Rising tides
For discussions and comments on the local blogs over last couple of days it’s become clear to me that the maps in the SunCal redevelopment concept plan (RCP) which depict the site constraints surrounding sea level rise are not clearly understood. Mainly, this is because the maps are not clearly explained. The map, presented below, shows a combination of 18 inch sea level rise and a 4 foot storm surge representing a once in 100 years flood.
It has become apparent that this map is being read by many as depicting solely sea level rise. Further, the map does not indicate the depth of the identified flooding, which in much of the area would be measured in inches (much of it as little as less than an inch it seems). And lastly, the map represents flooding that may occur if no amount of mitigation is undertaken.
Hopefully, SunCal can create some maps that indicate sea level rise shorelines at the existing site of depths from 18 inches to 36 inches (the current prediction made by realclimate.com, one of the most credible, science-based climate change related sites on the Internet), heck, one could put together a 6 foot prediction to cover the most consevative assumptions.
Given the wide ranging predictions, and ever changing numbers for the level of predicted sea level rise over the next hundred years, it would seem that no matter what project was created at the Point, a reasonable mitigation would allow for flexibility in years to come.
From the sounds of it, this project has looked at a dike system in the past, but the city of Alameda has not been extremely open to the possibility. I know that when I first heard about the idea, I imagined a walled in city something I don’t think it’s extremely desirable. However, reading a recent San Francisco Examiner article, posted as a link on Lauren’s site by Mark Irons, I realized with site grading, similar to what is currently being proposed, one could actually build a structural levee that would never have the feel of being walled in. Such a system, would give the site, and the city, the flexibility to adjust to changing circumstances in the future. It would seem that this should become a part of the discussion.
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DL Morrison
January 26th, 2009 at 4:57 pm
I’ve commented many times on the elevation and fill issues, but I haven’t tried to go into much detail because it’s difficult to do that concisely as this format requires.
In any event, I’d summarize it briefly as follows: Sea level rise is relentless and ultimately, nothing can be done to “mitigate” against it.
I’m looking into the future (as I think many proponents of development are) and I’m saying that this is an intolerable long-term risk. If this is site is subject to flooding *right now*, then where will it be 100 years from now?
I think a development of this magnitude, involving billions of dollars, requires a site that has a truly non-existent risk of flooding, no matter what happens.
At present the site “ranges in elevation” from “2 to 8 feet based on City of Alameda datum”. (Draft Plan, p.164 of Reader). The City of Alameda datum is equivalent to the average high tide. (If anyone wants further info on this assumption: I compared this datum to the City of Oakland datum, to tidal charts based on the MLLW level and to elevations based on the NGVD 29 datum.)
Figure 6.1 (p. 149 of Reader) indicates that w/ the 100-year maximum tide elevation (which would be only 3.5 feet above average high tide), a substantial portion of the site would be underwater. That includes much of the Adaptive Reuse area and the sports complex, which are not going to receive fill.
Figure 6.2 (above and at p. 150) shows most of the site underwater with the addition of the 1.5′ of sea rise (on top of the 3.5′ of tide), which means that this site is less than **five feet** above average high tide, as of *right now*. This is just not a feasible starting point, when in reality the predictions re sea level rise keep changing all the time, and may be much greater than anyone expects.
And of course the site is on fill, and fill tends to settle in earthquakes — it spreads “laterally”. The weight of new structures will also cause the fill to settle according to the Plan (p. 151). It will take Herculean efforts to try to stablize this site against earthquake damage alone, let alone stave off the ocean. Even if these efforts are partially successful in protecting the structures, they cannot protect underground utilities from earthquake damage.
So what happens if part of the site is underwater by the end of the century (the Adaptive Reuse area)? What happens if the access roads have to be raised (which isn’t addressed by the Plan)? What about storm drainage and the water table? What about the “nuisance flooding” on low areas of Main Street” which requires pumping? (p. 153) It seems very possible that much more of the site will need pumping in the not so distant future.
And what about all the other low-lying areas of the city, all of which are at risk? I think Alameda has enough to contend with as it is, and building on this obviously high-risk site is not advisable.
Mark Irons
January 26th, 2009 at 5:00 pm
John,
The article I posted which you link here does not give any indication of a gradual regrading in a bowl like formation to accomplish a raised lip effect while simultaneously avoiding an abrupt sea wall at the perimeter. That would seem to be the solution you are alluding to in your post where you say, “one could actually build a structural levee that would never have the feel of being walled in.”.
The article specifically says “to protect new buildings from floods, fill will likely be dumped beneath planned development sites”.
A couple things about the Point and RCP graphic. I did understand that the the light blue indicates the 100 year flood with the 18″ sea level rise, as opposed to the latter by itself, but if the 100 year flood was described as four feet in the text I may have missed it.
But to me none of that matters including the depth of any flood or amount of storm surge. To me any plan must build for a worst case scenario, whether that is a standing sea level or 100 year flood surge.
One of the articles I posted last week stated that the 18″ rise in sea level would turn the 100 year flood cycle into a 10 year cycle.
In the RCP there is no provision for sea wall, only the cursory mention of berms and grading in the most general context. The North shore which is most subject to lateral failure in a quake has limits on it’s ability to take the added weight from soil added to grade or sea wall. The RCP calls for most of the existing buildings on the historic north shore area to remain, which makes regarding beneath them a practical impossibility.
If there are plans to raise grades for some areas with new buildings while leaving others areas directly adjacent at existing grade, one begins to imagine a strange landscape. Any viable solution to this conundrum needs detailed explanation, including elevation diagrams to illustrate regarding.
Mark Irons
January 26th, 2009 at 7:26 pm
John wrote: “Given the wide ranging predictions, and ever changing numbers for the level of predicted sea level rise over the next hundred years, it would seem that no matter what project was created at the Point, a reasonable mitigation would allow for flexibility in years to come.”
John, would you be specific in what you refer to in the last phrase “a reasonable mitigation” which ” would allow for flexibility in years to come.”? What kind of flexibility, waiting to see how high the sea rises by 2025 before deciding on a plan of action, while continuing to build out the RCP plan as drawn?
The “wide range” to which you allude would BEGIN at 16″ rise by 2050, which has most recently been projected to accelerate to 55″ by 2100. It may not end up being that severe, but within reasonable scientific calculations it may also be worse!
It is not clear me whether the 55″ by 2100 is based on continued introduction of new carbon to the atmosphere at existing rates or if this is the projected impact for the carbon ALREADY introduced into the atmosphere. The difficulty with the projections relates to the fact that if we stopped introduction of any new carbon to the atmosphere today, the warming effect of the existing carbon has a momentum which will takes YEARS to dissipate.
DL Morrison
January 28th, 2009 at 7:16 pm
In response to Mark’s comment above re projected impact for carbon already in the atmosphere, here’s an article that appeared today on SFGate, and originally in the LA Times:
“Even if by some miracle of environmental activism global carbon dioxide levels reverted to pre-industrial levels, it still would take 1,000 years or longer for the climate changes already triggered to be reversed, scientists said Monday.”
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2009/01/27/MNQP15H779.DTL
This is sad news, really.
DL Morrison
January 28th, 2009 at 7:19 pm
A further quote from the article:
“The study looked particularly at ocean levels and rainfall. The team found that, just by thermal expansion of ocean water alone, sea levels will rise by 1.3 to 3.2 feet if carbon dioxide rises from the current level of 385 parts per million to 600 and twice that if carbon dioxide peaks at 1,000.
Melting of the polar icecaps could increase sea levels even more, inundating low-lying islands and much of the world’s shorelines, but the effects are too uncertain to quantify, Solomon said.
Reductions in rainfall also would last for centuries, according to the study, decreasing human water supplies, increasing fire frequency and devastating dry-season farming of wheat and maize.”