Sunday, January 29Hampton Roads Weekly

Storm Water Is Difficult

By Brad Martin
Professional Engineer

Stormwater is a difficult thing.  Especially when you’re as low and flat as Hampton Roads is.  Virginia Beach got a dramatic lesson on October 9, 2016, when Hurricane Matthew ended a twenty-day period during which some parts of the city endured more than twenty inches of rainfall.

For some perspective and definitions, approximately nine inches of rain in Tidewater within a 24-hour period is called a “100-year storm”.  A “100-year storm” is not a storm that comes along every 100 years; actually, it’s a storm intensity that has a 1 in 100 chance of happening in any given year.  A 10-year storm (six inches of rain) has a 1 in 10 chance of happening in any given year.  A 1-year storm (three inches of rain, a 1 in 1 chance) is almost certain to happen every year.  It is possible to have two separate 100-year storms within a couple weeks of each other, but the odds are against it.

If it seems like these rainfall intensities are happening more frequently, they might be.  In addition to the rain falling out of the sky, our stormwater management systems have to deal with high and low tide fluctuations, on the order of three feet, twice each day, plus issues like wind-driven surges and the occasional fall nor’easter.  If one of those other environmental conditions is already happening, and then Mother Nature dumps any amount of rain on us, we could have problems.  Three inches of rain at low tide with no wind might not create a problem, but a two-inch “rain bomb” at high tide and when the wind is blowing, trying to keep all the water in Back Bay – like just happened a few weeks ago – might have the potential to overwhelm our systems and create serious property damage.

Before 2014 (for most of the

developed property in Virginia Beach), the codified requirements of development were for the stormwater runoff from the proposed project to match both the “rate of flow” and the “timing of runoff” of the site under the existing (pre-developed) conditions during a 10-year storm.  Someone could analyze how well the developed projects in the City met that regulation, but the only measuring stick to evaluate that question is the computer models of how the design rain storms “should” fall.  It is an imprecise tool at best, and just because an area floods, doesn’t mean that it was designed or built improperly.  Neighborhoods with stormwater drainage systems that were built 50 and 60 years ago need some infrequent but important maintenance, and the ditches and pipe systems need to be kept close to their design capacities.

It might be difficult to predict what will happen to our City and our region during an epic, rare rainfall, but it was impossible to ignore the effects of Hurricane Matthew.  In the 19 days before Matthew, Tropical Storm Julia and the after-effects dropped about nine inches of rain on most of Virginia Beach.  The continuous rainfall saturated the ground, filled up our ponds and ditches, and fundamentally reduced the normal capacity of our stormwater systems in Virginia Beach.  Then, when Matthew brought another twelve inches of rain onto a City without its normal capacity for stormwater management, our systems were simply overwhelmed.  Roads were flooded, neighbors watched the rising water creep up their driveways, into their garages, and eventually into their homes.

I don’t know if there is an accurate accounting of the value of property damage, but I was talking to neighbors on Old

Forge Road in Windsor Woods in July of 2018, and some are still working to recover from the storm damage almost two years ago.

The City of Virginia Beach has responded aggressively in two specific ways: (1) they are looking much more closely at some proposed development projects (which was already underway, based on new State regulations which went into effect in 2014), and (2) the City has shifted the maintenance operations of our stormwater conveyance systems into high gear.  The former won’t have much of an impact on the areas of the City which currently suffer from recurrent flooding, but the latter is already showing remarkable results.  Our stormwater conveyance systems are the key to handling the infrequent rain events; keeping them

flowing should be a top priority for the City.

And the money is there to prioritize stormwater management and maintenance.  The City already collects $40 million each year in the Stormwater Fee that we all pay in our Utility Bill, and they’ve dedicated significant spending ($300 million over 15 years) in response to the property damage we endured resulting from Matthew.  It bears asking the question if this money is being spent in the right places.  The City Auditor studied the revenues and expenses of the Stormwater Fee in the fall of 2017, and the official report is on the City website.

The recent surprising flooding our City has experienced after brief but intense bursts of rainfall – on Shore Drive, on Laskin Road, and down in “the County” – should be a clarion call to the City Council and senior City staff to shift the maintenance clearing of our ditches and pipes into high gear.  Engineering studies and stormwater models will help us with new developments and into the future, but we have immediate needs to protect citizens’ property right now.  Most engineers agree we have fallen woefully behind in the maintenance of our pipes and ditches.  The City’s singular focus, until we catch up on the neglected storm systems, should be to enact an aggressive maintenance program throughout our City.

However hard it is to model and predict the specific effects of rainfall events, one thing is for sure: six inches of rain dropping from the sky is still six inches of rain, whether it meets the model parameters of a “10-year storm” or not, and the City’s infrastructure should be able to handle it.

Editor’s Note:

About Brad Martin – don’t let the boyish good looks and the mischievous grin fool you, Brad Martin is a candidate for the Bayside District City Council race on Tuesday, November 6th.  Brad has the skill-set and demeanor necessary to solve some serious problems in Virginia Beach for us.  Each of us has the opportunity to vote for him!