Rising Groundwater Could Cause More Flooding, Mosquitos

The groundwater level in Arlington is rising, officials say, which could cause more flooded homes and mosquito-filled backyards.

Arlington’s Dept. of Environmental Services says current groundwater levels are an average of 5 feet higher than they were during the past two years. Officials say one reason is last year’s 60-inch rainfall, which broke the 1889 record for the region’s rainiest year ever recorded.

Groundwater in the region is 5 feet higher than it's been in the last two years. Know how to deal with stormwater. https://t.co/MBIrMj9FSd pic.twitter.com/u58w2oV1F9

— Arlington Department of Environmental Services (@ArlingtonDES) April 12, 2019

“The potential for flooding, especially localized flooding, is affected with the ground being more saturated,” said DES’s Stormwater Outreach Specialist Lily Whitesell.

Whitesell explained that the “void” in soil which usually absorbs water is now filled with water. This mean water can’t be as easily absorbed and it’s more likely to cause runoff and flooding.

The likelihood of flooding will be highest when storms dump an inch or more of rain on the area, she said.

In addition to floods, Whitesell said residents can also expect:

• Softer, muddier ground in general
• More mosquitos as water “ponds” in backyards,
• Algae potentially growing on sidewalks and in gutters
• More sump pump discharge
• Plants that prefer drier weather to suffer

“Water ponding next to your foundation is not something that you want for the long-term structural safety of a home,” said Whitesell. “And certainly if you have a basement nobody wants water getting in there.”

She clarified that rising groundwater levels do not affect floodplain boundaries, which are drawn based on severe, “100-year” floods. However, the DES website notes that county waterways can be hit hard by stormwater runoff which causes:

• Erosion: The high volume of water erodes stream banks, compromising trails and trees along our stream valley parks.
• Pollutants: Stormwater washes pollutants like nutrients (nitrogen and phosphorus), sediment, bacteria, petroleum, pet waste and trash into our streams, causing poor water quality.
• Temperature: During the summer months, stormwater heats up as it flows over hot pavement, which then increases the temperature of the stream water by as much as 10 degrees Fahrenheit, causing stress or death to aquatic organisms.

Rising groundwater levels can also affect the underground vaults that protect controls for utilities like electricity, gas and telephone lines, Whitesell said. When these gather moisture or flood it can pose a risk to equipment and workers as NIOSH has reported.

“Some vaults are very shallow and so may not be affected,” said Whitesell. “But some are deep enough to be affected.”

When asked, Whitesell said the swell of rainstorms could be a symptom of climate change: “One of the effects we expect with global warming and climate change is that wet areas get wetter and dry areas get drier.”

In Arlington, Whitesell said the number of applications to the county’s Stormwater Wise Program that helps homeowners reduce stormwater run-off has doubled over the last year.

“We’re all hoping for a drier year,” she said.

In the meantime, DES recommends residents flood-proof their homes as much as possible and check whether they’re eligible for flood insurance. But in case all else fails the department suggests residents take the following precautions:

• Know how to shut off the electricity and gas to your house, in the event of flooding.
• Make a list of emergency numbers and identify a safe place to go.
• Make a household inventory of belongings, especially the contents in the basement.
• Keep important documents and medicine in a water proof container in a safe place.
• Gather supplies in case you have to leave immediately, or if services are cut off — medications, pet supplies, batteries.
• If your home needs a sump pump, get a battery backup in case the power goes out. Check on the pump regularly, especially if it’s more than eight years old.
• Read more tips for Preparing for Storms.