i see you are using modded minecraft try these
Buildcraft flood gate, is the best for survival
worldedit is best for creative
and yes world edit is aviable for forge so you can use it without a server
EDIT: oh my bad i forgot to tell you about unfilling
if you have the BC pump configured to actually consume water it may work but i don't know of any pump that can unfill a dock that large faster than water can repleinish itself so that may be tricky in survival
fillin and unfilling the water isnt a problem makeing a gate that will go up and down is my issue sorry for not being specific lol when i said fill /unfill i was refering the the way the /fill with command blocks will fill the spot a gate would with hard blocks and the refill them with air set with another command block.but you cant do this in 1.7.10 (that i know of) so i was looking for any kind of alternative....
tried frame motors also they would be awsome for this..... but they just bug out and the frame blocks break against any water.....