ECO DRAINAGE IMPLEMENTATION FOR FLOOD HANDLING IN DAS WELANG PASURUAN DISTRICT

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 8, August 2018, pp , Article ID: IJCIET_09_08_108 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed ECO DRAINAGE IMPLEMENTATION FOR FLOOD HANDLING IN DAS WELANG PASURUAN DISTRICT Hendra Wahyudi, Kamilia Aziz, Edy Sumirman Institute Teknologi Sepuluh Nopember, Indonesia ABSTRACT Welang river watershed management s authority is handled by the East Java Provincial government, has a topographical condition that varies greatly with the upstream part of the mountains with the highest elevation of m above sea level, while the downstream with an elevation of 0 to 9.25 m above sea level. Economic is often affected by the flood from downstream area in the north coast of east java causing. This research was carried out to apply eco-drainage to control flooding that often occurs in the Welang river. The methodology carried out in this study was carried out by collecting rainwater that fell into infiltration wells before flowing into the river so that the capacity of the river to still be able to accommodate The results obtained from this study are flood discharge that must be controlled by infiltration wells with Q2 years of 31.1 m3 / s and Q 5 th of m3 / sec while for controlling flood Q2th a well of pieces is needed while for flood discharge Q 5 is required well as many as 40,186 wells. Key words: Welang Watershed, Floods, Eco Drainage and Infiltration Wells. Cite this Article: Hendra Wahyudi, Kamelia Aziz, Edy Sumirman, Eco Drainage Implementation For Flood Handling In Das Welang Pasuruan District, International Journal of Civil Engineering and Technology, 9(8), 2018, pp BACKGROUND Welang river watershed based on Presidential Decree Number 112 in 2012 which consist of the Welang Rejoso river area. This river geographically across three places such as Pasuruan municipality, malany district and also pasuruan district, but the authority fully given to east java provincial government. According to the Director General of Water Resources regulation Number 05 / SE / D / 2016, it is written that operations and maintenance activities carried out by the East Java Provincial Government so that each year can be evaluated and monitored of its activities, along with the Water Resources Agency, which is given authority by Ministry of public work of Indonesia to handle water resources management activities in Welang River editor@iaeme.com

2 Hendra Wahyudi, Kamelia Aziz, Edy Sumirman The topographical conditions of the Welang river watershed vary greatly with the upstream part being hilly and mountainous with the highest elevation of m while the middle part has an elevation between 100 m above sea level to 310 m above sea level and the lower part with an elevation of 0 to 6.25 m above sea level. Welang River is a perennial river which water flows all the year but the difference in flow between the dry season and the rainy season is getting bigger and bigger, and influenced drastically by land function changes from the water absorption area into residential area so that when high intensity rain comes, increasing water flow and causes flood in downstream area which lead to economic disaster in west coast area Eco-Drainage is considered as environmental friendly drainage system, which used for increased water usage, minimalize water loss also 2. RESEARCH BORDER This research was done with certain border which explained below: Research conducted under the title "Implementation of Eco Drainage for Flood Mitigation in the Welang Watershed of Pasuruan Regency" has the following limitations: The amount of flood discharge that will be controlled based on the magnitude of the flood discharge passing on the existing dam building in the river is due to this condition because in this study no cross-sectional measurements of the Welang river were carried out. Eco drainage used to overcome flooding in the Welang watershed using rainwater harvesting systems by making infiltration wells. The roof of the house used for analysis using type 36 with a land area of 84 m2 This study uses primary data from observations of conditions in EXPECTED BENEFITS AND OBJECTIVES The benefits and objectives to be achieved from this research activity are as follows: This research, if viewed from the perspective of science, is expected to add to the repertoire of knowledge, especially the problem of flood mitigation. The results of this study are expected to be used as guidelines for policy makers related to handling flood problems. 4. THEORETICAL FOUNDATION The rainfall required for the preparation of a water use design and the design of flood control is the average rainfall throughout the area concerned, not rainfall at a certain point. This rainfall is called regional rainfall or regional rainfall which is expressed in millimeters (Sosrodarsono, 2003). Planning the river, to estimate the design flood hydrograph by means of unit hydrograph (hydrograph unit), it is necessary to know in advance the distribution of hourly rain with a certain interval. In this study the calculation of Mononobe formula is used, as follows: R T R 24 = t * Where : t T 2 3 R T = average rainfall intensity in T hours R 24 = rainfall in 1 day (mm) editor@iaeme.com

3 Eco Drainage Implementation For Flood Handling In Das Welang Pasuruan District T = rain concentration time (hours) While to analyze the magnitude of flood hydrograph can use Nakayasu unit hydrograph with the following equation form: Q p A. R = 3,6.(0,3. T p 0 + T 0,3 ) By: Qp = peak flood discharge (m3 / sec) R0 = Unit rain (mm) Tp = The time period from the beginning of the rain to the peak of the flood (hours) T0,3 = The time required for a decrease in discharge, from peak to 30% of peak discharge A = Area of drainage to outlets To determine Tp and T0.3 the following formula approach is used: Tp = tg tr T0,3 = α tg Tr = 0.5 tg to tg tg is the time lag which is the time between rain and peak discharge of floods (hours). but calculated with the following conditions: River with a groove length L > 15 km: tg = L River with a groove length L < 15 km: tg = 0.21 L0.7 By: tr = Unit Rain time (hours) α = Parameter hydrograph, for: α = 2 => In an ordinary drain area α = 1.5 => In the rising part of the hydrograph it is slow, and it drops quickly α = 3 => On the part of the hydrograph it rises rapidly, it drops slowly The amount of rainwater that can be harvested at each house can be analyzed using the following rational equation Qmax = C. HE In this case Qmax = debit that can be harvested in each plot (m3 / s) editor@iaeme.com

4 Hendra Wahyudi, Kamelia Aziz, Edy Sumirman C = flow coefficient I = rain intensity (mm / hour) A = area (hectares) 5. METHODS The research method is a step of research carried out from beginning to end so that a conclusion can be drawn. The steps can be seen in Figure 1. below. 6. RESULTS AND DISCUSSION Figure 1 Research Flow Chart Consistency Test Rainfall stations that are used for hydrological analysis include the rainfall stations (SCH) Purwosari, SCH Selowongko, SCH Wilo and SCH Prigen from the results of the test consistency of the existng data series showing results that are consistent with one another. Double mass curve for Purwosari SCH has a determination value (R2) = (99.54%), SCH Selowongko has a determination value (R2) = (99.58%), SCH Wilo has a determination value (R2) = (99, 86%) and SCH Prigen has a determination value (R2) = (99.79%) so that the data can be used to support further analysis. Maximum Daily Rain The maximum daily rainfall for the Welang watershed using the Thiessen polygon method for ten years from 2003 to 2016 can be seen in table editor@iaeme.com

5 Eco Drainage Implementation For Flood Handling In Das Welang Pasuruan District Table 1 Maximum Daily Rainfall Data (mm) No Years Max Rain (mm) , , , , , , , , , , , , , ,89 Test threshold (Outlier) Data threshold test using Grubbs and Beck method shows that the data limit that cannot be included is the lower limit of maximum rainfall is mm and the maximum limit of maximum rainfall is while the maximum rainfall data is between the upper limit and the lower limit so that the maximum rainfall data meets the threshold test. Rainfall Plan The height of the plan is determined using the Pearson Type 3 log method. The determination of this method is based on the results of Pearson type 3 log distribution test parameters, namely the value of Cs = and the value of Cv = with a plan rain height of mm. While the results of the horizontal distribution suitability test (Smirnov-Komogorov or vertical distribution test (Chi-Square) obtained that the determination of the height of the plan with frequency analysis using the Log Pearson Type 3 method can be accepted Flood Debit Plan Flood discharge plans are a major part of water building analysis. This study analyzes the planned flood discharge using Nakayasu method for Q 2 years and Q 5 years in selowongko dam can be seen in the Figure editor@iaeme.com

6 Hendra Wahyudi, Kamelia Aziz, Edy Sumirman Figure 2 Discharge of Welang River Watershed Selowongko dam is one of the existing dam in the Welang river whose position is located between Baong and Domas dam having an effective width of 33 meters in conditions that do not cause flooding can flow water at m3 / s so that from the flood hydrograph in Figure 2 the flood discharge which must be controlled in Welang River is the difference from Welang flood hydrograph reduced by the Welang River capability in selowongko dam which did not experience flooding which is for 2th Q of 31.1 m3 / s and Q 5 th of m3 / s Flood Control Flood control with eco drainage method is flood control by managing excess water infused into the soil or harvesting rainwater as a cause of flooding before flowing into the river to be absorbed into the soil so that the river capacity is not covered. Analysis of harvesting rainwater is done by making infiltration wells in each house. The condition of the house in Welang River in this study is assumed to be a type 36 house with a land area of 84 m2 so that each house is able to accommodate m3 / sec so that to control flooding Q 2th a well of pieces is needed while for flood discharge Q 5 each house is able to hold water at m3 / sec so that a well of wells is needed. 7. DISCUSSION Based on Presidential Decree Number 112 of 2012 and Circular of the Director General of Water Resources Regulations Number 05 / SE / D / 2016 that management of Welang River isbelong to East Java Province Government, since flood can t be predicted how far it can spread of eventhough the flood affects Pasuruan districts so that flood control using the method of harvesting rainwater, by using infiltration ponds requires a large number of wells to be applied,as consequences it must be supported by the Pasuruan district Government as the regions that have the authority and the authority to make regulations. 8. CONCLUSION Based on the results of the analysis of floods that occur in the watershed area (DAS) welang and countermeasures by using eco drainage, the following conclusions can be taken. 1. Discharge of floods occurring in the watershed of Welang for Q2 year is m3 / sec while for Q 5 years is 236m3 / sec editor@iaeme.com

7 Eco Drainage Implementation For Flood Handling In Das Welang Pasuruan District 2. The ability of the Welang river to accommodate flood flows of m3 so that the floods that have to be harvested are m3 / sec for Q2 years while for Q5 years it is m3 / sec. 3. Infiltration wells as one of the eco-drainage that is needed to overcome floods of 2 years is 39,448 pieces while to overcome flooding in 5 years is 40,186 pieces of wells. SUGGESTIONS There must be coordination between the Government of Pasuruan District and the East Java Provincial Government related to flood control in Welang River. REFFERENCE [1] Bisri, Mohammad Pengelolaan Daerah Aliran Sungai. CV Asrori. Malang. [2] Chow, V.T Handbook of Applied Hydrology. New York: Mc. Graw-Hill Book Company. [3] Frevert, R.K Soil and Water Conservation Engineering. New York: John Wiley & Sons, Inc. [4] Gray, D.M. 1970, Handbook on Principles of Hydrology. The Iowa State University Press, Ames, Iowa. [5] Haan, C.T., H.P. Johnson, and D. L. Brakenseik Hydrologic Modelling of Small Watersheds. American Society of Agricutural Engineers [6] Hadisusanto, N Aplikasi Hidrologi. Malang: Jogja Mediautama. [7] Hewlett, J. D. and W. L. Nutter, An Outline of Forest Hydrology. Athens: University of Georgia Press. [8] Linsley, R.K., M.A. Kohler and J.L.H. Paulus Surface Retention anddetention and overland Flow. Applied Hydrology. New York. Mc Graw Hill Book Co. [9] Nash, J.E., and J.V. Sutcliffe, River Flow Forecasting Through Conceptual Models Part ICA Discussion of Principles, Journal of Hydrology. Vol 10. [10] Seyhan, Dasar-dasar Hidrologi. Subagyo S, penerjemah; Prawirohatmodjo S, editor. Yogyakarta: Gajah Mada University. Terjemahan dari: Fundamentals of Hydroloy. [11] Sosrodarsono at al, Hidrologi Untuk Pengairan. Jakarta: PT Pradnya Paramitra. [12] Sri Harto, Pengkajian Sifat Dasar Hidrograf Satuan Sungai-sungai di Pulau Jawa untuk Perkiraan Banjir. Disertasi Doktor UGM (Tidak dipublikasikan). Yogyakarta [13] Sri Harto, Analisa Hidrologi. Jakarta, PT Gramedia Pustaka Utama. [14] Wu Y, Tang Y, Huang C, 2009, Harvesting of Rain water and Brooklets Water to ncrease Mountain Agricultural Produktiity : A Case Study from A Dry Valley of Southwestern China buah sumur Natural Resources Forum editor@iaeme.com