Irrigation water wells (water boreholes) must be capable of producing adequate water during peak seasonal use and under drought conditions. Without a reliable, efficient, and economical supply of water, the entire irrigation system, regardless of the most sophisticated well head equipment design, is renderedf useless. The water well is the “heart” of irrigation systems with groundwater supplies; it must be properly designed and compatible with the water pump and distribution system to ensure long life, efficiency, and economic operation.
Commercial Water Borehole Installation – Essex Glass Factory 2014
The potential ground water sources of irrigation water in Northern England include the surficial, intermediate aquifer systems. The choice of aquifer is often dictated by location. It also depends on the quantity and quality of water desired. The cavernous nature of Yorkshire’s limestone formations produces abundant quantities of water from open bore holes (generally 4-12 inches in diameter) constructed into the limestone. In some areas of Yorkshire, the depth of bore holes may be limited due to increases of salinity with depth. If well yield is too low, additional properly spaced wells may be required. Back-plugging of some irrigation wells has been successful as a remedy against upcoming deep saline waters.
A well consists of many or all of the following key parts:
- open bore hole
- well head configuration.
Water well construction in the UK is regulated by the National Ground Water Association address each of these parts with alternatives given to account for variation in geology in various areas.
The local water authority should be contacted to obtain an abstraction license and information on well specifications. In most cases, the National Ground Water Association will be able to provide sufficient geologic data to help select the best well design with regards to water supply and construction cost. The well drilling contractor should be licensed and have experience in the construction of screened irrigation wells.
The depth by which the water level is lowered below the static level in a well when pumping is in progress is called drawdown. Drawdown is the difference, measured in feet of water, between the static water level and the water level during pumping. This term represents the hydraulic head, in feet of water, that is needed to cause water to flow through the aquifer toward and into the well at the rate that water is being removed from the well.
Gravel-packed wells have a bore hole through the water-bearing formation that is larger in diameter than the well screen. The zone immediately surrounding the well screen is made more permeable than the aquifer by filling the space between the face of the bore hole and well screen with graded sand or gravel that is coarser than the formation.
Naturally Developed Well
A well in which the well screen is placed directly in contact with the water-bearing sand and gravel is a naturally developed well. The width of the openings in the screen is selected so that fine sand in the aquifer immediately surrounding the screen can be removed by pumping during development to create a highly permeable zone consisting of the coarser formation particles.
The yield of the well per unit of drawdown, usually expressed as gallons per minute (gpm) per foot of drawdown, is called specific capacity. It is obtained by dividing the pumping rate by the drawdown for a specific pumping period. For example, if the pumping rate is 1500 gpm and the drawdown is 20 feet, the specific capacity of the well is 75 gpm per foot of drawdown.
Well Capacity or Yield
The volume of water per unit of time discharged from a well is its capacity. Well capacity is usually measured as the pumping rate in gallons per minute (gpm) or cubic feet per second (cfs).
Static Water Level
This is the level at which water stands in a well when no water is being removed from the well either by pumping or natural flow. It is generally expressed as the distance from the ground surface (or from a measuring point near the ground surface) to the water level in the well. The level to which the water level rises in a well that taps an artesian aquifer is also referred to as the piezometric level. An imaginary surface representing the artesian pressure or hydraulic head throughout all or part of an artesian aquifer is called the piezometric surface. The piezometric surface is the real water surface, or the water table, in a water table aquifer. The artesian aquifer is different from the water table aquifer in that the saturated zone is confined by the confining layers or aquicludes.
We offer a turn-key solution that covers not just the technical aspects such as borehole prognosis, but also every requirement typical of any large commercial water borehole project:
- Health and Safety
- Project Management
If you would like to talk to us about your project, we are happy to give no obligation advice. Visit our website, use the contact form, or call us on 01246 743022
In Part II, we will be expanding on Water Well Design and Build and Water Well Development.
Thanks for reading!
Jenny Hormell,Director, Waterseekers Well Drilling Services Ltd
The post Design and Installation of Screened Water Boreholes for Agricultural Irrigation Systems – Part I appeared first on Waterseekers Water Well Drilling Services Ltd.