The Effects of Stone Mulching on the Surface Runoff Characteristics of a Bare Ground Slope

斜面ライシメータを用い，裸地斜面にストーンマルチを設置したときの表面流出特性の変化について検討した。ライシメータの2流出区を対象とし，他方の流出区を玉石の敷き詰められたストーンマルチ斜面とし，一方の裸地斜面に対して表面流出特性の相違について比較を行った。調査期間途中で，ストーンマルチを施す流出区と裸地のままの流出区とを入れ替えるという操作を施し，その後の流出特性の変化を追った。その結果，以下の2つの結果を得ることができた。(1)裸地斜面にストーンマルチを施すことによって即座に著しく表面流出が抑えられる。(2)逆にストーンマルチ斜面から石を取り除いた場合，しばらくの間(1)の傾向を維持し続け，次第に裸地の流出特性へと変化する。(1)については，ストーンマルチの設置による雨滴の細粒化や石表面をつたう流れの形成による浸透機会の増加，(2)については被覆物が除去された裸地斜面においては，雨滴衝撃による表層の目詰まりによって雨撃層が形成され，浸透能が徐々に減少してゆくことなどが考えられる。The surface runoff properties of a bare ground slope were investigated with and without stone mulching on the ground surface of a sloping lysimeter located in the Inuyama experimental site of the University Forest in Aichi, the University of Tokyo. Each section of the lysimeter was filled with the same soil materials and has a width of 3m, a length of 6 m, and is 2.5 m deep. Its slope angle is 20 degrees. In this study, the surface runoff characteristics of two sections were compared, one of which had stone mulching and the other of which was bare surface. Initially, one bare section was covered with stone mulching and the other was left bare. Halfway through the investigation period, all of the stones on the section with stone mulching were removed and put on the other section which had previously been bare. The results show that surface runoff from a bare section is immediately reduced by stone mulching on the ground surface. When the stones used for stone mulching are removed from the section, its surface runoff characteristics gradually return to those of a bare section. It is thought that rain-drop impact compacts the soil surface and gradually reduces infiltration, whereas stone mulching breaks the rain-drop size down and makes infiltration increase immediately