Analysis of flood control management in Ngontok Ring Kanal River

Transcription

1 Analysis of flood control management in Ngontok Ring Kanal River Gilang Idfi, and Wasis Wardoyo Citation: AIP Conference Proceedings 1887, (2017); View online: View Table of Contents: Published by the American Institute of Physics Articles you may be interested in Workability enhancement of geopolymer concrete through the use of retarder AIP Conference Proceedings 1887, (2017); / Effect of concrete strength gradation to the compressive strength of graded concrete, a numerical approach AIP Conference Proceedings 1887, (2017); / The effect of sintering temperature on the properties of metakaolin artificial lightweight aggregate AIP Conference Proceedings 1887, (2017); / E3 A user s interface for quantifying total cost, diesel consumption, and emissions from bulldozers and its comparison to field data AIP Conference Proceedings 1887, (2017); / Thermal performance of vertical greening system on the building façade: A review AIP Conference Proceedings 1887, (2017); / Marshall properties of asphalt concrete using crumb rubber modified of motorcycle tire waste AIP Conference Proceedings 1887, (2017); /

2 Analysis of Flood Control Management in Ngontok Ring Kanal River Gilang Idfi 1, a) and Wasis Wardoyo 2,b) 1 Department of Civil Engineering, State University of Malang 2 Department of Civil Engineering, Sepuluh Nopember Institute of Technology Surabaya a) Corresponding author: gilang.idfi@gmail.com b) wasis@ce.its.ac.id Abstract. Ngotok Ring Kanal river is a natural channel that acts as the water body of thirteen river branches and three drainage outlets. The catchment area of Ngotok Ring Kanal River is about 722 km2. This river is important for Mojokerto District since it plays an important role in controlling the yearly flood. Many efforts have been done to solve this flood problem but it remains to unsolve satisfactorily yet. Therefore, a research is taken to give one other possibility to overcome the flood effects caused by very high discharge peak at every rainy season. The aim of this research is to distribute the discharge peak by creating some scenarios on releasing the amount of discharge by building a pond at any river branch. By these, it can be known the best scenario of distributing the discharge peak based on the time of release and the place of the built pond. It offers 5 scenarios a number of ponds i.e. by simulating 2 ponds, 3 ponds, 5 ponds at any river banks respectively. The result of the study showed that scenario-5 with 5 ponds is the best scenario to reduce the peak discharge of Ngotok Ring Kanal River. This scenario becomes to reduce the peak discharge from m³/s become m³/s. INTRODUCTION Ngotok Ring Kanal river is a natural channel that acts as the water body of thirteen river branches and three drainage outlets. In fig.1 can be informed that the geometric system of Ngotok River. This river flows at Brantas River in Magersari Village, Mojokerto. From fig.2, the catchment area of Ngotok Ring Kanal River is about 722 km². This river is one of The Water Resources Utilization, so it is very important for Mojokerto District since it plays an important role in controlling the yearly flood [1]. FIGURE 1. Geometric of The Ngotok Ring Kanal River Green Construction and Engineering Education for Sustainable Future AIP Conf. Proc. 1887, ; doi: / Published by AIP Publishing /$

3 FIGURE 2. Location of The Ngotok Ring Kanal River Many efforts have been done to solve this flood problem but it remains to unsolve satisfactorily yet. Therefore, a research is taken to give one other possibility to overcome the flood effects caused by very high discharge peak at every rainy season. The aim of this research is to distribute the discharge peak by creating some scenarios on releasing the amount of discharge by building the pond at any river branch. It offers 5 scenarios i.e. by simulating 2 ponds, 3 ponds, 5 ponds at any river banks respectively. This study made by creating hydrology and hydraulics modeling of Ngotok Ring Kanal Catchment Area. The result of this study is known as the best scenario will be implemented to decrease the peak of discharge at Ngotok Ring Kanal River. HYDROLOGICAL CHARACTERISTIC AND ANALYSIS Areal Rainfall For assessing rainfall can be used Arithmetic Mean, Thiessen Polygon and Isohyet Method. This study used Thiessen Polygon to calculate the areal rainfall. The Thiessen Polygon method assumes that at any point in a catchment can be shown in Figure 3, the rainfall is the same that at the nearest rain gauge so the depth recorded at a given gauge is applied out to a distance halfway to next gauge in any direction. The relative weight for each gauge is determined from the corresponding [2]. FIGURE 3. Thiessen Polygon

4 If the area within the catchment assigned to each gauge is A, and its rainfall is R i, the areal average rainfall for the catchment is =. A R.. (1) with : average areal rainfall (mm) Ri : areal rainfall (mm) A : the catchment assigned (km²) Runoff Coefficient Runoff coefficient is the ratio between surface runoff and total of rainfall. The runoff coefficient depends on by soil characteristic, land use, and topography [3]. From Table 1 can inform several numbers a runoff coefficient. TABLE 1. Runoff Coefficient Description Area Range of Runoff Coeficient Recommended Value Business Downtown Neighborhood Residential Single-family Multiunits,detached Multiunits,detached Residential (Suburban) Apartement Industrial Light Heavy Parks, cemeteries Playgrounds Railroad yard Unimproved Apart from the above-mentioned site-specific factors which strongly influence the rainfall-runoff process, it should also be considered that the physical conditions of a catchment area are not homogenous. Even at the micro level, there are a variety of different slopes, soil types, vegetation covers etc [4]. Each catchment has, therefore its own runoff response and will respond differently to different rainstorm events. The design of water harvesting schemes requires the knowledge of the quantity of runoff to be produced by rainstorms in a given catchment area. It is commonly assumed that the quantity (volume) of runoff is a proportion (percentage) of the rainfall depth [14]. K=...(2) In rural catchments where no or only small parts of the area are impervious, the coefficient K, which describes the percentage of runoff resulting from a rainstorm, is however not a constant factor[5]. Instead, its value is highly variable and depends on the above described catchment-specific factors and on the rainstorm characteristics. Rainfall Intensity The intensity of rainfall is a measure of the amount of rain that falls over time. The intensity of rain is measured in the height of the water layer covering the ground in a period of time [6]. It means that if the rain stays where it falls, it would form a layer of a certain height. The amounts of rainfall per unit time referred as the intensity of rainfall that

5 commonly is expressed in mm/hour [13]. Therefore, the intensity of rainfall means the amount of precipitation/rainfall in a relatively short time (usually within 2 hours) [7]. Rainfall can be classified based on its intensity. The classification of rainfall intensity is shown in Table 2. TABLE 2. Rainfall Intensity Classification Rainfall Type Rainfall Intensity (mm) 1 Hour 24 Hour Very light rainfall Light rainfall Normal rainfall Heavy rainfall Extreme rainfall < 1 < >20 > 100 In this study, the mean deviation for each analyzed rainfall intensity by Mononobe. The correlation between intensity of short time rainfall duration and 24-hour rainfall follows the Mononobe s equation [8] =. / (3) with I: Rainfall Intensity (mm/hour) R24: 24-hour rainfall (mm) T: Time of rainfall (hour) DESCRIPTION OF MODEL Hydrologic Analysis using HEC-HMS The analysis of hydrologic is supported by using the application software of HEC-HMS. This application is designed to simulate the precipitation-runoff process of a dendritic watershed system [9]. The computation procedure in HEC-HMS consists of input data, computation and output as result. Input basin data used here are the area of a watershed, lag time, curve number and impervious [10]. Meteorological data consist of depth precipitation and the control specification is a time duration of the simulation [11]. The result of HEC-HMS is the computation of hydrograph at all of the junction. The existing modeling scheme can be shown in Fig. 4. Main Tributary Junction Sub Basin FIGURE 4. The existing scheme of modeling Ngotok Ring Kanal

6 Unsteady Flow Analysis using HEC-RAS The analysis of hydraulics is supported by using the application software of HEC-RAS. Generally, the computation produce in HEC-RAS consists of input data, computation, and the output as result. Input data used here are geometric data and boundary data [12]. The geometry data consists of basic map data of study location and channel cross section data from survey result. After processing data, the output is obtained as result [15]. The result can be arranged by using time control, computation interval, hydrograph interval output and detail output interval. The existing modeling scheme can be shown in Fig. 5. FIGURE 5. The existing geometric of modeling Ngotok Ring Kanal RESULTS Existing Condition This condition is modeled by precipitation for a return period of 25 years ( X25 = mm) for input basin data in HEC-HMS. The result of the computation is flooded hydrograph for a return period of years. Flood peak discharge is m³/s and hydrograph as shown in Fig. 6 below. Q25 = m 3 /s FIGURE 6. Hydrograph for Return of 25 years

7 This hydrograph can be used for the upstream boundary of Ngotok Ring Kanal River in HEC-RAS modeling. The Manning coefficient used is Figure 7 shows water surface profile in a long section of Ngotok Ring Kanal River. Water Surface Levee Elevation FIGURE 7. Existing conditions for water surface Scenario 1: Simulating with ponds at Panemon River and Brangkal River This condition is modeled by 2 ponds at Panemon River and Brangkal River. Flood peak discharge is m³/s and hydrograph as shown in Fig. 8 below. This hydrograph can be used for the upstream boundary of Ngotok Ring Kanal River in HEC-RAS modeling. The Manning coefficient used is Figure 9 shows water surface profile in a long section of Ngotok Ring Kanal River for scenario-1. Q25 = m 3 /s FIGURE 8. Hydrograph for Return of 25 years 4 3 ROB Water Surface Elevation Levee Elevation FIGURE 9. Water Surface Level of Scenario

8 Scenario 2: Simulating with ponds at Gunting and Panemon River This condition is modeled by 2 ponds at Balong River and Gunting River. Flood peak discharge is m³/s and hydrograph as shown in Fig. 10 below. Q25 = m 3 /s FIGURE 10. Hydrograph for Return of 25 years This hydrograph can be used for the upstream boundary of Ngotok Ring Kanal River in HEC-RAS modeling. The Manning coefficient used is Figure 11 shows water surface profile in a long section of Ngotok Ring Kanal River for scenario Water Surface Levee Elevation FIGURE 11. Water Surface Level of Scenario-2 Scenario 3: Simulating with ponds at Brangkal, Gunting and Panemon River This condition is modeled by 3 ponds at Brangkal River, Gunting River, Panemon River. Flood peak discharge is m³/s and hydrograph as shown in Fig. 12 below

9 Q25 = m 3 /s FIGURE 12. Hydrograph for Return of 25 years This hydrograph can be used for the upstream boundary of Ngotok Ring Kanal River in HEC-RAS modeling. The Manning coefficient used is Figure 13 shows water surface profile in long section of Ngotok Ring Kanal River for scenario ROB Water Surface Elevation Levee Elevation FIGURE 13. Water Surface Level of Scenario-3 Scenario 4: Simulating with ponds at Brangkal, Gunting, Sambong and Panemon River : This condition is modeled by 4 ponds at Brangkal River, Gunting River, Sambong River, Panemon River. Flood peak discharge is m³/s and hydrograph as shown in Fig. 14 below

10 Q25 = m 3 /s FIGURE 14. Hydrograph for Return of 25 years This hydrograph can be used for the upstream boundary of Ngotok Ring Kanal River in HEC-RAS modeling. The Manning coefficient used is Figure 15 shows water surface profile in long section of Ngotok Ring Kanal River for scenario ROB Water Surface Elevation Levee Elevation FIGURE 15. Water Surface Level of Scenario-4 Scenario 5: Simulating with ponds at Brangkal, Gunting, Sambong, Jombang Kulon and Panemon River This condition is modeled by 5 ponds at Brangkal River, Gunting River, Sambong River, Jombang Kulon River and Panemon River. Flood peak discharge is m³/s and hydrograph as shown in Fig. 16 below

11 FIGURE 16. Hydrograph for Return of 25 years This hydrograph can be used for the upstream boundary of Ngotok Ring Kanal River in HEC-RAS modeling. The Manning coefficient used is Figure 17 shows water surface profile in long section of Ngotok Ring Kanal River for scenario- 4 3 ROB Water Surface Elevation Levee Elevation FIGURE 17. Water Surface Level of Scenario-5 From Table 3 and Fig. 18 show the relation between peak discharge and the reduction on all scenario. TABLE 3. Peak Discharge and Reduction g Q Q SCENARIO Existing SCENARIO Q REDUCTION (m³/s) (m³/s) (m³/s) %

12 FIGURE 18. Scenario and Reduction CONCLUSION AND RECOMMENDATION From table 3 can be informed that the existing peak discharge is m³/s. If the scenario was implemented, it can reduce the peak discharge until m³/s or %. The fourth scenario shows that the water surface in the main channel of Ngotok Ring Kanal River is below from the levee elevation. But in Table 3, can be informed that the reduction between the third and the fourth scenario not significantly, at least just ± 1%. The result of The Fifth scenario shows that the all of the water elevation at Ngotok Ring Kanal River is below from the levee elevation and can decrease the peak discharge until %. So the fifth scenario is the best choice, it will be implemented at Ngotok Ring Kanal River. This study still needed the effort to be complete, especially hydrology and hydraulic effect at near area where the river control construction was built. REFERENCES 1. P.T.S.R. Nusantara, SID Normalisasi Kali Ngotok Ring Kanal di Kabupaten Mojokerto, edited by R.B. Antara, ( Balai Besar Wilayah Sungai Brantas, Mojokerto), pp.23-24, (2009) 2. S. Harto, Analisa hidrologi (PT Gramedia Utama, Jakarta), pp.9-10, (1993) 3. C.D. Soemarto, Hidrologi Teknik (Erlangga, Jakarta), pp.11-12, (1987) 4. Anggrahini, Hidrolika Saluran Terbuka (CV. Citra Media, Surabaya), pp.14-15,(1997) 5. V. T. Chow, Hidrolika saluran Terbuka (Erlangga, Jakarta), pp.46-47, (1992) 6. W.H. Graf, Fluvial Hydraulic (John Wiley & Sons, New York), pp.55-56, (1997) 7. Jansen, Bendegon, Berg, Vries and Zanen, Principle of River Engineering The Non-Tidal Aluvial River, ( Uitgevers Maatsschappij, Delft), pp.13-14, (1979) 8. Lensley, Ray, Franzini and Joseph, Teknik Sumber Daya Air Jilid II, (CV. Citra Media, Surabaya), pp.65-66, (1991) 9. E. Suhartanto, Panduan HEC-HMS dan Aplikasinya di Bidang Teknik Sumber Daya Air (CV Citra, Malang), pp (2008) 10. B. Triatmojo. Hidrologi Terapan (Beta Offset, Yogyakarta), pp.30-31, (2008) 11. L.C. van Rijn, Aqua Publ (2011). 12. U.S. a.c.e., User s Manual, Version (2010). 13. A.T. Oktaga and Suripin, Perbandingan Hasil Permodelan Aliran Satu Dimensi Unsteady dan Steady Flow pada Banjir Kota 21, (2015). 14. R. F. Luciana, Edijatno and F. Sofia, Analisa Sistem Drainase Saluran Kupang Jaya Akibat Pembangunan Apartemen Puncak Bukit Golf di Kota Surabaya 1, 1-5 (2013). 15. R. Wiganti, Soedarsono and T. Mutia, Analisa Banjir Menggunakan Software HEC-RAS (Studi Kasus Sub-DAS Ciberang HM 0+00-HM 34+00) 5, 2-13 (2016)