Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Chen, Ching-Nuo

Tsai, Chang-Tai

Tsai, Chih-Heng

Wu, Meng-Hsuan

English

Hydraulic Engineering Repository

Conference Paper, Published VersionWu, Meng-Hsuan; Chen, Ching-Nuo; Tsai, Chih-Heng; Tsai, Chang-TaiInfluence of Storm Surge on the Inundated Potential in theCoastlandZur Verfügung gestellt in Kooperation mit/Provided in Cooperation with:Kuratorium für Forschung im Küsteningenieurwesen (KFKI)Verfügbar unter/Available at: https://hdl.handle.net/20.500.11970/110075Vorgeschlagene Zitierweise/Suggested citation:Wu, Meng-Hsuan; Chen, Ching-Nuo; Tsai, Chih-Heng; Tsai, Chang-Tai (2008): Influence ofStorm Surge on the Inundated Potential in the Coastland. In: Wang, Sam S. Y. (Hg.): ICHE2008. Proceedings of the 8th International Conference on Hydro-Science and Engineering,September 9-12, 2008, Nagoya, Japan. Nagoya: Nagoya Hydraulic Research Institute forRiver Basin Management.Standardnutzungsbedingungen/Terms of Use:Die Dokumente in HENRY stehen unter der Creative Commons Lizenz CC BY 4.0, sofern keine abweichendenNutzungsbedingungen getroffen wurden. Damit ist sowohl die kommerzielle Nutzung als auch das Teilen, dieWeiterbearbeitung und Speicherung erlaubt. Das Verwenden und das Bearbeiten stehen unter der Bedingung derNamensnennung. Im Einzelfall kann eine restriktivere Lizenz gelten; dann gelten abweichend von den obigenNutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte.Documents in HENRY are made available under the Creative Commons License CC BY 4.0, if no other license isapplicable. Under CC BY 4.0 commercial use and sharing, remixing, transforming, and building upon the materialof the work is permitted. In some cases a different, more restrictive license may apply; if applicable the terms ofthe restrictive license will be binding.Influence of Storm Surges on the Inundated Potential in the Coastland  Meng-Hsuan Wu1, Ching-Nuo Chen2, Chih-Heng Tsai3 and Chang-Tai Tsai4  1 Ph.D. student, Department of Hydraulics and Ocean Engineering, National Cheng-Kung University No.1, University Road, Tainan 70101, Taiwan, e-mail: n8893105@mail.ncku.edu.tw 2 Post-Doctor, Department of Hydraulics and Ocean Engineering, National Cheng-Kung University No.1, University Road, Tainan 70101, Taiwan, e-mail: cnchen@mail.hyd.ncku.edu.tw 3Assistant Professor, Department of Resources and Environment, Leader University No.188, Sec. 5, Anjhong Rd., Annan District, Tainan City 709, Taiwan, e-mail: jht@mail.hyd.ncku.edu.tw 4 Professor, Department of Hydraulics and Ocean Engineering, National Cheng-Kung University No.1, University Road, Tainan 70101, Taiwan, e-mail: htct@mail.ncku.edu.tw   ABSTRACT   Storm surges do not only affect the capacity of drainage system but also lead to serious inundation damages in the coastland. The basin of the Jiangjyun river is used as an illustrative example in this study. The Physiographic Drainage - Inundation model is applied to evaluate the inundated potential for a historical typhoon event and twelve designed heavy-rains with the conditions for storm surges and astronomical tides as different individual conditions. The influence of the storm surge on the inundated potential in the basin of the Jiangjyun river is investigated by the simulation of above cases for inundated potential. The results obtained for the case of the surge storm for inundated potential simulation are compared with those for the astronomical tide. The simulated results obtained from inundated potential reveals that inundated potential in the coastland in terms of the inundation depth and area for the case of the surge storm are plainly greater than those for the astronomical tide. Therefore, it is crucial to consider the influence of storm surges when planning the scale of drainage systems and dikes in the coastland.   Keywords: storm surge, inundated potential, inundation depth, inundation area, climate changes   1. INTRODUCTION  Due to the development of economy, increasing population, and transportation infrastructure of the coastland, drainage system and land uses have been changed for decades in Taiwan. These changes along with groundwater over-pumping lead to not only the increase of surface runoff but also the acuteness of land subsidence. The retarding effect of roads might alter the basin boundary of the drainage. This effect induces the overbasin flow which can also exceed the capacity of the present drainage system. Therefore, there is a special need to evaluate the current drainage system and the influence of these changes. In addition to physical changes, we need to pay additional attention on extreme hydrological events due to climate changes. These extreme hydrological events include storms, super typhoons, and astronomical tides. Especially, super typhoons often bring heavy rain as well as rise the sea level because of the barometric depression. Therefore, these extreme hydrological events may further strike the drainage system and increase the damage of inundation. This study applies the Physiographic Drainage - Inundation model to evaluate the inundated potential in the coastland in terms of the inundation depth and area, and to estimate the influence of the storm surge on the inundated potential in the coastland. The basin of the Jiangjyun river is used as an illustrative example in this study. The Physiographic Drainage - Inundation model is applied to simulate the inundated scenarios for a historical typhoon event and twelve designed heavy-rains with the conditions for storm surges and astronomical tides as different individual conditions. The influence of the storm surge on the inundated potential in the basin of the Jiangjyun river is investigated by the simulation of above cases for inundated potential.   2. PHYSIOGRAPHIC DRAINAGE - INUNDATION MODEL  The computed cells in accordance with the landscape and drainage network of the watershed are automatically generated in the Physiographic Drainage - Inundation model. The water flow calculation uses the Physiographic Drainage - Inundation model, which is based on the continuity equation and discharge theory in each cell. The continuity equation for water flow is given (Yang, 2000).                 (∑+=kkikiiii hhQPedtdhAs ,, )                                   (1)  where = the area of the i-th cell; = water depth in the i-th cell; = time; = the discharge from the k-th cell, which is the adjacent cell of the i-th cell, into the i-th cell; = the effective rainfall intensity multiplied by the area of the i-th cell. The  in Eq 1 can be represented by any appropriate discharge formula as described below.  iAs ih tiQkiQ ,iPek, 2.1 Channel-Linked Discharge Formula  Selection flow conditions for the flow between cells without obvious obstacles can be treated as an idealized channel flow and the discharge can be calculated by the Manning formula (Yang and Tsai, 1997). The discharge can be calculated by Eq.2 and Eq. 3.                 0, <∂∂ikihQ, ikkiikikki hhhhhhhQ −⋅Φ⋅−−= )( ,,                       (2)                 0, >∂∂ikihQ, ikkiki hhhQ −⋅Φ= )( ,,                              (3)  where =kih ,  the water stage from the k-th and i-th cells, is given as:                 ikki hhh )1(, αα −+=                                          (4)  where α = an weighting-coefficient; Φ = the flow parameter, defined as xARnhΔ=Φ3/21)( . where = the distance of the canter between the k-th and i-th cells; =the Manning’s roughness coefficient of the cells; xΔ nA = the cross-sectional flow area between the k-th and i-th cells, )( ,kihAA = ; R = the hydraulic radius between the k-th and i-th cells, )( ,kihRR = .  2.2 Weir-Linked Discharge Formula  On the other hand, for the adjacent cell divided by roads or hydraulic structures, the flow over them can be treated as the weir flow. The discharge can be calculated by Eq.5 and Eq. 6. For a free over weir, )(32)( wkwi ZhZh −<−                  , 2/3, )( wkfki ZhQ −Φ= gbf 21μ=Φ                           (5)  For a submerged weir, )(32)( wkwi ZhZh −≥−                  , 2/1, ))(( ikwidki hhZhQ −−Φ= gbd 22μ=Φ                     (6)  where = the elevation of the weir crest; = the effective width of the weir; wZ b 1μ  and 2μ = the weir discharge coefficients, 1μ = 0.37~0.57 and 2μ = 2.6 1μ . Therefore, the explicit finite-difference representation of Eq. 1 can be written as                                                (7) sikkiii AthhQPeh /]),([ , Δ+=Δ ∑ where , ,and are the area, rainfall intensity of the i-th cell and the discharge from the k-th cell into the i-th cell at ; 、iAs iPe kiQ ,t tΔ  is the time step of  to ；  is the i-th cell increment of water stage in a time step. t tt Δ+ ihΔ  3. STUDY AREA  The basin of the Jiangjyun river is used as an illustrative example in this study. The lagoon of the lowland plain and hill along the coast from the south of the Bajhang river to the north of the Zengwun river was selected as the study area for investigating the inundation phenomena of the basin of the Jiangjyun river. In addition to the Jiangjyun river, the study area also contains the Jishuei and Cigu rivers. The area of the Jiangjyun river basin is about 158.4 square kilometer and the length of the main stream is about 28 kilometer. The basin of the Jiangjyun river in the study area is shown in Figure 1. ArcGIS™ software - ArcView® and ArcInfo® - are adopted in this study to analyze DEM, slope, and pool of the study site. Information of roads, drainage ditches, and land use are also included in the GIS database. The entire basin was divided into 6,626 irregular grids (as shown in Figure 2) by automatic modeling-cell-delimitation method that used the spatial analyst, hydrologic model, and Object-oriented Programming of ArcView. All attributes of data fields were also calculated to build the necessary database for Physiographic Drainage - Inundation model.    Figure 1 The basin of the Jiangjyun river in the study area   Figure 2 Construction of cells in the study area   4. RESULTS AND DISCUSSIONS  The basin of the Jiangjyun river is used as an illustrative example in this study. Based on the physiographic properties of the Jiangjyun river basin, GIS system is applied to construct the cells of the study area automatically. The hydrologic parameters and the physiographic parameters of each cell are obtained from above analyses. The Physiographic Drainage - Inundation model is applied to simulate the inundated scenarios for twelve designed heavy-rains with the tidal conditions for storm surges and astronomical tides as different individual conditions. Thus, the influence of the storm surge on the inundated potential in the basin of the Jiangjyun river is investigated by the simulation of the above cases for inundated potential.  4.1 Hydrologic Data  In order to test and verify the physiographic Drainage - Inundation model, the results of simulation of the historical typhoon event are compared with observation and investigation in the field. Floods are caused by twelve designed heavy-rains with different durations and return periods obtained from frequency analysis and storm pattern analysis. Influence of storm surges on the inundated potential in the coastland was investigated by simulating floods caused by twelve designed heavy-rains. The study area was divided into several control areas of the rain gage stations by utilizing the Thiessen polygons method. In this study, the rainfall data of each rain gage station for each cell were utilized to simulate the phenomena of the historical typhoon. Distribution and control areas of the rain gage stations possessed by the Central Weather Bureau were shown in Figure 3. The rainfall data of the rain gage stations in study area and the adjacent area were utilized to proceed frequency analysis and storm pattern analysis. Floods are caused by twelve designed heavy-rains with different durations and return periods obtained from the results of frequency analysis and storm pattern analysis. The tide levels in the coastland of the historical typhoon were obtained from the historical data of the Jiangjyun tidal gauge station. The tide levels in the coastland of the twelve were obtained from the results of the analyses of astronomical tide and surge deviation. The results of the tidal analysis were shown in Figure 4.   Figure 3 Thiesson polygons in the study area  0 20 40 60 80 100 120 140 160 180 200 220 240Time (min.)0.40.60.81.01.21.41.61.82.0Tide level (m)    5 year  10 year100 year 0 1 2 3 4 5 6 7 8 9 10 11 12Time (hr)-1.0-0.50.00.51.01.52.0Tide level (m)    5 year  10 year100 year0 2 4 6 8 10 12 14 16 18 20 22 24Time (hr)-1.0-0.50.00.51.01.52.0Tide level (m)    5 year  10 year100 year4 hour duration of rainfall 12 hour duration of rainfall 24 hour duration of rainfall Figure 4 Tidal boundary condition for the case of designed heavy-rains (in meter)  4.2 Simulation for a Historical Typhoon Event  Typhoon Haitang, which occurred in 2005 to cause serious inundated damages in the basin of the Jiangjyun river, was utilized as an illustrative example. The maximum inundated depth based on the simulations was shown in Figure 5. Further, the result of simulation of Typhoon Haitang is compared with observation and investigation in the field (Water Hazard Mitigation Center, Water Resources Agency, MOEA, 2007) in order to test and verify the physiographic Drainage - Inundation model. The simulated results contain the inundation depth, area, and so on. The results of observation and investigating in the field were shown in Figure 6. Based on the comparison of simulated results with the observed data shown in Figures 5 and 6 individually, the simulated results obtained from inundating potential reveals that inundated potential in the coastland in terms of the inundation depth and area are coincident with the results of observation and investigation in the field.   Figure 5 The simulated maximum inundated depth of Typhoon Haitang in 2005 Figure 6 The inundated depth of Typhoon Haitang in Tainan county in 2005  4.3 Simulation for designed heavy-rains  In order to investigate the influence of storm surges on the inundated potential in the coastland, the Physiographic Inundation model is applied to simulate the inundated potential of the study area with the hydrologic conditions for the duration of 2-hour, 4-hour, 12-hour, and 24-hour floods for 5- year, 10- year and 100-year return periods. The storm surge and the astronomical tide were used as tidal conditions. The results for simulating the inundated potential of the study area were illustrated in the figure of the inundated depth. The inundated potential of the study area with the hydrologic conditions for the duration of 4-hour, 12-hour, and 24-hour floods for 5- year and 100-year return periods were utilized as an illustrative example as shown in Figures 7 and 8.  4-hour duration 4-hour duration 12-hour duration 12-hour duration 24-hour duration 24-hour duration Figure 7(a) Comparison of the simulated maximum inundated depth of 5-year return period (storm surge) Figure 7(b) Comparison of the simulated maximum inundated depth of 5-year return period (astronomical tide)  4-hour duration 4-hour duration 12-hour duration 12-hour duration 24-hour duration 24-hour duration Figure 8(a) Comparison of the simulated maximum inundated depth of 100-year return period (storm surge) Figure 8(b) Comparison of the simulated maximum inundated depth of 100-year return period (astronomical tide)  As shown in Figures 7 and 8, the inundated area and maximum inundated depth increase significantly with rainfall duration on the condition of the same return period. The inundated area and maximum inundated depth increase significantly with return periods. Thus, the inundated area and maximum inundated depth increase significantly with return periods on the same rainfall duration. Further, in order to investigate the influence of storm surges on the inundated potential in the coastland, the inundated depths and volumes of 24-hour duration for 5- year 10-year, and 100-year return periods with storm surge or astronomical tide conditions were summed up individually. The increases in inundated depths and volumes were summarized in Table 1.  In Table 1, a negative value indicates the decrease in inundated volumes. The influence of storm surges on the inundated potential in the coastland is illustrated at Table 1. As shown at Table 1, the increases in inundated depths and volumes increase significantly when the storm surge occurs. As shown in Figures 7, 8 and, Table 1, the most difference in inundated volumes of different return periods and durations occurr in the coastland. The inundated volumes with the inundated depths of 5-year and 10-year return periods that were greater than 75 cm increase significantly when storm surge occurs. The inundated volumes with the inundated depths of 5-year and 10-year return periods that were less than 75 cm might increase. The inundated volumes with the inundated depths of 100-year return period that were greater than 25 cm increase significantly. The inundated volumes with the inundated depths of 100-year return period that were less than 25 cm might even decrease.  Table 1 Decrease in inundated volume (in 103 m3) of the cases in 2-hour duration floods for 2-, 10- and 100-year return-periods with storm surge or astronomical tide condition  Return-period (years) Inundation depth (m) Sum 0-0.25 0.25-0.50 0.50-0.75 0.75-1.0 1.0-1.50 >1.50 5 -373.92 1266.40 -3152.80 2371.84 5529.59 121736.50 127377.6210 171.60 459.26 -1504.54 339.76 7030.66 147986.50 154483.24100 -453.68 1770.05 3049.44 357.28 8238.54 264175.00 277136.62  5. CONCLUSIONS  In the same designed heavy-rains, regardless of storm surges occur or not, there are obvious influences on the inundation depth and area in the coastland. Inundating potential reveals that inundated potential in the coastland in terms of inundation depth and area in the case of storm surges  is plainly greater than that in the astronomical tide. When planning the scale of drainage systems and dikes in the coastland, proceeding typhoon and heavy-rain events and storm surges simulation of the inundating potential which caused by typhoons are necessary. In addition, it is crucial to compare and review the inundation phenomena of flood-prone areas and then to provide improvement.   ACKNOWLEDGMENTS  This study was supported fanacially by a grant from the Water Hazard Mitigation Center, Water Resources Agency, Ministry of Economic Affairs.   REFERENCES  Chen, C.N., Tsai, C.H. and Tsai, C.T. (2007), Reduction of discharge hydrograph and flood stage resulted from upstream detention ponds, Hydrological Processes, 21, pp. 3492–3506. Lee, H.Y. (1999), A Study on Automated District Cells of the Watershed, Master Thesis, Department of Hydraulics and Ocean Engineering, National Cheng-Kung University, Tainan, Taiwan. Water Hazard Mitigation Center, Water Resources Agency, Ministry of Economic Affairs (2007), A study on the surge and cross-watershed runoff for the drainage system of the coastland (1/2), Technical Report, MOEA, Taipei, Taiwan.  Yang , C. J. (2000), Study on Construction of a Physiographic Inundation Forecasting System, Doctoral Thesis, Department of Hydraulics and Ocean Engineering, National Cheng-Kung University, Tainan, Taiwan. Yang, C. R., and Tsai, C. T. (1997), Development of the GIS-Base Flood Information System for Floodplain Modelling and Damage Calculation, Journal of the American Water Resources Association, 36(3), pp. 567-577.   

Influence of Storm Surge on the Inundated Potential in the Coastland

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Influence of Storm Surge on the Inundated Potential in the Coastland

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