論文
山腹工の施工による土砂の生産・流出と下流河道への影響
キーワード:
erosion,
hillside works,
sediment routing,
aero photos,
old map,
riverbed elevation change elevated river
2009 年 61 巻 5 号 p. 12-20
詳細
2009 年 61 巻 5 号 p. 12-20
Tanakamiyama locates surrounding Seta at Ohtsu city and its had been completely devastated about 120 years ago because of over logging for firewood and lumber. In Edo period, a lot of sediment flowed out, to rise riverbed downstream and to cause flood frequently. Intense hillside works ; terracing and planting have been implemented for last 120 years. The area are covered green almost completely today. Erosion rate have been observed last 30 years in this area. We estimated sediment production in old days, since 120 years ago to the present from the recent 30 years observation data. And we calculated changes of sedimentation from 120 years ago to the present using numerical calculation method. The results shows as a below ; (1) Devastated area in the Daido river basin has been reduced from 19 km2 to 1 km2 during 120 years. In the Tanakamiyama district, devastated area has been reduced from 9 km2 to 0.89 km2, too. (2) The amount of sediment outflow from devastated area, is from 1,000 to 10,000 m3/km2/year, has been reduced to 100 m3/km2/year 10 years elapsed after implemented hillside works. (3) When vegetation coverage rate will recover to 60 percent, the amount of sediment outflow less than 1 m3/km2/year. (4) To construct the hillside work, the amount of sediment outflow has been reduced to 60 present after 120 years at the downstream end section of Uji river. (5)Tendency of the amount of sediment outflow after implemented hillside works is a high to decrease early close to sediment yield area. But the downstream area is the delay at the onset time, the less impact.
