Well Yield – Introduction
Well is a man made formation having structures which permits appreciable amount of water to move through them under ordinary conditions. 3 types of sources that a well get water from:-
- Unconfined Aquifer have water table as upper surface of zone of saturation
- Confined Aquifer have water confined by an impermeable or very low permeable strata.
- Aquiclude water is confined between two strata i.e. top and bottom strata which are impermeable.
Determination of well yield
Involves test to see the balance between the maximum amount of water that can be pumped out of the well and the amount of water that recharges back into the well from the surrounding ground water source.
Recovery Test Method
It is conducted by stressing the well and measuring its recovery. The rate of recovery is then converted to a rate of flow into the well.
Constant Rate Discharge Method
The constant rate discharge test is conducted by pumping or bailing the well at a constant rate of 0.5 GPM. If a pump is used, the intake of the pump should be set at level that will allow water levels to be lowered by at least 80% of the available head.
Factors affecting well yield
· Well location
· Well development methods
· Particle size
· Diameter of well
· Open Area of Screen
· Hydraulic boundaries
· Recharge to Aquifer
· Stratification of an aquifer
Designing of a well
Well yield is very much dependent of well design and its other essentials.
With proper design of well, we get a reliable an sustainable water supply consistent with our needs and capability of aquifer.
Proper design increases life expectancy of well.
It reduces operation and maintenance cost.
Ease of monitoring well performance.
Reduction in well yield
- Mineral incrustation
- Sediment plugging
- Lack of recharge water
- Improving well yield
Case study : municipal well – Glendora, California
Hydro-fracturing process – It involves the installation of an inflatable or mechanical packer into a proper position such that it does not break the seal. Then it is locked into position and water is pumped under pressure through the packer. If successful, pressure will steadily rise and to a maximum level, as rock formation will resist flow and then pressure will suddenly drop off and stabilize at a lower level.
It uses a cable tool drill machine. This cable tool method employs the principal of free falling weight to deliver blows on the bottom of the hole. Surging uses same concept by attaching either a standard drill bit or surging block.
- Artiola, J.F., and K. Uhlman. 2009. Arizona Well Owners’ Guide to Water Supply. University of Arizona Cooperative Extension Publication.(80 pp.)
- Uhlman, K. 2008. Arsenic in Arizona Ground Water – Source and Transport Characteristics. University of Arizona Cooperative Extension Publication.
- Fulton Allan, Dudley Toccoy, McManus Dan, and Staton Kelloy; Water Well Design, Construction and Development : Important considerations before making an investment, University of California Publication
- New Hampshire Department of Environmental Services fact sheet
- Mansuy, N., Water Well Rehabilitation: A Practical Guide to Understanding Well Problems and Solutions 1999: Lewis Publishers.
- The Sustainable Water Well Initiative Business Case Report, GW Solutions Inc. for the Agri-Environmental Services Branch of Agriculture and Agri-Food Canada