Flood Zones in Portsmouth, Rhode Island: What the State's Own Data Actually Shows
Portsmouth, Rhode Island sits on the northern end of Aquidneck Island, plus Prudence, Patience, Hope, and Hog islands out in Narragansett Bay -- meaning this is a town where water is not a backdrop but a majority of the town's own territory. This page does not state a specific FEMA flood-zone designation -- not "Zone AE," not "Zone VE," not a base flood elevation -- for any particular Portsmouth address, because no such current, parcel-level data was independently confirmed in the research behind this page. What it does report, in detail, is something most competitor sites will not surface: the Rhode Island Division of Statewide Planning's own Portsmouth fact sheet, which names specific roads and bridges and ranks Portsmouth against every other town in the state for sea-level-rise and storm-surge road exposure. That is real, sourced, town-specific planning data, and it is presented here plainly, without editorializing beyond what the state itself states.
A Town That Is Mostly Water: The Geography Behind the Risk
Per Wikipedia, Portsmouth's total area is 59.3 square miles -- but only 23.2 of those square miles are land. The other 36.1 square miles, or 60.86% of the town's total area, is water: Narragansett Bay, the Sakonnet River, and the channels between Aquidneck Island and Prudence, Patience, Hope, and Hog islands, all of which fall within Portsmouth's town boundaries. Britannica separately gives a rounder figure of about 23 square miles for the town, which appears to describe land area only -- a differently-scoped figure rather than a contradiction of Wikipedia's more detailed breakdown.
That water-to-land ratio is the physical reason Portsmouth's flood-risk conversation is genuinely different from a typical single-shoreline beach town: this is a town wrapped by bay and river on multiple sides, with island neighborhoods reachable only by ferry or bridge, and with a mainland connection at each end -- the Mount Hope Bridge toward Bristol and the Sakonnet River Bridge toward Tiverton. Both of those bridges show up, by name, in the state's own flood-vulnerability data below.
What the State Itself Projects: Sea-Level Rise and Specific Roads
The Rhode Island Division of Statewide Planning maintains its own town-by-town coastal-hazard fact sheets, and Portsmouth's is specific in a way that is worth reporting in full rather than summarizing away. At 7 feet of projected sea-level rise, the state projects approximately 7 miles of roadway inundation in Portsmouth, about 87% of it (roughly 6 miles) local roads -- a projection that ranks Portsmouth 11th most vulnerable town statewide for sea-level-rise road impacts.
The fact sheet names the specific roads most affected under that 7-foot scenario: Boyds Lane, with 1,385 linear feet affected; Narragansett Avenue, with 1,996 linear feet; Neck Farm Road, with 2,410 linear feet; Common Fence Point Boulevard, with 2,812 linear feet; and Park Avenue, with 2,687 linear feet. Common Fence Point Boulevard's appearance here lines up with Common Fence Point itself being a real, named Portsmouth neighborhood -- a genuine, sourced link between a place name residents will recognize and the state's own hazard data, not a generic "some roads may flood" statement.
The Combined Storm-Surge Scenario: 37 Miles of Roadway, Two Highways, One Bridge
The state's fact sheet also models a combined scenario -- a 100-year storm layered on top of that same 7 feet of sea-level rise -- and the numbers jump considerably. Under that combined scenario, roughly 37 miles of roadway inundation is projected in Portsmouth, about 78% of it (roughly 30 miles) local roads. That ranks Portsmouth 7th most vulnerable town statewide for storm-surge road impacts -- a notably worse ranking than its 11th-place standing for sea-level rise alone, which itself signals that storm surge, not gradual sea-level rise by itself, is the bigger road-network threat here.
Two state highways show significant exposure under that combined scenario: State Highway 24 North, with 6,569 linear feet exposed, and State Highway 24 South, with 7,900 linear feet exposed. The Mount Hope Bridge itself shows 233 linear feet of exposure in the same modeling -- a comparatively small figure next to the highway numbers, but still a named, quantified exposure on a bridge that is one of only two land connections off Aquidneck Island's northern end.
The Bridges: A Specific Warning About the Sakonnet River Bridge
The state's data treats sea-level rise and storm surge as separate bridge-risk questions, and the results are not identical. Under sea-level rise alone, only one bridge is flagged as a concern regionally: the Sakonnet River Bridge, which the fact sheet specifically describes as having "-84 inches of freeboard" under the 7-foot rise scenario -- meaning, in plain terms, that the bridge's clearance would already be insufficient at that level of rise, not merely reduced. That is a specific, sourced, genuinely alarming figure, and it is reported here exactly as the state states it, without adding speculation about timelines or consequences the fact sheet does not itself provide.
Under storm-surge scenarios, the picture widens: five bridges regionally are flagged as a concern, not just one. Taken together, the state ranks Portsmouth 13th most vulnerable town statewide for combined bridge vulnerability. Since the Sakonnet River Bridge is Portsmouth's own link to Tiverton and the mainland to the east, and the Mount Hope Bridge is its link to Bristol to the north, this bridge data is not an abstract regional footnote -- it describes both of the town's actual road connections to the rest of Rhode Island.
What This Page Cannot Tell You: A FEMA Zone for Your Address
None of the state sea-level-rise and storm-surge data above substitutes for a FEMA flood-zone determination, and this page will not pretend otherwise. No current, parcel-level FEMA flood-zone designation -- for a home on Boyds Lane, Common Fence Point Boulevard, Prudence Island, or anywhere else in Portsmouth -- was confirmed in the research behind this page, and none is invented here. For that, go directly to FEMA's Flood Map Service Center at msc.fema.gov and look up the specific address in question; that is the only reliable source for an actual zone letter and base flood elevation, and it should be checked before any purchase, insurance, or building decision.
Worth flagging separately, and clearly labeled as a different kind of issue: the Melville area, on Aquidneck Island's west coast within Portsmouth, is the site of a documented PFAS and fuel-tank-farm contamination story tied to Naval Station Newport's historical refueling depot there. That is an environmental contamination issue, not a flood-zone issue, and this page does not conflate the two -- but anyone researching Melville-area property should be aware both stories exist, and evaluate them separately, on their own facts.
What This Means If You Are Evaluating Property in Portsmouth
Put plainly: Portsmouth does not have a settled, address-level flood-zone story on this page, and none is manufactured here. What is real, confirmed, and reported in detail above is the state's own planning data -- specific roads, specific linear-footage figures, specific statewide rankings, and a specific, named bridge-clearance warning for the Sakonnet River Bridge -- all sourced directly from the Rhode Island Division of Statewide Planning's own Portsmouth fact sheet. That level of named, road-by-road, ranked detail is a genuinely different, more granular dataset than a general "this town is coastal and at risk" statement.
What is not confirmed, and should not be assumed, is any specific FEMA zone letter for any Portsmouth address. Before buying, insuring, or building on any Portsmouth property -- on Aquidneck Island proper, on Prudence Island, or anywhere else within town boundaries -- get a current, address-specific determination from FEMA's Flood Map Service Center, and treat the state planning data above as context about the town's broader road and bridge exposure, not as a substitute for that determination. This page is independent research, not a flood-zone determination, and it is not a substitute for FEMA's own current mapping, a licensed surveyor, or a qualified insurance professional.
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Get a Free Agent Referral →Independent research. No ads. No sponsored listings. Data sourced from: Wikipedia's own Portsmouth, RI entry (total area 59.3 square miles -- 23.2 square miles land, 36.1 square miles water, or 60.86% water) and Britannica's approximately 23 square miles figure, presented here as a differently-scoped, land-only approximation rather than a contradiction; and the Rhode Island Division of Statewide Planning's own Portsmouth coastal-hazard fact sheet (planning.ri.gov), which projects approximately 7 miles of roadway inundation at 7 feet of sea-level rise (about 87%/6 miles local roads, ranking Portsmouth 11th most vulnerable town statewide for sea-level-rise road impacts), names Boyds Lane (1,385 linear feet), Narragansett Avenue (1,996 linear feet), Neck Farm Road (2,410 linear feet), Common Fence Point Boulevard (2,812 linear feet), and Park Avenue (2,687 linear feet) as the most-affected roads under that scenario, projects approximately 37 miles of roadway inundation under a combined 100-year-storm-plus-7-foot-sea-level-rise scenario (about 78%/30 miles local roads, ranking Portsmouth 7th most vulnerable statewide for storm-surge road impacts), identifies State Highway 24 North (6,569 linear feet) and South (7,900 linear feet) and the Mount Hope Bridge (233 linear feet) as exposed under that combined scenario, flags the Sakonnet River Bridge alone under sea-level rise (with "-84 inches of freeboard" at 7 feet of rise) and five bridges regionally under storm-surge scenarios, and ranks Portsmouth 13th statewide for combined bridge vulnerability. This page could not confirm, and does not state, any current FEMA flood-zone designation (such as Zone AE or Zone VE) or base flood elevation for any specific Portsmouth address. The Melville-area PFAS and fuel-tank-farm contamination story tied to Naval Station Newport is a separate, documented environmental issue and is noted here only as a distinct matter, not folded into the flood-zone data above. For a current, address-specific flood-zone determination, use FEMA's Flood Map Service Center at msc.fema.gov directly. Nothing on this page is a flood-zone determination, insurance advice, or a substitute for a licensed surveyor, qualified insurance professional, or FEMA's own current mapping.