流域地貌演化的不同阶段沟壑密度与切割深度关系研究

主要探讨了在流域地貌演化的不同阶段,沟壑密度与切割深度的复杂关系,建立了沟壑密度随切割深度变化的理论极值模型及相应阶段的函数,补充了各演化阶段地貌形态要素的定量、定性描述;反之,可用沟壑密度与切割深度的关系推断流域地貌的演化阶段。

THE RESEARCH ON THE RELATION BETWEEN GULLYDENSITY AND CUTTING DEPTH IN DEFFERENT DRAINAGE LANDFORM EVOLUTION PERIODS

According to the geographical cycle theory, drainage landform evolution process is divied into three periods—young, mature and old period. In defferent evolution periods, the relation between gully density and cutting depth is various. However, it is sure that landforms are the most tattered and gully density reaches the maximum in the later young—early mature period. By presuming that the drainage landform is evoluted into hills in the period, the maths equation of the theoretical maximum of gully density was established, which is D=ctgθ^h∫_h0^maxdh/(hctga+c)² (1) where:D: gully density;θ: slope;h: cutting depth;c: gully bed average width;h₀: cutting depth minimum;h_max: cutting depth maximum On the above presuming base, the maths function on relation between gully density and cutting depth were established for the defferent development periods. The maths function shows that:①in the early young period, the gully density and cutting depth increase at the same time; ②in the later young—early mature preiod, gully density reaches the maximum and it decreases as cutting depth imcreases; ③ in the later mature—old preiod, gully density decreases as cutting depth decreases. Two example calculations demonstrate that the maths equation of the theoretical maximum of gully density may be used in practice. It can infer drainage landform evolution period and predict soil erosion developing tendency. It supplements quantitative anslysis on landforms shape elements with drainage landform evolution in defferent periods.