Pervious paving

[fringe]

I've been handed a design by a civil engineer for a little parking lot.

It is to ameliorate a severe parking deficit on an adjacent parcel where the greedy developer crammed too much building onto too little space.

His "design" calls for removal of topsoil to a depth of four to five inches and installation of #57 crushed stone to like depth, with parking spaces defined by re-bar anchored landscape timbers. He says it is "pervious paving."

I still can't believe he turned this in for my review with a straight face. Officially I can't start my review until city clerk is compensated for a bad check from the developer.

My search of this forum brought up the first, obvious objection of accessibility.

Has anyone here seen such a goofy design?

[Random Traffic Guy]

It is to ameliorate a severe parking deficit on an adjacent parcel where the greedy developer crammed too much building onto too little space.

I think you misspelled "Built to the finest new urbanist standards"

Anyways, I have seen parking lots like that (or at least gravel divided by railroad ties, unknown depth), I can't remember where but they seemed to work fine. There are certainly more modern pervious methods available now. In a rural context is is better than a dirt lot or plain gravel.

Can't comment on the accessibility stuff since I think that stuff should be the owner's choice anyways

[Richi]

Not uncommon around here. Seem to work ok as long as the stone is angular. Round "river pebbles" won't lock together and then spread out. If the parking lot is used a lot (many ins and outs each day) there may be issues with rutting.

[Gatrgal93]

Jacksonville allows a degree of pervious parking lots ("stabilized surfaces"), but our code forces you to account for ADA accessibility by requiring handicap parking to be paved with the appropriate dimensions and access aisle, as well as the provision of sidewalks with ADA accessible ramps to the front entrance of the building that the parking lot serves. I think we only allow this by a percentage of the overall lot (something like 20 percent), but I've noticed at least one redevelopment project close to where I live that they allowed the entire lot to be stabilized surface/pervious (it is covered with mulch), and only the handicap space is impervious (in this case, it is concrete) with the required sidewalk connection, and van aisle. If I'm remembering correctly, the Fire Marshal requires that the stabilized surface be capable of supporting the weight of a fire truck.

Our code also requires that landscaping, buffers/yards, etc. are still in place as normally required. Basically, there are provisions for pervious parking in our code, but there are limits and it still has to be accessible, as well as meet other ancillary code requirements such as landscaping and stormwater management/drainage.

(By the way, the Water Management Districts would also want to review that plan to ensure conformance with their requirements. I believe gravel and crushed concrete are considered semi-pervious surfaces and thus they get viewed differently for the purposes of drainage.)

[beach_bum]

If you have Clay soils, gravel or other methods such as pavers do not help with decreasing impervious surfaces. I believe that ADA requires that its parking spaces be paved with concrete or asphalt or something more stable. In my experience gravel lots tend to erode quickly unless they are meticulously maintained by the owner/developer. It has also been my experience that they never maintain their gravel parking lots

[JimPlans]

If there is at least some parking on the "greedy developer's" property, that could be designated for handicapped use, and the gravel lot could be for everyone else. I agree with others that a gravel lot by itself is probably not ADA compliant.

I assume that the owner needs to build a pervious surface lot because there are land availability constrictions that would preclude building an impervious lot with a traditional detention pond? Are there issues with installing underground detention? Or is the lot owner looking for the cheapest way to build a lot and trying to avoid paying for all of the drainage infrastructure (dingdingding)?

If this is an "el cheapo" situation and a pervious system is necessary, I would doubt that the lot owner would put in the maintinence effort needed to maintain an impervious asphalt or concrete surface, like vacuuming. Then you have a clogged impervious surface, i.e. an impervious surface, with all of the attendant run-off issues. They could do pavers, but gravel is probably much more pervious.

If you don't have any regs that mandate materials for parking lot surfaces in this zone, then mabe the gravel is ok (as long as the soil below it perks properly).

[fringe]

I appreciate all the replies. I will post more as this story unfolds.

[mike gurnee]

Crushed rock usually makes a poor pervious surface. I silts up from above and below. It can be acceptable with a membrane underlayment and periodic cleaning. I doubt that your developer has this in mind. As for ADA, those designated spaces need to be accessible--not crushed rock.

[Seana]

His "design" calls for removal of topsoil to a depth of four to five inches and installation of #57 crushed stone to like depth, with parking spaces defined by re-bar anchored landscape timbers. He says it is "pervious paving."

Is he trying to pass off five inches of crushed stone--nothing more--as "pervious paving"? Years ago that could be called "pervious paving," but not anymore. (At least in the U.S.)

As an example, the State of New Jersey's Standard for Pervious Paving Systems:
http://www.state.nj.us/dep/watershed...OCS/Paving.PDF
Figure 3 on page 115 ^^here shows the minimum number of material layers involved in pervious paving. This picture is worth thousands of words.


.

[fringe]

Muchas gracias Seana.

To answer your question, I think yes is the answer. This is maximo cheapo thinking. There are design professionals around here that stamp whatever comes across the desk with some cash attached, it appears.

This one I think will try to sell this method as "newthink" or "de-la-moda", as our county and others in the area have warmed to the idea of pervious surfaces to slow down stormwater runoff.

[Cardinal]

This is a gravel lot and nothing more. The question is whether your code allows gravel lots or requires pavement. If you do require pavement then your recommendation is obvious and hopefully the plan commission has a good nose to smell when the developer lays this BS in front of them. If you do allow gravel lots then I think you need to estblish whether the lot is justified by the amount of expected traffic. If it is only reqiured by ordinance and there are few cars that will ever use it, then perhaps it is acceptable. If it will be getting daily use then I think there are many reasons to deny it, from the questions of whether it will hold up or be maintained over time, to issues of rutting, mud, puddles, weeds, and other impediments cars and the people walking to/from them will have to deal with.

[Gedunker]

Our stormwater board assesses fees for gravel parking areas and circulation the same as concrete, asphalt, or any other hard surface.

[fringe]

Here's the latest on this design.

I e-mailed a prof in the neighboring county who "wrote the book" on porous paving, as follows:



Mr. Ferguson:

I am in charge of zoning admin/bldg inspection for Comer, a small town NE of Athens.

I've been given a plan for review by a local civil engineer for a small parking lot adjacent to a seriously underparked commercial development.

Less than a third of an acre, with approx three feet of fall in 125 feet, the designer calls for removal of the top four inches and replacement to same depth with #57 crushed stone. Parking spaces delineated by treated crossties at head end and "treated landscape timbers" at edges, all anchored by rebar.

He is calling it a "pervious" surface.

I posted a query on a national planner's forum and received some "sound's OK" replies from Florida and Texas, and some jeers and sneers from places like Wisconsin and New York.

I have lots of doubts about the feasibility of this in addition to doubts about its adherence to anything like sound engineering practice. (not to mention state accessibility)

Comer's current zoning ordinance does require typical hard paving for parking lots, but does contain one section that reads as follows:

5. Where appropriate, the use of porous pavement and/or specially designed brick or block should be considered to increase onsite water retention for plant material and groundwater supplies and to reduce problems associated with runoff.

I have downloaded one document of yours called Porous Pavements: The Overview that talks about porous concrete but doesn't appear to address this kind of low budget approach.

Do you have any comments about simple gravel lots passing as porous paving?

I am likely to direct this submittal to go the route of conditional use application, which would require public hearing and the vote of Mayor and Council for approval.




His timely reply:


Loose crushed-stone aggregate is stable under dead-end parking stalls, because in dead-end stalls there are very few vehicles per day and each of them is moving at close to zero miles per hour when it arrives. "Dead-end" parking stalls are those at the lot's perimeter, or terminated by wheel stops such as this engineer's timbers. Loose aggregate is not stable in a parking lot's moving lanes; numerous braking and turning vehicles displace it. Number 57 crushed stone is a very appropriate choice for aggregate parking stalls: it is angular to resist movement, extremely permeable, and comfortable enough for walking. Four inches might be sufficient thickness for aggregate parking stalls; it amounts to four or five particle diameters of No. 57 stone. Successful parking lots have been built with conventional asphalt moving lanes, and aggregate parking stalls. Those with aggregate moving lanes or cross-traffic across aggregate parking stalls have quickly been displaced by traffic.

Bruce K. Ferguson, FASLA
Franklin Professor of Landscape Architecture
School of Environmental Design
University of Georgia

[Chet]

My take. It depends.

Soil type will depend on the outcome. Here in south Texas, the soil is so compact that your plan will fail. Other places, it may work.