The farther water runs after it hits the ground, the less water there is.
If we collect water at the edge of a roof or street, we can collect about 80% of all the water that falls. If we wait until it runs down the streets to the Santa Cruz, less than 2% ends up as recharge. The rest evaporates and never does anybody any good.
One strategy we can use is to direct the street runoff of the 1st 1/2″ of any rain event into adjacent vacant lots and into in-street traffic calming devices like chicanes and traffic circles. This will capture about 2/3 of all rain and apply it directly into our urban food forest.
What remains (from large rainfalls) is about 1/3 of all rain. This can be captured and stored by means of dry-wells in Neighborhood Micro-Food Parks that could dot Tucson’s neighborhoods by the thousands. This would be similar to the thousands of dry-wells and retention basins that are used in Chandler to capture about 4000 acre-feet per year.