posted
My current story involves a coastal city that is having trouble getting supplies in past a reef. I have a lovely picture in my head of how it all works and how they solve the problem. The catch is that I really don't know all that much about ships and tides and ports and such, and Google can only take me so far.
Does anybody know an expert in this sort of thing? I would like to bounce some theories off of them to see if my plot would actually work.
(The unanswered question: Will my plot hold water?)
posted
Consider pursuing answers here at Hatrack forums for the memberships' benefits.
I have extensive naval, nautical, and maritime science education, training, and experience. I've explored reefs, sailed and motored over them, between them, and through them: manmade, natural. rock, coral, rubber tire, sunken ship, sand, weir, and breakwater, etc.
I need a few more details about the reef structure before I can say the "plot holds water." Foremost, whether the reef is an unbroken line and only high tides and riverine floods flush water over it. Preliminarily though, reefs are no impenetrable barrier to ocean-going vessels.
However, lightering was and still is a common practice when a suitable deep-water port is unavailable to a landing. Lightering is use of shallow-draft barges and small freighter craft to transfer to and from deep water to shallow water or shore landings.
Now that I think about it, it's the setting, rather than the plot, that might have trouble. It's not exactly a reef.
The setting is roughly contemporary and on the coast of a tropical continent (as opposed to island) on a secondary world.
A manufacturing city was built on the coast (it produces something heavy, possibly steel?) and all of the streets are lined with walls and the few windows on the street are barred.
A natural disaster occurred (earthquake?) and dropped the level of the city about 20 feet. It is now pretty much under water, except for the walls and tops of buildings at mid to low tide. Many people died, and the wealthy survivors left and those remaining are living on what was the high ground.
So the city is functioning as a reef.
The people built a dock/wharf/pier/whatever on the far side of the city so the ocean-going freighters can offload their cargo, and they use smaller boats to haul the load into shore. The catch is that the smaller boats can't keep up with the demand (not enough boats / tropical storms / general turbulence / something I haven't thought of yet), and there's a food shortage. Also, they would like to re-start the manufacturing, but they can't because they can't get replacement equipment in.
So they start looking for a way to get the big ships in closer to the city.
Now you can see why I needed a sailor.
If they wouldn't do things this way, what would they do instead?
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posted
Well, I'm not a sailor, but I'm a sea kayaker. I'm also married to a physical oceanographer and have read my share of sea yarns.
One thing you should be aware of is the relation between lunar gravity and the tides is more complicated than you learned in elementary school -- unless you're talking about an island in the middle of the ocean. Where a complex coastline interacts with water lunar gravity is a driving force in a resonant system -- the water in a bay can act like the air in a organ pipe.
As a result some places get two high tides a day, some get one. Some places like Galveston or Honolulu get tides that vary low to high by about a foot-and-a-half. The Gulf of Maine on the other hand has tidal amplitudes that run from six feet at Boston in the south to 47.5 feet in the Bay of Fundy in the north. The Wikipedia article on Fundy has good map of the Gulf of Maine; you can imagine the water sloshing around like in a bathtub.
I recommend you read Richard Henry Dana's TWO YEARS BEFORE THE MAST, one of the finest seafaring memoirs ever, but I'll cut to the chase. After Dana returns from his two year voyage in 1836, his ship spends several days anchored with in sight of Boston waiting for favorable combination of tides and winds for a safe approach to the harbor. Small sailing boats routinely make this approach, but it's challenging and dangerous for a less agile cargo ship.
No reef is needed to make the approach to a port treacherous; tidal currents and wind and islands are enough. Imagine a funnel shaped estuary or a bay with a restricted opening. These places can easily have 10 foot or even 30 foot tides and tremendous currents. Such places are unusual, but the do exist. I've seen navigational buoys in such places heeld over at 45 degrees by the current and throwing a rooster tail ten feet into the air.
If you had place like that with strong on-shore prevailing winds and semi-diurnal tides there would be only a couple of narrow windows per day in which you could approach with a sailing vessel. During peak ebb tide the ship could not make headway upstream. During peak flood tide there would be dangerous following and quartering seas that would tend to drive the ship off course and possibly aground.
A reef or shoal per se is not a serious barrier to shipping for an established port. Pilots who knew the safe passages would be rowed out to waiting ships. It'd be routine for them. If those pilots were kidnapped, that could bring commerce at *any* port to a halt. Bad weather combined with treacherous tides could also bring shipping to a halt despite the availability of experienced pilots. But a reef by itself? Not really a problem unless there are *no* safe passages through it. In that case the town would be like any other landlocked town, and wouldn't be supplied by boat.
One possible mode of research here is to pick some place that is infamous for shipwrecks and then read about them. The three most treacherous places I can think of off the top of my head would be Sable Island in Nova Scotia; the Elizabeth Islands off the SW elbow of Cape Cod, and the stretch of coast between Virginia Beach an the Outer Banks of NC. The latter two are covered in Eldrige's annual Tide and Pilot Book. You might look up works by historians about such places, like Graveyard of the Atlantic: Shipwrecks of the North Carolina Coast.
But seafaring memoirs like Dana's are probably the best source of material for learning the practical impact of navigational hazards given period technology. What a 20 foot recreational sailboat can do and what an 80 foot ship-rigged Brig can do are two different things.
Posts: 1459 | Registered: Dec 2010
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posted
A real-world analog to a manmade reef of buildings and walled streets might be D-Day invasion beaches' anti-amphibious landing construction, comparatively short scale though.
A tropic coastal continent city subsided below the sea, left a building and wall reef seaward. How? Perhaps from tapping a coastal aquifer to the point bouyant water no longer supported the limestone bedrock. One massive sinkhole complex. The city's capital fled; those who remained resettled on the city's high, interior land. Food shortages plague the survivors. They want to open a deep-water channel and restart manufacturing and trade lost to the land subsidence.
The reef would rapidly become a seafood bonanza. Grains and turf foods, though, are in short supply. They are not farmers; nor is farming a suitable import/export substitution solution.
Why? A trade-wind-facing climate would deposit ample orographic precipitation where the land uplifts, inland. Onshore trade winds would also create a coastal squall line inland due to daytime oceanic evaporation, onshore winds, and landward condensation eveningtimes and offshore winds over night. Precipitation would be ample enough for agriculture.
The city's survivors have neither the wherewithal nor the essential knowledge sufficient agriculture demands. Four principal requirements for industrialized agriculture are mechanized equipment, pesticide, herbicide, and fertilizer chemicals, suitably level, broad, fertile terrain, and irrigation. The survivors are ex-urbanites, mostly ex-industrial and service-economy laborer families. They don't know how to farm, having no brain trust for it, except small patch kitchen gardens. Nor do they have an economical source for equipment, chemicals, nor adequate land. They need to restart the industrial base in order to trade for grains and turf foods. They need a deep-water port.
The more economical solution is to open a channel, by demolishing a well-planned, deep-water channel through buildings and walls. Demolition might be explosives. Dredging and debris removal might move the matter to the channel's side as a rip-rap breakwater jetty lining the channel. Roadways could line the jetty.
The port itself would have a mooring basin, a dockside quay (pronounced key), resembling a skeleton key, the wharf the landside landing and handling apron with warehouses, key-like finger docks protruding into the basin for small vessels, and bulkhead docks for large vessel tie-ups.
The channel and the basin would have to be a depth that exceeds the largest anticipated ships' drafts. Conventional major world ports are eighty or so feet mean low water depths, average annual low tide. Industrial ports worldwide average more like fifty or sixty feet mean low water depths. A major capital investment, in any case, the city survivors cannot afford yet.
In the meantime, they work on opening the channel and receive and ship LASH barges carried by LASH cargo haulers. LASH, lighter aboard ship, is a cargo system developed for oceanic trade to and from seaside communities that do not or cannot establish deep-water ports and at one time used for riverine transport to and from seaside ports and upstream facilities. See Wikipedia: Lighter Aboard Ship. LASH shipment economically handles cargo where port facilities are limited or nonexistent. They can be loaded and unloaded from a shoreline firm enough to support forklifts and trucks or hand loaded and unloaded. While tidally dependent, a few hours wait for high tide is no practical bar to their use.
However, avoid getting bogged down in the minutia. That will delay or stall writing and reading satisfaction. Folk native to the milieu will more or less take the system for granted once it's implemented anyway. Demolish and open a suitable channel, begin transhipping LASH: the most economical solution.
quote:Originally posted by MattLeo: If you had place like that with strong on-shore prevailing winds and semi-diurnal tides there would be only a couple of narrow windows per day in which you could approach with a sailing vessel. During peak ebb tide the ship could not make headway upstream. During peak flood tide there would be dangerous following and quartering seas that would tend to drive the ship off course and possibly aground.
Take a look at Princess Louisa Inlet in British Columbia, too. It's really more properly called a fjord. With a sandbar (left behind by the glacier that carved it) at the mouth. I was there in a small cruise ship that had a very shallow draft. We still could only get in or out of the inlet at high tide. And they had a zodiac out ahead, checking the depth both times.
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posted
Meredith -- I hope you journaled that experience. Sounds like a good source for a scene.
Niki -- I'd suggest you look at a map of a real coastal city and imagine what would happen if it suddenly collapsed. Google maps provides a "terrain view" and street view may also be useful. Here's an example. Google Earth is another useful tool.
As for the cause of the collapse, earthquake subsidence is usually less than a meter (I'm married to a geophysicist, remember? I read her journals when they come in).
There's two kinds of scenarios I can think of that would produce the kind of sudden flooding you need. One would be a giant sinkhole forming. This could happen suddenly because of the gradual lowering of the water table (due to pumping? Sea level fall?). It could only happen in a city located in coastal karst landscape, like Trieste.
The other scenario would be a city that has been gradually subsiding for years and slowly building up flood control structures. Think New Orleans, which pretty much floats on muck. There's no place to collapse into but more muck, but a failure of the levees could render it uninhabitable. A disaster scenario could look like this: an earthquake undermines the sea wall by liquefying the soil underneath, then a tsunami sweeps the remains of the wall away. Don't underestimate the power of waves to move rocks around. Tsunamis have been documented to have move boulders of nearly eighty tons as much as forty feet vertically.
A third option, always worth considering, is not explaining the cause disaster at all. Even if you have some idea of why it occurred the reader doesn't necessarily get anything out of that explanation. I've seen many manuscripts bogged down in the author's explanation of how the current situation came to pass, when all the reader really needs to believe it is a compelling description of what the situation *is*.
What you *do* have to make clear is the ongoing situation -- why didn't the people move away when their city was destroyed? Perhaps it's the unobtanium mines in the hill, which is why they built the unobtanium mills here.
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quote:Originally posted by MattLeo: Meredith -- I hope you journaled that experience. Sounds like a good source for a scene.
Not really. I wasn't a serious writer back then.
But, it's one of those experiences that stay with me. I remember it quite well. And I took lots of pictures. Posts: 4633 | Registered: Dec 2008
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posted
Holland has extensive levees seaward. Florida's lower parrish has karst-like bedrock. Georgia, the Carolinas, and the DelMarVa peninusla have karst-like bedrock coastal plains. A few years back a geology panic was reported when cracks were noted in the mid Atlantic U.S. seaboard's continental shelf scarp face, attributed to coastal aquifer drawdown and threatens a land subsidence.
Venice too is built on estuary silt that won't support the city's buildings. Vietnam, China, karst-like coastal plains. For Earth, due to the Coriolis effect, mid Pacific and Atlantic continental coastal plains facing east are sandstone and limestone bedrock. A secondary oceania world would have a similar constitution.
A global warming threshold event could also cause a swift coastal innundation. A meteor impact offshore could buckle bedrock and cause a land subsidence, not to mention a tsunami. A bolide impact formed the Chesapeake Bay. Land subsidence is a fear for regions where shale oil fracking is done. A Los Angeles coastal island--Radio Island--sank after an oil deposit beneath it was tapped. Seawater pumped down the well saved the island.
Worth note--land structures cannot long withstand wave-action hydraulic forces; walls and buildings will topple within weeks of constant wave exposure. A riprap seaward sea wall brick, stone, block, reinforcing steel, and splintered wood jetty will form the first year and shelter structures behind it. A sand ridge will line the seaward rubble edge in no time. A river usually runs to sea past a coastal city. Port facilities are seaward of the city, the natural channel and basin dredged to depth if needed. And alluvial sediment bars run alongside the seaway channel, miles offshore.
Though the city need only label the event as The Flood, of a previous generation.
MattLeo raises a relevant contextural question: Why did the innundation event survivors stay?
Nowhere else to go is one answer. Couldn't afford to migrate is another. Love of place and an irresistible sense of belonging to place is another. Perhaps the flight of capital opened up desirable living spaces they'd been previously denied.
Again, though, avoid bogging down in the minutia. The story and its dramatic complication of people's lives, one personally, is what matters foremost and how that complication expresses a moral human condition crisis.
"On March 16, 1936, warmer-than-normal temperatures and torrential rain followed a cold and snowy winter, leading to the rapid melting of snow and ice on the upper Allegheny and Monongahela rivers. These rivers and their tributaries were already over their banks and were threatening the city of Pittsburgh. On March 17, 1936 the waters reached flood stage of 25 feet." More at http://en.wikipedia.org/wiki/Pittsburgh_Flood_of_1936
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