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Assessment of the Effect of Sand Dam on Groundwater Level: a Case Study in Chuncheon, South Korea

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Assessment of the Effect of Sand Dam on Groundwater Level: a Case Study in Chuncheon, South Korea The Journal of Engineering Geology Vol. 30, No. 2, June, 2020, pp. 119-129 pISSN : 1226-5268 eISSN : 2287-7169 https://doi.org/10.9720/kseg.2020.2.119 RESEARCH ARTICLE Assessment of the Effect of Sand Dam on Groundwater Level: A Case Study in Chuncheon, South Korea Bisrat Yifru1ㆍMin-Gyu Kim2ㆍSun Woo Chang3ㆍJeongwoo Lee4ㆍIl-Moon Chung5* 1Researcher, Department of Land, Water and Environment Research, KICT Student of Ph.D. Program, Department of Civil and Environmental Engineering, University of Science and Technology 2Research Specialist, Department of Land, Water and Environment Research, KICT 3Senior Researcher, Department of Land, Water and Environment Research, KICT Adjunct Professor, Department of Civil and Environmental Engineering, University of Science and Technology 4Research Fellow, Department of Land, Water and Environment Research, KICT 5Senior Research Fellow, Department of Land, Water and Environment Research, KICT Full-time Professor, Department of Civil and Environmental Engineering, University of Science and Technology Abstract Sand dam is a successful water harvesting method in mountainous areas with ephemeral rivers. The success is dependent on several factors including material type, hydrogeology, slope, riverbed thickness, groundwater recharge, and streamflow. In this study, the effect of a sand dam on the groundwater level in the Chuncheon area, South Korea was assessed using the MODFLOW model. Using the model, multiple scenarios were tested to understand the groundwater head before and after the construction of the sand dam. The effect of groundwater abstraction before and after sand dam construction and the sand material type were also assessed. The results show, the groundwater level increases substantially after the application of a sand dam. The comparison of model outputs, simulated groundwater head before and after sand dam application with and without pumping well, shows a clear difference in the head. The material type has also an effect on the groundwater head. As the conductivity of the material increases, the head showed a significant rise. Keywords: sand dam, recharge, groundwater level, MODFLOW, Chuncheon OPEN ACCESS In mountainous areas with ephemeral and intermittent rivers, water harvesting is *Corresponding author: Il-Moon Chung E-mail: [email protected] indispensable to secure ecological, agricultural, industrial, and domestic water supply demands in dry periods (Subagyono and Pawitan, 2008; Ertsen and Hut, 2009; Lasage et Received: 7 May, 2020 Revised: 21 May, 2020 al., 2015; De Trincheria et al., 2018). In this regard, sand storage dam is a successful Accepted: 21 May, 2020 water harvesting technology particularly in arid and semiarid environments (Quilis et Ⓒ 2020 The Korean Society of Engineering Geology al., 2009; Jadhav et al., 2012; De Trincheria et al., 2016). Sand dam harvests excess This is an Open Access article distributed under the terms of water, stores excess water mainly in the sand, to overcome drought periods in an the Creative Commons Attri- bution Non-Commercial License (http://creative- commons.org/licenses/by-nc/4.0/) which permits ephemeral river (Lasage et al., 2008, 2015; Quinn et al., 2019). Studies also show that unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original sand dams help to overcome water scarcity during long-term climate changes (Aerts et work is properly cited. 120 ∙ Bisrat YifruㆍMin-Gyu KimㆍSun Woo ChangㆍJeongwoo LeeㆍIl-Moon Chung al., 2007; Ryan and Elsner, 2016). Water harvesting using sand dams has several more advantages including minimizing evaporation, groundwater recharge, less pollution, and simplicity of construction (Baurne, 1984; Ertsen and Hut, 2009; Stern and Stern, 2011; Villani et al., 2018). In aquifers that have a full connection with the river, a sand dam may be considered as managed recharge (Quinn et al., 2019). Even though it is difficult to quantify, several researchers confirmed that the seepage from the riverbed and riverbank recharges the surrounding aquifer depending on the groundwater head (Hoogmoed, 2007; Hut et al., 2008; Quilis et al., 2009; Quinn et al., 2019). This phenomenon may last throughout the year. Consequently the groundwater level in the sand dam area increases (Yifru et al., 2018; Quinn et al., 2019). As the water table increases the natural vegetation-indigenous trees and riparian plants will get more water and live longer. The ecosystem restored and biodiversity has the potential to increase with the increase in groundwater level after the sand dam construction (Stern and Stern, 2011; Ryan and Elsner, 2016). Evaporation from sand is relatively low (Hellwig, 1973; Hut et al., 2008; Quinn et al., 2019). This makes the water available for a long time but it is dependent on the depth of the accumulated sand. Coarse gravel sand can be filled with water to 35 percent of its volume (Lasage et al., 2008; Maddrell and Neal, 2012). As the water level in the sand storage decrease to a few centimeters, the evaporation loss becomes significantly low (Baurne, 1984). And thus taking into consideration this concept in the study and construction of a sand dam is essential. The construction and the basic idea of water storage are relatively simple (Ertsen and Hut, 2009; Villani et al., 2018). The construction is mainly dependent on the locally available materials and it is economical (Lasage et al., 2008, 2015; De Trincheria et al., 2018). Moreover, the harvested water, using a sand dam, is clean because of the filtering effect of the sand material (Quinn et al., 2019). However, the successful application of a sand dam needs a good understanding of the hydrological processes in the dam area before and after the dam construction (Quilis et al., 2009). The socioeconomic aspect is also an important parameter, which needs to be investigated in the sand dam development process. Since the material accumulated on the upstream of the dam quality determines the ability of water-storing in it and transferring to the groundwater investigating all the possible issues is important. Silting is the most commonly reported problem which reduces the efficiency of a sand dam (De Trincheria et al., 2016). The efficiency and capacity can be improved by maximizing the accumulation of coarser materials and constructing a series large network of sand dams (De Trincheria et al., 2018). Selecting an area rich with several small upstream tributaries of the sand dam is also another way to maximize water storage and to get an adequate discharge at the dam site. Usually, more than one sand dam built in sequence to maximize the local storage capacity in a wider area or watershed scale. However, the total effect of the sand dam in the area may not be the aggregate sum of all the dams built. The result is site-specific and different for each sand dam. Therefore, it is important to evaluate each sand dam based on the specific site condition by including the most possible details in the numerical models (Quilis, 2007). If the sand dam site selection, height, downstream protection, and other hydrological changes are not studied well and acted accordingly the disadvantages may outweigh. Sand dam technology has a long-time history and implemented all over the world (Baurne, 1984; Hut et al., 2008; Yifru et al., 2018). The application is more common in arid and semi-arid areas. Recently it is widely used in Ethiopia ∙ 121 and Kenya dry riverbeds to increase the local storage capacity for small irrigation schemes and drinking purposes. The community gets water from the sand dam area in different ways. The most common water abstraction ways are using embedded pipe near the bottom of the sand dam wall on the downstream side, using pumping wells installed on the riverbank, and in the rural area of Africa scoop holes are also other ways (Borst and de Haas, 2006; Quinn et al., 2018; Villani et al., 2018). However, the studies on hydrogeology and the effect of a sand dam on the groundwater level are limited (Aerts et al., 2007). This work focuses on the assessment of the effect of the sand dam on the groundwater level in Chuncheon, South Korea. The groundwater head was evaluated using the MODFLOW model before and after the construction of a sand dam. The effect of groundwater abstraction and conductivity of sand material on the fluctuation of the groundwater table was also assessed. The location of the sand dam has a substantial effect on its effectiveness. To bring the desired hydrological impact the location should be selected cautiously (Ryan and Elsner, 2016). The selection of a sand dam site is practically similar to any surface water-storing dams. Keeping the length of the dam wall short, maximized storage in a minimum surface area, accessibility, suitable slope that maximize storage and accumulation of sand, good material type in the riverbed, social aspect, and water availability are the key issues need to be addressed in the selection process (Nissen-Petersen, 2000; Nissen-Patterson, 2006; Pauw et al., 2008). To minimize the length of the dam but get the maximum possible storage without submerging large area of land or valuable property the site should be a narrow valley or deep gorge. The upstream area should be large enough and ideal slope to store the maximum amount of sand. The availability of local construction materials and thickness of the riverbed are also important things to consider (Baurne, 1984). The current study area has a pronounced elevation difference, which varies from 350 m to 240 m above sea level. Fig. 1 shows the topography and model boundary of the study area. The elevation difference downstream and upstream of the dam site is easily noticeable. The slope difference along the river (from point A to point B) is also depicted in Fig. 1. Since the DEM is 30 × 30 m of horizontal resolution, it is not easy to see the gorge. However, the overlain contour is based on field data and it shows the elevation difference and the gorge clearly.
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