International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 11, November 2018, pp. 2054 2062, Article ID: IJCIET_09_11_202 Available online at http://www.iaeme.com/ijciet/issues.asp?jtype=ijciet&vtype=9&itype=11 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 IAEME Publication Scopus Indexed WAVE AND CURRENT HYDRODINAMICS STUDY AT BATANG AIR DINGIN RIVER MOUTHPADANG, INDONESIA Dalrino, Aguskamar, A. Indra and Syofyan, E.R Civil Engineering Department, Politeknik Negeri Padang, Indonesia ABSTRACT Batang Air Dingin estuary was located in Koto Tangah Sub-district of Padang City and facing to Indian Ocean. Problem that many encountered in the estuary was the occurrence of sedimentation due to changes in the flow pattern as the influence of the hydro-oceanographic components of rivers and sea at the mouth. Mathematical modeling was conducted to obtaining the current and wave patterns in Batang Air Dingin river mouth. Initial wave height was obtained from hindcasting for 10 years of wind data using the SMB method. Tidal height, current velocity, bathymetry depth contour and existing river cross profile are obtained from the measurements. The RMA2 and STWAVE modules of the SMS 8.1 software was used with validation to results performed on the measured current velocity at the specified location. Wave height forecasting obtained was around between 3.18-5.2 meters and 1.13-5.12 meters for each the region of wave generated area. Refraction coefficient is obtained between 0.40-0.48 and 0.13 and 0.51 with significant direction of waves coming from the west. The result of current velocity validation getting good value with mean of root mean square = 0,067 and 0,051 for each observation location Keywords: Wave and Current Hydrodynamics, Batang Air DinginRivermouth, Numerical Modelling Cite this Article: Dalrino, Aguskamar, A. Indra and Syofyan, E.R, Wave And Current Hydrodinamics Study At Batang Air Dingin River Mouthpadang Indonesia, International Journal of Civil Engineering and Technology, 9(11), 2018, pp. 2054 2062. http://www.iaeme.com/ijciet/issues.asp?jtype=ijciet&vtype=9&itype=11 1. INTRODUCTION Padang is a city that directly confined to the hills on the eastern side and the Indian Ocean on its western side. This topographical condition causes rivers with high steepness that flows from the hills will turn into a river with steep ramps in the plains of the city of Padang to further flow towards the estuary so resulting more slowing flows in middle area so its impact http://www.iaeme.com/ijciet/index.asp 2054 editor@iaeme.com
Dalrino, Aguskamar, A. Indra and Syofyan, E.R on increasing river water levels There are high potential for flooding in the Padang plains area so that the ideal river estuary condition is needed to function as a river flow outlet toward the sea. Batang Air Dingin river mouth was located in Koto Tangah District, that meeting between river of Batang Air Dingin and the Indian Ocean with flow characteristic that influenced by the hydro-oceanography of the river and coast. Batang Air Dingin catchment area has an 12,803 hectares area with a network of water supply and sediment to a main river covering 1,200 hectares of mountains at an elevation of + 1,800 m above SWL. With directly toward the Indian Ocean, dominant wave direction at river mouth was from the Southwest and West and tides at location was ranging from 1 to 1.2 meters. The current conditions at the mouth of the estuary have been narrowing due to sedimentation. If there is a large debit from the Cold River Batang, with the current condition is very potential to create a flood disaster in the city. The following figure shows the condition of the Cold River Batangriver that has been narrowed due to silting as a result of sedimentation in the mouth of the estuary. Figure 1 River Mouth condition Sedimentation problems at the mouth of the estuary have received attention from several researchers. Suspension sediment transport patterns using a case study sampling method at the coastal estuary of Vengurla representing the area along the coastal waters of southern Maharashtra, India was conducted. The results showed indications of variations in changes in sediment suspension levels depending on the conditions before, momentary and post monsoon season (SathishSathasivam et al., 2015) [6]. Numerical applications to study suspense sediment transport patterns in a case study at the coastal estuary of Vengurla, India using the MIKE 21 Mud Transport (MT) sediment transport model was conducted (N. Sravanthi, et al., 2015) [5]. Mathematical modeling was used by inputting wave parameters, configuration of breakwaters, groyne building configuration, coastal initial conditions and bathymetry as inputs to see coastline changes occurring at the mouth side of the estuary after simulation (A.M. Vaidya, Santosh K. Kori, M.D. Kudale, 2015) [2]. A comparison of three equations of longshore transport directions on the mouth of the mouth of the estuary was conducted (Achilleas G. Samaras, Christopher G. Koutitas,2014) [1]. The effects caused by waves that resulted in basal water liquefaction to http://www.iaeme.com/ijciet/index.asp 2055 editor@iaeme.com
Wave and Current Hydrodinamics Study at Batang Air Dingin River Mouthpadang Indonesia the re-forming of sediment suspensions in the Yellow River delta in China was studied (YonggangJia et al., 2014) [8] 2. MATERIAL AND METHOD Wave transformation is a change in wave value that was influenced by the phenomenon of refraction, diffraction, wave and current interaction, and also breaking wave. Calculation of wave transformation is a complicated process if done analytically, so in this study the value of transformation wave height obtained by using STWAVE module. Wave modeling performed on the formation of waves that are in the Mentawai Strait. This was done because of the long distance between the coast of Sumatra and the island cluster has the potential for wave formation (Figure 1). Modeling is done for the direction of the wind that has the potential to generate significant waves at the study location. Amount of Percentage of Direction Speed (m/s) Speed (m/s) < 2.5 2.5-5 5-7.5 > 7.5 Sum < 2.5 2.5-5 5-7.5 > 7.5 Sum N 121 271 37 8 437 0.51 1.13 0.15 0.03 1.83 NE 142 191 13 10 356 0.59 0.80 0.05 0.04 1.49 E 130 174 19 4 327 0.54 0.73 0.08 0.02 1.37 SE 62 131 1 0 194 0.26 0.55 0.00 0.00 0.81 SE 109 344 39 7 499 0.46 1.44 0.16 0.03 2.09 SW 325 1583 108 3 2019 1.36 6.62 0.45 0.01 8.44 W 719 2668 99 20 3506 3.01 11.16 0.41 0.08 14.66 NW 133 397 45 10 585 0.56 1.66 0.19 0.04 2.45 Total 23912 Total 100 Wind 7923 Wind 33.13 Calm 15989 Calm 66.87 No Data 12 No Data 0.05 Figure 2 Wind Data from TabingMeterological Station, Padang From the data we could see that significant wind direction are from West and South West with the largest percentage of wind speed range from 2,5 5 m/s and 66,87 % of data is calm. Wind speed and direction that illustrated as wind rose was can see in Figure 2. The process of wave and current modeling in general by using SMS can be divided into two, namely pre-processing and post-processing using SMS interface and knowledge of the numerical model used, i.e RMA2 and STWAVE modules. The RMA2 module solves the mass conservation and momentum that causes currents using the finite element method. The equation of continuity and momentum is:.. 1,486. /!," #$ % &'() 2, sin0 1 0 (1) http://www.iaeme.com/ijciet/index.asp 2056 editor@iaeme.com
Dalrino, Aguskamar, A. Indra and Syofyan, E.R.. 1,486.h / + +!," #$ % sin) + 2 h, sin0 = 0 (2) 34 35 + h637 3 + 38 3 9 + 34 3 + 34 3 = 0 (3) The above-mentioned mass conservation and momentum equations are solved by the finite element method by using Galerkin's weighted residuals method. As a regulatory equation, RMA2 uses mass conservation equations and momentum integrated into depth. Figure 3 Windrose at the study area. The governing equation of wave transformation in this STWAVE module calculates the radiation stress of the wave propagation. So that in this model can be generated paralleled current wave beach (wave induced current). The gradient of wave-induced stress radiation in this module is as follows: The fetch length was the length of the propagation of the wave from of its wave generated area. Its assume that the fetch length to study location was draw as a straigth line until the barrier such as Figure 3 bellow. http://www.iaeme.com/ijciet/index.asp 2057 editor@iaeme.com
Wave and Current Hydrodinamics Study at Batang Air Dingin River Mouthpadang Indonesia Figure 4 Fetch length based on wave generated area to the study area 3. RESULTS AND DISCUSSION Wave hindcasting with SMB method was conducted for getting the value of water depth height wave based on the direction of generated wave that caused by energy transfer from wind to sea water (CERC, 1984) [3]. Wave rose of the study area that was determined as illustrated in Fig 1. From the wave rose diagram the significant incoming wave direction was from West and South West. Figure 5 Wave rose of the study area From the result of modeling in STWAVE modules the wave formation is influenced by various factors such as geographical condition between study area and wave formation area, Changes in depth or Shoaling, and refraction - diffraction phenomena. The result for each coming wave direction as seen at Table I. On Fig 1 is the wave height transformation with wind formation from the West. http://www.iaeme.com/ijciet/index.asp 2058 editor@iaeme.com
Dalrino, Aguskamar, A. Indra and Syofyan, E.R Incoming wave Direction Table 1 transformation wave height for each incoming wave direction Deep water wave Height (Ho) in meter Transformation wave Height (Hi) in meter North West 2,9 1,45 West 5,2 2,6 South West 3,18 1,29 South 1,71 0,875 South East 1,13 0,15 Figure 6 Wave transformation with wind formation from the west The bathymetry in this simulation are obtained from measurement data as shown in the figure 6. Boundary Condition in Tidal simulation with RMA2 is Tidal and river flow discharge. In this model the tides are taken from the processed data of the tidal observation surveys. Figure 7 Bathymetry at study location http://www.iaeme.com/ijciet/index.asp 2059 editor@iaeme.com
Wave and Current Hydrodinamics Study at Batang Air Dingin River Mouthpadang Indonesia The result of RMA2 module modeling from SMS software is in the form of current velocity and direction of water level on the modeled area. The flow velocity, flow depth and the location of the modeling observation point in the modeled domain are shown in the following figures. Figure 8 Vector and current magnitude velocity Fluctuations in sea level changes due to tides will affect the flow velocity that occurs. This is due to the occurrence of damming the flow caused by rising sea level at high tide and where there is also a mass density between sea water and river. The relationship between sea level elevation changes to the flow velocity at each measurement site is shown in the following figure. Figure 9 Graph of the relationship between the water level to the measured flow velocity value at each location The rated velocity of the model results obtained the maximum velocity value for the observation location at point 1 (sea side) of 0.278 m / sec and 0.211 m / s for the current velocity at the river side observation location. The minimum current velocity values for each location are 0.046 m / sec and 0.105 m / s for the ocean current side and current velocity.the comparison between the rated velocity of the observed model and the measured velocity of http://www.iaeme.com/ijciet/index.asp 2060 editor@iaeme.com
Dalrino, Aguskamar, A. Indra and Syofyan, E.R the survey result which is located at the same location is shown in the figures in the following graph. Figure 10 Validation Results of Current Flow Rate on Observation Point -1 Figure 11 Validation Results of Current Flow Rate on Observation Point -2 From the graph it is noticed that there is a tendency for the formation of stability of the value of current velocity fluctuating following the rise and fall of sea level rise due to tides. In locations where current velocities are observed on the upstream side of the river the effect of tidal fluctuations is smaller, this is particularly true in upstream locations farther away from the estuary as a result of less tidal influence on the site. The results of the comparison between field observation and computational results show a fairly good level of verification between the modeling results of the measured data in the field. This is indicated by the mean value of rms (root mean square) = 0.067 and 0.051 for each observation location. 4. CONCLUSSION Wave forecasting based on SMB method resulting the wave heights range from 1.13 to 5.2 m with significant direction coming from the west and southwest. The wave height transformation based on modeling using ST WAVE module result is range from 0.15 to 2.5 m with refraction coefficient, Cr = 0.13-0.51. RMA2 module was using to simulating the current profile at the river mouth. The result of current velocity validation getting good value http://www.iaeme.com/ijciet/index.asp 2061 editor@iaeme.com
Wave and Current Hydrodinamics Study at Batang Air Dingin River Mouthpadang Indonesia with mean of root mean square = 0,067 and 0,051 for each observation location.the modeling results show the potential for estuarine closure due to sedimentation from longshore transport caused by waves from west and southwest on the left side of the river mouth. Need for estuarine handling to prevent the estuarine closure caused by sands pit at river mouth 5. ACKNOWLEDGEMENTS This research was conducted as part of a grant supported by Ministry of Research, Technology and Higher Educationof the Republic of Indonesia. REFERENCES [1] Achilleas G. Samaras, Christopher G. Koutitas, 2014, Comparison of three longshore sediment transport rate formulae in shoreline evolution modeling near stream mouths, Ocean Engineering, Volume 92, 1 December 2014, Pages 255-266 [2] A.M. Vaidya, Santosh K. Kori, M.D. Kudale, 2015, Shoreline Response to Coastal Structures, International Conference On Water Resources, Coastal and Ocean Engineering (ICWRCOE 2015), Aquatic Procedia 4 ( 2015 ) Pages 333 340 [3] CERC, 1984, Shore Protection Manual., Dept. of the Army, U.S. Army Corps of Engineers, Washington. [4] Mustafa Demirci, and M. Sami Aköz, 2013, Investigation of bar parameters occurred by cross-shore sediment transport, Int. J. Naval Archit. Ocean Eng. (2013) Vol. 5, Pages 277-286 [5] N. Sravanthi, R. Ramakrishnan, A. S. Rajawat, A.C. Narayana, 2015, Application of Numerical Model in Suspended Sediment Transport Studies along the Central Kerala, West-coast of India, International Conference On Water Resources, Coastal and Ocean Engineering (ICWRCOE 2015), Aquatic Procedia 4 ( 2015 ) Pages 109 116. [6] SathishSathasivam, K. Rasheed, R.S.Kankara, ManikandanMuthusamy, ArockiarajSamykannu, RajanBoopati, 2015, SSC Analysis Of South Maharashtra Coast: A Case Study From Vengurla Coastal Region, International Conference On Water Resources, Coastal and Ocean Engineering (ICWRCOE 2015), Aquatic Procedia 4 ( 2015 ) Pages 19 24 [7] Sri Ram Kumar P., Dwarakish G. S., Nujuma N., Deepthi I. Gopinath, 2015, Long Term Study Of Sediment Dynamics Along Mangalore Coast, West Coast Of India Using Sediment Trend Analysis, International Conference On Water Resources, Coastal and Ocean Engineering (ICWRCOE 2015), Aquatic Procedia 4 ( 2015 ) Pages 333 340 [8] YonggangJia, Liping Zhang, JiewenZheng, Xiaolei Liu, Dong-Sheng Jeng, Hongxian Shan, 2014, Effects of wave-induced seabed liquefaction on sediment re-suspension in the Yellow River Delta, Ocean Engineering, Volume 89, 1 October 2014, Pages 146-156 http://www.iaeme.com/ijciet/index.asp 2062 editor@iaeme.com