2016 International Conference on Material Science and Civil Engineering (MSCE 2016) ISBN: 978-1-60595-378-6

Hydrologic Correlation Analysis of Highway Bridge Community Along River*

Hua TIAN1,2 1Guangxi University , , 2Guangxi Transportation Research Institute Nanning, Guangxi, China E-mail: [email protected]

Jia-dong HUANG† Guangxi Transportation Research Institute Nanning, Guangxi, China †E-mail: [email protected]

In order to improve the accuracy of hydrologic calculation, three kinds of calculation methods were listed in this paper. Based on the analysis and comparison of the hydrologic calculation of bridge design flood flow at certain frequency in different situation in the same main river system, the hydrologic correlation of bridge community is introduced and the important application of hydrologic correlation analysis of highway bridge community along river that need to be solved are discussed.

Keywords: Engineering; Highway; Hydrology; Bridge Community.

1.Introduction Highway bridge failures caused by floods is one of the most common and important natural disasters [1]. Every year, transport disruption caused by mountain bridge floods failures accounted for vast majority of all natural disasters. Varying from eastern landform hills to western - Plateau landscape, Guangxi is one of the most hilly landscape provinces in China. , Liujiang river and of Xi-jiang river system, which made valley between the rolling mountains, ravines aspect, form a typical mountain foothills river valley landforms. Mountain highway is always designed along the river banks to save engineering investments because of the flat river banks terrain. But more bridges should be built to across tributaries and valleys. Therefore, how to determine the bridge design flood flow and water level which

*This work is supported by the Guangxi Science and Technology Project (Grant No. 1355008-2 and Grant No. 14124004-4 -12 ) Open Project of Guangxi Key Laboratory of Disaster Prevention and Structural Safety (Grant No. 2013ZDK08)

446

across tributaries and valleys to ensure bridge safety becomes the key factor of highway design. The river system often consists of a main river and several small tributaries. Slope of main river is often smaller than tributaries. Storm brings strong rainfall intensity in short duration, which causes floods surge in a short time. Unusually the large amount of debris with floods blocking near span make bridge failure. Hydrologic analysis of bridges should be considered within a bridge community in a certain rain catchment area, which has hydrologic correlation between each other. The actual design flood flow and water level is determined by comprehensive analysis of bridge community survey data and hydrologic calculation. Based in hydrologic analyzing of bridge community along the main river in Jinxiu Dayaoshan county of Guangxi, this paper has studied key hydrology correlation analysis factor of bridge community along the river.

2. Design Flood Flow Analysis Method Lacking Of Observation Data

2.1. Design Flood flow analysis with empirical formula Due to Chinese broad area, expense of constructing flow observation sites in all rivers is high. There is not any flow observation data in most local rivers except some main rivers. The flood survey data and other indirect or empirical data would be used to calculate the design flood flow for rivers without flow observation data. Ministry of transport of China has organized scientific research institutions to set up bridge hydrological analysis experience formula with different regions parameters, which is applicable to bridges across rivers within river basin area of 50000 sq.km. The calculation method is as following equations (1) and (2).

n QCF (1) QQC1 (2) P% VP _ F is the flow basin area, Q is average flow rate of partition area. Cv is coefficient of variation of P-III distribution curve. Cv, C, n, can look up in pre-calculate table. To calculate design bridge flood flow, the flow basin area should be drawn out firstly in topographic map above the river site of bridge. If flow basin area across two partition area and the calculation data of two partition is roughly equal, averaging the two date, or else, choosing the bigger one.

447

2.2. Design flood flow analysis with river section method Natural river water section generally consists of main river channel and river beach, as shown in figure 1. If the river water section meet the uniform hydraulic calculation model, then calculations with Chey-Manning formula areas following equations(3) and (4).

Figure 1. Typical cross-section structure of river.

River channel section: 1 QAvv, Ri2312 (3) ccccn c River bank profile: 1 QAvv, Ri2312 (4) ttttn t t

Qc, Qt, Ac, At, Vc, Vt, Rc, Rt, nc, nt correspond to the river channel water flow, river beach water flow, area, water velocity, water perimeter, roughness. Water perimeter is ratio of river channel width to corresponding area, I represents river bottom slope. After the bridge site is chosen, it should measured the shape of river cross section near the bridge and the average river bottom slope of river upstream and downstream, investigate the characteristics of river channel and beach to obtain corresponding roughness. Comparing the analysis results of flood flow with water marks in history and empirical formula results, the bridge design flood flow corresponding to certain frequency can be determined.

2.3. Flood flow of tributary analysis method considering the main river flow backward Highway along the river lay out in the river valley, more bridges should be built to across tributaries and valleys belonged to the same main river system, which hydrological analysis affected by the main river flood naturally. Therefore,

448

analyze the bridge design flood flow across tributary stream must consider influence of main river flow backward which divide into three different situations [3]. In the first case, analyze the bridge flood flow with empirical formula and river section method when tributary has floods and main river has not. In the second case, main river has floods and flow backward while tributary has not, as figure 2(a); The third case is the most dangerous while main rive and tributary has floods simultaneously; when main river floods faded away, the tributary has its peak water level, as figure 2(b).

(a) (b) Figure 2. Tributary stream estuary flow backward by main river.

3. Typicalexamples

3.1. Project overview Highway 314 is the local high-grade road which connecting Pingnan and Jinxiu county in Guangxi province with width of 10 meters and design speed of 60km/h. Part of highway along the Datong river is a typical mountainous road, as shown in figure 3. Datong river originated in Dayao mountains belong to Xijiang river system, which caused huge loss in flood disaster hit village in history. Along the Datong river, Shuiyan Bridge and Zhudutang bridge are set up to across Datong river near two different village separately. Shike bridge, Chusanping bridge and Malian bridge across three tributaries separately which belong to Datong river system, as shown in figure 3.

449

Figure 3. Relationship of highway 314 and Datong river.

3.2. Hydrologic correlation analysis of bridge community Shuiyan bridge and Zhudutang bridge acrossing the Datong main river, which are typical mountainous rivers and without the influence of other factors such as upstream and downstream reservoir, can be analyzed bridge design flood flow and water lever according to section 1.1 and 1.2 methods as shown in table 1.Qcand Qt represent design flood flow of river channel and beach respectively. Vc and Vt represent design flood velocity of river channel and beach respectively.

Table 1. Flood flow analysis of Shuiyan Bridge and Zhudutang Bridge.

Qc Qt Vc Vt Q project (m3/s) (m3/s) (m/s) (m/s) (m3/s) Shuiyan Bridge 1849.3 291.0 3.1 0.9 2140.3 Zhudutang Bridge 1835.5 0.0 3.2 0.0 1835.5

Shuiyan bridge is located in downstream while Zhudutang bridge in upstream. The water basin area of Shuiyan bridge is 430.1 sq.km, which is bigger than Zhudutang bridge 430.1 sq.km. Therefore, it resulted in 2140.3 m3/s design flood flow of Shuiyan bridge at one percent frequency, about 304.8 m3/s bigger than Zhudutang bridge. For other three Bridges crossing tributaries, method mentioned in section 1.3can be used to consider flood flow backward by Datong main river. The probability of main river and tributaries flooding at the same time are high. Therefore, its biggest bridge design flood flow is shown in figure 2(b). Q and

Q0represent bridge design flood flow at one percent frequency separately, as shown in table 2.

450

H and H0 represent bridge design flood water level of main river and tributaries without interfering each other. Hd is the bridge design flood water level in most unfavorable design conditions as shown in figure 2(b).

Table 2. Design flood flow and water level of bridge crossing tributaries.

Q Q0 H H0 Hd project (m3/s) (m3/s) (m) (m) (m) Shike Bridge 2043.8 276.8 95.85 95.35 96.48 Chusanping Bridge 2010.8 60.0 99.45 98.25 99.74 Malian Bridge 1820.6 578.1 117.68 116.82 118.19

4. Conclusion For mountain highway along river, with the advantage that consider the transportation of the towns and countries. Engineering cost is smaller than other. But more bridge should be build to across main river and tributaries to meet bridge design flood flow. The design flood flow and water level should be analyzed through the data of whole river basin. The correct designed flood stage can be calculated based on the main river flow and the considered the influence of tributaries peak discharge.

References 1. Cunning Zhang, Highway bridge hydrology in plain river network region. (Highway, China, 1997). 2. Yongshun Jiao, Hydrological Specifications for Survey and Design of Highway Engineering. JTG C30-2015. (China Communications Press, Beijing, 2015). 3. Dongguang Gao, Bridges in the river and ocean environment. (China Communications Press, Beijing, 2011). pp 95-139.

451