Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Hydrol. Earth Syst. Sci. Discuss., 11, 5487–5513, 2014 www.hydrol-earth-syst-sci-discuss.net/11/5487/2014/ doi:10.5194/hessd-11-5487-2014 HESSD © Author(s) 2014. CC Attribution 3.0 License. 11, 5487–5513, 2014 This discussion paper is/has been under review for the journal Hydrology and Earth System Infiltration well to Sciences (HESS). Please refer to the corresponding final paper in HESS if available. reduce the impact of land use changes on Infiltration well to reduce the impact of flood peaks land use changes on flood peaks: a case D. I. Kusumastuti et al. study of Way Kuala Garuntang catchment, Title Page Bandar Lampung, Indonesia Abstract Introduction Conclusions References D. I. Kusumastuti1, D. Jokowinarno1, S. N. Khotimah1, C. Dewi2, and F. Yuniarti3 Tables Figures 1Civil Engineerring Department, Engineering Faculty, University of Lampung, Lampung, Indonesia J I 2Study Program of Survey and Mapping, Engineering Faculty, University of Lampung, Lampung, Indonesia J I 3Magister of Civil Engineering, University of Lampung, Lampung, Indonesia Back Close Received: 6 May 2014 – Accepted: 13 May 2014 – Published: 26 May 2014 Full Screen / Esc Correspondence to: D. I. Kusumastuti ([email protected]) Published by Copernicus Publications on behalf of the European Geosciences Union. Printer-friendly Version Interactive Discussion 5487 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract HESSD Significant land use changes due to rapid development, a central issue in Bandar Lam- pung and high rainfall intensity are the main triggers for frequent flooding. This study 11, 5487–5513, 2014 was carried out to define design rainfall intensity based on analysis of hourly temporal 5 rainfall pattern for calculating design discharge, predict the impact of land use changes Infiltration well to on flood peaks, and predict the impact of infiltration well on flood peak reduction. The reduce the impact of results showed that rainfall distribution pattern for storm duration of 4 h are 40, 35, land use changes on 20 and 5 % for the first, second, third and fourth hour, respectively. Analysis on land flood peaks use changes underlined that if 30 % of the catchment area is maintained for green 10 land then flood peaks can be decreased. However, with city development, land con- D. I. Kusumastuti et al. versions are intended for settlements, industries and trading areas which will increase flood peaks significantly. Application of infiltration well in the catchment can reduce surface runoff depends on the density and dimension of the well. The results suggest Title Page that using infiltration well with diameters between 0.8 to 1.4 m which are applied each Abstract Introduction 2 15 in every 4000 m of land area will reduce flood peaks from 6.9 to 12.6 %. While the application of infiltration well with density of 500 m2 will reduce flood peaks from 55.21 Conclusions References to 99.8 %. Commitment and relevant government policies and community participation Tables Figures will encourage to undertake flood reduction measures. J I 1 Introduction J I Back Close 20 Flooding often occurs in several locations in Indonesia during wet season, that include Bandar Lampung, the capital city and economic hub of Lampung Province and the en- Full Screen / Esc try point to Sumatra. The province is located on Southeast Sumatera island. The city’s 2 area is about 169.21 km , with a population of approximately 881 801 people (Bappeda, Printer-friendly Version 2010). Over the last two decades the city has shown significant increase in population Interactive Discussion 25 and economic growth. Recently several flooding events in the city had caused inun- dation. In one instance several patients were evacuated from a public hospital located 5488 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | near a river. Landslide in a canal within the Bumi Kedaton National Park caused severe damage on road and bridge, the central town was inundated for few hours and caused HESSD massive traffic jam and some casualties. 11, 5487–5513, 2014 The most common causes of flooding are high rainfall intensity, land use changes, 5 reduced infiltrated area, insufficient drainage system and reduced river capacity. Sig- nificant land use changes due to rapid development in most part of Indonesia’s larger Infiltration well to cities are considered as one of the major cause of flooding. The land use changes reduce the impact of include urbanisation, deforestation and industralisation. The changes in land use as- land use changes on sociated with urban development contribute to flooding in terms of the peak discharge, flood peaks 10 volume, and frequency of floods. The effect of land use changes on hydrologic response has gathered interest among D. I. Kusumastuti et al. researchers recently due to intensified developments in developing countries (Ashagrie et al., 2006; Doe et al., 1996). Numbers of researches use GIS based model to evaluate Title Page the impacts of land use changes on hydrologic response (Gumindoga, 2010; Hacket, 15 2009; He and Hogue, 2012; Juahir et.al., 2010; Koch et al., 2012; Camorani et al., Abstract Introduction 2005; Nobert and Jeremiah, 2012). Beside surface hydrology responses, the effect Conclusions References of land use changes on groundwater hydrology is also becoming a research interest (DeSmedt and Batelan, 2001). This study investigates the impact of land use changes Tables Figures on surface runoff that contribute flood discharge.Information about streamflow and the 20 impact of land use changes to the flow can help communities reduce their current and J I future vulnerability to floods. Flood peak is influenced by many factors, including the intensity and duration of J I storms. In common engineering practice there is the specification of a rainfall event Back Close as design rainfall which must reflect required levels of protection, local climate, and Full Screen / Esc 25 catchment conditions as well as to ensure safe, economical and standardised design. Design rainfall temporal patterns are used to represent the typical variation of design Printer-friendly Version rainfall intensities during a typical storm burst. A number of hydrology analyses in In- donesia used van Breen method to determine design rainfall intensity, a method which Interactive Discussion considers temporal distribution of rainfall within the design rainfall (Ilmiaty et al., 2012; 5489 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Kusumastuti, 2009). Van Breen method was developed in the early twentieth century using rainfall data of Java Island, Indonesia. The temporal distribution of rainfall within HESSD the design storm is an important factor that affects the runoff volume and magnitude 11, 5487–5513, 2014 and timing of the peak discharge. 5 Increase in settlements, industries, trading and roads due to rapid development of Bandar Lampung city has a dire consequence on flooding. To reduce the impact of Infiltration well to flooding, use of infiltration wells was investigated. Infiltration well is one of water con- reduce the impact of servation techniques which help reducing surface runoff and peak flow. Study about land use changes on infiltration well in indonesia was initiated by Sunjoto (1988). It was based on the con- flood peaks 10 cept of natural water balance as a part of hydrological cycle (Sunjoto, 1993, 1994). When the ground surface is permeable, some precipitation will infiltrate naturally and D. I. Kusumastuti et al. the rest as runoff along the ground surfaces. However, massive land use changes in recent times promote more runoff because much of ground area is covered by im- Title Page pervious layers such as roofs and pavements which prohibit water infiltration process. 15 Infiltration well will be ideal in this situation because collected water from roof and chan- Abstract Introduction nels can be directed to the wells for infiltration (Fig. 1). Some researches on infiltration Conclusions References well found that with appropriate well dimensions and numbers, it can reduce surface runoff significantly. Furthermore, the application of infiltration well support the policy of Tables Figures zero delta discharge which limits water discharge to drainage system (Arafat, 2008; 20 Iriani et al., 2013; Indriatmoko, 2013). J I Study area for this research is Way Kuala Garuntang catchment, one of the two major catchments in Bandar Lampung, has an area of 63.9 km2 and lies across the J I centre of the city (Fig. 2). The catchment experienced frequent flooding due to sig- Back Close nificant land use changes. This research will focus on how land use changes in the Full Screen / Esc 25 Way Kuala Garuntang catchment influence the hydrologic responses. The hydrologic analysis using rational method was applied on some land use change scenarios to see Printer-friendly Version the changes of peak flow of Way Kuala Garuntang catchment. Design rainfall intensity analysis was also carried out to support the rational method calculation in the begin- Interactive Discussion ning of hydrologic analysis. Finally, analysis of the impact of infiltration well in the Way 5490 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Kuala Garuntang catchment to reduce flood discharge was carried out. The aim of this study is (1) to define design rainfall intensity based on analysis of hourly temporal rain- HESSD fall pattern, (2) to predict the impact of land use changes on flood peaks, and (3) to 11, 5487–5513, 2014 predict the impact of infiltration well on flood peak reduction. Infiltration well to 5 2 Methodology reduce the impact of land use changes on Four scenarios of land use changes were applied on a simple rainfall–runoff model, us- flood peaks ing rational method to see the pattern of flood peak generated by the catchment. The study also concerns to the effort for flood reduction in Way Kuala Garuntang catchment D. I. Kusumastuti et al. by using infiltration well.