金沙江干热河谷冲沟沟床草被对径流水动力特性的影响

Effects of Grass Belt Length to Runoff Hydrodynamic Properties in Gully Beds in Jinsha River Dry-hot Valley Region

研究冲沟沟床草被对径流水动力特性的影响,有助于探明该区冲沟发育过程及其动力机制。采用野外放水冲刷试验,研究冲沟沟床草被带长度对径流流态、流速和阻力系数的影响。研究结果表明:(1)试验条件下,沟床径流为紊流缓流状态。径流雷诺数Re随时间表现为先增大再减小的周期性变化趋势。沟床各断面径流雷诺数Re均随着草被带长度的增加而减小;径流佛罗德数Fr随时间呈现先急剧减小后趋于平稳的趋势,而在沟床沿程上呈减小趋势。草被带长度越长,佛罗德数Fr的变化幅度越小。(2)不同草被带长度小区,径流流速在时空上的变化有一定差异,且草被带越短径流流速在时间上的减小趋势越明显。各观测时段,径流流速均随草被带长度的增大而减小。(3)各小区径流阻力系数在时空上均表现出增大趋势。其中,12m草被带小区径流阻力系数在沟床各断面上均大于其他草被带长度小区。(4)12m草被带是减小径流流速、增大径流阻力的优势草被带长度。

Studying on the influence of grass belt to runoff hydrodynamic properties was of great importance to verify the development processes and dynamic mechanism of gullies.Based on filed scouring experiment under different grass belt length,the effects of grass belt to runoff pattern,velocity,and resistance were coefficient.The results indicated that：（1）Runoff was turbulent and subcritical in the gully beds from the beginning to end of the tests.The Re performed as cyclical variations,which firstly increased and then decreased with test time.The Fr decreased sharply first and then tended to stability on time series.As the grass belt length increased,values of Re at each monitoring section decreased,and the rangeability of Fr decreased.Meanwhile,the Fr showed a trend of decrease along the gully beds.（2）Grass belt length made much differences to the temporal and spatial variation of flow velocity in gully beds.With the decrease of grass belt length,the flow velocity was more obviously reduced on time series.The flow velocity decreased with increasing of grass belt length in each monitoring period.（3）The resistance coefficient showed increasing trend with test time and along the gully beds.And the resistance coefficient of gully 4（the grass belt length was 12m）was greater than the other gullies at each monitoring section.（4）When the grass belt length was 12 m,the grass belt had superior effect in reducing flow velocity and increasing resistance coefficient of runoff.