Exploration of groundwater:

• Objective is to locate aquifier capable of yielding water of suitable quality, for irrigation, drinking water, agricultural and industrail purpose.
• Done by geophysical drilling.

Methods:

1. Surface exploration:

• Geological method.
• Remote sensing.
• Surface geophysical method.

2. Sub- surface exploration:

• Test drilling.
• Geophysical logging.

Aquifer:

• Aquifer is underground water bearing layer of permeable rock.
• Types:

a. Confined aquifer: Presence of underground water.

b. Unconfined aquifer: Open to atmospher.

• Advantage of ground water:
• Less investment required.
• No channel required.

1.2 Types of well:

• Well are vertical holes driven below the ground surface to extract water from ground.

a. Shallow well:

• Hole which has been dug, bored, driven or drilled into ground for purpose of extracting water.

        b. Deep well:

• Well drilled to an aquifer below an impervious strata.
• Water is hard and contains dissolved salt.

1.3 Components of tube well:

• A tube well consist of 100 to 200 mm wide stainless steel tube or pipe which is bored into underground aquifer.

Components:

a. Temporary reservoir:

• Small reservoir of water made at outlet of tube well.

b. Casing:

• Support to the well.
• Protect borehole from collapse.

c. Screening:

• Help to maintain good water supply from aquifer.
• Allow for long term satisfactory operation of well.

1.4 Design consideration of shallow and deep well:

• Determining location of well.
• Water well design and installation.
• Well drilling.
• Well development (includes well screen, well casing is developed and borehole is cleaned).
• Well head protection (construction of well seal and use of backflow prevention device).

1.5 Type and selection of pump:

Types of pump:

1. Centrifugal pump:

• Mechanical device designed to move a fluid by means of transfer of rotational energy from one or more driven rotors called impeller.
• Simple design and produce high flow rate and high efficiency.

2. Reciprocating pump:

• Pump which uses backward and forward movement to move a fluid.
• Provide steady, unchanging flow rate.
• Better than centrifugal pump.

Selection of pump:

• Should be capable of pumping required quantity of water.
• Intial cost should be cheap.
• Maintenance cost should be cheap.
• Should be reliable.
• Should be high efficeient.
• Should have long life and depreciation cost should be small.
• Cost of labour should be low.

1.6 Conveyance and distribution system in ground water irrigation schemes:

• Water is conveyed from ground water source to cropped field using network of open channel or pipe line.
• Pipe line have more advantage than open channel because it save water and energy consumption.
• Though underground pipe distribution system is expensive it have many advantage such as:
  • Farmers receive water near the field.
  • Seepage, evaporation loss are avoided.
  • Quantity of water delivered is same in each outlet.
  • Maintenance cost is low.
  • Full control of water supply.

1.7 Conjunctive use of surface and ground water:

• Conjuctive use is the combined use of surface water and ground water resource in a unified way to optimize water use and minimize adverse effect of using a single source.
• Efficient and ecnomic way to maximize agricultural production.

Advantage:

• Problem of water logging is reduced.
• Promotes sustainable water management.
• Improves environmental condition of irrigated area.
• Enhance water use efficiency.

Limitation:

• Reduce pump efficiency due to large fluctuation of water level.
• Active participation of people required for proper conduction.
• Construction of ground water recharge structure required.

References:

• WECS (1998), Design Guidelines for Surface Irrigation in Terai and Hills of Nepal, (Vol. I and II)
• Michael, A.M.(2011). Irrigation theory and practice
• FAO(1977). Guidelines for Predicting Crop Water Requirements. FAO Irrigation and Drainage Paper No. 24.

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