I have a very simple suggestion, no need to beat around the bush.
Just ask those in charge what are the studies, if any, done on measuring the min/max/avg inflow and outflow rates before and after the construction of MB. These figures will tell you whether the MB is able to handle the heavy rains. If there were no studies done, then you can ask them to commit harakiri.
I will bet you they will most likely be scratching their heads. Why? Because those idiots will never dare to suggest that they conduct the studies over years in order to be able measure the min/max/avg values with some confidence. In SG, when the green light is given, it is a rush job from start to end with no questions asked.