Fenomena urbanisasi yang terjadi di kota-kota besar mengakibatkan peningkatan kebutuhan ruang kota, sehingga menyebabkan keterbatasan sumber daya lahan yang berakibat pada alih fungsi lahan dari yang tak terbangun menjadi terbangun. Hal ini berdampakan pada peningkatan alrian permukaan sehingga dapat menyebabkan banjir. Untuk mendapatkan langkah-langkah yang tepat dalam mengatasi banjir di perkotaan, perlu adanya identifikasi sifat-sifat DAS di perkotaan. Oleh karena itu penelitian ini bertujuan untuk mengetahui kondisi hidrologi DAS Kedurus. Metode analisis yang digunakan untuk mencapai tujuan tersebut adalah analisis hidrologi menggunakan model SWAT. Hasil penelitian menunjukkan bahwa DAS Kedurus yang terbagi menjadi 27 sub-DAS, mengalami banjir pada 12 Sub-DAS. Debit simulasi tertinggi terjadi pada 15 Maret 2016 yaitu sebesar 15,59 m 3 /s. Volume luapan yang terjadi di DAS Kedurus adalah sebesar 546.797,53 m 3 .

Purpose This paper aims to advance the idea of sustainable flood reduction. Flood reduction through the use of the drainage system is considered an unsustainable approach that decreases the use of water. In contrast, the Water Sensitive City is a sustainable concept aimed at increasing the value of water for human needs and reduce flooding. Design/methodology/approach The current approach of relying on drainage systems is ineffective and must be combined with green infrastructures to reduce flooding. Green infrastructures can increase infiltration rates or facilitate rain harvesting. The study developed four scenarios that combine green and grey infrastructures and used the Soil and Water Assessment Tool (SWAT) model to select the most effective scenario based on the remaining amount of flood volume in every scenario. Findings Green infrastructures that are related to increased infiltration and rain-harvesting instruments reduced flooding by 22.3 and 27.7 per cent, respectively. Furthermore, a combination of the two types of green infrastructures reduced flooding up to 45.5 per cent. Conversely, applying only grey infrastructures (by increasing drainage capacity) to reduce the flooding to zero is unfeasible, as this requires more than double the current capacity. Therefore, a combination of green and grey infrastructures can significantly reduce flooding in a water sensitive and feasible manner. Originality/value Applying a combination of green and grey infrastructures is a new and effective approach to reduce flooding in the Kedurus Catchment Area.

The rapid growth population phenomenon has causes excessive land demand for residential and economic activity. Moreover, the rapid urbanization also increases the contribution of land constrains. Land conversion from conservation to cultivation uses affects the surface runoff volume that leads to flooding. According to these problems, it is necessary to take steps to control flood in Kedurus Watershed. One of the proper urban development concept is the Water Sensitive City (WSC). The protection against flood in WSC can be accomplished with the land use arrangement that can reduces the surface runoff. The aim of this research is to determine the proper land use scenario to reduce floods in Kedurus Watershed. In order to reach this aim, the writer uses sensitivity analysis to identify the proper land use scenario to be applied in the watershed and SWAT to select the best scenario. The efforts to reduce flood through the land use scenario (scenario 2) could reduce the flood volume by 44,320.32 m3 or 8.11% of the total volume of flood in the area. The average reduction of flood volume in each sub basins is 12,92% and the highest number of reduction is 65,67% (sub basin 22).

This article discusses the reliability of flood inundation information that is obtained from participatory mapping. The commonly applied method to map flood inundation requires both direct and interpretive measurement data based on remote sensing images. Such assessments have limited availability of data; as a result, participatory mapping has become the solution. A number of studies have conducted participatory mapping to obtain flood hazard information in areas with limited sources of data, however, there has been little discussion about its reliability. This research conducted participatory flood inundation mapping by involving local leaders as respondents. The mental map drawn by the local leaders was digitised to obtain a shapefile format map. The information obtained from the semistructured interview was then included in the geographic information system (GIS) data as attributes. The obtained information was compared with the field data to determine its quality. A literature study was then conducted to discuss how the participatory mapping could support managing a disaster. Information obtained through participatory mapping can be effectively applied to disaster management because of its precise location information, lower cost and less time-consuming nature. The reliability of the information has weak accuracy of quantitative data; however, it has advantages in terms of qualitative data, especially in the detailed descriptions of flood information. In the future, participatory mapping should rely on integrating the perspectives of cross-disciplinary researchers, a comprehensive study of multidisciplinary knowledge and level of understanding of the stakeholders.

Spatial plans are key instruments in directing future developments and reducing a city's flash flood risk. This study conducts a surface runoff simulation using SWAT analysis in the Kedurus catchment area. SWAT analysis is a hydrological analysis to measure surface runoff from precipitation with consideration of land uses, soil types, climatic data, topography and related infrastructure systems. Based on the simulation, four sub-catchment areas are currently experiencing flash flooding. Surabaya's detailed spatial plan (RDTR) could reduce the total flood volume in the city by fifty-one per cent if all measures (drainage and other infrastructures) in the plan are implemented successfully. Nevertheless, the implementation of the measures is still questionable due to limited budget and land acquisition. In the case of plan failure, the planned developments will cause higher surface runoff, putting Surabaya is at higher risk of flooding. Therefore, Surabaya needs to diversify its flash flood risk reduction approach to ensure that the plan will achieve a low-risk city in the future.