平原河网地区河流结构特征及其对调蓄能力的影响

平原河网地区是河流高度发育并受到城市化深刻影响的区域。本文以上海为例,基于上海及周边城市普遍采用的河流分类和水利片管理系统,分析不同城市化水平地区河流结构的共同特征及其差异性,探讨河流结构对河网调蓄能力的可能影响,提出估算河网调蓄能力的方法。研究表明,平原河网地区河流结构指标反映了该地区河流数量、长度以及低等级河流高度发育的自然地理特征,城市化在达到一定程度后即会干扰河流结构的自身发育规律,并表现为河流发育能力的下降;河流结构在城市化影响下表现出由复杂到简单、由多元到单一的变化趋势;河网调蓄能力受低等级河流数量及结构的影响更大,并随着城市化水平的提高而下降;就整体而言,城市化对河网调蓄能力的影响大于对河流结构的影响;以水面数量和河流结构两项指标作为参数能够更准确地估算河网调蓄能力。

Stream structure characteristics and their impact on storageand flood control capacity in the urbanized plain river network

Stream structure in urbanized river network area has unique characteristics under the effect of physical factors and human modification. Hence the issues of what and how such changes worked on river network storage and flood control capacity become the focus of this study. Taking Shanghai as a sample area, which is one of the largest cities in China located in the eastern Yangtze Delta, by using Horton-Strahler classification and Horton laws as reference based on the stream classification system that is commonly adopted in Shanghai and other cities around it, this paper analyzed the stream structure characteristics in each catchment under various urbanization levels;approached the effect of urbanization on stream structure development; and demo nstrated the possible relations between stream structure and river network storage and flood control capacity. The flood storage and control functions of streams in each order were further discussed in this paper. The main results are: (1 ) The stream number and length within the river network were highly developed in the study area. Stream number developed better than stream length. (2) The stream structure could only be modified when urbanization was up to a certain high level. Physical laws still played important roles in those catchments with lower urbanization level. (3) The stream structure expressed the possible trends from comprehension to simplicity, from multiform to singleness during the process of urbanization. (4) There was an obvious converse change between river network storage and flood control capacity and urbanization level. River network stor age and flood control capacity was influenced both by the quantity of water area and stream structure and much more closely related to the number and length of streams in the lower order. (5) For those streams in the higher order, the stor age capacity was stronger than the control capacity and the converse situatione xisted in those streams in the lower order. (6) proper quantity of water area and better stream structure were the infrastructures to assure ecological flood storage and control in urban area.