Couple of questions on this one:
1) Are you aware that the activated ability of Trident // Poseidon is called tsunami?
2) Does the clause about extra damage trigger when trident // poseidon is used?
This does bear a slight resemblance to dry spell and desiccation, and might arguably be better than those, depending on whether you value the extra quanta or the extra damage more. (and the fact that the upped one damages your own creatures, whereas desiccation does not)