Rising sea levels a growing concern for Milford flooding

A puddle by the strip mall containing the Gigante International Market and Benvenuto’s, where water from Milford’s drainage system often backs up onto Northeast Front Street when it rains. Special to the Delaware State News/Ariane Mueller

MILFORD — Severe rainstorms and tidal flooding events have become more common in Milford, and with rising sea levels, they will likely become even more prevalent in the future.

Rob Pierce, Milford’s planning and economic development director, said residents and visitors should expect increased flood depth and floodwaters creeping further away from the Mispillion River on wet days in the future.

“If the water goes up, it will go out depending on the elevation,” he said. “I think you can anticipate a little bit of both.”

According to Flood Factor, a nongovernment organization dedicated to flood research, the number of properties that will be at risk in what is known commonly as a “100-year flood” will increase by 42.8% in Milford during the next 30 years.

To take into account concerns that climate change will lead to heavier flooding, Milford collaborated with the University of Delaware’s Institute of Public Administration in August 2017 to create a pilot program for a more comprehensive approach to city planning.

That plan estimates that in a 100-year flood, 3½ miles of the city’s roads and 13.7% of its historic district would be flooded.

In addition, if sea levels were to rise by 3 feet, almost 30% of Milford’s historic district would be underwater, per the analysis. That would cover 6 miles of roads, the police station, the post office and the library.

Milford’s plan was meant to be a model for other Delaware municipalities to work from and is largely focused on flooding as a product of climate change.

“I think that’s the only real source that I can point to and say, ‘Why are we getting more of these heavy downpours now than what we were getting 25 or 30 years ago?’ ” said Mark Whitfield, Milford’s city manager.

He said the city prepares for two flooding events: heavy summer downpours, “where we get 2 inches of rain in 35 or 40 minutes,” and big Atlantic storms.

These events tend to overwhelm the city’s underground piping system, which then overflows, leading to pooling in some areas. This is common at locales like Northeast Front Street near the Gigante International Market and Benvenuto’s or on North Walnut between Second and Fourth streets.

“It’s not an area that would typically be prone to flooding if there were no structures there … or if there were pipes of adequate size to get the water down to the river,” Mr. Whitfield said.

According to the Federal Emergency Management Agency’s flood insurance maps, the Mispillion River’s flood plain in Milford is mainly the area between the two Front streets and along Mullet Run, which joins the river from the northeast around Truitt Avenue.

The city has received grants to research the possibility of expanding pipe diameters for its stormwater management system, something Flood Factor recommends in the community solutions section of its website.

People eating on the back porch at Arena’s, a popular Milford restaurant that overlooks the Mispillion River and is within the current 100-year flood plain, meaning there’s a 1% or higher chance of the restaurant flooding annually.

During large, more sustained Atlantic storms, wind is also an issue.

“Typically, that is wind blowing the tide up the Mispillion River with a whole bunch of rain being deposited upstream, and there, the two meet,” Mr. Whitfield said. “They’ve got the river pushing up and the rain coming down and pushing the other direction with no place to go.”

Mr. Pierce identified expanding and preserving wetlands and open spaces as an effective way to deal with this tidal flooding.

“Instead of having some of these properties that could be prone to flooding be developed for residential or commercial uses,” he said, “you could possibly have the city look at acquiring them to preserve them as open space, which would reduce flood risk.”

Providing open spaces for “managed flooding” is the very first idea mentioned in Flood Factor’s section on green infrastructure. It deems this a cost-effective and sustainable solution.

Mr. Pierce said Flood Factor may have overstated the risk in concluding there are currently 505 flood-prone properties in Milford.

“There could be,” he said, but it’s possible many of “those properties have nothing on them. They could be parkland, they could be full of wetlands, they could be open space, they could be things that are not built on.”

He noted there are several properties in town that slope down toward a body of water. The lower sections of these lots are more flood-prone than the higher sections, which is generally where people have built homes.

“An unusable portion of that property could be within the flood plain,” he said, “but there’s no risk to damaging any structures.”

Mr. Pierce estimated that of Milford’s roughly 6,200 properties, between 125 and 130 structures are in the current 100-year flood plain. Few of those are residences, he said, and many of those that are homes are actually apartments on the upper floors of buildings housing storefronts.

A significant chunk of those buildings in the flood plain are old commercial buildings in Milford’s historic downtown. Some do not meet current construction standards, according to Mr. Pierce.

He said the city’s zoning code has special stipulations for development in parts of town in the 100-year flood plain, another idea listed in Flood Factor’s community solutions section.

“For development activity in special flood hazard areas,” Mr. Pierce said, builders are “supposed to submit a hydraulic and hydrologic engineering analysis reflecting the proposed development activity will not negatively impact the flood plain or flooding in the surrounding area.”

Additionally, Mr. Pierce said the first occupied floor of any new residential structure built in the flood plain has to be elevated 18 inches above where the water is expected to rise in a 100-year flood. He said these factors, in conjunction with prohibitively high flood insurance rates, have led developers to look elsewhere.

“If you look at most of the new developments in Milford — Milford Ponds, Simpson’s Crossing, you name it — those projects are all outside the flooding areas,” he said.

The construction standards are different for new commercial structures in the flood plain, according to Mr. Pierce. They don’t necessarily have to be elevated, but if they aren’t, he said, builders must use a “dry-proof flooding technique,” meaning that any element of the building below the water level expected in a 100-year flood has to be entirely watertight.

He said a lot more research is needed to understand the economic impact future flooding could have on Milford.

“I wouldn’t be able to quantify a value,” Mr. Pierce said. “There’s different types of damage. There’s light flooding, (and) that damage would be a lot different than if there was moving water that swipes buildings away.”