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.
Type-III channels the vertical velocity distribution at location AA and BB are shown in Figs. 4.15.1- Fig.4.15.6 and Figs. 4.15.7- Fig. 4.15.12. For the meander channel with floodplains (Type-II) at locations AA and BB the vertical velocity distributions of the channels are shown in Figs. 4.16.1- Fig. 4.16.6 and Figs. 4.16.7- Fig. 4.16.12 respectively. For the meander channel with floodplains (Type-III), the vertical velocity distributions in contour form at bend apex is shown in Figs. 4.17.1- Fig.
4.17.6 and at the geometrical cross over the corresponding contours are shown in Figs. 4.17.7- Fig. 4.17.12 respectively. For the straight compound channels of Type- I, the radial distribution of vertical velocity are shown in contours forms in Figs.4.18.1-Fig. 4.18.5. According to the sign convention by the micro-ADV upward vertical velocity shows positive sign and down-ward vertical velocity shows negative sign.
Fig.4.14.1 In-bank depth h’ = 5.31 cm Fig.4.14.2 In-bank depth h’ = 6.08cm (Type-II channel at bend apex AA) (Type-II channel at bend apex AA)
Fig.4.14.3 In-bank depth h’ = 7.11cm Fig. 4.14.4 In-bank depth h’ = 8.55cm (Type-II channel at bend apex AA) (Type-II channel at bend apex AA)
Fig.4.14.5 In-bank depth h’ = 9.34 cm Fig.4.14.6 In-bank depth h’ = 11.01cm (Type-II channel at bend apex AA) (Type-II channel at bend apex AA) Fig.4.14.1-4.14.6 Contours showing the distribution of vertical velocity
components at bend-apex (Section AA) of simple meandering (Type-II) channels.
Fig.4.14.7 In-bank depth h’ = 5.31 cm Fig.4.14.8 In-bank depth h’ = 6.08cm (Type-II channel at cross over BB) (Type-II channel at cross over BB)
Fig.4.14.9 In-bank depth h’ = 7.11cm Fig.4.14.10 In-bank depth h’ = 8.55cm (Type-II channel at cross over BB) (Type-II channel at cross over BB)
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Fig.4.14.11 In-bank depth h’ = 9.34 cm Fig.4.14.12 In-bank depth h’ = 11.01cm (Type-II channel at cross over BB) (Type-II channel at cross over BB)
Fig.4.14.7 Fig.4.14.12 Contours showing the distribution of vertical velocity at geometrical cross-over (Section BB) of simple meandering (Type-II) channels.
Fig. 4.15.1 In bank depth h’ = 5.3cm (Type-III channel at bend apex AA)
Fig. 4.15.2 In bank depth h’ = 5.62 cm (Type-III channel at bend apex AA)
Fig. 4.15.3 In bank depth h’ = 5.93 cm (Type-III channel at bend apex AA)
Fig. 4.15.4 In bank depth h’ = 6.18 cm (Type-III channel at bend apex AA)
Fig. 4.15.5 In bank depth h’ = 6.71 cm (Type-III channel at bend apex AA)
Fig. 4.15.6 In bank depth h’ = 7.33 cm (Type-III channel at bend apex AA) Fig.4.15.1-Fig.4.15.6 Contours showing the distribution of vertical velocity
components at bend apex (Section AA) of simple meandering (Type-III) channels.
Fig. 4.15.7 In bank depth h’ = 5.3 cm (Type-III channel at cross over BB)
Fig. 4.15.8 In bank depth h’ = 5.62 cm (Type-III channel at cross over BB)
Fig. 4.15.9 In bank depth h’ = 5.93 cm (Type-III channel at cross over BB)
Fig. 4.15.10 In bank depth h’ = 6.18cm (Type-III channel at cross over BB)
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Fig. 4.15.11 In bank depth h’ = 6.71 cm (Type-III channel at cross over BB)
Fig. 4.15.12 In bank depth h’ = 7.33cm (Type-III channel at cross over BB) Fig.4.15.7-Fig.4.15.12 Contours showing the distribution of vertical velocity at
cross-over (Section BB) of simple meandering (Type-III) channels.
4.7.1 SIMPLE MEANDER CHANNEL
From the distribution of vertical velocity components in Type-II and Type-III simple meander channel sections in contour form at the locations AA and BB, the following features are noted.
(i) For in-bank flow, the maximum upward components are found at outer wall and maximum down-ward components are found at inner wall. With increase in flow depths, the values of vertical velocity are found to decrease.
(ii) At the geometrical cross-over region, the vertical components of velocity are mostly towards down-ward direction. With increase in flow depth the magnitude of vertical velocity decreases.
(iii) At geometrical cross-over section the vertical components of velocity at the water surface is observed to be higher than that at the bottom of the meandering channel.
(iv) At cross-over section of Type-III trapezoidal meandering channels, up- ward components are also observed. This is due to the phase lag of the channel geometry with the flow geometry.
(v) Magnitudes of vertical velocity components for meandering channels are found to be less when compared to the magnitude of radial component of velocity.
(vi) Magnitude of vertical velocity component is found to be the order of around 1.4% of longitudinal velocity for type-III channel and as high as 14% for type-II channel of the corresponding longitudinal velocity.
Fig. 4.16.1 Over-bank depth (H- h)= 1.68 cm (Type-II channel at bend apex AA)
Fig. 4.16.2Over-bank depth (H- h)= 2.42 cm (Type-II channel at bend apex AA)
Fig. 4.16.3 Over-bank depth (H- h)= 3.28 cm (Type-II channel at bend apex AA)
Fig. 4.16.4 Over-bank depth (H- h)= 4.08 cm (Type-II channel at bend apex AA)
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Fig. 4.16.5 Over-bank depth (H- h)= 5.10 cm (Type-II channel at bend apex AA)
Fig. 4.16.6Over-bank depth (H- h)= 6.15 cm (Type-II channel at bend apex AA) Fig.4.16.1-Fig. 4.16.6 Contours showing the distribution of vertical velocity at
bend apex (Section AA) of meandering compound (Type-II) channels.
Fig. 4.16.7 Over-bank depth (H- h)= 1.68 cm (Type-II channel at cross over BB)
Fig. 4.16.8 Over-bank depth (H- h)= 2.42 cm (Type-II channel at cross over BB)
Fig. 4.16.9 Over-bank depth (H- h)= 3.28 cm (Type-II channel at cross over BB)
Fig. 4.16.10 Over-bank depth (H- h)= 4.08 cm (Type-II channel at cross over BB)
Fig. 4.16.11 Over-bank depth (H- h) = 5.10 cm (Type-II channel at cross over BB)
Fig. 4.16.12 Over-bank depth (H- h)= 6.15 cm (Type-II channel at cross over BB)
Fig.4.16.7-Fig.4.16.12 Contours showing the distribution of vertical velocity at geometrical cross-over of (Type-II) meandering compound channels.
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Fig. 4.17.1 Over-bank depth (H- h) = 0.74 cm (Type-III meandering compound channel at bend apex AA)
Fig. 4.17.2 Over-bank depth (H- h) = 1.74 cm (Type-III meandering compound channel at bend apex AA)
Fig. 4.17.3 Over-bank depth (H- h) =1.92 cm (Type-III meandering compound channel at bend apex AA)
Fig. 4.17.4 Over-bank depth (H- h) = 2.17 cm (Type-III meandering compound channel at bend apex AA)
Fig. 4.17.5 Over-bank depth (H- h) = 2.93 cm (Type-III meandering compound channel at bend apex AA)
Fig. 4.17.6 Over-bank depth (H- h) = 3.01 cm (Type-III meandering compound channel at bend apex AA)
Fig.4.17.1-4.17.6 Contours showing the distribution of vertical velocity at bend-apex of (Type-III) meandering compound channels.
Fig. 4.17.7 Over-bank depth (H- h) = 0.74 cm (Type-III meandering compound channel at cross-over BB)
Fig. 4.17.8 Over-bank depth (H- h) = 1.74 cm (Type-III meandering compound channel at cross-over BB)
Fig. 4.17.9 Over-bank depth (H- h) = 1.92 cm (Type-III meandering compound channel at cross-over BB)
Fig. 4.17.10 Over-bank depth (H- h) = 2.17 cm (Type-III meandering compound channel at cross-over BB)
Fig. 4.17.11 Over-bank depth (H- h) = 2.93 cm (Type-III meandering compound channel at cross-over BB)
Fig. 4.17.12 Over-bank depth (H- h) = 3.01 cm (Type-III meandering compound channel at cross-over BB)
Fig.4.17.7-4.17.12 Contours showing the distribution of vertical velocity at geometrical cross-over of (Type-III) meandering compound channels.
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4.7.2 MEANDER CHANNEL WITH FLOODPLAIN
From the vertical velocity contours (Figs. 4.16.1-Figs. 4.16.12 and Figs. 4.17.1-Figs.
4.17.12) for meander channel with floodplains corresponding to Type-II and Type-III channels respectively, the following features can be observed.
(i) At the bend-apex for meandering compound channel of Type-II, the direction of vertical components are upward in outer region and down-ward at inner regions of the main channel.
(ii) At the bend-apex of the Type-III meandering compound channel, the direction of vertical velocity are upward at the outer region, both for floodplain and main channel with higher contours appearing near the outer wall of floodplain. The down ward velocity contours are at the inner regions of floodplain with large contours appearing at the central region of inner floodplain.
(iii) At the geometrical cross-over regions of meandering compound channels of Type-III, the direction of vertical components are mostly upward except small value looking vertical velocity contours down-ward near the wall of inner floodplain. Down ward velocity components are observed at both floodplains.
For low depths of flow over floodplain, the velocity components in floodplain is found to be down ward direction but at higher over-bank depths, the velocity components in floodplain region are found to be upward.
(iv) The threads of upward vertical velocity are found near the inner wall and down ward components are found near the outer wall of the main channel.
(v) The magnitudes of vertical velocity in the floodplain regions are observed to be less than the main channel area at the bend-apex as well as at the geometrical cross-over.
Fig. 4.18.1 Over-bank depth (H- h)= 2.12 cm (Type-I compound channel)
Fig. 4.18.2 Over-bank depth (H- h)= 3.15 cm (Type-I compound channel)
Fig. 4.18.3 Over-bank depth (H- h)= 5.25 cm (Type-I compound channel)
Fig. 4.18.4 Over-bank depth (H- h)= 6.75 cm (Type-I compound channel)
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Fig. 4.18.5 Over-bank depth (H- h)= 8.21 cm (Type-I compound channel)
Fig.4.18.1-Fig.4.18.5 Contours showing the distribution of vertical velocity of Type-I straight compound channels.
4.7.3 STRAIGHT COMPOUND CHANNEL
From the isovels of vertical velocity for the straight compound channel geometry (Type-I), the following features can be noted (Figs. 4.18.1-Fig. 4.18.5).
(i) The magnitude of vertical velocity is less when compared to the tangential velocity. The vertical component of velocity is found to be of the order of around 25% when compared to the transverse velocity at lower depths over floodplain (Fig.4.13.1-Fig.4.18.1) and 20 % at higher depths over floodplain (Fig.4.13.5–Fig.4.18.5).
(ii) At lower over-bank depths, upward positive velocity components are found in the main channel region and down-ward velocity components are found at the flood plain regions.
(iii) For lower over-bank depths, higher upward vertical velocity are observed at the junction between main channel and flood plain and the magnitude reduces with increase in depth over floodplain.
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ANALYSIS AND DISCUSSION OF THE RESULTS
5.1 GENERAL
The results of the experimental runs involving flow in simple meander channels, straight compound channel, and meander channel - floodplain geometry are analysed. Basing on the experimental data, discussion on the variation of channel resistance with depth of flow, the boundary shear force distribution, and analysis of momentum transfer are made. From the model out puts, the location of interface plain with zero shear for separating compound channel section into zones for discharge calculation using divided channel method is proposed. Various 1D discharge predictive models for straight and compound meandering channels are analysed and tested with the experimental data. Better alternative approaches to predict discharge in over-bank flow are suggested. Division of flow between main channel, lower main channel, and floodplain are attempted. The discharge adjustment factor-coherence relationships and the evaluation of interaction lengths at different interface plains are discussed. The experimental and computed parameters concerning the flow in simple straight channels (Type-I, runs S1 to S11), mildly meander channel (Type-II, runs MM1 to MM15) and for high meandering and wide channels (Type-III, runs HM1 to HM15) are given in Table 5.1. Similarly for over bank conditions, the corresponding data for Type-I (runs S12 to S21), Type-II (runs from MM16 to MM27), and for Type-III (runs HM16 to HM27) channels are given in Table 5.2.
5.2 VARIATION OF REACH AVERAGED LONGITUDINAL