Emergency scenarios in the Banger polder, Semarang City: a case study to identify different emergency scenarios S. Imam Wahyudi a, *, Rick Heikoop b , Henny Pratiwi Adi a , Tom Overgaauw b , Bram Schipper b and Roel Persoon b a Sultan Agung Islamic University, Jl. Raya Kaligawe KM 4, Semarang 50112, Indonesia b Rotterdam University Applied Sciences, G.J. de Jonghweg 4-6, Rotterdam 3015 GG, The Netherlands *Corresponding author. E-mail: wahyudi@unissula.ac.id Abstract In Semarang urban coastal areas experience daily flooding from the sea during high tide (tidal flooding). Flourish- ing residential areas have changed into unhealthy slums with the nuisance of daily flooding in parts of the city. To overcome these problems a polder system was implemented to address the tidal flooding. The Semarang polder system is the first fully operational polder system in a densely populated urban area in Indonesia. This article describes the polder system that prevents flooding in the Eastern part of the city; the Banger polder area. An important element of the polder system is an emergency response plan that prepares for a flood emergency con- dition. The emergency response plan provides different emergency scenarios and identifies emergency levels and criteria. The management of emergency situations can be divided into four phases, namely mitigation, pre- paredness, response and recovery. The research results provide a detailed description of four emergency scenarios with 3 emergency levels for each scenario in the Banger polder area. The scenarios are; pumping stations operational damage, high-intensity rainfall in combination with high tide, failure of levees and dams, and an inflow of water from the west and east side of Polder system area. Key words: drainage, emergency response, flooding, floods, polder, scenario INTRODUCTION Land subsidence forms a serious threat for millions of people in the Northern Part of Java Island in Indonesia. As a result of land subsidence, several cities in Java like Semarang, Jakarta and Pekalongan are partially flooded during high tide. A polder system can be a solution to manage the water levels and protect residential areas. A fully operational polder system in a densely populated urban area is a new phenomenon in Semarang. The Banger Polder is a small polder system which covers an area of around 670 hectares. There are about 90,000 inhabitant living in this area. The Polder area is prone to flooding caused by high water levels during high tide and during heavy rain. This area is also facing land subsidence, with a typical rate of land subsidence in the range of 5 to 10 cm per year (Wahyudi et al. 2012a). Climate change which may result in sea level rise forms a serious daily threat for the coastal areas of Semarang that are located at sea level. A river embankment protects the Banger polder area from flooding caused by the influx of seawater during high tide in the Java Sea. The sea water then flows into the Banger River and the East Flood Canal. The flood protection consists of a levee along the East Flood Canal and the North levee for protection against high water levels in the Java Sea. Recently a dam in the Banger river was © IWA Publishing 2017 Water Practice & Technology Vol 12 No 3 638 doi: 10.2166/wpt.2017.067 Downloaded from https://iwaponline.com/wpt/article-pdf/12/3/638/380298/wpt0120638.pdf by guest on 12 June 2020