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Raw-Water Intake Structure

(example of a raw water intake structure under construction)

(example of a raw water intake structure)

    The purpose of a structure such as this is to pull and store water for a power plant from a local water source, usually a river or a dam.  The basic set-up consists of an intake structure, one or several pumps, air-burst cleaning equipment, and a holding reservoir.
   A general overview of the project might be:

initial schedule:
getting permits/conducting surveys: 3 months
engineering:  10 days (review of designs?)
procurement:  2 months
construction: 2 months

final schedule:

permits/engineering:  3 months               14%
procurement:  75 days                             37%
construction:  85 days                              42%
site restoration/clean-up:  13 days          06%

        total days:  203

    My examination of this project began with the schedule of objectives and obtaining required permits for the project:

Duration  week of

Corp Permit Amendment Complete  
DEQ Permit Amendment by May 1 Apr 22--May 6
VMRC Permit Amendment by mid May
 Apr 22--May 13
Corp Approval of Mussel Survey Complete  
Capacity Deliverability Study Conclusion
by mid May  
Owner Decision to Proceed Event  may 13
Initiate Mussel Survey 

Perform Survey 2 days   June 03--July 01
Submit Survey Report to Agencies 5 days  July 01--July 08
Agency review of report 10 days  

Construction Stormwater Permit 60days  May 13--July 15
316(b) Permit Related (if needed) NA  
Contractor Scope of Work
Engineering/Design 10 days  May 13--May 20
Procurement 60 days  May 27--July 22
Construct 60 days  

            DEQ -- Department of Environmental Quality
            VMRC -- Virginia Marine Resources Commission
            Corp -- Army Corp of Engineers

          click to see more about these organizations:  Environmental Regulation
    A more in depth schedule lists sample dates for the design, ordering/receiving needed items, construction, and site restoration.


    The intake structure itself is sunk into the bed of the river.  Many variables factor into the construction of the structure, such as daily water use (pipe diameter, pump size), water availability (reservoir capacity), intake screen face velocity, seasonal river levels, and environmental regulations.

    The example power plant requires 9 million gallons of water per day.  This requirement dictates the pump size and pipe diameter required to supply the water to the plant.

    The reservoir, 650 acre-feet, is usually measured in days of water it supplies.  One acre-ft = 43,560 cubic ft.  One cubic ft = 7.48 gallons of water.  At 9 million gallons per day, a 650 Acre-feet reservoir would supply water for about 23 days.

    Intake screen velocity is another important factor in the design of the intake structure.  There are two common intake screen velocities:  face velocity and screen velocity.  Face velocity simply measures the speed of the water as it approaches the structure.  Not enough velocity means that the screen has a larger surface area than required.  This does not negatively effect the design, but it means that extra money was spent on a screen size that was not needed.  Too much velocity can be detrimental as debris and animals cannot escape its pull. 

    A screen opening velocity measures the velocity of the water as it moves through the screen openings.  This is important to measuring the environmental impact of the structure. 
A screen opening velocity of 0.25 f/s is generally accepted maximum.

    The entire structure is cleaned through use of pressurized air blown through the pipes to dislodge any debris on the intake screens that could cause problems with the water flow.

    In this design, water is taken in the screens from where it is depressed into the river bed.  From there it is pumped into the pump house, where it is diverted to the water reservoir for storage.  When needed, water is brought to the pump house from the reservoir, filtered, and pumped to the power plant for use.

(construction of the intake screen vault)

(intake screen before installation)


see aditional diagrams and charts:  Charts and Diagrams