Chapter 13

Micro-Irrigation Systems for Vineyards

Groundwater Wells

A well is an opening stretching from the ground surface to the underground aquifer, where the groundwater is located. The depth of the well may vary from a few feet to several thousand feet. Wells are typically drilled with special drilling equipment able to penetrate the various layers of the ground, such as sand, clay, bedrock, and the like. Inside the drilled hole a casing (pipe) is typically installed, which prevents the well from collapsing around the pump. Below the casing and in line with the aquifer is another “casing” with fine slots. This is the well screen, where the slots allow the water to enter the well. It holds back sand and larger particles trying to enter the well (See Figure 13.9).

Well Drilling

Wells can be constructed in a number of ways. The most common drilling techniques are rotary, reverse rotary, air rotary, and cable tool. Auger drilling is often employed for shallow wells that are not used as supply wells. In unconsolidated and semi-consolidated materials, (reverse) rotary and cable tool methods are most commonly employed.

Well Design

A well consists of a bottom pump, well casing (pipe), and well screen surrounded by a gravel pack and appropriate surface and borehole seals (See Figure 13.9).

Well Pump

The well pump may be either mounted directly over the well, offset from the well, offset from the casing with pipes buried below the soil surface, or submerged in the well above the well screen.

Well Casing

At the surface of the well, a surface casing is commonly installed to facilitate the installation of the well seal. The casing (or well pipe) is a very critical element in well construction. The casing serves as both a housing for the pump and as a vertical conduit through which water flows upward from the intake portion of the well to the level where it enters the pump.

Well Screen

The bottom of the casing must be fitted with a well screen which allows water to enter the well freely but prevents the entrance of coarse sand. Wells can be screened continuously along the bore or at specific depth intervals. The latter is necessary when a well taps multiple aquifer zones, to ensure that screened zones match the aquifer zones from which water will be drawn. In alluvial aquifers, which commonly contain alternating sequences of coarse material (sand and gravel) and fine material, the latter construction method is much more likely to provide clean, sediment-free water and is more energy efficient than the installation of a continuous screen.

Gravel Pack

The annular space between the well screen, well casing, and borehole wall is filled with gravel or coarse sand (called the gravel pack or filter pack). The gravel pack prevents sand and fine sand particles from moving from the aquifer formation into the well.

Well Development

Before the well can be put into operation, it must be developed. The purpose of well development is to provide sand-free water at maximum capacity. The drilling operation alters the hydraulic characteristics of a waterbearing formation in the immediate vicinity of the well caused by compaction, relocation of natural fine materials and/or migration of drilling fluids into the formation.

Well Testing

After a well is developed, a pumping test should be performed in order to determine potential well yield, to select an efficient pump, and to determine the drawdown which can influence pump location for submersible or deep turbine pumps.

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