The Dutch Lower Rhine Delta, a transitional area between the Rivers Rhine, Meuse and the North Sea, is at risk of flooding induced by infrequent events of storm surges or fluvial floods, or the combination of both. To protect the delta from storm surges, it can be closed off from the sea by large dams and controllable storm surge barriers. Also, along the branches of the rivers controllable floodgates are operated to regulate the fluvial discharge. A former study quantified the flood frequency derived from three different sources that potentially may cause a flood and indicated that high water levels was mainly caused by the simultaneous occurrence of storm surges and Rhine floods. In the present water operational management system, the Haringvliet gates and the Maeslant Storm Surge Barrier with the Hartel Storm Surge Barrier should be closed in time when the simultaneous extreme event occurs, and therefore the extreme fluvial flow that accumulates during the closure would result in a very high water level within the delta area. Moreover, this frequency will increase significantly in the context of climate change. As a suggested adaptation measure, a controllable floodgate is proposed in Pannerdensch Canal and the other three floodgates in Merwede, Drechtse Kil and Spui are designed in the East and South of Rotterdam and Dordrecht. These floodgates are expected to decrease the potential extreme water levels which are driven by the simultaneous extreme events. This study will investigate the operational management of these four gates, and further apply a large number of scenarios of the simultaneous extreme event to estimate the effect on the flood frequency in the delta. The results can assist to make better decisions in the adaptation of the present operational water management system.