Drainage of Agricultural Lands - Practices of Irrigation and On-farm Water Management - page 375

(14) What are the factors to be considered in designing subsurface drainage system?
(15) Briefly describe systematically the design procedure of subsurface drainage.
(16) Draw a schematic layout for a subsurface drainage system.
(17) How you will estimate the drainage intensity in an area?
(18) What is controlled drainage? Briefly discuss its principle and procedure.
(19) Do you think that envelop materials should be used around subsurface drain?
Justify your answer.
(20) Why envelope materials should be designed and selected with proper care?
(21) Name some envelope materials from organic, mineral, and synthetic group.
(22) What are the design criteria for selecting envelope material? Briefly describe
the procedure for selection and design of envelope material.
(23) Briefly describe the use of particle size analysis curve in designing envelope
material.
(24) What are the methods of placing drain and envelop?
(25) What are the methods of disposing drainage outflow?
(26) How the drainage outflow can be treated?
(27) Narrate the economic considerations in drainage design and material selection.
(28) Briefly explain the concept, principle, and procedure of performance evalua-
tion of drainage system.
(29) What are the challenges and needs in drainage design and management?
(30) A soil contains 42% moisture (by volume) at saturation. The moisture content
becomes 35% when the capillary pressure is raised to 100 cm of water. Find
the drainable porosity, void ratio, and the drainable water volume at 100 cm
water tension from a (10 m 10 m) plot of 1.0 m depth.

(31) A soil column consists of 3 layers, having 0.50 m depth of each. The horizontal
hydraulic conductivity of the layers (from to bottom) are 0.25, 0.15, and 0.30
m 3 /m 2 /h. Determine the resultant horizontal hydraulic conductivity of the soil
column.
(32) A surface drainage should be provided within an agricultural farm. Maximum
rainfall intensity at the site in 20 years record is 40 mm/h. The tertiary drain
would have to carry discharge from 5.0 ha land. The secondary drain would
have to carry of 4 tertiary, and the main drain to carry discharge of 5 secondary
drains (of similar discharge). Determine:

×

(a) drainage outflow to be generated at tertiary, secondary, and main drain
level
(b) performance of hydraulic design of the secondary and main drainage
canal

(33) Determine the drain spacing of parallel subsurface drains if the hydraulic con-
ductivity of the soil is 15 cm/d, the recharge rate is 12 cm/d, drain diameter is
12 cm, drains are placed at 2.0 m deep, the water table is to be no closer than
1.2 m to ground surface, and the impervious layer is 3 m below the ground
surface.
(34) A subsurface drainage should be provided through an agricultural farm.
Maximum rainfall intensity at the site in 20 years period is 80 mm/d. The