An irrigation well is a specialized borehole drilled into the earth to access underground water supplies specifically for watering landscapes, gardens, or agricultural crops. Because the water is not intended for human consumption, the system typically does not include the extensive filtration and purification measures found in a potable water system. Irrigation wells, especially those used for commercial agriculture, are frequently designed for a much higher capacity and flow rate to meet the substantial water demands of large fields. Using these private water sources allows users to bypass municipal water costs and avoid potential restrictions on outdoor water use during drought conditions.
How Irrigation Wells Access Groundwater
An irrigation well taps into an aquifer, which is an underground layer of rock, sand, or gravel saturated with water. This groundwater reservoir exists in the pore spaces and fractures of the earth’s geology. The drilling process creates a vertical shaft that penetrates the layers of earth until it reaches the targeted water-bearing stratum.
To maintain the integrity of the borehole, a tubular structure called casing, usually made of steel or plastic, is inserted into the shaft. The casing prevents the surrounding soil and rock from collapsing and seals off shallower surface water from mixing with the deeper aquifer water. Attached to the bottom of the casing, in the aquifer zone, is the well screen.
The well screen is a specialized filtering device with precisely sized slots that allow water to flow freely into the well while blocking out larger particles of sand and gravel. Sometimes, a filter pack composed of clean, uniformly sized quartz-based gravel is placed around the screen. This gravel pack enhances filtration and improves the flow of water from the aquifer into the well shaft. When water is withdrawn by a pump, the water level drops from its static level to a lower pumping level, a difference known as drawdown.
Different Types of Wells Based on Depth and Construction
Irrigation wells are categorized based on their depth and construction method. Shallow wells access the uppermost, unconfined aquifers, typically ranging from 10 to 30 meters deep. These wells are constructed using simpler, less expensive methods like jetting or driving a pipe into the ground, suitable for areas with a high water table and sandy soil.
The water supply from shallow wells is susceptible to seasonal variations and can run dry during periods of drought or heavy usage. While adequate for residential lawns or small gardens, their limited yield makes them less ideal for large-scale agricultural operations. Deep wells are drilled, often reaching depths of 50 to hundreds of meters, to tap into deeper, more stable, and confined aquifers.
Deep wells require specialized drilling rigs and more robust casing, resulting in a higher upfront cost. They provide a more consistent and higher volume of water, making them the preferred choice for commercial farms with extensive irrigation needs. The greater depth means the water is naturally filtered through more soil and rock layers, offering a more reliable water quality baseline, though testing is necessary for naturally occurring contaminants.
Essential Surface System Components
Several surface and downhole components are necessary to deliver the water for irrigation. The well pump provides the mechanical force to move the water from the subterranean source to the surface. For deeper wells, a submersible pump is installed inside the well casing to push the water upward.
Shallow wells may utilize a jet pump, which is located above ground and uses suction to pull water up, though this method is limited to depths of about 33 feet. The pump’s operation is managed by a control box, which regulates power flow and startup. This control system works in conjunction with a pressure switch that monitors the water pressure.
Water is routed through a pressure tank, which stores a volume of water under pressure. This storage is crucial because it reduces the frequency with which the pump must cycle on and off. This reduced cycling minimizes wear on the motor and helps maintain a steady flow of water to the irrigation system.
Regulatory Requirements and Water Use Management
The installation and operation of an irrigation well are subject to regulations designed to protect groundwater resources and public health. Before drilling begins, a construction permit or a notice of intent must be filed with the relevant local authority. These requirements ensure that the well is constructed safely and sustainably. Requirements also include adherence to setback rules, which dictate minimum distances from septic systems, property lines, and other potential sources of contamination.
Upon completion, the well driller must submit a detailed well log, which records the well’s depth, geological formations encountered, and the static water level. For large-volume users, particularly in areas designated as “capacity use areas,” there may be requirements to register the withdrawal and submit annual reports detailing the quantity of water used.
Excessive or unsustainable withdrawal can lead to significant drawdown, potentially impacting nearby wells or the long-term health of the aquifer. Proper management involves monitoring water levels and flow rates to ensure that the well’s pumping rate does not exceed the aquifer’s ability to naturally recharge over time. These practices are essential for maintaining the groundwater supply as a viable resource for future irrigation needs.