论水库的三角洲淤积(二)

DELTA DEPOSITION IN RESERVOIR(Ⅱ)

根据不平衡输沙方程,论证了水库淤积的三角洲趋向性.用水库淤积与河床演变通用数学模型对水库淤积过程进行了“试验”,得到了典型三角洲的形成与发展的全过程.据此对于已形成三角洲的水库,利用非均匀悬移质不平衡输沙理论,推导了一整套三角洲形态特征的理论表达式,包括三角洲淤积百分数、前坡淤积百分数、洲面线方程、水面线方程、前坡长度、洲面和前坡淤积物级配及各特征断面的悬移质级配。阐述了三角洲推进的定量方程和三角洲形成的条件,包括水库淤积百分数及水位变幅。对三角洲的形成、形态特征、推进及转化作了较全面和系统的定量分析。

There exist three typical profiles of sediment deposition in reservoir, among which delta profile is the most general one. Based on the nonequilibrium transportation equation, it is verified in theory that the delta formation is the tendency of reservoir sedimentatiom. A general mathematical model of reservoir sedimentation and river fluvial established by the author is used to simulate the entire process of the formation and development of delta, thus its characteristics and mechanism involved are clearly exposed. A series of theoretical results are presented , including : 1. deposit percentage of delta, which is dependent on the grade curve of suspended load during sedimentation; 2. equations of gradient and longitudinal profile of top-slope of delta. The former belongs to the second order polynomial and the later to the third order polynomial, both of which are concave-up curves, meaning that the curve slope is decreased along the flow direction and the top-slope of delta is not a linear curve as shown in some previous papers; 3. expressions of water level upon the delta top-slope and the slope of water level, which are also third order and the seceond order polynomials respectively and the concave-up curves as well. But the decreasing of water level is smaller than that of the delta bed and the water depth is increased along the flow direction; 4. expression of the length of the front slope, the end of which is the location where the deposit percentage is just equal to that of the delta; 5. deposit percentage of the top-slope, which is derived from the calculation of profile; 6. variation of size distribution of suspended load at each section of the delta and the grade curves of deposit at the front and top-slope respectively. All these theoretical results are verified by the measured data at Guanting Reservoir, a typical depositional deltaic one, showing a satisfactory agreement.