- Email: [email protected]
Hydraulic design for check method of irrigation
/. ugric. Engng Res. (1969) 14 (4) 319-322
Hydraulic
Design
for Check
Method
of Irrigation
V. V. N. MURTY* The check method of irrigation consists in making the area into square or rectangular plots surrounded by levees and irrigating each plot. An expression to estimate the deep percolation losses in such a system has been derived. It has been shown that the deep percolation losses will depend upon the time required to initially cover the entire area with water, and the lesser this time, the lesser will be the losses. A procedure for determining the size of the check for the particular site conditions and stream size has been outlined. 1.
Introduction
Surface irrigation methods may be broadly classified as the check method, border strip method and the furrow method though large modifications are made to each of the individual methods Among the surface irrigation methods, the to suit the crop, topography and soil conditions. check method of irrigation (also referred as check flooding’) has not received adequate attention. The reasons for this are some of the disadvantages that are associated with this method, viz. the requirement of a large number of field channels and ridges as compared to the border strip method of irrigation, greater labour requirements to make the ridges and channels and finally difficulty in operating the mechanical equipment for different agricultural operations, like interculture and harvesting. In spite of these disadvantages the check method of irrigation is widely used when the available stream size or the plots are small or for irrigating nurseries and vegetable crops grown in small plots. This method can also be adopted when the soils are having large infiltration rates in which case the soils are to be quickly covered to avoid deep percolation losses at the head or in case of soils of low infiltration rates in which case the water is to be allowed to stand for the required time to enable the water to penetrate to the desired depth. In the check method of irrigation the land is divided into square or rectangular level plots surrounded by levees and water is introduced into each plot individually. 2.
Deep percolation losses
An analysis is presented here, which will help in determining the size of the check for a given stream size and soil conditions and will help in estimating the deep percolation losses under the given set of conditions.
KEY TO SYMBOLS area of the check stream size depth of water application or depth of irrigation infiltration rate constants in the inflltration equation I==kt” time of application or time of irrigation time by which the whole check is covered with water time required to fill the root zone of the soil to field capacity moisture content total time of irrigation (t,+t,) * Punjab
Agricultural
University,
Hissar
(Haryana
State),
India
319
from the initial
HYDRAULIC
320
DESIGN
FOR
CHECK
METHOD
OF IRRIGATION
Using the basic infiltration quotation I= Kt”, Criddle2 showed that by integration the depth of water absorbed in a given time is given by : d=
Kt”,’
60(n+ 1)’
. . (1)
In a check immediately after the water is introduced, the water will take a time t, to spread itself all over the area. After the water has spread all over the area, the water should be allowed to stand for a period of time t, so that the whole plot gets irrigated. The deep percolation losses will depend upon t, and the lesser the t, value, the lesser will be the loss. Amount of water lost due to deep percolation:
..
This is obtained on the basis that in time 0 to t,, the water has spread over the entire check and the average area with which the water is in contact is A/2. It is from this area that the deep percolation losses will occur, as water will be standing for a period oft, in addition to t,, but the deep percolation losses will start after a lapse of time, t,, i.e. the time required for irrigation. Total amount of water absorbed:
A =T.
&[T”t’fl,“+‘].
. . (3)
Percentage of deep percolation losses (P) T”+‘-_t =T”+l+t:“+’
n+l
X100.
...
It can be seen that if tl=O, T==t, and the deep percolation losses are nil, i.e. if the water could be spread instantaneously all over the check, the amount of deep percolation losses will be nil. Taking R-tand
substituting the same in the above formula: (tz= Rt, and T= tl+ Rt,) p=(R+I)“+l-R”+l (R+ l)“+‘+R”+l’
. ..(5)
321
V. V.N.MURTY
This equation works out to be the same as that derived by Bishop3 for border strip method of irrigation. As further derived by Bishop, this equation reduces to:
assuming a straight line relationship for the value of P between n=-1 to n=O. This formula gives the values of deep percolation losses for any known set of conditions, i.e. the infiltration characteristics of the soil and the time taken to cover the check. The infiltration characteristics of the soil can be experimentally determined by the double ring infiltrometer method (Haise et aL4). The time taken to cover a check will have to be determined by observation for a particular stream size and the size of the check. 3. Relation between stream size and size of the check The relation between the area, depth of irrigation, stream size and size of irrigation as given by Israelson’ is: . ..(7) dxa=qx t where d =depth of irrigation a =- area to be irrigated 9 == stream size t =- time of irrigation The value of d is calculated from the formula: d-k
xA,:
where P,
= available field moisture capacity A, = apparent specific gravity
D = depth of the soil to be wetted. Thus the product of d and a gives the amount of water required to bring the root zone of the soil to field capacity. But invariably there will be some percolation losses and this amount should be added to get the total amount of water needed for irrigation. The deep percolation losses can be calculated for the particular site conditions as per the method outlined earlier. t is the time for which period water is run into the check and is different from the time required (T) to replenish the root zone over the entire check. The value of t cannot be greater than T for the reason that in such a case there will be deep percolation losses; t cannot also be equal to T in which case the stream size should be a high value in the beginning and gradually taper down to match the infiltration characteristics. In practice this is also not possible to achieve. As such, invariably t will be smaller than T, i.e. the required amount of water is introduced into the check and allowed to stand for completing the irrigation. This gives the conclusion that the check method is more suitable for soils of low infiltration rates, the reason being that generally soils of low infiltration rates are less erodible so that higher stream sizes can be adopted, whereas soils of high infiltration rates are more erodible prohibiting the use of higher stream sizes. 4.
Rational procedure for design
With this discussion the logical steps in designing the check method of irrigaton may be outlined as follows.
322
HYDRAULIC
DESIGN
FOR
CHECK
METHOD
OF
IRRICiAllOl
(1) Determine
the infiltration characteristics of the soil and from the cumulative time intiltration curve tabulate the time required for putting different depths of water into the soil.
(2) Know
the stream and wilting point.
size available
and the soil properties
like
bulk density,
tield capacity
(3) For each irrigation calculate the depth of irrigation u’from Eqn (8). (4) Assuming a plot size calculate the total amount of water required for irrigation. (5) With the stream size available, calculate the time of irrigation (t). If this time is less than T, it is satisfactory. Otherwise reduce the plot size. (6) After determining
the plot size, have a few trial runs with the stream to cover the entire plot (t,).
required
to find out the time
(7) From
Eqn (6) calculate the percentage of deep percolation losses and consequently the amount of water that will be lost due to deep percolation. The deep percolation losses should be within the acceptable range. The amount of deep percolation losses can be reduced by decreasing time t, which will require higher stream size, a factor limited by the erodibility of the soil.
(8) Calculate
the total time of irrigation
by adding
5. Stream Depth
the time obtained
by steps (5) and (6).
Example
size available
1 cusec
of irrigation
5 in
Time required to put 5 in of water into the soil
180 min (3 h)
Area of the check
100x 100 ft=10,000
Total
10,000 x 5 12
water required
sq. ft
=4166 cu. ft or (say) 4200 cu. ft. Time of flow =4200 As this time is less than the time required 20 min to cover the entire check. Total time of irrigation Percentage
20+70=90
of deep percolation
s=~&Y=~O
min
for irrigation
it is satisfactory.
Say a trial run gives
min.
losses (assuming
the value of II in the infiltration
equation
as
-0*5)=6.25% from Eqn (6). If it is desired to reduce the deep percolation size increased as the conditions permit.
losses the plot size can be reduced
or the stream
REFERENCES ’ Israelson, 0. W. Irrigation principles andpractices, 3rd ed. John Wiley and Sons, New York, 1962 * Criddle, W. D.; Davis, S.; Pair C. H.; Shockley, D. G. Methods for evaluating irrigation systems. Agriculture Handbook No. 82, Soil Conservation Service U.S.D.A., 1956 ’ Bishop, A. A. Relation of intake rate to length of run in surface irrigation. J. Irrig. Drain. Div. Am. Sot. civ. Engrs, 1961, 87 (IRI) 4 Haise, H. R.; Donan, W. W.; Phelan, J. T.; Lawhon, L. F.; Shockely, D. G. The use ofcylinder infiltrometers to determine the intake characteristics ofirrigated soils. U.S.D.A. ARS, and SCS, May, 1956
Hydraulic
Design
for Check
Method
of Irrigation
V. V. N. MURTY* The check method of irrigation consists in making the area into square or rectangular plots surrounded by levees and irrigating each plot. An expression to estimate the deep percolation losses in such a system has been derived. It has been shown that the deep percolation losses will depend upon the time required to initially cover the entire area with water, and the lesser this time, the lesser will be the losses. A procedure for determining the size of the check for the particular site conditions and stream size has been outlined. 1.
Introduction
Surface irrigation methods may be broadly classified as the check method, border strip method and the furrow method though large modifications are made to each of the individual methods Among the surface irrigation methods, the to suit the crop, topography and soil conditions. check method of irrigation (also referred as check flooding’) has not received adequate attention. The reasons for this are some of the disadvantages that are associated with this method, viz. the requirement of a large number of field channels and ridges as compared to the border strip method of irrigation, greater labour requirements to make the ridges and channels and finally difficulty in operating the mechanical equipment for different agricultural operations, like interculture and harvesting. In spite of these disadvantages the check method of irrigation is widely used when the available stream size or the plots are small or for irrigating nurseries and vegetable crops grown in small plots. This method can also be adopted when the soils are having large infiltration rates in which case the soils are to be quickly covered to avoid deep percolation losses at the head or in case of soils of low infiltration rates in which case the water is to be allowed to stand for the required time to enable the water to penetrate to the desired depth. In the check method of irrigation the land is divided into square or rectangular level plots surrounded by levees and water is introduced into each plot individually. 2.
Deep percolation losses
An analysis is presented here, which will help in determining the size of the check for a given stream size and soil conditions and will help in estimating the deep percolation losses under the given set of conditions.
KEY TO SYMBOLS area of the check stream size depth of water application or depth of irrigation infiltration rate constants in the inflltration equation I==kt” time of application or time of irrigation time by which the whole check is covered with water time required to fill the root zone of the soil to field capacity moisture content total time of irrigation (t,+t,) * Punjab
Agricultural
University,
Hissar
(Haryana
State),
India
319
from the initial
HYDRAULIC
320
DESIGN
FOR
CHECK
METHOD
OF IRRIGATION
Using the basic infiltration quotation I= Kt”, Criddle2 showed that by integration the depth of water absorbed in a given time is given by : d=
Kt”,’
60(n+ 1)’
. . (1)
In a check immediately after the water is introduced, the water will take a time t, to spread itself all over the area. After the water has spread all over the area, the water should be allowed to stand for a period of time t, so that the whole plot gets irrigated. The deep percolation losses will depend upon t, and the lesser the t, value, the lesser will be the loss. Amount of water lost due to deep percolation:
..
This is obtained on the basis that in time 0 to t,, the water has spread over the entire check and the average area with which the water is in contact is A/2. It is from this area that the deep percolation losses will occur, as water will be standing for a period oft, in addition to t,, but the deep percolation losses will start after a lapse of time, t,, i.e. the time required for irrigation. Total amount of water absorbed:
A =T.
&[T”t’fl,“+‘].
. . (3)
Percentage of deep percolation losses (P) T”+‘-_t =T”+l+t:“+’
n+l
X100.
...
It can be seen that if tl=O, T==t, and the deep percolation losses are nil, i.e. if the water could be spread instantaneously all over the check, the amount of deep percolation losses will be nil. Taking R-tand
substituting the same in the above formula: (tz= Rt, and T= tl+ Rt,) p=(R+I)“+l-R”+l (R+ l)“+‘+R”+l’
. ..(5)
321
V. V.N.MURTY
This equation works out to be the same as that derived by Bishop3 for border strip method of irrigation. As further derived by Bishop, this equation reduces to:
assuming a straight line relationship for the value of P between n=-1 to n=O. This formula gives the values of deep percolation losses for any known set of conditions, i.e. the infiltration characteristics of the soil and the time taken to cover the check. The infiltration characteristics of the soil can be experimentally determined by the double ring infiltrometer method (Haise et aL4). The time taken to cover a check will have to be determined by observation for a particular stream size and the size of the check. 3. Relation between stream size and size of the check The relation between the area, depth of irrigation, stream size and size of irrigation as given by Israelson’ is: . ..(7) dxa=qx t where d =depth of irrigation a =- area to be irrigated 9 == stream size t =- time of irrigation The value of d is calculated from the formula: d-k
xA,:
where P,
= available field moisture capacity A, = apparent specific gravity
D = depth of the soil to be wetted. Thus the product of d and a gives the amount of water required to bring the root zone of the soil to field capacity. But invariably there will be some percolation losses and this amount should be added to get the total amount of water needed for irrigation. The deep percolation losses can be calculated for the particular site conditions as per the method outlined earlier. t is the time for which period water is run into the check and is different from the time required (T) to replenish the root zone over the entire check. The value of t cannot be greater than T for the reason that in such a case there will be deep percolation losses; t cannot also be equal to T in which case the stream size should be a high value in the beginning and gradually taper down to match the infiltration characteristics. In practice this is also not possible to achieve. As such, invariably t will be smaller than T, i.e. the required amount of water is introduced into the check and allowed to stand for completing the irrigation. This gives the conclusion that the check method is more suitable for soils of low infiltration rates, the reason being that generally soils of low infiltration rates are less erodible so that higher stream sizes can be adopted, whereas soils of high infiltration rates are more erodible prohibiting the use of higher stream sizes. 4.
Rational procedure for design
With this discussion the logical steps in designing the check method of irrigaton may be outlined as follows.
322
HYDRAULIC
DESIGN
FOR
CHECK
METHOD
OF
IRRICiAllOl
(1) Determine
the infiltration characteristics of the soil and from the cumulative time intiltration curve tabulate the time required for putting different depths of water into the soil.
(2) Know
the stream and wilting point.
size available
and the soil properties
like
bulk density,
tield capacity
(3) For each irrigation calculate the depth of irrigation u’from Eqn (8). (4) Assuming a plot size calculate the total amount of water required for irrigation. (5) With the stream size available, calculate the time of irrigation (t). If this time is less than T, it is satisfactory. Otherwise reduce the plot size. (6) After determining
the plot size, have a few trial runs with the stream to cover the entire plot (t,).
required
to find out the time
(7) From
Eqn (6) calculate the percentage of deep percolation losses and consequently the amount of water that will be lost due to deep percolation. The deep percolation losses should be within the acceptable range. The amount of deep percolation losses can be reduced by decreasing time t, which will require higher stream size, a factor limited by the erodibility of the soil.
(8) Calculate
the total time of irrigation
by adding
5. Stream Depth
the time obtained
by steps (5) and (6).
Example
size available
1 cusec
of irrigation
5 in
Time required to put 5 in of water into the soil
180 min (3 h)
Area of the check
100x 100 ft=10,000
Total
10,000 x 5 12
water required
sq. ft
=4166 cu. ft or (say) 4200 cu. ft. Time of flow =4200 As this time is less than the time required 20 min to cover the entire check. Total time of irrigation Percentage
20+70=90
of deep percolation
s=~&Y=~O
min
for irrigation
it is satisfactory.
Say a trial run gives
min.
losses (assuming
the value of II in the infiltration
equation
as
-0*5)=6.25% from Eqn (6). If it is desired to reduce the deep percolation size increased as the conditions permit.
losses the plot size can be reduced
or the stream
REFERENCES ’ Israelson, 0. W. Irrigation principles andpractices, 3rd ed. John Wiley and Sons, New York, 1962 * Criddle, W. D.; Davis, S.; Pair C. H.; Shockley, D. G. Methods for evaluating irrigation systems. Agriculture Handbook No. 82, Soil Conservation Service U.S.D.A., 1956 ’ Bishop, A. A. Relation of intake rate to length of run in surface irrigation. J. Irrig. Drain. Div. Am. Sot. civ. Engrs, 1961, 87 (IRI) 4 Haise, H. R.; Donan, W. W.; Phelan, J. T.; Lawhon, L. F.; Shockely, D. G. The use ofcylinder infiltrometers to determine the intake characteristics ofirrigated soils. U.S.D.A. ARS, and SCS, May, 1956