，対になって移動することが実証できた。海浜底質の粒度組成の考察にさいし，ビーチカスプの大カスプと小カスプの相関関係，また，ビーチカスプと海岸砂丘砂との相関関係も検討した。, This author has considered the grain size composition of the beach sediment, which moved along a natural providence, at Jogehama's coast. This author has carried out sounding, from south west to north east, 200m offshore along the shoreline, on Aug.6.2001 and Aug.31.2002. In doing this, this author has been able to show by means of evidence, that both the sea bottom profiles and big cusps, have moved with one-to-one correspondence. When this author considers the grain size composition of the beach sediment, this author has examined the correlation between the big cusps and the small cusps. Further more, this author has examined the correlation between the beach cusps and the coastal recent dune sand.

大潟海岸の中央部に位置している, 京大観測用桟橋を用いて, ひと月に一回測深と海底底質採取を行っている。また, 上下浜で2001年8月6日に測深と海底底質採取を行った。そのうち夏期及び冬期以外で, 両地点の海底地形の変化と海底底質の粒度組成の岸沖方向変異を考察するとともに, 両地点のそれぞれの差異も考察した。また, 海底底質と新砂丘砂の相関関係も検討した。, The Observational Pier which is located at the center of Ogata 's coast, belongs to Kyoto University. This author is carring out sounding using the Pier, to gather sediment from the sea bottom, once a month. Also, this author has carried out sounding and the gathering of sediment off of the sea bottom at Jogehama, on Aug.6.2001.In doing this, this author has considered the changes in the sea bottom profile, and variation from the shore to theoffshore, in the grain size composition of the sediment of the sea bottom. This author has considered the differences between the two places. This author has considered the samples which were observed every year from spring to the fall season, too. Further, this author has examined the correlation between the sediment of the sea bottom and samples from recent dune sand.

大潟海岸の中央部に位置している, 京大, 観測用桟橋を用いて, ひと月に一回測深と海底底質採取を行っている。冬期と冬期以外で海底地形の変化と海底底質の粒度組成の岸沖方向変異を考察した。また、ビーチカスプにおける大カスプと小力スプについて考察した。そのうち, 性質と綿塵組成り両者の相関関係を検討した。桟橋に沿った海底底質とカスプにおける海浜底質の粒度組成の相関関係も検討した。, The Observational Pier which is in the center of Ogata's coast , belongs to Kyoto University. This author is carring out sounding using the Pier, to gather sediment from the sea bottom, once a month. This author has considered change of the sea bottom proffies, and variation from the shore to the offshore, of grain size composition, in winter season and other season too. Also, this author has considered that both big cusps and small cusps, on the beach, need to be examined. In doing this, this author has examined the correlation between the cusp's characteristics and the grain size composition.Futher, this author has examined the correlation between the sediment of the sea bottom along the Pier, and the grain size

冬季季節風時の日本海沿岸海域では、高波浪の他、沿岸域の広い範囲にわたって吹送流場が形成される。この吹送流場は、砕波により形成される海浜流場と重ね合わさった形で、広域海浜流場を形成し、海浜変形や環境変化の主外力となる。本研究は, 新潟県の上越・大潟海岸において、1998年12月より1999年3月初旬にかけて行われた, 沿岸から水深20mまでの海域の波浪・流れ場の観測結果を解析したもので、冬季季節風による広域海浜流の特性として、以下のような現象を見出した。沿岸域の海水流動は, 冬季季節風(海上風)の影響を強く受け, 沿岸方向には東向きの流れが卓越し、岸沖方向の流れは水深により異なる。すなわち、砕波帯近傍(岸近く)ではundertowと呼ばれる沖方向流れが卓越し, その強度は風速・波高に比例する。また、沖浜帯における岸沖方向流速は、小さいながらも卓越方向が岸向きとなる傾向がある。, In the Central Japan Sea, winter monsoon winds develop high waves together with strong wind-induced currents in the wide area of nearshore zone. Nearshore currents generated by breaking waves in the surf zone superimpose on the wind-induced currents to generate coastal currents, which are the dominant external force of beach changes and coastal environment.In order to investigate the structure of coastal current fields, a current observation in the wide area of Joetsu-Ogata coast (shore to 20m depth in cross-shore, 10km in longshore) has been conducted from December 1998 to March 1999.The following characteristics of coastal current fields have been observed.(1) Generation and variation of longshore component of coastal currents have close correlation to monsoon wind fields rather than wave fields.(2) Strong undertow (offshore-going currents) often observed under the stormy condition in the area shallower than lOin depth (near the surf zone). (3) Cross-shore component of coastal currents in deeper area is weak and going onshore.

Ogata Wave Observatory, Kyoto University is located in Yotsuyahama coast, Niigata Pref., Japan. Yotsuyahama coast is in the center of Joetsu-Ogata Coast. In this region, Katamachi sand dune develops very much, and the sediment in Joetsu-Ogata Coast is composed of both sand and gravel. Jogehama coast is another coast in Joetsu-Ogata Coast and is in a natural state. The distance between Yotsuyahama and Jogehama coast is about 3.0km long. The seashore between Yotsuyahama and Jogehama coast has been suffered from severe beach erosion. Both sounding and sediment sampling on the sea bottom have been carried out in Jogehama coast on Nov.7 2010, July.27 2011, July.24 2012. The longshore measurement section is about 200m offshore from shoreline, and the cross-shore measurement sections are at the joint region and the central region of a crescent-shaped bar. The sediment sampling has been conducted in the cross-shore measurement sections at intervals of 1.0m deep. The results of data analyses on both the bottom profile and the grain size composition of the sediment on the sea bottom provide some ideas to understand the reasons for the coastal erosion.