When we first moved to Albuquerque 15 years ago, we lived in an apartment in the northeast heights right behind a Wal-Mart. On the south end of the Wal-Mart parking lot was a depression dug into the ground and lined with river rocks. A couple of trees – I think Russian olive – were growing in it.
Over time, I noticed similar constructions at other shopping centers and developments, and assumed their purpose was to catch runoff from summer storms, adding bits of capacity here and there to the flood control system of this paved metropolis, with no bare earth left any more for water to soak in. These little hollows are gross, the rocks stained with the black crud – motor oil, ground-up lead from wheel weights and the like – that builds up in our urban environment. There’s no chance of groundwater recharge here. The aquifer is far too deep for that to happen. It’s just an ugly mess.
That came to mind this afternoon when I ran across a discussion of the way the Maya handled this:
The Maya paved plazas and courtyards and canted these catchment surfaces toward the elevated reservoirs where water was collected and held for extended periods. In short, the city planners designed their cities to be watersheds…. (T)he plazas and other catchment zones are always free of trash middens containing food or human waste, as for example, the whole of the Central Acropolis at Tikal. It would appear that any waste that was produced in the catchment areas was carefully collected so that it did not enter the water system and foul the water.
We’re not quite so careful here.
 The Great Maya Droughts, Richardson Gill, University of New Mexico Press, 2000, P. 263-264