料源起始形狀對土石流數值模擬結果之影響

許多研究皆顯示土石流是一種具有降伏應力的非牛頓流體，黃名村(2003)也藉此流變關係發展出一套數值模式Debris-2D來模擬具有降伏應力的土石流。在模擬的過程中，一般是將已知體積量的土石以某種形狀堆置於溪谷上游後，讓其開始流動。然而，本研究所推導的控制方程式顯示，土石料源的起始形狀，在土石中的某一點所造成的壓力梯度，在加上坡度的重力效應之後，若不足以克服降伏應力的大小，該點將無法啟動。因此，料源的起始形狀確實會影響到土石流的起動與否，間接影響到後續的流況。本研究分別以一維渠道及新北市新店區屈尺里的一條野溪為對象，在相同的地形和材料參數的條件下，分析不同的料源起始形狀會對模擬結果產生多大的差異性。結果顯示，一維流況中，在流路上某一位置的土石流最大流深、最大流速及土石流的影響範圍，其最大差異分別僅約為3.26%、3.41%及0.46%。現地模擬部分，土石流最大流深、最大流速及土石流的影響範圍，其最大差異則是分別約為4.26%、3.78%及3%。以上有關土石流流速、流深及影響範圍等在防災上的各項重要參考數據，因為不同料源起始形狀所產生的差異均不超過5%`，這表示料源起始形狀對於土石流數值模擬結果所造成的影響，非常有限。

關鍵字

土石流；起始形狀； Debris-2D數值模式

並列摘要

Many researches have shown that debris flow is a non-Newtonian fluid with yield stress. According to this rheology, we developed a numerical model, Debris-2D, to simulate debris flows with yield stress. Usually, the initial debris sources with given volume are distributed at the head of the target stream as inputs. However, we are now interested that if the initial shape of the debris source will affect the simulation results. It is shown that debris flow can move only if the sum of pressure and gravitational effects exceeds the yield stress effect, or the mass will stay stationary with zero velocities and unchanged flow depth. Therefore, the initial shape of the debris source can have influence on the simulation results, but we don’t know if it is significant. With the same topography and rhelogical parameters, this study focused on how the initial shape of debris source can affect the results simulated by Debris-2D model. In this thesis, simulations including a one-dimensional case and a field study show that the errors of some important information for debris-flow disaster prevention (depth, velocity, danger zone) due to different initial shapes of the debris source will not exceed 5%.