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No.46 (1999/12) >

 
Title :沖縄における赤土等流出の経緯と対策
Title alternative :The Outline of Red Soil Loss and Erosion control Measure in Okinawa
Authors :翁長, 謙良
米須, 竜子
新垣, あかね
Authors alternative :Onaga, Kenryo
Komesu, Ryuko
Arakaki, Akane
Issue Date :1-Dec-1999
Abstract :本研究では,沖縄県におけるこれまでの赤土等流出防止に対する研究を踏まえ,土砂流出が及ぼす影響や年間流出量等を考察し,これまでの赤土等流出の歴史的経緯を概観し,対策の提言を行った。その結果,次のように要約できる。赤土流出の影響としては,道路や田畑等の損傷の物理的面,沿岸の景観の悪化という精神的面,川や海の底生生物への影響と云った生物的面等がある。土壌侵食と土壌保全の歴史的経緯の概略についてこれまでは,次の四つの時代,即ち(1)17世紀以前の焼畑農耕時代,(2)18世紀半ばの蔡温時代,(3)1920∿1930年の杣山(官有林)開墾時代,(4)1950年代後期∿現在までの時代に区分したが,昭和18年代の我謝栄彦の提言を考慮し,時代区分を六つの時代とした。急激な畑地造成の結果,土砂流出が著しいものとなり,現在では赤土等流出防止条例(1994)の施行によって,具体的な対応策が講ぜられている。赤土等流出防止条例の施行後,歴史的に侵食の最大原因とされていた開発事業に関してはかなりの改善策が取られ,流出量は大幅な減少を見ている。また対策としては,土木的対策として,圃場の区画の形態をUSLE(Universal Soil Loss Equation : 汎用土壌流亡予測式)を基に検討し,排水路,承水路の配置については耕区単位ごとに承水路を設けることや畑面の傾斜を緩やかにすること,また沈砂池等の砂防施設のあり方等についてはその大きさ,真水と濁水の分離排水を提言した。営農的防止対策としては,マルチングの効果やミニマムティレッジによる土壌保全の効用等を提言した。
On the basis of collecting and analyzing the researches on loss of red soil etc., the soil loss and it's impact and annual discharge were discussed here in this paper, then the historical outline of red soil loss had been reviewed, soil erosion countermeasures are suggested. The main opinions could be briefly summarized as following. The red soil loss impacts so many aspects of human life, including physical events such as damage to traffic line and farmland, moral events just like deteriorating coast landscape, and biological events for instance of influencing substrate organisum in river and sea. Although the history of soil erosion and conservation could be divided into four ages, i.e. shifting cultivation age before 17 century, Saion age in the middle of 18 century, age of cultivating the mountainous area (Somayama, national forest stands) from 1920 to 1930,and the age from 1950 to present time, it is better to be divided into 6 ages in considering of the proposal of Gaja in 1943. Rapid development of farmland brought up serious soil losses. The physical erosion control countermeasures are being conducted since implementing the SOIL LOSS PROTECTION REGULATION (1994). After implementing the REGULATION, soil erosion control measures are undertaken, and soil losses greatly declined too in the developing project, which was considered as the main factor caused erosion historically. Generally speaking, soil erosion countermeasures include engineering and agricultural measures. As to engineering measures, the following measures could be suggested, such as designing the optional form of farmland plotting on basis of USLE, setting diversion ditch in every tillage plot when arranging the drainage canal and diversion ditch, making the farmland gradient gently, scale of the settling basin and the diversion of fresh and muddy water when choosing the allocation method of soil catch facilities (i.e. settling basin); Within the agricultural measures, mulching and minimum tillage could be considered as effective soil erosion control methods.
Type Local :紀要論文
ISSN :0370-4246
Publisher :琉球大学農学部
URI :http://hdl.handle.net/20.500.12000/3666
Citation :琉球大学農学部学術報告 = The Science Bulletin of the Faculty of Agriculture. University of the Ryukyus no.46 p.71 -82
Appears in Collections:No.46 (1999/12)

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