Question: Water flow dynamics in Pompeii

A student question I am unable to answer ... Can anyone else help?

How did rainwater and water from the overflows behave in the streets? Were there structural attempts to keep flowing water from developing into torrents? For example, how could water coming down Via del Mercurio into Via del Foro be kept from flooding the forum proper before slamming into the three administrative buildings at its southern end? Or if in the forum, how could it be channeled out? Or was this never a problem? Has anybody ever studied the dynamics of water in the streets? Do you know of a diagram or map which would allow for a visual impression of the gradients in the city?