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Chapter 4 - Experimental setup and test procedure 4.1.5 Filtering basket After the outlet pipes, the mixture water-sediments was filtered in a basket (see Fig. 4.10). The basket is a cube of 1.00 x 1.00 x 1.00 m covered on the sidewalls and on the ground with a doubled grid layer (openings 1 mm wide). The bottom can be opened to allow a fast emptying. A skirt was mounted around the basket to prevent the lab from a general inundation. Four small steel wheels allowed to position the basket at the right position on rails below the two outlet pipes. LEFT-TOP: Structure of the filtering basket, LEFT-BOTTOM: view from inside, CENTER: Basket with the skirt, RIGHT TOP: Closing mechanism, RIGHT-BOTTOM: wheel and back flap Figure 4.10: Pictures of the sediment filtering basket page 76 / November 9, 2002 Wall roughness effects on flow and scouring
Parameters of the experiments 4.2 Parameters of the experiments 4.2.1 General test parameters The following paragraph gives an overview over the general test parameters. The chosen indicative 1 geometric scale is of 1:30. a) Channel geometry The bend radius at the centerline is 6.00 m. The channel is composed of a 2 m long inlet box, a 7.50 m long entry reach, followed by a 90° bend with a radius of 6.00 m at the centerline, a 6.00 m long exit reach and finally a 1.5 m long outlet box. The cross-section is rectangular (1.00 m wide and 1.00 m high). The ratio bend radius at the centerline to channel width ( R c ⁄ B ) is 6.0 (see also § 4.1.1). Before a test serie, the bed was levelled to fit the desired initial longitudinal bed slope; in every cross-section the bed was horizontal (perpendicular to the centerline of the channel). During the test, the sediment supply was adjusted to keep the longitudinal bed slope in the straight inlet reach as constant as possible. b) Flow conditions (discharge, bed slope) The used discharges ranged between 70 and 210 l/s: 70 l/s were used for the initial armoring of the bed (before the test started properly); 150, 180 and 210 l/s were used for the main tests. These discharges correpond to propotype discharges of about 350, 750, 890 and 1040 m3/s at a model scale of 1:30. The flow regime was maintained subcritical. The bed slope in the inlet reach was maintained as constant as possible (as close to the initial bed level), by adjusting the sediment supply. c) Sediment transport The tests were performed for a constant discharge at equilibrium conditions in the straight entry reach. The sediment transport balance in the channel depends on the sediment supply, the transport capacity and the equilibrium conditions. The quantity of sediments introduced in the channel was variable to maintain the desired longitudinal bed slope in the entry reach (see also § 4.3) except for the preliminary tests where it was maintained at a constant rate. The ratio of water depth to mean sediment diameter is of about h m ⁄ d m ≈ 15 . S 0 Since the slope and sediment density coefficient s are the same for the laboratory experiments and a test reach in nature, the Shields parameter (eq. 3.42) will be proportional to R h ⁄ d . In order to have the same transport characteristics, this ratio needs to be the same for the prototype and 1.The present study does not test a specific site. But if we consider prealpine rivers, the following set of parameters is quite representative: width of the river = 30 m, with a radius of about 200 m (e.g. the Emme River close to Wolhusen LU, Switzerland) <strong>EPFL</strong> Ph.D thesis 2632 - Daniel S. Hersberger November 9, 2002 / page 77
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WALL ROUGHNESS EFFECTS ON FLOW AND
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Abstract By applying vertical ribs
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Résumé En disposant des nervures
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Zusammenfassung • Ein markanter S
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Acknowledgments page x / November 9
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Table of contents 4. Smart & Jäggi
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Table of contents 7.6 Summary and c
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Chapter 1 - Introduction 1.1 Contex
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Chapter 1 - Introduction page 4 / N
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Chapter 2 - State of the art 2.1 Fl
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Chapter 2 - State of the art 2.2.2
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Chapter 2 - State of the art Theref
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Chapter 2 - State of the art resolu
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Chapter 2 - State of the art comple
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Chapter 2 - State of the art ORLAND
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Chapter 2 - State of the art 2.6 Me
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Chapter 2 - State of the art page 2
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Chapter 3 - Theoretical considerati
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Chapter 8 - Summary, conclusions an
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Notations K S [m 1/3 /s] roughness
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Notations bed b bf c cr d e g w o o
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References de Vriend H.J. (1981). S
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References Meyer-Peter, E., Favre,
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References Williams, R. (1899). Flu
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References by chapter Keulegan (193
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References by chapter page 214 / No
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Index of Authors Hoffmanns 13 Hoffm
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Index of Authors page 218 / Novembe
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Index of Figures Fig.4.19: Frame po
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Index of Figures 22] 183 Fig.7.15:
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Index of Tables Table 7.3: Table of
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Index of Keywords dimensional analy
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Index of Keywords sediment sampling
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Index of Keywords parameter 77 Pete
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Publications (continued) 1997 Hersb
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