grade surface的用法和样例：
例句
- The fine grains are more at the tail than at the foreside at the same parallel to the slope surface.
沿坡面方向，在离土面相同距离的位置，后部细颗粒多，前部细颗粒少。 - The wetting front moved nearly parallel to the soil surface, and its length could be described by a power function of time, when the distribution of initial soil water was uniform.
当初始含水量分布均匀时，降雨入渗过程中湿润锋面几乎平行坡面运移，湿润锋深度与时间的关系可用幂函数描述。
