Flow Stability in Pool-and-Weir Fishways, Plunging and Streaming Flows

2007 ◽  
Author(s):  
Kouki Onitsuka ◽  
Juichiro Akiyama ◽  
Yohei Iiguni ◽  
Daisuke Kiuchi ◽  
Noriaki Kawara
Keyword(s):  
Flood Control ◽  
Flow Regimes ◽  
Electromagnetic Current ◽  
Flow Formation ◽  
Typical Type ◽  
Japanese Rivers ◽  
Surface Profiles ◽  
Streaming Flows ◽  
New Criterion ◽  
Stream Type

In Japanese rivers, there are many river constructions, i.e., dams, weirs, drops, for the purpose of flood control. Fishways are river constructions which facilitate migration of fish past dams and weirs. There are a lot of fishway types such as pool-and-weir type, stream type, operation type and so on (see Nakamura, 1995). The pool-and-weir fishway is typical type in Japanese rivers. There are three types of flow regimes in pool-and-weir fishways such as a plunging flow, streaming flow and intermixed flow of plunging and streaming flows. Rajaratnam et al. (1988) proposed a prediction formula of these flow regimes. However, this formula has no physical meaning. Further the accuracy of formula is not high. In this study, the criterion formula, which can predict the flow regime in the pool-and-weir fishway, is suggested semi-theoretically. The experiments were conducted with changing the aspect ratio and discharge in the pool-and-weir fishway. The water surface profiles were measured with a point gauge and also two components velocities were measured with a 2-D electromagnetic current meter. A new criterion formula, which is able to predict the flow formation, is proposed.

scholarly journals Characteristics and determinants of flow regimes across Japanese rivers

2019 ◽  
Vol 21 (2) ◽  
pp. 75-92
Author(s):  
Yuya WATANABE ◽  
Kento YOSHIMURA ◽  
Takumi AKASAKA ◽  
Terutaka MORI ◽  
Yo MIYAKE
Keyword(s):  
Flow Regimes ◽  
Japanese Rivers

Impact of reservoir operations and climate variability on regulated flow regimes

2020 ◽  
Author(s):  
Marta Ferrazzi ◽  
Roberto Vivian ◽  
Gianluca Botter
Keyword(s):  
Climate Variability ◽  
Water Supply ◽  
Flow Regime ◽  
Flood Control ◽  
Flow Regimes ◽  
Reservoir Operations ◽  
The Mean ◽  
Annual Changes ◽  
The Impact

<p>The simultaneous growth in climate-driven fluctuations of river flow regimes and global freshwater demand threatens the security of anthropogenic and ecologic uses of streamflows. Dams have long been designed to reconcile the conflict between patterns of human water uses and the temporal variability of flows, and are operated worldwide. In this context, there is a need to understand the combined influence of reservoir operations and climate variability on regulated streamflow regimes, and disclose whether observed hydroclimatic fluctuations can be accommodated by existing reservoirs. Here, these issues are addressed through a quantitative analysis of flow regime alterations by dams as driven by heterogeneous uses and variable regulation capacities (i.e., storage capacity scaled to the average inflow). In particular, the concept of streamflow stability is used to compare inter-annual changes in the occurrence probability of synchronous flows observed upstream and downstream of dams. The selection of structures considered in this study is distributed throughout the entire Central-Eastern United States, so as to span heterogeneous hydroclimatic settings and reservoir functions (i.e., flood control, water supply, hydropower production and multi-purpose). Our results reveal that reservoirs devoted to flood control and those operating for water supply produce distinctive impacts on flow regimes. Flood control does not alter the mean discharge downstream, but decreases long-term discharge variability and, thus, homogenize regional flow dynamics. However, regulation for flood control is unable to mitigate the impact of variable climate drivers on the stability of streamflows and hydroclimatic fluctuations typical of unregulated regimes are transferred unaltered in downstream reaches, or even amplified. Water supply, instead, reduces the mean flow of regulated reaches but increases the long-term streamflow variability, thereby enhancing the regional heterogeneity of flows. In this case, regulation smooths inter-annual changes of flow regimes, though at the cost of systematically filtering out medium-to-high discharges, with negative consequences on stream ecosystems. The observed connection between reservoir functions and the features of downstream flow regime alterations by dams represents a critical step forward for a sustainable management of water resources.</p>

Polishing process effect on the image of dispersed precipitates

1984 ◽  
Vol 42 ◽  
pp. 534-535
Author(s):  
C.T. Hu ◽  
C.W. Allen
Keyword(s):  
Matrix Material ◽  
Specimen Preparation ◽  
Second Phase ◽  
Precipitate Particle ◽  
Polishing Process ◽  
Second Phase Particles ◽  
The Matrix ◽  
Surface Profiles ◽  
Thinning Process

One important problem in determination of precipitate particle size is the effect of preferential thinning during TEM specimen preparation. Figure 1a schematically represents the original polydispersed Ni3Al precipitates in the Ni rich matrix. The three possible type surface profiles of TEM specimens, which result after electrolytic thinning process are illustrated in Figure 1b. c. & d. These various surface profiles could be produced by using different polishing electrolytes and conditions (i.e. temperature and electric current). The matrix-preferential-etching process causes the matrix material to be attacked much more rapidly than the second phase particles. Figure 1b indicated the result. The nonpreferential and precipitate-preferential-etching results are shown in Figures 1c and 1d respectively.

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