Natural Floods vs Manmade Floods

Localities on the Virginia Peninsula are facing the prospect of spending millions of dollars to prevent or repair damage from storm water flooding. Floods have been with us since Biblical times, but dysfunctional human settlement patterns makes them worse. As a Daily Press editorial observes, “Nature has its way of dealing with heavy rain.” Some of the rain filters through the soil where it joins underground water tables; run-off gets buffered by vegetation before it enters streams and rivers.

But development has in many places robbed the land of its ability to cope with a deluge. Residential and commercial development has replaced open land with rooftops and asphalt. It has stripped the vegetation that hung on to soil, so it erodes and runs off, clogging streams and rivers. When heavy rains come along, with hurricanes or just big storms, the water backs up. Into houses and apartments, and deep on roads.

Well said. I would observe only that it isn’t entirely helpful to blame “development,” as if all development was created equal. Land-intensive development that paves over thousands of acres of roads and parking lots make the problem of storm-water run-off even worse. Asphalt is impermeable. The more of it you have, the more run-off you have.

Any long-term solution to stormwater run-off should contain at least two elements: (1) new techniques for creating natural, vegetative barriers to buffer the flow of run-off into Virginia waterways, and (2) human settlement patterns that disrupt less land and create less run-off to begin with.

Update: This from today’s News Virginian: “Hayes, Seay, Mattern & Mattern Inc. outlined eight different ways the council could pay for the stormwater management plan approved earlier this year, with each option centered around the same idea of charging property owners based on the amount of impervious surface they own. … A proposal to offer discounts as an incentive to those who improve their onsite stormwater management facilities was met with a more favorable reception.”

A fundamental principle for any tax that pays for stormwater management systems should reward landowners who (a) reduce the area of impermeable surface or (b) improve onsite stormwater management facilities.

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16 responses to “Natural Floods vs Manmade Floods”

  1. Greenways offer possible buffers to stormwater runoff.

    Also, on a more individual level, ‘green’ pavers should be encouraged instead of parking lots.

    There are alternatives if citizens demand them.

  2. related:

    AbTech Industries has spent seven years and $16 million developing its Smart Sponge filtration technology. The sponge, made from the same plastics found in automotive dashboards and sneakers, can be molded to fit any catch basin, drain or pipe. It absorbs oils, PCBs and other toxins while allowing water to pass through. AbTech’s latest version, due to hit markets in mid-January, comes dipped in an antimicrobial coating that destroys bacteria as well. AbTech ( has been testing the new sponge since 2004, lining 1,950 storm drains near the shore of Southern California, where high levels of E. coli and enterococcus bacteria sicken nearly 1.5 million swimmers each year and force cities to close beaches. On average, the Smart Sponge has killed about 75 percent of those types of bacteria and costs about one-tenth the price of systems currently used to clean up polluted water.

  3. E M Risse Avatar

    There are a lot of ways to mitigate the problem of flooding.

    The best strategy is to evolve settlement patterns in places that are not suseptable to flooding. Another aspect of a smaller ecological footprint.

    If citizens need 4 percent of the Commonwealth for urban settlements, that leaves 96 percent where occasional (or frequent) flooding is not a problem. Four percent is a generous allocation for urban use at minimum sustainable densities.

    As Joel Garreau pointed out in the Style section of WaPo on Sunday, insurance rates are making the right thing a lot easier to do.

    This is one example of how a fair allocation of location-variable costs can help evolve functional human settlement patterns.


  4. Anonymous Avatar

    EMR – Standing alone, doesn’t density result in more run-off than more traditional “suburban” SF developments? I’m not arguing against density per se, rather, just that tearing down my house with its fairly large yards and trees (we must have at least 40 on the property) and replacing this with condos or even PUD would likely create additional run-off.

    I would think that we will see stricter requirements to address run-off problems in urban areas, which will make urban development more expensive.

  5. Larry Gross Avatar
    Larry Gross

    well you asked EMR.. but I’ll add my voice.

    I think there is NO question that denser development patterns – no matter where they are sited – will have higher volumes of runoff… because very little grass/tree covered soil is left.. most covered up by concrete and other impervious services.

    HOWEVER – in dense areas – if parking lots are UNDER ROOF – parking garages… then they do have major advantages over areas that have acres and acres of exposed parking lots – your traditional suburban sprawl.

    This one of the issues that I have questions about with respect to compact development and new urbanism.

    Originally – “compact development mean that you’d take 100 acres – and put 100 homes on 20 of those acres and then leave the other 80 open – for open space… runoff filtration, etc.

    But now it seems to mean that every square inch of open land is devoted to dense development – which is a totally different concept – from an environmental perspective.

    I’m a paddler in my other life. I canoe Virginia’s streams. I have been on major sections of every major river in Virginia .. many of those sections close to cities and towns… and I highly recommend that folks take a little canoe trip right after a rain to see what is flushing into .. the Chesapeake Bay…

    We’ve all been duped into believing that FARMS are the problem. Logic and Common sense should tell everyone that urbanizing development is the culprit. Trees and Vegetation are stripped.. including steep slopes…

    take a canoe trip past a farm after a rain.. then paddle on down to a fast growing suburban area – and you’ll end up with no doubts about where the vast majority of the runoff is coming from.

  6. One thing that also needs to be taken in to account, much of the lands in the counties of Surry, South Hampton, Isle of Wight, and Suffolk use to be heavily forested. The rivers used for shipping through those counties were dredged to help support a large timber and logging industry. They have stopped the dreading of the rivers and they have since silted up. I think you can figure the rest..

  7. Jim Bacon Avatar

    I don’t pretend to be an expert on this subject but that never stopped me before. Here goes…

    Yes, dense development will mean more concentrated run-off. There is a higher impermeable surface/impermeable surface ratio in densely developed areas. Presumably, there is less vegetative buffer area as well. That’s why urban areas have some of the worst run-off problems.

    However, in less densely settled areas, there is significantly more square footage of impermeable surface per person. We’re talking more roadway, longer driveways (often dirt roads) and larger parking lots. The impact of this run-off is more diluted, hence less visible. But it is any less bad?

    That’s an empirical question that I don’t know the answer to. But I would advise against jumping to conclusions either way.

  8. Larry Gross Avatar
    Larry Gross

    Jim – yes .. it is by far far less bad.

    First – oil and antifreeze and other nasty stuff FILTERS even in dirt driveways… as well as grass, forests, etc

    Second – the is less oil and antifreeze to start with because there are less vehicle per unit of land

    Urban Runoff is highly concentrated waste (that includes not insignificant amounts of pet feces (which becomes fairly harmless degrading into “soil” in vegetative areas. But pet feces in an flooded urban creek just adds to the witches brew.

    So one could take the same number of cars and park them on one acre of grass and then an equivalent number and park them on one acre of asphalt and there is absolutely no question which one will flush more pollutants into streams.

    This is one of the tougher realties that I feel requires some level of intellectual honesty of those of us who advocate compact development.

    and like I said before.. it “used” to be 100 acres … build on 20 of it.. and leave the rest to filter runoff and provide open space and recreation…. and if one wanted to be really righteous – you built on the 20 acres that was most suitable and less vulnerable to runoff problems… like you might have a snake-like ridge where you put the homes… and the steeper slopes and wetlands would remain forested and covered with vegetation.

    LID is the current BMP approach… where filtering pavers are used and engineered swales that basically are huge filtering basins…. adjacent to parking lots. Some places actually have underground tanks to absorb and hold the runoff and gradually meter it out… through the subsoil.

    Developers don’t like either of these options because … ta da …. they cost more… and HORRORs they have to be maintained to maintain their effectiveness ( as opposed to paving and forgetting… and letting everything run off directly into the streams – that’s developers ideas of what is more “effective” – and local governments go right along with it because they rather have a Target without paving stones that no Target at all.

  9. Larry Gross Avatar
    Larry Gross

    on the general issue.. some flooding issues are taking care of themselves via the marketplace (excerpts):

    “Insurers Retreat From Coasts

    Alarmed at the sharply rising cost of hurricanes and other disasters, home insurers are pulling back from some U.S. coastal markets, warning of gathering financial storm clouds over how the United States pays for the damage of catastrophe.

    The development is yet another legacy of Hurricane Katrina, whose mounting toll of destruction along the Gulf Coast has crystallized a growing industry debate about the combined effect of climate trends and population growth in coastal areas.

    Since Aug. 29 — when the hurricane made landfall along the Gulf Coast — Allstate Corp., the industry’s second-largest company, has ceased writing homeowners policies in Louisiana, Florida and coastal parts of Texas and New York state. The firm has stopped underwriting earthquake coverage in California and elsewhere. Other firms have pulled back from the Gulf Coast to Cape Cod, notifying Florida of plans to cancel 500,000 policies.”

    Lately though – even areas inland – are being closely examined by insurance companies for their vulnerability to higher than normal rain events.

    This could result is some kinds of development along steep slopes and stream beds as ending up being very expensive in terms of insurance costs….

    My own insurance company was asking where our house was relative to the 100 year flood zone…. they wanted it verified that we were NOT only not in the zone but not near to it either…

    this is going on because the 100 year flood zones themselves are being questioned .. since some of them… have seen 3 100-year floods in less than a decade.

    The culprit is much higher levels of runoff from development.

    When the original 100 year zones were delineated – they were based on the presumption that most of the watershed was forested and vegetated AND would remain so – and we know now that is not true.

  10. E M Risse Avatar


    Re: your “density” question. This is an area where actual experience building projects provides useful answers. Here is a quick note off the top of my head:

    If you have natural ground cover, a grasscrete driveway and rain gardens for your downspouts your lot contributes little to peak runoff.

    Most folks have short grass (aka lawn), driveways and no raingardens.

    On a per acre basis single family detached (2.5 du ac) generates more runoff than a well designed project with a mix of uses at 10 to 12 du per acre.

    This is in large part because of the opportunity for shared stormwater management and far less paved surface for streets and driveways.

    On a per dwelling basis there is no comparison. A factor of 10 plus or minus. This is why the Occaquan 5 acre lifestyle downzoning is such a hoax to call it “conservation.”

    Stormwater runoff is another area where fair allocation of the total cost would have a big impact on settlement pattern.

    Most residential development and almost all agricultural land uses are still in the dark ages re storm water management.


  11. Ray Hyde Avatar

    Well the environmental types say that any place that has more then ten percent impermeable surfaces contributes to runoff problems. It seems to me that if we followed that ruel we woul eliminate runoff problems and trafic problems as well, unless of course we persist in putting all the jobs in one spot.

    Yes, there are technological solutions and products to help, but they all cost money, whereas simply leaving the right areas vacant solves the problem at little cost – unless you happen to own the land that is put off limits. In that case, you are put in the position of providing a service to others for which you are not paid.

    We already have laws designed to curb runoff, and that is why developments frequently include lakes, ponds, and catch basins, such that runoff after construction is no worse than before. The real problem is going to be retrofitting all the places that were built before the laws were created. One way to do that is to simply tear down and turn into highly desired green spaces those urban areas that are decayed. Again, this would reduce the population density, restore the green to covered ratio, and reduce traffic.

    Finally, even if we left things in their completely natural state, we would eventually find ourselves with another Grand Canyon. Being natural does not eliminate runoff or erosion. Even on my relatively flat fields I mow up a few new rocks every year, and even though my fields are heavily vegetated, I can see signs of the soil moving down hill. Even though my driveway is gravel, it still has runoff due to compaction.

    Water and soil have been running downhill for eons, and I expect they will continue to do so. I have no doubt that even if we accept EMR’s preposterous 4% rule that the result would be more runoff, not less. The reason is that if we build and design to keep runoff to a minimum we are better off than we are by leaving 96% of the area uncontrolled.

    As for building in scattered areas, my house sits in the middle of 170 acres. I’m pretty sure that the amount of water that runs off the farm is independent of whether the house is here or not.

    Is runoff a problem, yes, but we have taken steps to address this, and modern construction has virtually eliminated the problem. Let’s not make a mountain out of a molehill, but at the same time let’s think about how our new knowledge can be used to help solve other related problems, and let’s figure out a way to do it fairly.

  12. Ray Hyde Avatar

    Frankly, right now I’m a lot more concerned with the more or less free parking Dominion power is going to get for a couple of high tension power line towers right through the middle of the farm.

    It is one more case where those who work the hardest to keep the land the longest at the least government expense get hammered hardest in the end.

  13. Larry Gross Avatar
    Larry Gross

    sorry if this appears twice…

    Well.. Ray is right about water running off land for eons.

    But what is different is stripping away too high a percentage of vegetation and replacing it with concrete and impervious surfaces.

    When the percentage of impervious surfaces exceeds certain (arguable) levels – profound changes will occur in the receiving streams. This is demonstrated by biological surveys of the critters that live (or no longer can live) in receiving streams. A simple example is that we know certain kinds of fish cannot live in streams that are polluted. The same is true of small “bugs” and the “bugs” are used as indicator species to access the water quality.

    Yes, there are now storm ponds and yes the newer regs require ponds with larger capacities but there still are major issues even with modern ponds. For one thing – they take up (in some folks minds – developable) land. For another, if we built them for 100 year storm events rather than 20 year events – they’d have to be several times the size they are now.

    Why is size important? Because the pond retains the toxic runoff – oil, antifreeze, feces, etc – UNLESS the runoff flow exceeds it’s capacity – at which point it dumps the excess flow through emergency overflow pipes.

    Folks so interested .. next time you visit a recent vintage development (even convenience stores) .. look around for the pond – then walk over and take a look at it. Depending on the when the last rain was the the design of the pond.. it may or may not be full but pay attention to the emergency overflow structure because when that pond is full.. and rain still coming down, the remaining runoff goes straight into the receiving creek.

    So the ponds work well only for storm events that are within their design criteria and as stated earlier almost none of them are sized for 100 year flood events – because of cost and size issues.

    Unfortunately – the state regulates in terms of what can be dumped in terms of volume and water quality rather than require that the receiving streams water quality not be compromised – a much more difficult standard.

    Their current approach would not be so bad because “in theory” the effluent standards are reasonable on a per facility basis but the overall process if fatally flawed in terms of cumulative impacts.

    In other words – the standards are the same no matter what percentage of the land becomes impervious so ultimately if the percentages go high – the sheer amount of runoff exceeds what the intent of the standards was envisioned; think of the opposite of dilution – the point where pollutants overwhelm the ability of a receiving stream to mitigate via dilution. Each facility is allowed to “dilute” pollution so that when all of them are added up – dilution still “works”. But if the numbers of discharge facilities increases in number (because of more impervious surfaces) – then there are too many pollutants for the stream to absorb – and it goes downstream until it hits a major river – and thence into the Chesapeake Bay.

  14. Ray Hyde Avatar

    If you had every catchment basin sized for a hundred year event there wouldn’t be any runoff, and where would that leave the streams?

    Yep, the water runs off pavement faster, but it doesn’t take much of the pavement with it.

    So if you have 4% urban development and 96% natural runoff, which one contributes more to the streams?

    Yep, the runoff from urban areas is full of nasty stuff, and that’s because urban areas are nasty places.

  15. Larry Gross Avatar
    Larry Gross

    The ponds need to “meter” runoff similiar to how natural vegetation does it.

    LID – low impact development using porous paving surfaces and engineered filtering swales also accomplish metering plus they filter out the nasty stuff whereas the ponds do not.

    and of course this “costs” more money even though it “saves” money downstream … for subsequent clean-up efforts.

    There is an interesting juxtaposition between the concept of compact new urbanism development and LID development.

    The former is to foster more efficient use of the land – and transportation facilities while the latter seeks to minimize damage to the environment – and the two don’t match up yet in my mind.

    New urbanism is all about infrastructure … and not so much about limiting harmful runoff.

    I’d like to see an example of New Urbanism that incorporates LIDS – and mabye this is a case of ignorance on my part. (my most favorite quote is ” We’re ALL ignorant – just on different subjects”).

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