The effect of comprehensive harness of small
watershed on flood preventing and sediment reducing was systematically analyzed
and studied according to the small
watershed hydrological data collected from Beizhuang observing station. The results showed that for single rainfall, the dominating way of
runoff yield was a type of "filled with water" for the unharnessed small watershed, while a type of "excessive infiltration" for the harnessed small watershed. The runoff of torrential rain (W) in the small watershed was correlated with rainfall (P) and preceding effective rainfall (P a), the equation could be illustrated as W=0.00047 P 1 794 P 0 786 a ,and equation for the peak flow of small watershed as Q m=0 3797 A 0 6867 W 0 5842 . The benefits of comprehensive harness for flood prevention calculated from the two equations above was 16.7%～37.5%, and the benefit for reducing peak of flood was 9.1%～28.6%. For the analysis of sediment produced by single rainfall, the daily average sediment was reduced as the delay of rainfall duration. The daily average sediment (Q s) was positively correlated with daily average flow (Q) and the equation could be illustrated as Q S=-0 0436+19 297Q, the benefit of comprehensive harness for reducing sediment after 10 years calculated from this equation was above 90%. The effect of reducing both flood and sediment was obvious for the normal years that the average rainfall during the raining season was less than 900mm.