Assessment of rainwater harvesting potential based on field observations in Jagakarsa District area, South Jakarta

. Jagakarsa is one of the districts in South Jakarta that has a rainwater catchment area. Problems arise as a result of the high rate of population growth, which has an impact on changes in land use and increased surface runoff, causing flooding. On the other hand, the absence of clean water provision facilities from the government means that people use groundwater-drilled wells to meet their daily clean water needs. Sustainable groundwater consumption has an impact on land subsidence and vulnerability to groundwater availability. Therefore, it is necessary to carry out research. This research seeks to assess the potential for rainwater harvesting based on field observations. The research was carried out by analyzing rainfall data, field surveys, research program socialization, and community socio-economic analysis. Rainfall is high, with an annual average of 2809.7 m. 98% of respondents use drilled groundwater wells with a wells depth in the deep aquifer layer, and public interest in rainwater harvesting (RWH) technology is high. These show the potential for implementing RWH in the study location. This research is an initial study; for the integrated implementation of RWH, further research is needed after this study.


Introduction
Jagakarsa is a rainwater catchment area for Jakarta and is one of the South Jakarta Districts.It is situated at coordinates 6°20'9.83"South Latitude and 106°49'32.42"East Longitude [1].The average population growth rate is 2.83, the highest in South Jakarta City compared to other districts [2], and the lack of clean water supply network facilities (Figure 1) is resulting in an increasing need for clean water being taken from groundwater.In Figure 1, it can be seen that the entire Jagakarsa district area (delimited by the red line) is white; this means that in the Jagakarsa area, there are no clean water service facilities from PT Aetra or PT PAM Lyonnaise Jaya (Palyja).PT Aetra and PT Palyja are two official companies providing clean water in Jakarta.Continuous exploitation of groundwater makes Jagakarsa vulnerable to land subsidence [3,4].Their research provided an overview of the 2009-2010 land subsidence map, stating that there was a decline of around 2 cm/year in the Jagakarsa area.The government's inability to respond to groundwater utilization with a lack of facilities for providing clean water is one of the triggers for land decline.The government's clean water supply facilities are currently inadequate in every area of Jakarta, and as a result, some residents use drilled groundwater wells (Figure 2). Figure 2 shows groundwater withdrawal data for the years 2013-1015 from the Public Works Department in research [5] and 2018-2019 from DKI Jakarta Department of Industry and Energy (https://statistik.jakarta.go.id, 2019).South Jakarta residents contribute the most to groundwater extraction when compared to residents of other cities in the Jakarta province.Due to continuous groundwater extraction, the availability of groundwater is vulnerable to future groundwater exploitation.Fig. 2. Groundwater withdrawal in Jakarta, adapted from DKI Jakarta Department of Industry and Energy (2019) [5].Another problem that arises is frequent flooding in the Jagakarsa District area.Rainfall data at the study location is shown in Figure 3 and Figure 4 below:  High rainfall intensity and population growth are the main causes of floods, which affect how land is used by expanding the built environment, the impervious surface layer, and runoff.The soil's ability to absorb precipitation is dwindling, and the existing urban drainage system isn't enough to handle the resulting runoff.Due to this, there were numerous floods in the research area (Figure 5).The issues mentioned above are urban-area phenomena.This situation gets worse since water resources aren't managed properly [6][7][8].An alternate method is rainwater harvesting (RWH); therefore, effective and sustainable management is required [9][10][11].RWH is an example of low-impact development (LID), which is a long-term strategy to protect the environment and nature.Increases in raw water supplies decreased flood discharge, and groundwater replenishment can all be achieved with RWH [12][13][14][15][16]. RWH is also used to overcome pluvial flooding in urban areas [17][18][19][20][21]. RWH technology and managed aquifer recharge (MAR) combination is a feasible groundwater conservation method [22][23][24][25][26].
Significant issues in the Jagakarsa District area require investigation, including the frequency of urban flooding, rapid population growth rates, groundwater extraction, and land subsidence events.As a result, we made an effort to do a study by looking at the community's current natural and environmental circumstances as well as its socio-economic situation.Based on field survey observations in the Jagakarsa District area, this study seeks to evaluate the potential of RWH.

Methods
The assessment of RWH potential was done based on rainfall data, natural characteristics of the surrounding environment, and the socio-economic condition of society.The closest rain station in the study area, Kampus UI, provided the rainfall data that was used as the primary component of RWH.Analysis of rainfall data is done by counting the annual rainfall and monthly rainfall.
Direct field surveys and the gathering of pertinent data were used to explore the current natural and environmental conditions at the study location.The leaders of each sub-district in the Jagakarsa District area were invited to the research socialization, together with the district leader and relevant field employees.The socialization of the background and goals of the research, an explanation of the tutorial for completing the research questionnaire, and direct discussions regarding responses to the research plan to be carried out and the conditions of residents going around the neighborhood and examining the state of the homes' yards and roofs allowed for direct observations.A Google Form link was used to distribute research questionnaire questions and conduct in-person interviews with several community members to gather data on raw water sources and socioeconomic conditions.The potential for rainwater harvesting was determined by validating the survey's data and then analyzing them.

Analysis of rainfall data
This analysis used rainfall data for 20 years (2003-2022).After a data consistency test, it was determined that the rainfall data was reliable and could be used for further research.
Annual and monthly rainfall graphs are shown in Figure 3 and Figure 4 above.Figure 3, shows that the maximum annual rainfall is 4042.2mm, the average annual rainfall of 2809.7 mm, and the maximum monthly rainfall intensity is 830.6 mm. Figure 4 demonstrates that there have been rainy days in every month for the past 20 years except 2015 July and September.The high annual rainfall and monthly rainfall point to the possibility of RWH.Therefore, it can be concluded from the data in Figure 3 and Figure 4 that the Jagakarsa District area has the potential for RWH.

Socio-economic analysis of Jagakarsa District residents
Socio-economic information was gathered through direct observation of environmental conditions (Figure 6), community interviews, research socialization (Figure 7), and responses to the research questionnaire.We found several houses with gutters, capturing rainwater with the roof, then channeling it through pipes, and then the rainwater was discharged and directed to the road surface, as shown in Figure 6.Many rainwater and waste drainage channels in front of the house are covered with concrete.This is one example of the reason for the increase in runoff capacity.Research socialization was carried out at the Jagakarsa district office, attended by the district leader, economic and development staff, and sub-district leaders (Figure 7).They agreed to support research into the potential of RWH in the Jagakarsa district area and they helped distribute the google form link to the research questionnaire to community members in each sub-district.The questionnaire questions were designed to obtain data on socioeconomic conditions and community interest in RWH.Data on the socio-economic conditions of the community include the type of work, education level, average monthly income; condition of the residence including the number of occupants of the house, the area of the house, the type of roofing material, whether or not the roof has roof gutters, the area of the yard and the type of cover for the yard; raw water supply facilities in the form of raw water sources used, depth of drilled wells and raw water procurement costs; community perceptions and interest in RWH technology.
We were able to recruit 1751 respondents to complete the research questionnaire.There are 1716 valid data, which means a 2% data error (see Table 1).The error data rate under 10% is considered satisfactory and can continue to be processed and analyzed.Some of the results of processing questionnaire data are shown in Figure 8, Figure 9, and Figure10.Figure 8, there is 98% (79% + 19%) of the community's residents use groundwater for their daily needs of clean water, which is a very high percentage.In Figure 9, the depth of the drilled well is 10.1-20.0m (45%) and 20.1-30.0 m (43%).This depth position is located in the deep aquifer layer.If groundwater conservation efforts are not carried out now, it can be predicted that groundwater sources will be vulnerable in the future.It should be grateful that the majority of the Jagakarsa community is interested in rainwater harvesting as a groundwater conservation effort.This is shown in Figure 10.

Conclusions
Implementing rainwater harvesting in the Jagakarsa District is an alternative approach to solving the issues.We conclude that there is potential for rainwater harvesting in the Jagakarsa District area based on the examination of rainfall data, field surveys, and socioeconomic surveys of community members at the study location.This study is the first stage of our research, we will conduct a thorough examination of our plans for deploying rainwater harvesting technology in a comprehensive and integrated way.

Table 1 .
Recapitulation of total respondents and % error data.