There has apparently been much talk of low-impact development (LID) standards in the Los Angeles area recently and now their public works board is calling for a new requirement that 100% of runoff from a 3/4 inch storm must be contained on-site on all new developments and some redevelopments. The plans are detailed in an LA Times article here.
Tucson has a rainwater harvesting ordinance that is aimed primarily at collecting rainwater to replace use of potable water for on-site landscape irrigation, but also has incidental effects of reducing off-drainage of stormwater. The LA proposal is strictly aimed at realization of benefits from reduced runoff.
In some respects, the LA proposal is much stricter than Tucson's ordinance because it requires containment of all water produced by a 3/4 inch rainstorm, while the Tucson ordinance requires using on-site generated rainwater for at least 50% of on-site landscaping irrigation. Tucson does have regulations about managing runoff generated by property development - and these have resulted in a few recent developments around town that manage stormwater on-site to avoid costly mitigation of runoff effects - but in most cases there is infrastructure in place to handle some or most runoff from developed property.
If LA successfully implements this change it could prove difficult to comply with. As the story notes, in some locations getting the runoff to infiltrate into the soil will be a real challenge. And a 3/4 inch rain might occur over 30 minutes or over 36 hours - with the amount of runoff generated varying greatly between the two. This definitely changes the type of development you do - how much of a lot is built on, use of underground parking (if storage of runoff is necessary) - it could get costly. As this is just a proposal at this point it will undoubtedly undergo some changes before implementation. But should be interesting to keep an eye on it.
h/t to Aquafornia for bringing the Times article to my attention.