Cost for developing in a flood plain

[petrosoft]

I would like to ask a general question about a development plan which my town, the City of Sebastopol, CA is formulating. It will allow development of 54 acres of an old industrial section of town. It envisions New Urbanism, with municipal buildings, commercial and four story residential structures.

Much of the development is below the 100 year flood line and close to the Laguna, a wetlands area. The plan calls elevating the development either on a parking podium or on 8 feet of fill. Also, the soils are prone to liquifaction and will probably need deep piers.

My question is about the cost of developing this type of land. I'm afraid that the City is going to set itself up for some very expensive real estate. That's not the intention of the Planners who want to encourage local businesses. They say they don't want to see big box stores and chains take over the town.

Does anyone have a guess about how much a pier system like this would cost and or if fill is a reasonable option? Would this kind of foundation add significant costs to the development? Would it make the commercial and residential costs much more expensive than surrounding development?

Thanks for your feedback.

 

[civilperson]

Development in a flood plain is poor management of land resources. If you fill to elevate out of the flood elevation, the adjacent property is affected and becomes vulnerable to flooding and the owners are liable to sue for damages after the change in flow characteristics. Parks, pastures, bike and pedestrian trails, and soccer fields are uses of flood plains less susceptible to flood damages and enhance urban quality of life while maintaining the flood plain.

 

[cvg]

note that without conducting a hydrology study, you cannot conclude to what extent the adjacent property will be affected by this development. It may not be affected at all. However, development in floodplains is inherently more expensive. Its hard to say how much the pier system would cost, however hauling in 8 feet of fill isn't cheap either. It doesn't sound like the best site to develop to me.

 

[petrosoft]

The City hired an hydrologist to show that the plan wouldn't impact the surrounding flood plain, at least not enough to notice. They also put a no net fill clause in the plan.

I agree that the best use would be a park or pasture. But, the City is determined to make some money out of the 54 acres. I'm trying to get a sense of how much this kind of development might cost. That issue hasn't really been addressed in all the EIR debates.

Thanks---Peter

 

[fattdad]

Are you trying to address a political issue or an engineering issue? Engineering controls can be designed to mitigate post-construction flood plain affects. They will cost money. Encroachment into wetlands requires permitting and further mitigation at increased cost and delay to the schedule. If the land has previously been in industrial development, I'd rather see it converted to modernization then to see development encroach into land that has not been previously developed.

Just some idle ramblings. . . .

f-d

¡papá gordo ain’t no madre flaca!

 

[petrosoft]

I'm trying to get a sense of the cost of developing 55 acres using deep piles to elevate the structures above a floodplain and potentially liquifiable soil. I'm sure it can be done technically. I'm more concerned that the cost of developing the area will result in very expensive real estate and that the only businesses which could afford it would be big box stores. The City wants to make the place usable for Government offices, median income housing and local businesses. Is that still possible with the cost of the foundation?

Thanks---Peter

 

[cvg]

the question is quite broad and really cannot be answered without a lot more information provided by you. quite a few issues have already been raised that you will need to estimate the cost and schedule impacts. depth to suitable foundation, number of piles, availability of borrow material and cost to fill the site, cost for flood and environmental mitigation are just a few.

 

[queque]

One alternative is to select one acre, 2 acres and 5 acres.
Select the site or sites based on the greatest cost (low elevation, high water surface, large area inundation, etc).
Prepare a strategy to improve the area with fill, FEMA LOMR (with fill) etc. Request bids for each project. This is enough to give the planners a basis to continue their efforts and to justify to
the citizens their rational.
Once the public is provided with this data, they will support or reject the idea.