13,000 gallons of water would be quite a flood if something were to breach such a water fence. Perhaps a falling fir tree or an earthquake would do it. Even a small leak would be a disaster because how do you plug such a leak?
Interesting idea.
It rather depends on the size and shape of the hole and the material the tank is made of.
But for a round hole there are any variety of expansion plugs.
For other shape small holes they make putty that solidifies when exposed to water.
Large holes you most likely would just have to wait until the tank is empty.
But this tank could be constructed by connecting a number of smaller tanks with PVC ball valve between them. In the event of a leaks you could close the connecting ball valves until the leaking tank was repaired.