Off Stream Reservoir Design & Cost

[sewerratt]

I am looking for resources on estimating costs of off-stream reservoir construction. I have been tasked with doing an order-of-magnitude estimate to construct a 10000 ac-ft reservoir. Having never done anything with reservoirs (we're primarily groundwater), I need to educate myself on the issues and considerations before I even begin. A good design manual, or guideline, a textbook, some sort of publication to inform me as to what every good reservoir should include is necessary before I can begin estimating costs of the constituents. That is what I'm looking for. Any thoughts?

 

[cvg]

you might start with your state division of dam safety and see if they would be willing to sit down with you and discuss the intracies of dam design and construction. They might be willing to share some cost estimating numbers. Then speak with the corps of engineers to determine what the environmental issues might be. Start with "Design of Small dams" by the BUREC to get an idea of what the dam might require (realizing that a 10,000 ac-ft reservoir may not be considered a "small" dam).

However, your best bet is to hire a consultant with dam design background to help you put together the estimate. Realistically, you would need a consultant team with geologist, geotechnical engineer, hydrologist and probably structural - plus archeologist and biologist to process the bugs and bunnies requirements

http://www.damsafety.org/

 

[DMcGrath]

The costs are certainly driven by the location and type of reservoir. I suppose the worst case would be a "from scratch" reservoir that does it's best to tie in to the topography to a likely best case of an old quarry that just happens to be nearby and have enough capacity. Just for consideration, however, consider the reconstruction of the Upper Taum-Sauk Reservoir in Missouri. Reservoir volume = 4,350 acre-feet, construction cost ~$350 million (2.7 million CY of RCC).

 

[cvg]

impressive, but Taum Sauk is a very unique structure to say the least. A more typical reservoir will cost way less (order of magnitude less) than $350 million. But not to be lost is the fact that dams cost a lot for engineering, right of way acquisition, construction, environmental permitting and maintainenance. And since you say your reservoir is off line, also include the cost of the channel or pipeline used to divert the water into the reservoir.

 

[sewerratt]

We will employ a consultant for this if we proceed, but before we spend the money on that, we need to know if it is even worth that effort. My gut is no, but I need to quantify that for management. thanks for the pointers. Any old timers with a rule of thumb of $X/ac-ft for flat terrain, sandy, silty soil with non existent bedrock?

 

[cvg]

Some questions you need to answer

if flat terrain (how flat is "flat"), how will you contain the water - the dam must tie into an abutment. Excavation to store below grade is expensive.

How will you prevent water from infiltrating into the sandy/silty ground through the bottom of the reservoir? Some solutions might be bentonite or hypalon liner

To prevent leakage through your dam you will need core material for the dam. Where will you get that?

Does your proposed reservoir site have a significant watershed? (If so, you will need to divert the stream, provide an outlet works and construct an emergency spillway.)

You will need bank protection for the dam and possibly for the banks. Where will you get the riprap and what is the cost?

note, we can provide tips on this forum, but in my opinion there is no way to give you a rule of thumb estimate for this that would make any sense. How about $1,000 per ac-ft?

 

[sewerratt]

Sorry, I jumped the gun on estimate amounts. I appreciate the dam safety direction. I'm pursuing that now. But I'm surprised at the lack of a published 'authoritative' resource for considerations on design. I want to find an authority, be it AWWA or the like (which I've checked, unsuccessfully), that has published something that deals with all the considerations necessary to design one from the beginning. eg, site constraints, liners, as you mentioned. WHen to use bentonite, when native clay is OK, when to go to EPDM, depths above 'storage' necessary to prevent algal growth, etc. We are in the coastal plain, so traditional Hoover Dam type reservoirs are out the window. Probably end up looking like an elevated rectangular lake with a levee perimeter. I personally think the idea is a non-starter but I have to quantify that to those who think them up. Thanks again.

 

[DMcGrath]

I take it you are looking for something like this:

http://www.catoctinpower.com/aspnetpages/Applications.aspx?CPCN

(see figure 3.1-5)

The general approach was to estimate a cost on a conceptual berm cross section, calculate the volume of the berm and the cost to build it ($/CY). Other considerations for liner, land costs (purchase, clearing, etc) were done on a per-unit basis. Choose an economical depth to perimeter ratio (e.g. deeper water = smaller reservoir footprint, but larger berm).

Your bigger-ticket costs are going to be earthwork, land acquisition, environmental permitting, and liner (if so equipped).

Just to throw another wild card out there, would aquifer storage and recovery (ASR) be worth considering in your area?