International Journal of Civil Engineering and Technology (IJCIET) Volume 10, Issue 11, November 2019, pp. 107-112, Article ID: IJCIET_10_11_012 Available online at http://iaeme.com/Home/issue/IJCIET?Volume=10&Issue=11 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 © IAEME Publication

IMPLEMENTATION OF ARTIFICIAL STORAGE FOR FLOOD MANAGEMENT IN WELANG WATERSHED, DISTRICT

Hendra Wahyudi and Edy Sumirman Lecturer at Civil Engineering and Planning Department, ITS, , Indonesian

ABSTRACT Welang Watershed (DAS) based on Presidential Decree number 112 of 2012 is included in the Welang Rejoso River Basin and administratively this river is a cross river between Pasuruan City, Pasuruan and Regency so that the management of the Welang river becomes the authority of the Government of East Province The Welang River is a first order river with 21 tributaries having a total watershed area of 509.50 km2 and a length of approximately 53 km with the characteristic shape of the river meandering and the shape of the watershed widened in the upstream and topography so that it often causes flooding in the downstream area As a result, the existing transportation routes are often disrupted. The concept of handling floods that are environmentally friendly by storing them in the ground at a place called an aquifer by using the Artificial Storage Recharge (ASR) method what if this method is implemented to deal with floods that occur at welang times. The results show that the watershed watershed is possible to be overcome by using artificial recharge storage, but because the quality of the river water is polluted, it needs to be treated first before it is included as a source of artificial recharge storage water. Keywords: DAS Welang, Flood, ASR and polluted Cite this Article: Hendra Wahyudi, Edy Sumirman, Implementation of Artificial Storage for Flood Management in Welang Watershed, Pasuruan District. International Journal of Civil Engineering and Technology 10(11), 2019, pp. 107-112. http://iaeme.com/Home/issue/IJCIET?Volume=10&Issue=11

1. INTRODUCTION The paradigm for flood management that has been carried out is to drain rainwater into the sea as fast as possible. However, along with the increase in population and increasing water demand and during the dry season often there is a lack of water, the flood management paradigm that has been carried out needs to be done by maintaining the hydrological conditions of the developed area by increasing the intensity of infiltration, filtering, storage,

http://iaeme.com/Home/journal/IJCIET 107 [email protected] Hendra Wahyudi, Edy Sumirman evaporation and increasing roughness surface so that flowing water can be retained but its impact on the environment can be reduced. Welang watershed (DAS) based on Presidential Decree number 112 of 2012 is included in the Welang Rejoso River Basin and administratively this river is a cross river between Pasuruan City, and Malang Regency so that the management of the Welang river becomes the authority of the Government of Province This Welang River is a first order river with 21 tributaries having a total watershed area of 509.50 km2 and approximately 53 km in length with a characteristic shape of winding rivers and widened watershed form in the upstream and topography so that it often causes flooding in the downstream area As a result, the existing transportation routes are often disrupted. Changes in the function of the land from forests to housing and agricultural land resulted in reduced water catchment areas, so that when there is relatively high rain, water flows directly into rivers and few are retained by the ground because the number of trees that function to bind water has been greatly reduced. Discharge of water flowing rapidly towards Welang River, whose condition is not able to accommodate peak discharge. The capacity of the river starting from the upstream of Grinting Dam to the downstream is decreasing because of the very large sedimentation. Meanwhile the left-hand side of the river from the upstream to the downstream is used as housing and agricultural land, so that the water also flows quickly without anyone holding back. This is what causes the peak flood time is very short. With the development of comprehensive thinking and driven by the spirit of anticipation of climate change that is happening today, it is necessary to change the concept of handling flooding that is environmentally friendly by storing it in the ground at a place called an aquifer by using the Artificial Storage Recharge (ASR) method.

2. RESEARCH METHODS

Figure 1. Research Flowcart

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The flowchart in Figure 1 shows the research methodology. The research began by conducting a field orientation and looking for secondary data. Table 1 shows the secondary data used in this study are the rain data from the Pager, Purwodadi, Purwosari, Selowongko, Tutur, Wonorejo, Ngempit, and Telebuk stations from 2004 to 2017

Table 1. Maximum Rainfall Maximum NO Years Rainfall 1 2004 118.32 2 2005 93.84 3 2006 92.42 4 2007 88.81 5 2008 123.03 6 2009 90.35 7 2010 122.07 8 2011 87.48 9 2012 91.41 10 2013 92.22 11 2014 100.07 12 2015 123.57 13 2016 113.54 14 2017 115.21 The rainfall plan for the Welang River Basin using the Pearson log type 3 method is as follows: Table 2 Rainfall Plan Reccurent Period K Log Rt Rt (mm) (Year) 2 -0.044 2.009 102.186 5 0.826 2.062 115.249 10 1.306 2.090 123.162 25 1.839 2.122 132.568 50 2.194 2.144 139.237 100 2.520 2.163 145.663 1000 3.477 2.221 166.264 Flood discharge analysis plan

Figure 2. Land use in the Welang watershed

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Before analyzing the planned flood discharge using the Nakayasu synthetic unit hydrograph method, the parameter that must be known is the drain coefficient obtained from the Welang watershed land use as shown in Figure 2, an average C value of 0.501 is obtained. The results of flood discharge analysis using the synthetic nakayasu unit hydrograph method with a return period of 25 years can be seen in Figure 3.

DAS Welang 1000

900

800

700 ) t 600 de / 

m 500 (

t

bi DAS Welang e 400 D

300

200

100

0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Waktu (jam)

Figure 3 The hydrograph shape of the Welang watershed with a return period of 25 years Measurement of absorption capacity of absorption wells is done by entering a certain volume of water into the injection well and observing the amount of water that can be collected by the soil through the well in a certain time unit. The results of this measurement are actually not suitable because in this injection test well water flows to all layers not just the aquifer layer. However, measurements are still being made because the results of infiltration can give an idea whether this conclusion can be broadly applied. The results of the following measurements made on injection wells can be seen in Table 3

Table 3 Injection Well Measurement Results Well Description Information Ground water level rise initial ground water level (Initial Tma) 2.8 End ground water level (End Tma) 0.64 Thick well water (∆d) 2.16 charging time (∆t) 21 Minutes Injection discharge 86.7 Liter/Minutes total incoming water 1820.7 Liter decrease in ground water level initial ground water level 0.8 End ground water level 1.51 Thick well water (∆d) 0.71 long time decline (∆t) 75 Minutes well infiltration capacity Well in Selowongko Pasuruan 0.93 m3/Hours

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Figure 4. Changes to the Groundwater graph Based on the above filling results, it shows that a lot of water can be injected and the decline is also relatively fast so this condition is an indication that the soil in Welang has good soil infiltration so that flood handling with the implementation of artificial recharge storage methods can be applied in the Welang River’s watershed River water quality in the Welang river during flooding can be seen in Figure 5

Figure 5. Welang River Pollution Index’s Graph in the Rainy Season The condition of water quality from Welang river water shows indications of being polluted so that if the water is stagnant, the Welang River will be put into ground water then it must be treated first.

3. CONCLUSIONS AND SUGGESTIONS The conclusions that can be drawn from the results of research on the application of artificial storage for flood control in Kali Welang Pasuruan Regency are as follows:  Flood control that occurs in Welang River can be handled by using an artificial recharge storage method by injecting water into the ground.

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 However, due to the quality of flood water that occurs in the Welang River in polluted conditions, it must be treated first before being used as a source of water for artificial recharge storage. Suggestions for flood control in the Welang River involve the community because the condition of the existing water quality is the condition of activities in the Welang watershed so that the handling must be integrated.

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