4.5.3 STRAIGHT COMPOUND CHANNEL
(i) Symmetrical and uniform nature of boundary shear stress distribution is found for straight compound channel of Type-I when compared to the meandering compound channels of Type-II and Type-III.
(ii) The boundary shear at the main channel junctions are generally found to be more than that compared to other points of the wetted perimeter.
(iii) The total shear carried by flood plain is found to be larger than that of the main channel.
(iv) Boundary shear in the main channel and floodplain regions increases proportionately with the over bank flow depth.
(v) Total shear carried by the wetted perimeter of the compound channel compares well with the energy gradient approach.
4.6 DISTRIBUTION OF RADIAL (TRANSVERSE) VELOCITY
(Type-II channel at bend apex AA) (Type-II channel at bend apex AA)
Fig.4.9.3 in-bank depth h’ = 7.11 cm Fig.4.9.4 in-bank depth h’ = 8.55 cm (Type-II channel at bend apex AA) (Type-II channel at bend apex AA)
Fig. 4.9.5 in-bank depth h’ = 9.34 cm Fig.4.9.6 in-bank depth h’ = 11.01 cm (Type-II channel at bend apex AA) (Type-II channel at bend apex AA) Figs.4.9.1-Fig.4.9.6 Contours showing the distribution of radial velocity at bend- apex (Section AA) of simple meandering (Type-II) channels.
Fig.4.9.7 in-bank depth h’ = 5.31 cm Fig.4.9.8 in-bank depth h’ = 6.08 cm (Type-II channel at cross-over BB) (Type-II channel at cross-over BB)
Fig.4.9.9 in-bank depth h = 7.11 cm Fig.4.9.10 in-bank depth h = 8.55 cm (Type-II channel at cross-over BB) (Type-II channel at cross-over BB)
Fig.4.9.11 in-bank depth h ‚= 9.34 cm Fig. 4.9.12 in-bank depth h’ = 11.01 cm (Type-II channel at cross-over BB) (Type-II channel at cross-over BB)
Figs.4.9.7-Fig.4.9.12 Contours showing the distribution of radial velocity at geometrical-crossover of simple meandering (Type-II) channels.
Fig. 4.10.1- In bank depth h’ = 5.3 cm
(Type-III channel at bend apex AA)
Fig. 4.10.2- In bank depth h’ = 5.62 cm
(Type-III channel at bend apex AA)
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Fig. 4.10.3- In bank depth h’ = 5.92 cm
(Type-III channel at bend apex AA)
Fig. 4.10.4- In bank depth h’ = 6.18 cm
(Type-III channel at bend apex AA)
Fig. 4.10.5- In bank depth h’ = 6.71cm
(Type-III channel at bend apex AA)
Fig. 4.10.6- In bank depth h’ = 7.33 cm (Type-III channel at bend apex AA)
Fig.4.10.1-Fig.4.10.6 Contours showing the distribution of radial velocity at bend apex (Section AA) of simple meandering (Type-III) trapezoidal channels.
Fig. 4.10.7- In bank depth h’ = 5.3 cm (Type-III channel at cross-over BB)
Fig. 4.10.8- In bank depth h’ = 5.62 cm (Type-III channel at cross-over BB)
Fig. 4.10.9- In bank depth h’ = 5.92 cm (Type-III channel at cross-over BB)
Fig. 4.10.10- In bank depth h’ = 6.18 cm (Type-III channel at cross-over BB)
Fig. 4.10.11 In bank depth h’ = 6.71 cm (Type-III channel at cross-over BB)
Fig. 4.10.12- In bank depth h’ = 7.33cm (Type-III channel at cross-over BB)
Fig.4.10.7-Fig.4.10.12 Contours showing the distribution of radial velocity at geometrical cross-over (Section BB) of simple meandering (Type-III) trapezoidal channels.
4.6.1 SIMPLE MEANDER CHANNEL
From the distribution of radial velocity in contour form for the flow confined within the meander section only for Type-II and Type-III channels (Figs. 4.9.1-Fig. 4.9.6 and Figs. 4.10.1-Fig. 4.10.6), the following information can be drawn.
(i) The radial velocity is observed to be smaller than tangential velocity. For the trapezoidal Type-III channels, the radial velocity is observed to be around 10 % of the longitudinal velocity (Fig.4.10.3 and Fig.4.4.3).
(ii) Higher radial components are found for Type-II rectangular main channel section of the order of 67 % of longitudinal velocity (Fig.4.9.1 and Fig.4.3.1).
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(iii) At the bend-apex, the micro-ADV readings for radial velocity directions are found to be mostly negative indicating that it is pointing inward direction.
Higher velocity contours are seen near the inner bank and lower contours at the outer banks.
(iv) At the geometrical cross-over region, the radial components are towards in- ward direction having lesser magnitudes when compared to that at the bend- apex, indicating a phase lag between channel cross-over and flow cross over.
Fig. 4.11.1 Over-bank depth (H- h) = 1.68 cm (Type-II channel at bend apex AA)
Fig. 4.11.2 Over-bank depth (H- h) = 2.42 cm (Type-II channel at bend apex AA)
Fig. 4.11.3 Over-bank depth (H- h) = 3.28 cm (Type-II channel at bend apex AA)
Fig. 4.11.4 Over-bank depth (H- h) = 4.08 cm (Type-II channel at bend apex AA)
Fig. 4.11.5 Over-bank depth (H- h) = 5.10 cm (Type-II channel at bend apex AA)
Fig. 4.11.6 Over-bank depth (H- h) = 6.15 cm (Type-II channel at bend apex AA)
Figs.4.11.1- Fig.4.11.6 Contours showing the distribution of radial velocity at bend-apex (Section AA) of compound meandering (Type-II) channels.
Fig. 4.11.7 Over-bank depth (H- h) =1.68 cm (Type-II channel at cross over BB)
Fig. 4.11.8 Over-bank depth (H- h) = 2.42 cm (Type-II channel at cross over BB)
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Fig. 4.11.9 Over-bank depth (H- h) = 3.28 cm (Type-II channel at cross over BB)
Fig. 4.11.10 Over-bank depth (H- h) = 4.08 cm (Type-II channel at cross over BB)
Fig. 4.11.11 Over-bank depth (H- h) = 5.10 cm (Type-II channel at cross over BB)
Fig. 4.11.12 Over-bank depth (H- h) = 6.15 cm (Type-II channel at cross over BB)
Figs.4.11.7- Fig.4.11.12 Contours showing the distribution of radial velocity at geometrical cross-over (Section BB) of compound meandering (Type-II) channels.
Fig. 4.12.1 Over-bank depth (H- h) = 0.74 cm (Type-III meandering compound channel at bend apex AA)
Fig. 4.12.2 Over-bank depth (H- h) = 1.74 cm (Type-III meandering compound channel at bend apex AA)
Fig. 4.12.3 Over-bank depth (H- h) = 9.92 cm (Type-III meandering compound channel at bend apex AA)
Fig. 4.12.4 Over-bank depth (H- h) = 2.17 cm (Type-III meandering compound channel at bend apex AA)
Fig. 4.12.5 Over-bank depth (H- h) =2.93 cm (Type-III meandering compound channel at bend apex AA)
Fig. 4.12.6 Over-bank depth (H- h) = 3.01 cm (Type-III meandering compound channel at bend apex AA)
Figs.4.12.1-Fig.4.12.6 Contours showing the distribution of radial velocity components at bend-apex (Section AA) of compound meandering (Type-III) channels.
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Fig. 4.12.7 Over-bank depth (H- h ) = 0.74 cm (Type-III meandering compound channel at cross-over BB)
Fig. 4.12.8 Over-bank depth (H- h) =10.74 cm (Type-III meandering compound channel at cross-over BB)
Fig. 4.12.9 Over-bank depth (H- h) = 1.92 cm (Type-III meandering compound channel at cross-over BB)
Fig. 4.12.10 Over-bank depth (H- h) = 2.17 cm (Type-III meandering compound channel at cross-over BB)
Fig. 4.12.11 Over-bank depth(H- h) = 2.93 cm (Type-III meandering compound channel at cross-over BB)
Fig. 4.12.12 Over-bank depth (H- h) = 3.01 cm (Type-III meandering compound channel at cross-over BB)
Figs.4.12.7-Fig.4.12.12 Contours showing the distribution of radial velocity components at geometrical cross-over (Section BB) of compound meandering (Type-III) channels.
4.6.2 MEANDER CHANNEL WITH FLOODPLAIN
From the distribution of radial velocity for Type-II and Type-III meander channel with floodplains, the following interesting features can be observed (Figs. 4.11.1 through Fig. 4.11.12 and Figs. 4.12.1 through Fig. 4.12.12).
(i) At the bend apex (AA) of meandering compound channel of Type-II, the micro-ADV reading shows negative signs of the radial velocity indicating the flow direction is towards inner flood plain.
(ii) At both the bend-apex (AA) and cross-over regions (BB) of Type-III meandering compound channels, negative contours are found in flood plain regions and positive contours are found in the main channel regions. At the bend apex, the higher positive velocity contours concentrate near the inner wall of main channel.
(iii) The radial velocity at geometrical cross over region is found to be more than that at bend-apex showing almost 900 phase lag between channel geometry and flow geometry.
(iv) At the bend apex AA, the thread of larger in-ward radial components are found just above the bed of the main channel.
(v) At higher over-bank depth, higher magnitude of inward radial velocity is observed near the inner side of floodplains for both Type-II and Type-III channels.
(vi) At the cross-over regions (BB) for Type-III channel, for higher over bank depths the large magnitude of inward radial velocity is observed at both sides of flood plain and the out-ward velocity components in main channel area.
Fig. 4.13.1 Over-bank depth (H- h)= 2.12 cm (Type-I compound channel)
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Fig. 4.13.2Over-bank depth (H- h)= 3.15 cm (Type-I compound channel)
Fig. 4.13.3 Over-bank depth (H- h)= 5.25 cm (Type-I compound channel)
Fig. 4.13.4 Over-bank depth (H- h)=6.75 cm (Type-I compound channel)
Fig. 4.13.5 Over-bank depth (H- h)= 8.21 cm (Type-I compound channel) Fig.4.13.1-4.13.5 Contours showing the distribution of radial velocity of Type-I
straight compound channels. Radial velocity contours in cm/s.
4.6.3 STRAIGHT COMPOUND CHANNEL
The present Type-I experimental compound channel is classified as deep as the width to depth ratio is less than five. For this channel, the wall effects are felt through out the cross section when compared to a shallow channel. The following features are noted from the isovel plots of radial velocity for straight compound channel geometry of Type-I (Figs. 4.13.1. through Fig. 4.13.5)
(i) The radial component of velocity for straight compound channel is observed to be of smaller magnitude when compared to that of meandering over bank flow of about same depth ratio.
(ii) At low over bank depths, the radial velocity component is towards the direction of floodplain. For higher over bank depths, the direction of radial velocity component is from floodplain to the main channel, showing of reversal of its behaviors with depth over floodplain.
(iii) Higher radial velocity contours are seen near the junction of main channel and floodplain showing the higher momentum transfer at these regions.