After heavy rain I was experiencing flooding in my basement. It appeared to be coming from under the shower pan so I took a crowbar to the pan and this is what I found underneath! What's happening is that the water level under the concrete slab in my basement is rising until the point that it reaches the top of this hole and overflows. I am taking steps outside the house to divert water away, but was wondering if I should fill this hole with concrete, or whether it should be left open for any reason (e.g. future maintenance )? I look forward to hearing your thoughts. Thanks!