Study on roughness coefficient for unsubmerged reed in the Changjiang Estuary
- PDF / 432,148 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 99 Downloads / 199 Views
Study on roughness coefficient for unsubmerged reed in the Changjiang Estuary GU Fengfeng1∗ , MU Lin2 , QI Dingman1 , LI Junhua3 , KONG Lingshuang1 , WAN Yuanyang1 1 2
3
Shanghai Estuary and Coastal Science Research Center, Shanghai 201201, China National Marine Data and Information Service, State Oceanic Administration, Tianjin 300171, China College of Ocean Environment and Engineering, Shanghai Maritime University, Shanghai 200135, China
Received 4 January 2011; accepted 14 June 2011 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2011
Abstract The influence of density, foliage and stem flexibility on the roughness coefficients under unsubmerged conditions, such as Manning’s n, is investigated experimentally. An instrumentation system has been developed for measuring the flow rate ranging from 0.1 to 0.3 L/s under the condition of different artificial foliated reeds. Based on the experimental results, the influence on the relationship between n with different density, foliage, flexibility and flow depth is discussed. It is found that the foliage and the density are the important factors affecting Manning’s n. At a range of relatively low velocity and relatively large bending stiffness of stem, Manning’s n is not influenced significanthy by the flexibility of stem. Key words: Manning’s coefficient, foliage, density, flexibility, reed
sults well agree with each other. On the other hand, some researchers dropped the influence of characteristics of vegetation from their analysis and tried to make relatively common conclusions. Generally they conducted experiments with replicas of some species of vegetation made to scale the biomechanical properties from real vegetation, such as Carollo and Ferro et al. (2002), Ni and Gu (2005, 2007), and Wilson et al. (2003), or with real vegetation directly, such as Petryk and Bosmajian (1975), Jarvela (2005) and James et al. (2004). Most of empirical or semi empirical equations and methods for estimating the flow resistance caused by vegetation are based on Manning’s n. It has been widely used and developed in many practical applications and researches. Petryk and Bosmajian (1975) developed a quantitative procedure to define Manning’s n as a function of flow depth and vegetation characteristics which showed that the increased Manning’s n with flow depth was influenced largely by vegetation density. James and Birkhead (2003) presented the n − h (h is the water depth) curve which varied
1 Introduction Reed is a common species of vegetation existing in the Changjiang Estuary, which has been considered by many hydraulic engineers as a source of flow resistance. This kind of vegetation consumes a great amount of energy and momentum from the flow, and is often found to dominate the most roughness. So estimation of the flow resistance caused by vegetation is important to the management of natural waterways and estuary. Considering the resistance of a vegetation community, the characteristics of vegetation have a large influence on it. Fathi-Maghadam and Kouwen (1997) made a dimensional
Data Loading...
