No.158 研究課題 / Project
多摩川上流域における開発と水害Relationship between development and flood damage in the upper Tama River basins| 一般研究 General Research |
No.158 |
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| 代表研究者 Principal Investigator |
増淵 和夫 Kazuo Masubuchi |
| 所属（採択当時） Affiliation |
川崎市博物館振興財団 日本民家園 学芸員 Kawasaki Municipal Museum Foundation, Japannese House Museum |
| 研究内容要約 Research Summary |
とうきゅう環境浄化財団助成研究第1999 - 7 号「多摩川の洪水と環境変動―近世多摩川洪水史と完新世段丘―」をベースに、多摩川上流域における林業、薪炭などの開発行為が、水害などの自然災害発生に与えた影響について検討した。調査項目は、以下の6 項目である。（１）青梅より上流域における近世以降の水害、斜面崩壊土石流等の発生状況と史的変遷、（２）林業及び薪炭林育成の近世以降の史的変遷、（３）林業からみた近世以降の上流域の植生復原、（４）近世以降の材需要の傾向、史的変遷、（５）近世における民家等の建築用材の検討と林業との関連、（６）斜面崩壊、土石流をもたらした水害事例の検出。 林業については、文献調査を主に、多摩川林業史年表を作成するとともに、江戸時代の材需要の画期を区切ると思われる火災に注目した。江戸時代の火災頻発期は40 ～50 年ごとに現れ、この年数は伐期年数とほぼ等しいことや、青梅林業に代表される上流部林業成立地が、材の搬出に制限され、奥地の開発は明治頃まで遅れること等から、江戸時代における上流域の林業及び薪炭生産などの開発行為は、優良樹木の枯渇は招いたとしても、林地の荒廃に大きな影響を与えなかったと推定される。鉄道の敷設や道路整備により、明治中期以降、青梅林業に代表される短伐期の小径材生産が多摩川上流に確立され、「無立木地」が多摩川上流域に拡大した。「無立木地」の出現は林業のみならず、薪炭生産、養蚕も影響を与えていると思われる。明治時代の多摩川洪水氾濫は、江戸時代に比較し、発生件数の増大をみせないものの、被害は大きい傾向がある。更に、上流部山地や上流部から下流部まで左岸、右岸を含めて、全般的に洪水氾濫が及び、特に下流部での被害が大きくなっている。これは、新聞資料など記録資料の充実もあるが、上流山地部への降雨の集中を示唆するとともに、森林の持つ洪水緩和機能の低下を示唆する。但し、洪水緩和機能の低下＝森林の荒廃化は、単に上流山地のみでなく、流域の丘陵、台地上の荒廃も寄与していると思われる。 We examined the effect of forestry and firewood production activity in the upper Tama River basin on the occurrence of flood damage and other natural disasters. This study was based on “Flooding in the Tama River and Environmental Changes: Modern History of Flooding in the Tama River and Holocene Terrace,” Research No. 1999-7 supported by the Tokyu Foundation for Better Environment. This study consists of the following six themes: (1) situation of occurrence and changes over time in the frequency of flood damage, slope failure, and mudflow in the Tama River upstream of Ome during and after modern times; (2) changes over time of forestry and firewood forest development during and after modern times; (3) restoration of vegetation in upper river basins during and after modern times, from the viewpoint of forestry; (4) trends and changes over time in wood demand during and after modern times; (5) research on building materials used for houses during modern times and the relationship with forestry; and (6) detection of flood damage that induced slope failure and mudflow. We created a Chronology of Forestry in the Tama River Basin, based mainly on literature study. In addition, we paid attention to fire disasters that are believed to have divided wood demand into certain groups in the Edo period. The Edo period experienced frequent fire disasters several times at 40-50 year intervals, which virtually matched the cutting age of trees. In addition, backwoods areas were not developed until the Meiji era because, as can be seen in the Ome Forestry, only limited areas were developed for forestry in upper basins in consideration of the convenience of carrying logs out. For these reasons, it is believed that forestry and firewood production activity in the upper Tama River basin during the Edo period did not bring about effects that would accelerate the destruction of forestall areas, though it might have induced the shortage of healthy trees. The development of railways and roads led to the establishment of short-rotation small-diameter wood production systems, like Ome Forestry, after the middle of the Meiji period. This resulted in an increase in non-wooded areas, which are believed to have had adverse effects not only on forestry but also on firewood production and sericulture. Floods and inundations of water from the Tama River were less frequent, but more damaging, in the Meiji period than in the Edo period. The Tama River flooded everywhere from its upper to lower reaches from both its right and left banks, including in upper mountainous areas. Lower basins, especially, suffered severe damage. These trends, which may be influenced by the improved data availability from sources such as newspapers, indicate concentrated rainfall in upper mountainous areas and the decreased flood-control function of forests. It is believed, however, that the decreased flood-control function, namely destruction of forests, is caused not only by the environmental destruction of upper mountainous areas, but also by that of hills and plateaus. |
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