Aquatic Systems Engineering Free Flooding 2

W etting is done of only a part of the field, unlike flooding.

T o achieve it, irrigation systems are required Irrigation system includes Planning, Design, Construction, Operation and maintenance of structures Efficient irrigation system is engineer s responsibility.

Dr.SanjeevGadad,AITBangalore.

Due to non uniform distribution of rainfall with space and time, it is essential to have scientific and engineering solution.

Irrigation is required when, InadequateLess rainfall Transfer from abundance to deficit area Indira Gandhi canal from Sutlej to Thar desert Uneven distribution Area Intensity and T ime scale A verage annual rainfall: Thar (100mm) to Assam (2500mm) Mawsynram, Meghalaya, India (highest avg.

Practised in delta regions Also by artificially built inundation canals Perennial Irrigation system W ater is supplied when required, at regular intervals Source may be river, wells or other perennial water source T ypes of Irrigation 11 Dr.SanjeevGadad,AITBangalore.

This system lies somewhere between inundation type and perennial type of irrigation.

A Bandhara is a low masonry weir (obstruction) of height 1.2m to 4.5m constructed across the stream to divert water into a small canal.

The length of the main canal is usually restricted to about 8km.

Trapezoidal section us is vert ical ds slope is 1:2 to 1:5 Crest width (H) 12, minimum of 1.2m Discharge Q 1.7 L (h) 32.

Aquatic Systems Engineering Free Flooding 2

Free flooding 2. Contour laterals 3.

Border strips 4. Checkslevers 5.

Basin flooding 6.

Reduce wastage of water Reuse of water is made possible Minimum land (of fields) is used for irrigation systems Method properly fits the boundary of land to be irrigated 16 Dr.SanjeevGadad,AITBangalore.

During high stream flow, water from source is allowed on land and is to made to spread along natural slope.

Suitable for smooth, flat land W astage of water is high Practised in areas with abundance and irrigation is less expensive.

Free Flooding Commonly adopted in India Field is divided in to small size plots having horizontal surfaces W ater is fed at the higher end and made to flow till the end and then cut off.

Flow of water is sheet like, (Q 14 to 28 litres) Slope is lengthwise between 0.5 to 1.5 Initial 6 to 12m length is made level for uniform spreading of water Length of strips depends on infiltration rate of soil, slope and size of irrigation stream.

Steeper: soil erosion, insufficient at upper reaches Flat: slow movement of water, percolation losses, insufficient at lower reaches 22 T ype of soil Length of strip (m) Slope () Sandy and sandy loam 60-120 0.25 to 0.60 Medium loam soils 100-120 0.2 to 0.40 Clay loam clay soils 150-300 0.05 to 0.20 Dr.SanjeevGadad,AITBangalore.

Comparatively large stream supplies water w.r.t plot size W ater is controlled by surrounding the check area with low and flat levees.

Surrounded by levee- width: 2-3m (at bottom) and height: 15-30 cm.

The check is filled with water at a fairly high rate and allowed to stand until the water infiltrates The confined plot area varies from 0.2 to 0.8 hectares.

If the ground has slope, then levees follow the contours.

Suitable for low as well as high intake soils and for rice or other crops which can withstand temporary flooding.

Pipes also can be used to supply water to individual trees 25 Dr.SanjeevGadad,AITBangalore.

Application efficiency is comparatively high.

When desired depth is attained, water supply is closed Suitable for level plots but not for machine farming 28 Dr.SanjeevGadad,AITBangalore.

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