中文摘要：

地表糙率是影响坡面流流速特征及变化过程的重要因素。本研究采用变坡试验水槽在粗糙粒径（d≤10mm）、单宽流量（0.04-0.24 L·s^-1·m^-1）和坡度（2°-12°）范围内,利用定床阻力冲刷试验系统研究坡面流平均流速与粗糙粒径、流量和坡度之间的关系。结果表明：随着地表糙率的增加,水流克服阻力做功增加,能量降低,流速呈指数函数减小。地表糙率不同会导致坡面流速的主要控制因素不同,当粗糙粒径较小（0≤d≤2.5mm）时,糙率、流量和坡度对流速均有显著影响,解释方差分别为19.8%、44.8%和27.8%;当粗糙粒径较大（2.5〈d≤10mm）时，糙率和坡度对流速的影响很小（影响程度分别占8．8％和1．5％），流量为主要影响因素（占84．1％）。经多元回归分析发现，糙率对流速的影响最大（54．6％），流量次之（30．8％），坡度最小（6．6％），三者可以较好模拟定床条件下的水流流速（R^2=0．919），且流速与糙率负相关，与流量和坡度正相关。该研究结果有助于深入了解不同糙率的定床阻力下坡面流流速的时空分布特征，为坡面土壤侵蚀过程物理模型的建立提供科学依据。

英文摘要：

Surface roughness is a key factor of overland flow velocity and its variation. This study systemically discusses variations of average overland flow velocity 11, surface roughness d and discharge q with slope gradient S using data of fixed-bed model tests. Flow velocity was measured on a flume with adjustable surface roughness （d≤ 10mm）, unit discharge （0.04-0.24 L·s^-1·m^-1）, and slope gradient （2°-12°）. Results show that when surface roughness increases, the water flow consumes more energy in overcoming resistance and flow velocity is decreased exponentially. Different roughness leads to different main control factors of overland flow velocity. At lower roughness （0≤d≤2.5mm）, roughness, discharge and gradient are dominant factors that contribute 19.8%, 44.8% and 27.8% of the flow velocity variance respectively, while at higher roughness （2.5〈d≤10mm）, roughness and gradient have a slight influence contributing only 8.8% and 1.5% respectively. In the latter case, flow discharge becomes a major factor accounting for 84.1% of the variance. Statistical regression shows that, of the dominating factors of flow velocity, roughness comes first （54.6%）, discharge second （30.8%）, and gradient last （6.6%）. Three factors could be used to simulate the velocity of overland flow （R^2=0.92） on fixed-bed models, and in this case the velocity was negatively correlated with roughness but positively with discharge and gradient. This study would shed light on further understanding of temporal and spatial distributions of overland flow velocity under fixed-bed resistance with different surface roughness, and lie a theoretical basis for physical model development of soil erosion.