SURFACE IRRIGATION HYDRAULICS. BORDER IRRIGATION CHECK BASIN IRRIGATION FURROW IRRIGATION. BORDER IRRIGATION Land is divided into a number of strips, separated by low levees called "borders". Each strip is 3 to 15 meters in width depending on stream size available and levelling.
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CHECK BASIN IRRIGATION
Q = Discharge through the supply ditch.
y = Depth of water flowing over the border strip.
f = rate of infiltration of soil.
A = Area of land strip to be irrigated.
t = Time required to cover the given area.
I = constant rate of infiltration
Then by volume balance,
Q.dt = I.dt (A+dA) + y.dA
Neglecting second order differential term and re-writing, we get,
dt = y.dA/ (Q-IA)
Integrating both sides of the equation bet’ limits,
For a uniform width border (W), the advance distance x at any time t is given by
The hydraulics of flow in check basins may comprise four stages.
Vs = volume of water stored in a given time ts, cm3
q = average size of the entrance stream, cm3 / min
ts = storage time, min
Is = average infiltration rate during the storage time, cm/min
Ac = area of check basin, cm2, and
Ds = depth of storage during ts,cm
Rate of rise of water level = d (ds) / dts
The water is applied to the land through a series of long, narrow channels, called furrows.
The furrows are dug at a regular interval at right angle to the field channels.
The water flowing in the furrows infiltrates the soil and spreads laterally and reaches the roots of the plants between the furrows.
The wetted area varies from 1/5 to ½ of the total area. It helps in reducing the evaporation losses and achieving a high water-application efficiency.
Depth of furrow is 20 and 30 cm for orchards.
For vegetables and the row crops , such as sugar beet ,potatoes cotton and tobacco the depth is @ 7.5 to 12.5 cm
Length of furrow
The length varies from 30 to 60 m for sandy soil and 100 to 500 m for clayey soils.
garden crops, the length is usually kept shorter as compared to the field crops.
Furrows should be provided with a proper longitudinal slope. The steeper slopes lead to high velocity of flow, which may cause erosion of the bed and sides of the furrows.
Spacing of furrow
Vegetable crop such as carrots and onions, planted at 30 to 40 cm apart, may have two rows of plants between two successive furrows. Crops like potato and cotton planted at 60 to 90 cm apart, have one row of plants between two successive furrows.
The size of the furrow stream usually varies from 0.5to 2.5 litres per second.
The maximum non-erosive flow rate is estimated by the following empirical equation:
qm = 0.6/S
qm = maximum non erosive stream , lps.
s = slope of furrow, %.
The average depth of water applied during an irrigation can be calculated from the following relationship:
d = average depth of water applied, cm
q = stream size , litres per second
t = duration of irrigation, hour
w = furrow spacing , m
l = furrow length, m
X= Q / I * T. (1- e –(I * T * t) / a)
X = distance traveled by wetting front, cm
Q = discharge, cm3 / sec
I = rate of infiltration, cm / sec
T = Top width of furrow, cm
t = Time of application of water, sec
a = Area of c/s of furrow, cm2