Going bananas over water quality in Orange County

September 8, 2009 § 2 Comments

This just in.

Yesterday I was bemoaning the Los Angeles Regional Water Quality Control Board for their failure to complete their review of a 401 Permit application from the County of LA, leading to it being approved by default.

And here’s what happened when a full review was completed.  Down in Orange County, the Santa Ana Regional Water Quality Control Board approved the County of Orange’s stormwater discharge permit (a MS-4 in Clean Water Act jargon).  They determined that new development must retain 100% of stormwater runoff (from a 2-year storm) if the stormwater will flow into a natural stream.  Good good, yes?  The conventional wisdom is a big yes.  Development increases rates of runoff and stream velocities, so retaining the 2-year storm will reduce this.  It also keeps urban non-point source pollutants (car oil drippings and doggie doo, for example) out of the streams.  But I wonder, will it also starve the stream of the low flows they need to maintain channel form?  Would there be a way to allow runoff that mimicked the pre-development condition? I realize that my scientist buddies will point out that in developed areas, streams tend to be “starved” of sediment so a reduction in runoff wouldn’t affect them.  Yet I have seen that urban streams, given enough time and an absence of new disturbances, often do tend to adjust their channels to a geometry (width and depth of stream) suited to the available sediment they receive.  Will we be starving them anew, not only of sediment now, but also the frequent storms that prevent channels from getting silted up, keep emergent wetland vegetation from colonizing and taking over?  I know we need to get urban pollutants out of the water, but some consideration for how a stream functions from the standpoint of its channel-forming processes also is needed to sustain habitat.

OK, so that’s just me being troublesome and thinking out loud and probably out of turn – isn’t that what blogs are for?  But here’s the next part.

New development that would drain into an engineered channel (hello, ex-creeks everywhere in the OC) are exempt from this requirement.  In other words, any incentive to restore these former streams has just been yanked off the table.  And what’s to ensure that this doesn’t get abused, turned on its head as an incentive to lay streams in concrete?

After all, the California Environmental Quality Act won’t outright ban it.  So who will?

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§ 2 Responses to Going bananas over water quality in Orange County

  • Hi Jessica,

    When they are storing the 2 year storm are they talking about storage in rainwater tanks or a detention/raingarden setup for slow release back into the creek?

    I agree that there needs to be more thought into the impacts of new stormwater urban design controls on stream geomorph, especially with the higher urban sed loads matching the high peaked hydrograph.

    But I wonder what percentage of your catchment is going to be affected by these new conditions compared to the rest of the old developments that are just gunna let that 2yr event fly straight down the channel? Would be cool to have an analysis that could say “at X percent of the catchment coverned by the new development regs are gunna have X effect on the flow velocity in channel” with an idea of sediment loads you could work out at what point you expect to start seeing higher sediment deposition in channel (there’s probably a PhD in it for someone keen enough).

    I think your point about channelled streams being considered exempt is very worrying. Even if it isn’t used as a reason to concrete, the only hope for these poor stream’s rehab is if planning instruments start treating them as such.

    • Jessica Hall says:

      Hi Phil, I don’t think they are prescribing how the water is retained, but they are encouraging Low Impact Development standards. I don’t know how release would be designed.

      Yes I think there is a PhD in there – too bad I’m not a fluvial geomorphologist! (never too late, tho’!)

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