Design of Infiltration Well in Wetlands Area that Suitable for Giving Maximum Groundwater Recharge

Growth in residential, industrial, and office area ,are significantly occurred in all city in Indonesi a. Unfortunately, this is also caused more land that b eing covered by pavement and concrete in the cities . Realized or not it will disturb the availability of the groundwater and also lead to flooding in the r ainy season. One of the effective solutions to solve thi s problem is by making sufficient numbers of infilt ration well in the city, especially in the residential are . This research was conducted to analyze the ideal design of the infiltration well in the residential area. The d sign was made according to the equation by Sunjot o, which also refers to Indonesia standard (SNI) No: 03245 3-2002. The results show that the ideal dimension f or the infiltration well is to use the radius of the well (R) of 1.25 m. With the R of 1.25 will give a signi ficant recharge to the groundwater as much as ≈ 2.400 liter. It is expected that this research enc ourage a development in the urban drainage systems which wil l consider the environment and the groundwater reservation for the balance of our ecosystem.


INTRODUCTION
Nowadays, flooding has become a routine agenda that occurred in several big cities in Indonesia. A fast growth of cities in Indonesia is one of the causes of this problem. New residential, industrial, and office area that opened made the water catchment area become smaller. This condition can lead to imbalance in the ecosystem which will cause to surface runoff, erosion, and lack of groundwater reservation.
According to the conventional concept, urban drainage system is only trying todrain the water from the flooded area to the river, retention areas and/or sea. This system will only move the puddles from one place to another place. Thus, new concept that is being developed nowadays is a drainage system which is environmentally friendly which so called as eco-drainage system.
Correspondence: Irfan Prasetia, Dept. of Civil Engineering, Faculty of Engineering, Lambung Mangkurat University. Email: prasetia.07@gmail.com An effective solution that can be offered through this eco-drainage system is by making the infiltration well.The infiltration well can recharge the ground water by injecting the rain water to the soil. The area that need this infiltration well such as farming area, residential, industrial, office area, and another public service areas. For the infiltration well's design in the residential area has to comply to the Indonesia standard (SNI) No: 03-2453-2002(Litbang Pemukiman PU, 1990. This standard define how to design the infiltration well for residential yards, including the general and technical requirements regarding the ground water level limit, the value of the permeability of the soil, the distance of the building, the calculation and determination of the infiltration well. However, this standard has not yet determines the ideal design for infiltration well. Therefore, this research obtective is to determine the ideal design infiltration well in the residential area. The design was made according to the equation by Sunjoto (1993), which also refers to Indonesia standard (SNI) No: 03-2453-2002. It is expected that this research will encourage a development in the urban drainage systems which will consider the environment and the ground water reservation for the balance of our ecosystem.

METHODS
The design was made according to the equation by Sunjoto (1993). To facilitate the research works, the residential area of Lambung Mangkurat University's lecturer at Banjarbaru city, South Kalimantan Province, Indonesia, was chosen. As for the equation, these data have been set as the reference: 1. the roof surface area: ranged between 50 m 2 until 1.000 m 2 2. the radius of the well (R): ranged between 0,5 m until 1,5 m 3. the depth of the infiltration well: For impermeable wall of the infiltration well is F = 2 π R (eq. 2) (eq.2)

Hydrology Data
Hydrology data of the research works area was taken from the community service report of the lecturer team of the Faculty of Engineering Unlam Banjarbaru (Shadiq et al, 2006). The data that being obtained from the team are: 1. The maximum discharge of rainwater (Qp) according to rational method:

Design of the infiltration well
With the hydrology data that already mentioned above, the depth of the infiltration well can be calculated according to the eq.1. The calculation can be seen in Table 1. In addition, maximum volume of the infiltration well can be seen in Table 2.
From Table 1, with the radius of the well ranging between 1 m until 1.5 m, the depth of the well is below 1 m. Thus,with a depth of less than 1m will facilitate the process of excavation. Therefore, the radius of the well between 1 m until 1.5 m is an ideal dimension for the depth of the infiltration well. Furthermore, according to the Table 2, it could be seen that the difference in the maximum volume of the infiltration well between R = 1.25 m with R = 1.5 m is not significant. Thus, it is more efficient to use R = 1.25 m.
Available on line at: http://ijwem.unlam.ac.id/index.php/ijwem ISSN: 2354-5844  Based on calculation showed in the Table 1 and 2, it can be concluded that the ideal design for the infiltration well that can be build in the residential area is by using R = 1,25 m. With this R value, it can make the building process of the infiltration well easier. In addition, with this R value will also facilitate the process of excavation which is not to deep and wide. Therefore, it is easy to build this infiltration well and structurally safe. In addition, with the R of 1.25 m will give a significant recharge to the groundwater as much as ≈ 2.400 liter.