Wave Run-up of a Possible Anak-Krakatau Tsunami on Planned and Optimized Jakarta Sea Dike M.R. Badriana 1,a) , H. Bachtiar 2,b) , D. Adytia 1,c) , L. Sembiring 2,d) , Andonowati 1,e) , and E. van Groesen 1,f) 1 LabMath-Indonesia, Jl. Dago Giri 99, Bandung 2 Balai Litbang Pantai, PUSLITBANG-SDA, Kementerian PUPR, Jl. Musi-Buleleng, Bali a) riambadriana@gmail.com; b) huda.bachtiar@gmail.com; c) didit@labmath-indonesia.org; d) leo.sembiring@gmail.com; e) Corresponding author: andonowati@labmath-indonesia.org; f) groesen@labmath-indonesia.org Abstract. The infrastructural plans in the Jakarta Bay to reduce risks of flooding in Jakarta city comprise a large Sea Dike that encloses a retention lake. Part of the planned dike has the shape of the iconic Garuda bird. This paper shows that if in the future an explosion of Anak Krakatau will occur with strength 1/4 th of the original Karkatau 1883 explosion, wave crests of 11m and troughs of 6m may collide against the bird’s head. As an alternative example, a more optimized design of the dike is constructed that reduces the maximal wave effects considerably. INTRODUCTION Indonesia’s capital city Jakarta suffers from regular floodings, caused by soil inclination, increased run-off from the Bogor region and rising sea level. The ‘National Capital Integrated Coastal Development’ (NCICD) programme [1] is being designed to prevent Jakarta from future flooding. In the so-called “phase B” of that programme, an outer sea dike is being considered to be built in the Jakarta Bay (JB). This dike will create a retention area, with a water level that is controllable by large pumping devices so that the maximal expected run-off water from the Jakarta main land can be accommodated. The present design of this ‘giant sea wall’ contains a part that will be the northern boundary of a reclamation lake in the form of the ‘Garuda’, the bird that is the national symbol of Indonesia. Looking in the northerly direction towards the Java Sea, the wings of the bird form a convex shaped curved dike, with in the middle the bird’s head that may accommodate a planned business centre [1]. The water levels in the JB are under normal circumstances well known and rather modest, with significant wave height less than 2m, and the semi-diurnal tidal range of 1m; occasional storm surges from (local winds induced by) cyclones in the South China Sea are less than 1m. Hence, modern design techniques and constructions will be sufficient to construct dikes that can withstand these water heights, also when including expected sea level rise (less than 1m until the end of the century) and somewhat larger wave heights from climate change. [1] For large infrastructural works that should last for centuries, in a seismic active country as Indonesia, it is necessary to take effects of future earthquakes and possible resulting tsunamis into account. There are two reasonable sources that could lead to significant tsunami waves in the JB. One is a tsunami generated by tectonic motion, a tsunamigenic earthquake along the subduction zone in the Indian Ocean which could propagate waves into the Sunda Strait that diffract into the Java Sea and from there into the JB, see [1] for a preliminary study.