中文摘要：

沙袋在水面抛放后，受重力和水流阻力的作用，在向水下沉降的同时，还产生顺水流方向的落距。本文通过对水槽中沙袋沉降过程的观察，结合对沙袋运动过程中的受力分析，建立并推导了沙袋沉速运动方程，此方程包括了沉降开始时的加速阶段和达到平衡后的匀速阶段，对于沙袋来说，加速阶段的时间很短。建立了沙袋落距的微分方程，推导了均匀流速分布下沙袋落距的表达式，此公式可以简化为与现有公式一致的形式，通过实测资料，确定了公式中的系数。

英文摘要：

After being released on the water surface, the sandbags, under the influence of gravity and water flow, may have a horizontal movement while sinking down. The equation for the settling velocity of a sandbag is derived based on the observation of settling process and the analysis of the forces on the sandbag. This equation includes the accelerating phase and the uniform velocity phase. Under the condition of uniform flow velocity, the differential equation for the settling distance of a sandbag is also built. It can be simplified to the similar expression with existing equations. The coefficients in these equations are obtained by the experimental data and the field data.