...to preserve, protect, develop, and restore coastal resources for all Rhode Islanders
CRMC’s Coastweeks event focuses on sea level rise in urban landscape
December 6, 2019, PROVIDENCE – Walking along the river in Downtown Providence one unseasonably warm day in late October, it’s clear that the impacts of past storms and expected future sea level rise is woven into the urban landscape of the city.
The recent walking tour of the river and city was one of the Coastweeks events organized by the R.I. Coastal Resources Management Council (CRMC) and Rhode Island Sea Grant and the Coastal Resources Center at the University of Rhode Island Graduate School of Oceanography. The tour began at the Providence hurricane barrier.
Providence has a history with storms and flooding. CRMC’s Coastal Geologist Janet Freedman provided the 30 attendees with maps showing the area in which they were standing, which would have been under water during Hurricane Carol. In 1954, the major hurricane submerged areas of Providence in 12 feet of water from flooding and storm surge. The hurricane barrier, completed in 1966, is comprised of river gates, earthen and rock dikes along each shore, vehicular gates along the shores where roads pass through the dikes, canal gates at the west end of the barrier, and a pumping station.
Clara Decerbo, deputy director of the Providence Emergency Management Agency (PEMA) spoke about the coordination between the city, PEMA, the U.S. Army Corps of Engineers, and other agencies to operate and maintain the barrier. Decerbo said the five pumps operate with Grid power, so a power outage is a concern during a major storm event.
“In order for the whole system to be closed, they only do it when it’s absolutely necessary, and in the last 15 or 20 years, we’ve been really fortunate in the Northeast that we haven’t had any major events,” Decerbo said. Luckily, there is not much residential property in the immediate area near South Water Street, but infrastructure would still be vulnerable.
When asked about the future viability of the barrier, she said, “We’re all aware that sea levels are rising, climate change is happening, and are we looking at this barrier and how long it could stand. We just finished our hazard mitigation planning process for the city a couple of months ago, and one of the major actions is a study of the hurricane barrier and feasible options for retrofitting it, whether it needs to be replaced, and what the best options are looking to the future and likely sea level rise projections for the usability and sustainability of the barrier.” The city and PEMA are in the process of applying for a grant to do this work, Decerbo said.
Though the barrier still works well, the future is of concern. CRMC’s Freedman noted that there had been a recent study done by the University of Rhode Island Ocean Engineering department which looked at the barrier as part of a whole class project. The senior students conducted an analysis of both the hurricane barrier and its wing walls.
“They looked at the height of the barrier and whether it would be able to withstand a hurricane or 100-year storm, which has a five percent chance of occurring in any given year,” Freedman said. “They also looked at the wing walls to see if they would be the appropriate height. They found the barrier is okay – we’ve got plenty of time to think about any retrofits that we would need in the future. But the west wing wall was built onto a rubble rock wall with a permeable core, and riprap around its edges, and was probably built on some marsh sediments that were built up over time, so it’s a silt base that has compressed a bit since they constructed the barrier.”
Freedman said the study discovered the west wall is now 1.3 feet lower than design level, despite the structure having been designed for a 500-year storm. That area will likely need retrofitting, she said. Another part of the study included modeling expected damages in the Providence area from river flooding (one scenario with the gates closed and pumps on, another with the gates closed and pumps not on), another concern for the city. The maps emphasize how important it is for all of the pieces of the barrier system, as well as the multiple agencies, working together, Freedman said.
“[The students] looked at one foot of sea level rise, will it work, and they also modeled a 100-tear storm with seven feet of sea level rise,” she said. “At seven feet, the west wing wall will probably fail - not completely, but because the capstone is pervious (porous), you will be getting water coming through.”
Sea level rise is another issue entirely, Freedman said, and it wouldn’t be feasible to close the barrier for rising sea levels. The pumps would have to be operating constantly, and it would change the entire river ecosystem, she said. Storm levels come and go, but sea level rise is permanent and incremental.
Farther up the river at the new pedestrian bridge, constructed over the old I-95 bridge abutment, Freedman informed the attendees about how the bridge was built in accordance with mapping tools made available by the CRMC through its R.I. Shoreline Change Special Area Management Plan (SAMP). The CRMC provided mapping information via STORMTOOLS – developed by the CRMC as part of the SAMP – which provides different storm and sea level rise scenarios to plan for future conditions.
While erosion might not impact a mostly manmade shoreline like that of Providence, sea level rise is definitely a concern.
“The first plans that came in from [R.I. Department of Transportation] to build the pedestrian bridge, the bridge was proposed very close to the water level,” Freedman said. “We recommended that they look at future sea level rise so that the public would be able to use the bridge for a longer period of time. We recommended they elevate it and at least plan for three feet of sea level rise. It’s not only for pedestrians to walk over the water, but you want to have kayaks and other small boats going under the bridge. As sea level rises, you won’t be able to get under the bridge.”
The DOT elevated the structure 18 inches, and also incorporated some elements that would make the bridge resilient to salt water for the extent of its design life. The project, which received federal funds, was required to consider sea level rise in its design, Freedman said, which the CRMC echoed in its permit recommendations. There are also some newly designed areas surrounding the bridge, including a rain garden, and a small urban forest with seating and a walking path, located along the riverbank.
With the CRMC, City of Providence, and other partners looking at the future with sea level rise, the landscape will have to change.
“We could see two feet of sea level rise by 2035 and three feet by 2050,” Freedman said. “Hopefully that’s a worst-case scenario, but things are looking worse that what has modeled. That’s part of the study, and one of the things students proposed was to build a berm along the waterfront.”
In Amsterdam and other places in Europe, they design parks and other spaces to be flooded, and that is something to consider in Providence, Freedman said. What can be flooded? What would you like to transition to salt marsh, for example?
Bryce Dubois, an assistant professor at the Rhode Island School of Design, and representing Downcity Design, along with Adam Anderson, a landscape architect and founder of Design Under Sky, a landscape studio, and also an instructor at RISD, described their considerations and methods for installing 10,000 Suns, the public park.
Through Downcity Design, a participatory design studio last year invited local artists and other interested adults to submit proposals for a temporary public design project along Providence’s Riverwalk to explore themes of community resilience, climate change, and place-based history. A group of 15 fellows provided their talent to work on the project, Dubois said.
“We worked with the Providence Parks Department and Providence Planning to help us envision what we could do in the space to address resilience,” Dubois said. The site is a Providence park parcel allocated to the group, and is partially on 195 Commission property, he said, and is held for the public good. “Many stakeholders had input and educated the group on resilience, culture, heritage, and history as context. The fellows invited proposals from the community-at-large, and Adam Anderson provided the winning design.”
“In terms of how I think about landscape architecture, it’s really how we negotiate the combination of nature and culture, with nature being ecology and the living world, and culture being us and how we can sort of coexist and both inhabit this world,” Anderson said. “This competition was an ambitious one, talking about resiliency, place-based history, and with a relatively limited space and budget. Just last April the site you’re looking at now was almost entirely lawn.”
For more information on the other 2019 Coastweeks events, go to http://www.crmc.ri.gov/news/2019_0912_coastweeks.html. For more information on Downcity Design, go to https://www.downcitydesign.org/cityworks.