Page - 351 - in Book of Full Papers - Symposium Hydro Engineering

The data series began from 2001 spring and end to 2014 spring. A further analysis on the data showed that Dayu River was too close to the dam of the Xiaolangdi reservoir, the cross-section of that was influenced by the fluctuation of water level before the dam. As a result, the gradient of the main channel of Dayu River changed quickly and sometimes turned negative. Additionally, the phenomenon of sand bar is not significant in the river mouth of Dayu River. As to fix on the evolution of sand bar, we deleted the data series of Dayu Rvier, focus on the other five tributaries. 3. STUDY INDEXES Using dimensionless parameters, this paper set a multiple regressive formula between the height increment of sand bar and different influencing factors. The form of the formula is as follows: ?̂? = 𝐾 ?̂? 1 𝛼 1?̂? 2 𝛼 2 …?̂? 𝑛 𝛼 𝑛 [1] In which ?̂? is a dimensionless dependent variable, ?̂? 1, ?̂? 2,…, ?̂? 𝑛 are dimensionless independent variables, K, α1, α2,…, αn are undetermined coefficients. The research aim is the evolution of sand bar, so the annual height increment of sand bar Δh (m) and annual depositing volume ΔV (m3) are chosen as dependent variables, the dimensionless forms are: ?̂? 1 = ∆ℎ 𝐷 50 , ?̂? 2 = ∆𝑉 𝐷 50 3 [2] [3] In which D50 (m) is the median grain size of bed material load in the river mouth of the tributaries, which is measured every year before flood season. As the former research, the evolution of sand bar is related to water and sediment conditions, local terrain factors and flow regimes. So the selected independent variables should include all these aspects (See Table 2 and Table 3): 351