2017 3rd International Conference on Applied Mechanics and Mechanical Automation (AMMA 2017) ISBN: 978-1-60595-479-0

Waterway Regulation Scheme in Daijiazhou Reach of River Ya LIU1,*, Li ZHENG2 and Shi-ming YAO1 1Yangtze River Scientific Research Institute, Key Laboratory of River Regulation and Flood Control of MWR, City, Province, People’s Republic of China 2Changjiang Waterway Planning Design and Research Institute, Wuhan City, Hubei Province, People’s Republic of China *Corresponding author

Keywords: Branched river, Waterway regulation, Yangtze River.

Abstract. Due to complicated riverbed evolution and numerous navigation-hampering shoals, Daijiazhou reach is the main navigation-hampering channel in the middle Yangtze River for a long time, so it is the key and difficult point for the waterway dimension improvement in the middle and lower Yangzte River. Based on the demand of 6m navigable depth and the research on navigation conditions of Dajiazhou, this paper summarize the characteristics of the navigation-hampering shoals, organizes the regulation thoughts of “improve the bank and shoals protection, partially adjust the morphologies of floodplain and channel” and proposes the detailed solutions.

Introduction to reach in Yangtze River is 1026km long and accounts for 1/3 length of the entire Yangtze River waterway, which connects the waterway of Reservoir Region in upstream and links the deep channel of Yangtze estuary in downstream, so it is the core channel to promote harmonious development of the middle-lower reaches[1]. In recent years, with the construction of 12.5m deep channel from to estuary and the formation of the Three Gorges Reservoir Area in upstream, the navigation conditions in the upper and lower reaches of Yangtze River have substantial improvement. At present, the waterway downstream from Fuling in the Three Gorges Reservoir Region is 4.5m deep and the Anqing-Nanjing reach is over 6m deep, so the planning objective in 2020 that determined in the “Master Planning Outline of Yangtze River Waterway” has been achieved ahead of schedule. However, the navigable depth in Yichang-Anqing is only 3.5m~4.5m, which is obviously less than its upstream and downstream segments[2]. Therefore, it is urgent to carry out waterway improvement project, so as to align with the upstream and downstream segments, yield the maximum benefit of Yangtze River transportation, meet the shipping demand with rapid economic development along the river, and stimulate the coordinated development between the east middle and west regions. Due to complicated shoal-channel evolution and numerous navigation-hampering shoals, Daijiazhou is the main navigation-hampering channel in the middle Yangtze River for a long time, so it is the key and difficult point for Yichang-Anqing channel dimension improvement[3-5]. A series of channel improvement projects for Dajiazhou had been implemented successively in 2009~2013, but the improvement was hardly accomplished in one step by the reasons of severe scouring- depositing processes and many external restrictive factors such as bridge project, port dock and water intake facility, etc[6-7]. Based on intensive study on navigation conditions changing characteristics since impoundment of the Three Gorges Reservoir, the paper preliminarily proposes the renovation target and project scheme in the next stage, and provides technical supports for further dimension improvement and navigation safety.

219 Study of Site Daijiazhou Reach, with the total length of 34km from Echeng to Huifengji, is located in middle Yangtze River and 100km downstream from Wuhan, seen as Fig.1. As a typical branching channel with bend in the middle-lower Yangtze River, it has 20km long slight-bend left branch and 16km long straight right branch, seen as Fig. II. In decades, despite both branches went through scouring- depositing processes and experienced water levels’ rise and fall by turns, no absolute main branch was formed and the diversion ratio of each branch was never exceed 65%. In general, the right branch occupied more dominant diversion period. At present, the minimum maintenance dimension of the channel in dry season is 4.5m×200m×1050m with relatively poor stability, and dredging is required for some years. In view of the navigation condition and renovation difficulty degree, the right branch is more preferable[8]. N

Ju River

er Wuhan Ba Riv Han Ri ver Daijiazhou Reach Anqing Wan River ce in Hu Hubei P ov be rovince r i P Pr i ov hu in n ce A

Hukou Province Poyang Lake Figure 1. Location map of Daijiazhou reach of Yangtze River. Both sides of Daijiazhou have flood-control banks. Floodplains of varying widths (normally small width) exist between the banks and main channel. Parts of high floodplains have protection banks, which efficiently limit the spread of flood width and stabilize the river regime. Protection and maintenance project for Daijiazhou and the floodplains with the function of controlling flood spreading were carried out in two phases during 2009~2013, which significantly enhanced the stability of Dijiazhou and further stabilized the river regime. Considering the recent scouring-depositing situation, the stability of shoals at head of the central bar affects on maintaining the diversion situation of both branches to some extent, but the floodplains outside the project area still go through scouring-depositing processes, which changes the inflow conditions of both branches accordingly. Regards the diversion ratio seen as Tab.1, although the right branch keeps the dominant branch for most of time, the diversion volume was less than the left branch in the dry seasons of 2006, 2008 and 2010. Thus, the right branch does not hold dominant position stably, which means the two branches may dominate alternately. Table 1. Flow diversion ratio of two branches in Daijiazhou Reach.

Flow Flow Diversion ratio (%) Date of Discharge High water level Median water level Low water level survey (m3/s) Right Left Right Left Right Left 2004.9 30696 branch 60.0 branch 40.0 branch branch branch branch 2005.11 20632 53.54 46.46 2006.2 9119 47.6 52.4 2006.6 21231 56.26 43.74 2006.9 16995 53.83 46.17 2006.11 10273 48.57 51.43 2007.3 11352 50.05 49.95 2008.3 13301 48.6 51.4 2010.26 9842 49.9 50.1 2011.2 11576 52.0 48.0

220 Flow Flow Diversion ratio (%) Date of Discharge High water level Median water level Low water level survey (m3/s) Right Left Right Left Right Left 2012.2 11611 branch branch branch branch branch 58.2 branch 41.8 2013.3 12121 55.6 44.4 2013.10 21760 56.5 43.5 2014.3 9950 60.0 40.0 2015.2 9882 61.1 38.9 2016.3 15804 60.9 39.1 2016.8 44064 62.6 37.4

Verification of Navigation Conditions The navigation-hampering shoals concentrate on the inlet, middle and outlet of the right branch according to the navigable depth changes in recent years. The recent scouring of channel bar in Chihu Port at inlet of the right branch and continuous collapses on the left edge of shoal tail result in broadening of nearby channel, dispersed flow, and numerous scattered navigation-obstructing shoals, which causes insufficient navigation width or over-bended channel. The 6.0m isobath of the shoal area is interrupted at times. The isobaths was interrupted August 2012~March 2013 with the break distance of 1500m in; it was connected in February 2014~March 2016, but the minimum width is no more than 80m. Comparing to the middle-upper section, the middle section of the right branch is obviously broadened, the point bar is cut to short channel bar, which is difficult to form stable right boundary. Besides, the erosion ditches distributed on the right bank have certain development over the years, which further suck and scatter the river flow, and make water hardly concentrated for scouring the channel. Therefore, the 6m navigation channel of the middle-lower section from Guafuji to Lejiawan is unstable. The 6m isobath in the middle section of the right branch was connected in February 2014, but the minimum width is no more than 100m; it was interrupted in February 2015 with the break distance of 200m; it was connected in March 2016, but the minimum width is no more than 130m. The shoal areas in the right branch concentrate on Erfangwan. In addition to the broad outlet channel of the right branch, the shoal on the right side is lowered by erosion and the deep channel on the left side is deposited, which causes broad-shallow section and dispersed river flows. The 6m isobath below the design level of the shoal at outlet of the right branch was thoroughly connected in February 2014, but it was interrupted in February 2015 with the break distance of 600m. Till March 2016, the deep channel deposited up to 10m with the break distance increasing to 1100m.

Waterway Regulation Scheme Seen from the current channel situation and the scouring-depositing characteristics of shoals, it is lack of efficient control on the front shoal at the head of Daijiazhou, the cental bar in Chihu Port and the point bar in middle-lower section of the right branch, which causes severe scouring- depositing process and results in difficulties to stabilize flow condition of the navigation channel, so the channel depth of shoal is insufficient. In such cases, this paper proposes the renovation idea of “Improve the bank and shoals protection, partially adjust the morphologies of floodplain and channel”. Please refer to following details: For the inlet of the right branch, the head of Daijiazhou is the key renovation point, because its changing situation closely relates to the navigation channel depth and position. Therefore, the shoal channel condition at inlet can be improved by stabilizing and extending upward the head of Daijiazhou, and stabilizing the diversion condition of both branches; or stabilizing point bar and guarding the head of Daijiazhou at the same time.

221 Due to the characteristics of slight-bending shape and broad river width, the positions of the point bar and shoals (of different years) of the right branch are uncertain, which means the point bar is either left or right and there could be one or multiple shoals. Therefore, it is required to utilize the slight-bending shape and stabilize the point bar to renovate shoals in the middle-lower section and form a slight-bending low flow channel. Based on above renovation idea, this paper proposes following plans, seen as “proposed regulation work”in Fig. 2.

D Ba River aij iaz Enhancement of hou bank protection

Guafuji Yanji fish-bone dike

Point bar control project N Longwangji Legend Lejiawan 0m 4.5m Huifengji beach protection band 6m Erfangwan E-Huang Chihu Port Existed mid-channel bar Regulation Work Bridge Proposed Regulation Work ０ 11kmkm 2km 3km Figure 2. River regime of Daijiazhou reach. (1)Point bar protection project in Chihu Port: Build two protection cofferdams for point bar in Chihu Port. (2)Extension project of the existing fish-bone dike:Extend the existing fish-bone dyke at the head of Daijiazhou with smooth joint, and build six tooth-shape protection zones in the extension section. (3) Point bar control project in Lejiawan Area: Build three submerged spurs and three shoal protection cofferdams in Lejiawan area on the right bank of the right branch. Take the erosion ditch area at the root of shoal protection cofferdam as the spur body that is aligned with the shoal face. (4) Enhancement of river bank protection on the right border of Daijiazhou:Enhance the existing bank protection area on the right border from 200m upstream of the 1st dam body of Lejiawan point bar control project to the end of Daijiazhou.

Conclusion Due to complicated shoal-channel evolution, Daijiazhou section is the navigation-hampering channel in the middle Yangtze River for a long time, and the key and difficult point for channel dimension improvement in the middle-lower reaches of Yangtze River. Based on the demand of 6m navigation depth and the research on navigation conditions of Dajiazhou, this paper concludes the characteristics of the navigation-hampering shoals, organizes the renovation thoughts, and proposes the solutions. Seen from the current navigation channel conditions, the critical matters of Daijiazhou are insufficient navigation depth (6m) in shoals and instability of partial shoals. The navigation- hampering shoals are mainly distributed to the inlet, middle and outlet of the right branch. The shoals in the inlet section are formed by the channel bar scouring in Chihu Port; the shoals in the middle section are formed by cutting the point bar in Guafuji to channel bar, which are of low elevation and hard to be the stable right border of navigation channel; the shoals in the outlet section are caused by scouring and lowering of the right-side point bar, as well as broadening and shallowing of the river. The general idea for Daijiazhou renovation is to further improve the protection of shoals- channels and properly enhance the restraint function of shoals on river flow under the premise of maintaining the diversion stability of both branches. The renovation plans are as follows: improve the navigation conditions in inlet section of the right branch by building shoal cofferdams to protect the point bar of Chihu Port, and extend the fish-bone dam to keep the integrity of Daijiazhou; 222 gradually improve the navigation conditions of the middle-lower sections of the right branch by building groynes and shoal cofferdams to stabilize convex bank shoals, blocking the erosion ditches at the root of point bar and reinforcing the bank protection at the end of Daijiazhou to stabilize the channel border.

Acknowledgement

This study was financially supported by the National Natural Science Foundation of China (Grant No. 51609011, Grant No. 51339001, Grant No. 51379018), CKSG2016874/HL

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