최근 집중호우가 빈발함에 따라 도심지역에서의 토사재해가 증가하고 있어 도심권의 좁은 공간에 있어서 방재적 효과가 우수한 사방구조물의 도입이 요구되고 있다. 이 논문에서는 유목 혹은 토석 유입 시 및 유목과 토석의 동시 유입 시 바닥스크린의 포착효과를 검증하기 위해 수리모형실험을 통해 정량적으로 파악하였다.
1. 무시설시에 있어서 계상재료의 이동특성 1) 유목의 이동 실험을 5 반복하였을 경우 유목은 150cm의 퇴적부에 500개의 유목 중 4개만이 체류하여 평균 유목체류율은 0.8%로 매우 낮았다. 2) 토석의 이동 토석의 경우는 퇴적부로 유입된 후, 소량이 0∼10cm 구간에 퇴적되었고, 40∼50cm 구간부터 퇴적양이 증가하다가 50∼60cm 구간에서 가장 많이 퇴적된 후에 점차 감소하였으며, 나머지는 하류로 유출되었다. 3) 유목+토석의 이동 유목과 토석을 동시에 유입하였을 경우, 전술된 토석의 체류형태에 영향을 받아 유목의 일부가 퇴적된 토석에 의해 포착되어 체류되기도 하였으나 대부분의 유목이 하류로 유출되는 경향을 나타냈다.
2. 바닥스크린의 포착효과 1) 유목의 포착 순간격 3mm, 6mm, 9mm 바닥스크린의 평균 유목 포착율은 3mm에서 100%, 6mm에서 99.6%, 9mm에서 98.6%로 각각 높게 나타났다. 2) 토석의 포착 순간격 3mm, 6mm, 9mm 바닥스크린의 경우 상대적으로 입경이 작은 토사는 전혀 포착되지 않았지만, 거석과 자갈의 포착율은 3mm에서 99.1%, 6mm에서 97.2%, 9mm에서 83.5%로 나타났다. 3) 유목+토석의 포착 순간격 3mm, 6mm, 9mm 바닥스크린의 경우 유목+토석 중에서 토사는 전혀 포착되지 않았지만, 거석 및 자갈의 평균 포착율은 3mm에서 98.7%, 6mm에서 97.4%, 9mm에서 90.6%로 나타났다. 한편, 유목의 평균 포착율은 실험에 사용한 1,500개의 유목 중 36개만 유출되어 97.6%로 나타났다.
실험결과, 바닥스크린은 유수와 유목 및 토석을 순간적으로 분리시켜 운동에너지를 저감시킴으로서 바닥스크린 위에 포착시키는 기능을 확인할 수 있었다.
Recently, sediment-related disasters, such as landslides and debris flows, have increased due to frequent and heavy rainfall events in urban areas, where are densely populated and thus make heavy land-use. Therefore, there is a demand for introducing erosion control structures which have excellent prevention effects against the sediment-related disasters. In this paper, through hydraulic model experiment, I examined quantitatively the effect of float-board screen for catching bed-materials including drift woods and/or debris flows, compared to the results regarding bed material movements obtained from the untreated control case.
1. Characteristics of bed material movements in untreated control case 1) Movement of drift woods When the experiment was repeated for five times, the average storage rate of drift woods was very low with the average of 0.8%; that is, only 4 of 500 drift woods stored at the depositional segment with 150 cm in length. 2) Movement of debris flows Only a small amount of debris flows was stored within the 0~10 cm section of the depositional segment with 150 cm in length. Within the 40~50 cm section, the storage amount was higher than it stored within the 0~10 cm section, and it leached to peak within the 50~60 cm section. After that, the storage amount of debris flows decreased gradually and rest of them were exported to the downstream. 3) Movements of drift woods and debris flows In case of the combination with drift woods and/or debris flows, the distribution of debris flows showed similar pattern with the case of debris flows, described in the previous paragraph, and this pattern led to accumulation of some drift woods. However, most of them were fluvially exported to downstream.
2. Effect of float-board screen for catching bed-materials 1) Effect of float-board screen to catch drift woods The average catch rates of the float-board screen whose the lattice spacings were 3 mm, 6 mm, and 9 mm for drift woods were 100%, 99.6%, 98.6%, respectively, showing high rates for each one of them. 2) Effect of float-board screen to catch debris flows In case of the float-board screen whose the lattice spacings were 3 mm, 6 mm, and 9 mm, sediment with a relatively smaller grain size was not caught at all, but the catch rates for boulders and gravels with larger grain sizes were 99.1%, 97.2%, and 83.5%, respectively. 3) Effect of float-board screen to catch drift woods and debris flows In case of the float-board screens whose the lattice spacings were 3 mm, 6 mm, and 9 mm, sediment was not caught at all. However, the average catch rates of larger boulders and gravels were 98.7% for 3 mm, 97.4% for 6 mm, and 90.6% for 9 mm. Meanwhile, only 36 of 1,500 drift woods used for the experiment were fluvially exported, so the average catch rate for drift woods was 97.6%.
As the results of the experiment, it confirmed the function that the float-board screen instantaneously separates running water, drift woods and debris flows, and reduces kinetic energy, catching them on the float-board screen.