• An agricultural land is said to be water logged if productivity gets affected by high water table.
• Due to high water in root zone, oxygen gets removed and bacteria cannot get enough air to produce sufficient food for plant.
• Cause:
  • Over irrigation.
  • Seepage of water through canal.
  • Excessive rain.
  • Irregular or flat topography.
  • Inadequate surface and natural drainage.
• Effects:
  • Hamper’s nitrification.
  • Cultivation operation becomes difficult.
  • Restricted root growth.
  • Leads to salinity (presence of salt).
• Control:
  • Lining of canal and water course.
  • Reduce intensity of irrigation.
  • Crop rotation.
  • Increase natural drain.
  • Optimum use of water.

1.2  Consideration in the design of surface and sub-surface drainage system:

Drainage:

• Process of taking out excess water from irrigated land to minimize water logging.

Types:

1. Open or surface drainage:

• Constructed at land surface having open channel flow in drain.
• Types of open or surface drainage:

a. Shallow drain:

• Depth of drain is small.
• Used to accelerate storm water removal.

b. Deep open drain:

• Depth of drain is large.
• Used to discharge collected rain and seepage water safely to natural drain.

Design consideration of surface drainage:

• If ground has good natural slope no drain required.
• Drain are required for area having very mild slope and heavy rainfall.
• Alignment should follow natural slope.
• Strom water should drain with 3 to 5 days.

2. Subsurface irrigation:

• Drainage of water through underground drains.
• Subsurface irrigation:
• Also known as drip irrigation.
• Effective for coarse texural soil.
• Cultivable land loss is minimum.

1.3 Objective of river training:

River training work:

• River training work is known as all engineering work which are constructed to guide, controll or regulate river.

Objective of river training work:

• To prevent river from changing it course.
• To provide safe passage of flood.
• To protect river bank.
• To ensure effective disposal of sediment load.
• To control and regulate river.

1.4 Types of river training work:

1. High water training:

• Purpose to control flood.
• Protect land from flood.

2. Low water training:

• Provide sufficient water depth for navigation.
• Groyne’s are constructed to contact the width of channel and increase the depth.

3. Mean water training:

• Effeciently dispose suspended and bed load.
• Example: Check dam.

1.5 Specific design consideration in hill irrigation:

• The length of canal should kept short as possible.
• Local manpower and locally available material should be utilized.
• Proper design should be adopted so that farmers can easily maintain and repair.
• Non-modular and semi- modular outlet are used.
• Slope should be cut to maintain uniform gentle gradient.
• Manning’s equation is used to design canal.
• Narrow canal is used to reduce risk of erosion and seepage.

1.6 Choice of intake, control and regulation structure:

Intake:

• Used for collecting water from the surface source such as river, lake and conveying it for irrigation purpose.

Selection criteria of intake:

• Sufficient flow is available in both monsoon and dry season.
• Sufficient availabiluty of head of water.

Sedimentation control of river:

• By construction of intake outside the river bank.
• Afforestation.
• Use of divide wall.
• Construction of setting basin.

1.7 Environmental protection measure in hill irrigation:

Problem:

• Mass movement.
• Weathering due to high velocity.
• Cutting of river.

Solution:

• Construction of small dams.
• Construction of retaining wall.
• Construction of surface and sub-surface drainage.
• Bamboo planting can be used for soil erosion on slope.
• Use of stone pitching to reduce velocity of water.

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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