Abstract: In this paper, we tried to set up a new criterion. First of all, the average deposition ratio of the key dams was calculated year by year from 1950 to 2011 using 4157 key dams data in Water Census. The results showed that the average deposition ratio was around 0.77 as of the year 1980 and then decreased; the average deposition ratio of the small and medium-sized dams was calculated year by year from 1956 to 1989 using survey data for 1640 warping dams in northern Shaanxi. The results showed that the average deposition ratio was around 0.88 before 1980 and decreased gradually afterwards. Therefore, 0.77 and 0.88 were considered as the block sediments criterion for key and mid-small sized warping dams respectively. And then, the survey data for warping dams in northern Shaanxi were used for validation for the criterion of key dams and the results are consistent, which confirmed the applicability of the new criterion. With Wuding and Yanhe river basins as an example, the variation trend of the sediment transportation at hydrological stations is highly correlated with that of the warping dams. This paper also explains the formation of the criterion for the engineering structure of the warping dams, indicating that the spatial movement of water and sand drain point is the main reason.

Key words: warping dams, block sediments, deposition ratio, Loess Plateau