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Candlestick Development Wind Tunnel Tests
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pthorner



Joined: 29 Mar 1994
Posts: 160

PostPosted: Wed Oct 29, 2008 5:31 pm    Post subject: Candlestick Development Wind Tunnel Tests Reply with quote

The City of San Francisco is getting ready to run wind tunnel tests to evaluate the impact that new tall buildings near the freeway may have on the launch and sailing area at Candlestick. I am including a graphic showing the locations (yellow dots) for which the model would generate estimates of any changes in wind velocity and turbulence. It looks to me like they have picked the right points to look at including points upwind of the launch and upwind of the where impact are more likely to occur. Let me know any thoughts you have as the City is expecting the tests to be run shortly. A secondary question once the test is done it to try and evaluate how accurately it portrays what is likely to happen in the real world.

Peter Thorner
San Francisco Boardsailing Association
thorner@sfba.org



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FredFX



Joined: 20 Aug 2008
Posts: 220
Location: South Bay Area, CA, USA

PostPosted: Wed Oct 29, 2008 8:47 pm    Post subject: Reply with quote

I guess since I'm not a pro, I don't know if this is accurate, but when I went kitesurfing for two weeks in france I heard that trees/buildings/other things mess up the wind for ten times their height.

So like, if a building is 20 feet tall, 20 * 10 = 200feet after that building the wind will be messed up.
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pthorner



Joined: 29 Mar 1994
Posts: 160

PostPosted: Wed Oct 29, 2008 9:41 pm    Post subject: Reply with quote

The 10x rule of thumb commonly cited by sailors seems to apply more to velocity but turbulent effect can run as far as 20-50x height. With structures, the key variables beyond height are width and shape. The air going around a very narrow building should come back together and smooth out more quickly than air going around a very wide building. A building with rounded corners or a curves could create less turbulence as wind passes the building. The sensors in the wind tunnel can measure turbulence as variations in velocity over a short period, but I don't think that they capture variations in direction that you can have from vortex effect or swirling wind.

Peter
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ctuna



Joined: 27 Jun 1995
Posts: 1007
Location: Santa Cruz Ca

PostPosted: Wed Oct 29, 2008 10:03 pm    Post subject: I'm surprised that this would be a consideration Reply with quote

I would think windsurfing would be non existent on there priority list.
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FredFX



Joined: 20 Aug 2008
Posts: 220
Location: South Bay Area, CA, USA

PostPosted: Wed Oct 29, 2008 11:19 pm    Post subject: Re: I'm surprised that this would be a consideration Reply with quote

ctuna wrote:
I would think windsurfing would be non existent on there priority list.


Well, windsurfers in the SF bay do wield a lot of power. E.g. they stopped the advancement of SFO.
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pthorner



Joined: 29 Mar 1994
Posts: 160

PostPosted: Thu Oct 30, 2008 12:16 am    Post subject: Reply with quote

Windsurfers didn't stop SFO on their own but were taken very seriously as part of a coalition that held SFO at bay and worked to educate the public and the decision makers about the facts that made the project a really bad idea all the way around - 90 million cubic yards of fill to be financed with bonds backed by the profits of United Airlines (who subsequently went bankrupt) and other airlines. Major losses at the airlines and 9/11 put the nails in the coffin. From early on, SFO talked with us because they knew that they would have to mitigate impacts on our recreational use. They offered to spend major amounts of money but had to be educated to understand that there are a very limited number of spots where good windsurfing can be accommodated. You can't just build a ramp and a parking lot at any old spot. You need steady, regular side shore wind near the shore and deep enough water to allow access at all tide levels, etc.

State law (environmental quality act) requires that impacts be analyzed and that significant impacts be mitigated if practicable. I think the SF Planning Department takes the wind issue seriously. If the consultant preparing the environmental impact report found that there would be a significant impact to the windsurfing recreational use, then the city could require some kind of mitigation such as lowering height or improving access to another launch out of the wind impact area. If the city approved a project with impacts, they would have to make a finding that the community benefits of the project justify the negative impact. A project like this gets voted on by the planning commission and then can be appealed to the Board of Supes. Any developer obviously wants to maximize profits (especially in uncertain times), but it is also a given that projects will get modified to avoid impacts. For the developer, height can improve profits because they only pay for one foundation but gets extra square footage and units by adding more floors and higher floors generally bring more money with better views. The city has been moving toward more high density/high rise projects to add many housing units with the idea that it will keep prices more affordable and might create housing near jobs.

Peter
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SWE106



Joined: 14 Feb 2005
Posts: 264
Location: San Mateo

PostPosted: Thu Oct 30, 2008 10:33 am    Post subject: Reply with quote

Thanks for keeping everybody updated! I agree that they've captured most of the (sailing) area of interest. I would have liked to see a few more upwind locations though.
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victor



Joined: 03 Aug 1998
Posts: 581

PostPosted: Thu Oct 30, 2008 10:45 am    Post subject: Reply with quote

It doens't look good for the Stick. The lower part of Vistacion Valley is the last undeveloped land in SF and the light rail line is already in place extending the 3rd St. corridor almost all the way to So.SF. There are condos planned for most of the area upwind with quite a few already in place or under construction.

Rod and Gun Club has a very similar set up although on a smaller scale. It was apparently affected by a couple of new, 3 story buildings directly upwind of the launch. It was always a little dead on the inside but this last season hardly anyone even sailed there.
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Epenrose



Joined: 05 Nov 1997
Posts: 403

PostPosted: Thu Oct 30, 2008 6:48 pm    Post subject: Reply with quote

Would be really sad to lose this site, especially as so many of us learned the ropes at this spot.

What are the chances this will fail I wonder.

Surprised it is still an economically viable plan.
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pthorner



Joined: 29 Mar 1994
Posts: 160

PostPosted: Fri Oct 31, 2008 12:53 pm    Post subject: Reply with quote

The economics of the proposed area plan might or might not be that great right now, but the land owners can always wait to build until the market is better. The 200'+ buildings would be a good distance from the launch but might still have an impact in the launch area. The sailing area farther out from the launch would not be affected by this project, but you have to get out and manage to get back in far upwind to make the launch. The other site that could have impacts on the launch is the ball park and associated parking lot. The last conceptual plan I saw for this envisioned a neighborhood across most of that are that would be low-rise residential which beats mid/high rises or a mega mall.

http://www.sfgate.com/cgi-bin/object/article?f=/c/a/2008/10/23/BANK13LI7B.DTL&o=0

Another issue down the line might be wind turbines that are be looked at for Brisbane. Ideally they would be located as far south as possible, but for a project to pencil out, they typically want to place as many turbines as possible. In a perfect world they would be offshore and downwind where the wind would be cleaner, but I don't know much about the foundation required to site them on mud and they would have to deal with the BCDC and State Lands Commission.
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