Morrissey is always the leading indicator of trouble, since it gets closed all the fucking time during Nor'easters for storm surge flooding. At least there's not very much damage to be done down by Day Basin except for more potholes to patch and a few shorted-out streetlights, but take this nearly yearly occurrence. . .
. . .and project upward from there.
Re: transit corridors. . .
The Red Line itself, despite running on a vulnerable corridor, should handle a 50-year flood better than all 3 of its rapid transit counterparts. The Kendall and Beacon Hill portals are dozens of feet above ground level preventing the drainage sink effect, Dot Ave. where the SS-Andrew tunnel goes is the last strand of thoroughfare that stays dry, and because Kendall + Central stations frame the dry ends of Main St.'s minor issues there shouldn't be any tunnel breaches in East Cambridge. In the worst rain events of recent memory, Red on those stretches has stayed dry while the others have had more serious problems. It's mainly going to be the Braintree Branch at North Quincy and Wollaston (Wollaston's fare lobby floods all the damn time).
BTW...I say this all the time on the Crazy Transit Pitches thread...do not even
think about tunneling the Grand Junction under Red @ Kendall for some rapid transit build. The GJ used to be the ancestral tidal flat shoreline before the last of the East Cambridge landfilling, and ran on a causeway through Cambridgeport to the Main St. grade crossing. Burrow under Red and you WILL create exactly the fatal storm drain effect that Red is more or less inoculated from in Cambridge, and it WILL breach the Red level and destroy everything out to Harvard.
Downtown you just get wall leakage on the stations where Red's at the lower level. But that's a state-of-repair vs. water table problem like the neverending Porter Sq. & Alewife leaks rather than a drainage problem. Those stations need some long-overdue sealing, but that's not a leading indicator of trouble (especially Porter-Alewife, where Alewife Brook's high water table is totally disconnected from tidal influence). You would need to have good flood doors installed at Columbia portal to keep that one vulnerability tight, and have an evacuation plan in advance of the surge for all the trainsets stored at Cabot Yard so there's no goofs akin to NJ Transit letting its commuter rail coaches get damaged during Sandy by parking them in a flood-prone yard. But Red from Alewife-Ashmont + Mattapan would be the FIRST thru transit lifeline reopened after a major breach. And the first priority because it's the largest in ridership.
Blue from Charles/Bowdoin to Maverick would be second back online. All subway stations high-and-dry, and that line was constructed before some of the last Eastie landfilling. May need flood doors at the Logan portal, but Jeffries Point is *just barely* in the least-concern 0-2 ft. area so cleanup and reopening of transit from Logan to downtown should likewise be doable within a couple days of a disaster. Note also that Orient Heights carhouse is high-and-dry per its namesake. Boston, Revere Beach, & Lynn RR built their HQ there
before all of the Eastie landfilling. Main inundation consideration for bringing Blue back up to full strength all points south of OH is a quick cleanup of the OH-Logan tracks, which helps when all the electrical plant is mounted up high. Wonderland's gonna be out for awhile, but except for the high-and-dry denizens of "Beachmont Island" cut off from the rest of the world there'll be no passengers to pick up at the outer stops.
Orange's problem is less the probable damage than fact that it's likely going to get chopped into 3 pieces. Forest Hills-Ruggles should be OK, which is a lifeline for the outer neighborhoods and commuter rail/Amtrak to have a pair of makeshift terminals at the two gigantic FH & Dudley/Ruggles bus terminals to distribute around downtown. The oldest Chinatown-Haymarket tunnel + stations shouldn't suffer any damage. And Sullivan-Oak Grove won't see any inundation at all because of the track elevation through all the Mystic floodplain. The South Cove tunnel and SW Corridor to Mass Ave. are going to be fuuuuuuuuuuuucked, however, though the storm drain effect that ruins Tufts & BBY should stop before rising to shallow-level Chinatown. You need more vehicle storage at the south end to keep that FH-Ruggles lifeline going, because BBY is going to be gone for...like, 6 months or more. Less concern about immediate downtown being severed for too long because the Community College portal is in the 0-2 ft. range and the Sullivan-CC tracks run on an El under the 93 decks. Sensible flood doors and a pumping plan for CC station and NS superstation do the trick for getting the downtown transfers back online.
Green? Dear God. I mean,
DEAR...GAWD! The 1919 Central Subway extension from Public Gardens to Kenmore is a total loss. Kenmore portal(s) are already the storm drain to end all storm drains and a vulnerability exploited every single 25-year flood event. They should be able to get Park St. to GLX up and running without too much trouble if the GLX carhouse is adequately proofed against the 0-2 ft. floodwaters (shouldn't be difficult if trunk utilities aren't mounted underground and they have pumps + extra-good drainage underneath the storage tracks). But you're looking at 6 months of D's turning at Reservoir, C's @ St. Mary's, B's @ Packards then BU West then Blandford...and the rest just gone. Maybe within several months of 24/7 emergency repair you get bare skeletal shuttling on ruined infrastructure like the aftermath of the '96 flood x100. But you're looking at a >$B rebuild, years of crippled service, and painful weekly shutdowns a la NYC Subway post-Sandy.
I doubt there's anything that can be done to prevent this. You simply can't waterproof the Muddy Basin storm drain well enough. Urban Ring isn't going to save you since that'll be chopped up in pieces too (though should bounce back much quicker if it's built as surface route). Parallel-flank Huntington Subway? If built-to-code should bounce back near-unscathed from Brookline Village to NEU, but it's going to have a hole in it at Prudential for awhile. Riverbank Subway? The shallow tunneling at level of the Back St. retaining wall gives it a baked-in 4-6 ft. flood barrier, but all bets are off if you can't keep Charles Basin capped to *only* that much inundation.
Commuter rail? Well, that's mostly a terminal district thing. Northside is where they can help themselves the most with judicious waterproofing of Boston Engine Terminal; the buildings themselves are high-and-dry, and the storage tracks barely scraped by the 0-2 ft. inundation. Shore up those trackbeds with good subsurface pumps. If things get hairy, Alewife maint yard and Billerica Shops are the evacuation routes for storing equipment. Billerica has 495-area access points to all lines but Eastern Route, plus the southside via Ayer-Worcester. Flood doors obviously on any NSRL portals, though those are likewise in the 0-2 ft. range and a least concern.
South Station comes out unscathed (yay!), but the terminal district is sacrificed to the gods. Readville is the high-and-dry equipment evac route because Widett Circle + Southampton and Beacon Park are destroyed. NSRL may be a lifesaver here if it has REALLY GOOD FLOOD DOORS on the portals. Like...eleventy flood doors and eleventy million pumps on the NEC side (wonder why that tunnel's going to cost much?). I don't even know what that would entail, but you have to keep that tunnel airtight with Back Bay being lost or the entire thing is going to become a storm drain. But note well: the Amtrak building at Southampton is only an 0-2 ft. inundation, and the Old Colony and Fairmount portals flank that building. You can shore up the drainage a la northside...more difficulty because the surrounding destruction leaves little place to pump the drained water. But, do a good enough job here and the Fairmount Line can feasibly be that last fragile tendril that actually reaches South Station and gets intercity service up and running again. Put eggs in that basket as the one to throw kitchen-sink flood prevention at.
Per individual lines, having rapid transit and bus terminal stops to turn at makes a big difference: NEC @ Ruggles, Fitchburg @ Porter, Haverhill/Reading @ Malden (or a temp wood Sullivan platform, as was done in the '80s when the North Station drawbridges burned). Those lines fare very well on mobility. Ditto Lowell/Downeaster if you can supersize shuttle buses to College Ave. + Davis out of West Medford or do the temp platform thing at a GLX stop. Old Colony would have problems at Braintree or QC because of the Red Line being knocked out longer-term at Wollaston, and this winter exposed that vulnerability for all to see. They're gonna need a way better shuttle bus strategy. Fairmount sans NSRL will have to turn at Newmarket, and that problematic rapid transit gap between Mattapan and Blue Hill Ave. rears its head for ham-fisted transferring. East-west buses upon buses upon buses are going to be Dorchester's lifeline, but they'd fare pretty well overall with Fairmount + Ashmont/Mattapan maintaining near-full uptime through the neighborhood.
The two worst cases by far: Worcester and Eastern Route. Worcester is going to be lost inbound of Newton Corner for a long, long time. And the Green Line being lost for a long long time doesn't help things there, because a jury-rigged Riverside turn doesn't get you further inbound on the D than Brookline. Worcester-proper has the inland option via Ayer and Fitchburg Line to Porter as augmentation, but inbound of Framingham? Pike shuttle buses aren't going to save them because the Pike will be gone too. Eastern Route is going to lose the Rockport Line for few weeks, and need the Salem Tunnel storm drain pumped out...but those are more time-wasters than infrastructure-destoyers. Otherwise, high-and-dry to Lynn and on the Newburyport Branch where the RR pre-dates all landfilling. Lynn bus terminal + the Tobin gives the North Shore a leg to stand on if the bus surging + prioritization works well. Forget about service through Chelsea, though; the railroad originally was causeways + bridges pre-landfill there and on the East Boston Branch, so you're not getting further inbound. While Blue Line to Lynn would also be knocked out for awhile north of Suffolk Downs, the BRB&L was also built pre-dating the landfilling and probably bounces back a *bit* faster than superduper fucked Chelsea. The rapid transit transfer is going to be needed, because you probably won't see commuter rail or Urban Ring service through Chelsea for months upon months. And there won't be anyone to pick up.
