Benefits of Stormwater 2

[CJWE]

I have been referencing eng-tips.com for a while but have never posted. I don't do a lot of environmental but when I do, I can't help but wonder if all these efforts make a difference. Are there any conclusive studies that illustrate that stormwater efforts are making a substantial impact on our environment?

 

[cvg]

what efforts? storm drains? or stormwater retention? or SWPPP? or first flush requirements? perhaps some other BMP?

 

[CJWE]

When a land owner or developer looks to develop a property, and he is told of the environmental requirements that will need to be met (stormwater retention/detention, sediment control, infiltration, water quality) they usually start grumbling about it being hocus pocus. Sometimes I can't help but to agree. So I would like to satisfy myself and be able to pass on the positive impact.

 

[IRstuff]

Have you been on the original Universal Studios tour ride with the vaguely south of the border town and the flash flood? Where do these owners think the rainwater should go? Raging Waters thrill ride into their neighbors' properties? Or vice versa? What do they think will happen if they suck out all the groundwater and not replace it?

I don't get why there's even a doubt that there are real and tangible benefits.

TTFN
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[bimr]

If you investigate older sections of municipalities, you can observe problems caused by the lack of the requirements. People formerly located in flood areas, there is poor drainage that causes street flooding, drainage canals fill up with sediment, etc.

In my older neighborhood, the Village actually bought properties that frequently flooded and then built stormwater retention basins.

 

[cvg]

sure, retention basins capture a lot of sediment as well as hydrocarbons and other nasty stuff. preventing the sediment and trash from ending up in waterways is a benefit. It could be argued however that prior to development, natural conditions might have resulted in more sediment in the river than after development. that upsets the natural equilibrium, might result in increased degradation. Hydrocarbons end up in the retention basin and then soak into the ground, not much benefit there. drywells in the basin allow the nasty water to infiltrate even faster. bleedoff lines allow it to drain back to a watercourse. when do the retention basins ever get cleaned out? Allowing vegetation to grow in basins would be a good mitigation effort, but that usually doesn't happen. bioswales are great, but only for very low flows. Pervious pavement works for a while but then usually plugs up, it never gets maintained. Storm drains help to maintain roadways and prevent some minor flooding, but increase peak flows downstream. Silt fences typically work until a big storm and then they concentrate flow and cause erosion. same with wattles. I have seen more failed riprap than I can shake a stick at.

 

[CJWE]

cvg...those great points. I asked the regulatory agency if there is a program in place to ensure these facilities are taken care of and the answer was no. It is basically the honor system which means there will not be any maintenance. I get there should be no question as to the benefits, but as engineers we are taught to verify with numbers. So are there studies that exist that show ground water is in fact being recharged or that flooding will soon be just a memory?

 

[IRstuff]

Here's a brochure that describes Orange County's groundwater replenishment system

TTFN
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[racookpe1978]

One unsung benefit of the ages-old practice of cross-connecting street gutter storm drains with the sewer system pipes is that irregularly flushes the trapped scum and residue from in the sewer system out.

It puts it in the drained water - often leading to surface disposal, but at least it gets it out of the pipes. 8<)

San Francisco has several areas in downtown now flooding with raw sewage from pipes backing up due to low flow toilets: There is not enough water in each flush to push the waste solids down the pipes to the larger drains.

 

[bimr]

CJWE,

The storm water programs did not come out of a vacuum. The programs were recreated to address existing problems. You can argue that the programs do not address the problem, but not that a problem does not exist.

 

[darthsoilsguy2]

Maintenance of stormwater measures is not just the honor system. There is a long history of property damage cases to choose from where the property owner's negligence in maintaining their BMPs contributed to off-site damage.... in addition to damages to the property owned on the property.

IMHO Recharge is the weakest of the requirements with regards to showing the benefits. (treatment, channel protection, recharge, overbank flood, extreme flood... or at least in my state). If i were a regulator, recharge would be the only one i would be willing to allow concessions. The other 4 treatment requirements are much easier to demonstrate the merits of.

 

[Spartan5]

darthsoilsguy2: Recharge is important as it relates to the ecological health of waterways and wetlands; being that the ground water table elevation has a strong influence on baseflow and the extent and function of the wetlands. If there are no waterways or wetlands, and no one is relying on groundwater as a water supply, recharge is less critical, sure. But even absent those things, it does help mitigate the pollutants in the "first flush" and allows for some physical and biological processes to work on them.

Of course, a healthy water table and wetlands are detrimental to what we are trying to accomplish with development. Those bioswales, micro-bioretentions, green roofs, wet ponds, stormceptors etc. are expensive liabilities as well; not assets. Far better for the developer to put more parking spots or square footage in those places from their standpoint.

But that's what stormwater management is. A way to try to strike some sort of balance on a site between the profit a developer can squeeze from a site and the negative externalities associated with turning it into our habitat instead of Mother Nature's. Absent that balance, all you'd get is acres of asphalt shedding hot, dirty water at rates unsustainable by the watercourses they discharge into to. Sure, you'd get some turfgrass here and there, and a few ornamental trees to make it look nice. But that's it.

So, CJWE, it is too bad there is not a requirement for maintenance in your area; or inspections for that matter. It was the "honor system" that used to get us acres of asphalt (poor planning requirements contributed no doubt). SWM regulations are the first part of fixing that. I'm sure they were fought tooth and nail by those who harvested the fruits of negative externalities as profit. And I'd wager that they plowed a lot of that profit into fighting against maintenance requirements as well. There's not too much money to be had in protecting the environment vs. paving it so it's not quite a fair fight. But like other municipalities with a maintenance requirement, yours will get there some day. Maybe. Hopefully.

[/soapbox]

 

[darthsoilsguy2]

i was speaking more to the way Recharge is handled in practice. i don't disagree with the general overview spartan gave. Although i would like to state that my point was that planned Recharge measures are the least critical to the other 4 elements i named, regardless of the presence of streams/wetlands and wells. i see a lot more potential for environmental/property damage in the other 4.

on a side note....in Vermont USA, i'm not allowed to infiltrate first flush or any polluted stormwater to meet "Recharge" requirements. Water destined for recharge has to be routed first through a treatment element, then we can claim it to be suitable water for groundwater injection. seems like the result is a bunch of civil egrs putting grass swales between their wet ponds and the wetland/stream discharge pts, all while covering their ears if someone says "hey, do you think that region might already be close to saturated and not really want to take more water?"

 

[beej67]

There are huge, very well documented benefits to recharge. Groundwater table health. Base flow in streams. Increased habitat. Reductions in stream erosion. Water quality.

There is very little documentation for the *real* benefits of slapping an oil grit separator at the end of the pipe that catches a parking lot. That method of "stormwater treatment" is mostly founded on a correlation (impervious area > TSS) for which causality was never proven. In truth, when you pave a watershed, the TSS you see in streams doesn't come from the parking lots, it comes from increased bed and bank erosion due to a lowered water table, less base flow, and increased event flow.

Don't tell a proprietary BMP manufacturer that. Or do, but do it nicely, and recommend they get into the recharge game.

The benefits of detention ponds, as opposed to regional flood control ponds, have been debated. And there are compelling arguments on both sides.

Just my 0.02.



Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[CJWE]

beej67...would you please give reference to the very well documented items?

 

[darthsoilsguy2]

now to be fair.... oil/grit separators are generally considered pre-treatment by most permitting authorities. i don't think anybody is saying those things provide anywhere near the treatment of a wet pond with/without a detention structure. the more appropriate comparison metaphor would be choosing between a large detention/infiltration pond which infiltrates a portion of the flow and the rest discharges without treatment vs a large detention/wet pond which can't claim infiltration but does an excellent job at treating solids and phosphorous. i'm not sure about 'regional flood control ponds' since the name doesn't intrinsically exclude detention ponds (or at least to me, probably a regional nomenclature thing).

not trying to hijack with a debate about recharge in general being a good thing. the point i was making is about how Recharge-points play out in the design/permitting process and the ability to relate that to Owners.

 

[bimr]

Here is a benefit. Lack of road closures during storms.

 

[beej67]

beej67...would you please give reference to the very well documented items?

I did some masters degree research on the effects of permeable pavements on urban watersheds. Here's a few references I used:

Quantity/Quality research from England:

http://www.sciencedirect.com/science/article/pii/027312239500539Y

http://www.iwaponline.com/wst/02108/wst021080769.htm

Really impressive research from Japan: (esp 2nd and 4th link)

http://www.sciencedirect.com/science/article/pii/S0273122397005672

http://www.sciencedirect.com/science/article/pii/027312239500534T

http://www.iwaponline.com/wst/02901/wst029010255.htm

http://www.researchgate.net/publication/246466061_Infiltration_structures_in_Tokyo

There's more, including some stuff stateside, but I didn't have time to go through my entire research folder. The Japan studies, particular the 2nd and 4th link, were very impressive. In one town, they replaced all the streets with porous pavement, replaced the pipes with perforated RCPs, and tied the base stone of the road into the base stone of the pipes. The runoff from their infrastructure went down to almost zero for any event under the 1 year storm, and creeks that had dried up 30 years prior due to urbanization reappeared in (clean) base flow conditions.

When we had our big drought here in the southeast in the 2000s, several county regulators I spoke to said the only healthy creeks we had left were ones near subdivisions on septic, because of the groundwater recharge.

The water management districts in Florida have been doing first flush capture/infiltration for many decades, and have quite a lot of data on it. If you've got half a day to kill, check out the Harper study:

http://www.dep.state.fl.us/water/nonpoint/docs/nonpoint/SW_TreatmentReportFinal_71907.pdf

It's fantastic, and very detailed. I don't think it's based on enough data to truly draw the conclusions they drew, but it's about as good an attempt at actually quantifying the real benefits of different kinds of BMPs that I've seen. Not just infiltration BMPs either - wet ponds, dry detention ponds, etc. And not just for TSS, they also look at phosphorus and nitrogen.

now to be fair.... oil/grit separators are generally considered pre-treatment by most permitting authorities. i don't think anybody is saying those things provide anywhere near the treatment of a wet pond with/without a detention structure.

There are plenty of proprietary BMPs rated for 80% TSS removal, and are used in many high density urban stormwater applications. I've used them as our only water quality measure in different cities within different states down here in EPA Region 4. And their ratings aren't a lie. And they also do a great job with pollutants that aren't TSS. I think they have their place, but in much of Region 4 the surrogate pollutant of concern is TSS, regardless of whatever the basin TMDL might say, so the (false) acting premise for the past decade and a half has been to "stop the TSS from getting into the stream from the parking lot." Which is nonsense, but that's how the regulatory bodies approached the problem. They're only now starting to see their error, that although other pollutants may be coming from the parking lot, the TSS isn't.

The TSS is a result of changes in stream morphology. But the framework of the Clean Water Act makes it very difficult to enforce a limit on a pollutant that originates in the stream itself. You'd have to label the increase in water volume the actual pollutant. And unless I'm misremembering, the EPA tried that recently in in Virginia and it was struck down in court. Maybe someone can google it. I remember seeing it on LinkedIn.



Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[darthsoilsguy2]

well, all i can say is oil/grit separation is not "treatment" in Vermont or Mass. No phosphorous removal = No treatment. Old urban stormwater systems are not the example of how the permitting rules are written, they are the reason why they are written. i gather from the 2nd post of the OP, we are discussing larger sites with lots of new impervious which triggers state review of operational stormwater system. Those sites tend to be outside of urban areas for obvious reasons. Rules tend to be very favorable to the designer for urban settings because the damage is usually already done and the land owner is grandfathered in. If the existing conditions are mostly hardscape, then the design doesn't need to consider much recharge because there is nothing to offset. Also, if the existing urban hardscaped site discharges into the local storm sewer, then the land gets to continue that discharge. Perhaps a requirement is added to throw a device like an oil/grit separator in the works, but i'm not going to assume anybody thinks the town sewer is carrying treated stormwater because of them.

on a side note, i saw a lot of permeable pavements references there. Those materials are still gaining traction in permitting rules. Much of our land use rules center around impervious surfaces and perv surfaces are a bit of a monkey wrench. Although there are benefits to pervious surfaces, there are many who are hesitant about it because much of the land use rules are tied to impervious surfaces not for water quality but for development constraints. Pervious surfaces look like impervious surfaces and people really want to see green pervious surfaces.

 

[Matewan]

Probably the best "big picture" viewpoint on stormwater detention that I have seen, comes from the book "Handbook of Hydrology" (edited by David Maidment):

"Limiting hydrograph peaks from a single design storm, or even two or three design storms at an individual development site does not address the consequences of the increases in the runoff volume....Nevertheless, on-site detention will continue to be used.

One should not conclude that use of on-site detention is poor policy. It is not. On-site detention can be beneficial when used properly, and it does help mitigate some of the impacts of urbanization. It is the easiest way for a local authority to implement runoff controls for new development sites, since on-site detention is financed by the land developer. From a political perspective, a city or county can point to its on-site detention policy as evidence that it requires new development to control increases in runoff from the site. This can provide a defense, albeit not a perfect one, against claims resulting from increased flooding or environmental damages that may be occurring downstream."

I remind myself of this excerpt every time that I have to design a detention or water quality system that doesn't seem to make much sense. Like so many things in life, it is an imperfect solution.