(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:My examination of this project began with the schedule of objectives and obtaining required permits for the project:
getting permits/conducting surveys: 3 months
engineering: 10 days (review of designs?)
procurement: 2 months
construction: 2 months
permits/engineering: 3 months 14%
procurement: 75 days 37%
construction: 85 days 42%
site restoration/clean-up: 13 days 06%
total days: 203
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.
See the Intake screen used in this design: http://www.johnsonscreens.com/js/groups/public/documents/johnsonscreens/js_intakescreens.hcsp
see aditional diagrams and charts: Charts and Diagrams