Analysis of basin irrigation performance with variable inflow rate

Agricultural Water Management, 5 (1982) 295--308 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

295

ANALYSIS OF BASIN IRRIGATION PERFORMANCE WITH VARIABLE INFLOW RATE

J. MOHAN REDDY and WAYNE CLYMA Department of Agricultural and Chemical Engineering, Colorado State University, Fort Collins, CO 80523 (U.S.A.) (Accepted 7 July 1982)

ABSTRACT Reddy, J.M. and Clyma, W., 1982. Analysis of basin irrigation performance with variable inflow rate. Agric. Water Manage., 5 : 295--308. Basin irrigation systems were designed for a constant flow rate. The operation of the designed system was simulated using the zero-inertia model of surface irrigation. The performance of the system was obtained for modified design flow rates. Three patterns of flow variation -- sinusoidal, !nitially low then high, and initially high then low -- were studied. The average of a variable flow rate in a given simulation equalled, was less than and greater than the design flow rates. The flow rate variations did not lower the performance of the system when the average flow rate during irrigation was greater than or equal to the design flow rate. Significant reductions in system performance occurred when the average flow rate was equal to 50% of the design. Basin irrigation systems should be designed for the average of the variable flow rate available at the field outlet.

INTRODUCTION S u r f a c e irrigation is t h e m o s t w i d e l y p r a c t i c e d m e t h o d o f irrigation. In m a n y o f t h e u n d e r d e v e l o p e d c o u n t r i e s , basin irrigation is p r a c t i c e d o n a large scale. These basins are small in size, have u n e v e n t o p o g r a p h y a n d are irrigated as if t h e y were level. Water is supplied f r e q u e n t l y b y canals either c o n t i n u o u s l y or o n a r o t a t i o n a l basis. Design p r o c e d u r e s for surface irrigation o f level basin s y s t e m s a s s u m e a c o n s t a n t flow rate into t h e basin d u r i n g irrigation. In E g y p t w h e r e t h e w a t e r t o irrigate t h e field m u s t be lifted b y a w a t e r wheel (Sakia) or an A r c h i m e d e s screw ( T a m b o u r ) , wide variations in flow rate are c o m m o n . B o t h a n i m a l and h u m a n p o w e r are subject t o r e d u c t i o n s in p o w e r level a n d c o m p l e t e interruptions o f p o w e r m a y o c c u r f o r varying intervals o f time. Similar variations in flow exist even u n d e r gravity delivered f a r m irrigation s y s t e m s elsewhere in t h e w o r l d , such as in Pakistan ( C l y m a , 1 9 7 8 ) a n d I n d i a ( C l y m a et al., 1 9 8 1 ) . R e d u c t i o n s in f l o w rate t o a l o w level o r zero m a y have significant effects o n level b a s i n p e r f o r m a n c e . T h e objective o f this s t u d y was t o evaluate t h e effects o f f l o w rate variation o n b o t h e f f i c i e n c y a n d d i s t r i b u t i o n u n i f o r m i t y .

296 DESCRIPTION OF THE EXISTING SYSTEM Data from Egypt are used in the present analysis.

Variability of flow rates The variability of flow rates into a farm is a random p h e n o m e n o n . Apart from the upstream operating conditions o f the canal and irrigations by ot her farmers the variation of power in lifting water by humans or animals affect the flow rate into an individual basin. The flow rates also may vary considerably due to the closing and opening of different basins in the same field. An example o f the flow rate variations into farms are shown in Fig.1 (El Kady, 1979). The average flow rate into farm No. 3-1 was 15.41 ls -1 with a standard deviation of 10.71 and a coefficient of variation of 3.27, whereas the average flow rate into farm No. 2-5 was 16.90 ls -~ with a standard deviation o f 3.22 and a coefficient o f variation of 1.79. 25

2Ooo 5

o

~o

u_

[ _ _

i

i

i

J

i

J

200 TIME

OF

INFLOW

(min)

Fig.1. Inflow rate variability into a farm during irrigation.

Actual operating conditions The actual operating conditions of different field sites in Egypt were studied by El Kady (1979). Data on minimum and m a x i m u m flow rates, dimensions o f the basins, infiltration characteristics o f the soils and average d e pth o f irrigation applied were collected both in the Beni Magdoul and E1 Hammami area (Table I). Each field was divided into small basins or units called bunded units. The soils at E1 Hammami are either sandy or sandy loams whereas the soils at Beni Magdoul are clay loams (D ot zenko et al., 1979). The infiltration rates were obtained f r om E1 Kady (1979). The clay loam

297 TABLE I Average operating conditions in some parts of Egypt (El Kady et al., 1979) System characteristics

Beni Magdoul

E1 Hammami

Inflow time into the bunded unit (min) Average flow rate (1 s -1) Average depth applied (ram) Length of the basin (m) Width of the basin (m)

14.7 13.0 80.0 13.0 11.0

4.5 32.0 60.0 12.0 12.0

soils at Beni Magdoul are characterized by a final intake rate of less than 12 mm/h, and the sandy loam soils of E1 Hammami have a final intake rate of 60 to 120 mm/h. The soils at both the sites are low in organic matter which affects the soil structure and the infiltration rate. Hence, the final intake rates were: Beni Magdoul 9 m m / h , and E1 Hammami 60 m m / h (El Kady, 1979). The final intake rates were subtracted from the data presented by E1 Kady, and were plotted on log-log paper to obtain the infiltration constants. The infiltration data are presented in Figs.2 and 3. The basins in Egypt have an unlevel topography. In an irrigation system improvement program, precision leveling of fields are being evaluated (Metawie et al., 1981). Farmers can eliminate most field ditches and change the geometry and area of each field. A length of run of approximately 150 m, which is the distance between the irrigation distribution ditch (Meska) and the drain, is possible. Therefore, a length o f run of 150 m was taken to evaluate the effect of a variable inflow rate on system performance. I00(

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I III

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I00 Time

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(min)

Fig.2. Infiltration characteristics of the soils at El Hammami.

298 I000

r

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100

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Time ( m i n )

Fig.3. Infiltration characteristics of soils at Beni Magdoul.

DESIGN OF BASIN IRRIGATION SYSTEMS

A procedure for the design of level basin irrigation systems, based upon dimensionless variables, was developed by Clemmens et al. (1981). A1Hassan (1978) found that the SCS (USDA-SCS, 1974) design procedure for level basin irrigation is acceptable. Since the objective of this study was to evaluate the effects of variable inflow rates, any reasonable design procedure is adequate. Hence, the latter procedure was used to design basin irrigation systems with "an appropriate efficiency" for the conditions at El Hammami and Beni Magdoul. In the SCS design procedure, the values of application efficiency and the design (requirement) depth must be specified. The following application efficiencies were assumed (because of lack of data under level field conditions) to be reasonable for the two different soil types: clay loams (Beni Magdoul) 80%, and sandy loams (El Hammami) 65%. Farmers at Beni Magdoul applied, on average 80 mm per irrigation except for the first irrigation (El Kady et al., 1979). Therefore, the net depth of application (with 80% application efficiency) was 64 ram. The same net depth was used for the sandy loam of E1 Hammami for a direct comparison of the results. The time required to infiltrate the net depth of application was calculated using the infiltration data (Figs.2 and 3). The selection of an appropriate SCS intake family was based upon the method presented by Fangmeier and Strelkoff (1979). The softs at E1 Hammami are sandy loams. For design purposes a net

1.86 3960 65 98

0.15 64.0 1.5 0 . 0 8 6 5 t 0. 799 + 7.0 4.64 3240 62 101

0.15 64.0 1.5

1.12 10680 80 80

0.50 0.75 1.00 1.50

Design flow rate variation parameter,

T i m e of application

0.93 1.39 1.86 2.77

7860 5280 3960 2640

(s) 2.32 3.48 4.64 6.96

6480 4320 3240 2160

(s) 0.58 0.84 1.12 1.67

(l s-' m-')

L = 150 m F l o w rate

L = 150 m F l o w rate (I s - ' m - ' )

L = 75 m F l o w rate (1 s -1 m - ' ) Time of application

Beni Magdoul

El H a m m a m i

21420 14040 10680 7140

Time of application (s)

0.15 64.0 0.3 0 . 0 4 8 8 t 0. 72, + 7.0

L =150m

L =75m

L =150m

Beni Magdoul

El H a m m a m i

I n f l o w rates and t i m e o f application into basins at El H a m m a m i and Beni Magdoul

T A B L E III

Parameters Field roughness, n Design depth, D u (ram) I n t a k e family, If I n t a k e e q u a t i o n , z (ram) Variables I n f l o w rate, qd (1 s - ' m - ' ) A p p l i c a t i o n time, t a (s) A p p l i c a t i o n efficiency, E a (%) Gross depth, D a (ram)

Design parameters/variables

Values o f design parameters and variables for basins at Beni Magdoul and E1 H a m m a m i

T A B L E II

t~ ¢D

300

depth of 64 mm was assumed appropriate. Field lengths of 75 m and 150 m were assumed to be reasonable to attain 65% application efficiency for these soils. Using the SCS (USDA-SCS, 1974) design procedure, design parameters for both 75 m and 150 m lengths of run are given in Table II. Later, the design flow rate was modified. The modified design flow rates were equal to/3 times the design flow rate, where/3 takes on the values of 0.50, 0.75, 1.0 and 1.50. The design and modified design flow rates and time of inflow are presented in Table III. For the soils at Beni Magdoul a net depth of irrigation of 64 mm was assumed for design. The infiltration characteristics of the soils fall into the intake family " 0 . 3 " of the SCS design procedure. A field length of 150 m was assumed to obtain 80% application efficiency. Also here, the modified design flow rates were applied. The design parameters required for the SCS (USDA-SCS, 1974) design procedure are given in Table II. VARIABLE INFLOW RATE

The analysis consisted of simulating flow onto level basins with characteristics of the sites in Beni Magdoul and E1 Hammami in the Mansouria District, Egypt. Different irrigations were simulated for different constant inflows called modified design flow rates equal to/3 times the design flow rate. Since two lengths of run were investigated for the sandy loams of E1 Hammami, twelve different cases (Table III) were simulated for the two soil types. Later, a sinusiodal inflow rate with a periodicity of 8 min and an amplitude of 0.5q d around the design and modified design flow rates was simulated (Fig.4). Under some circumstances the flow rate into the field might fluctuate between zero (0.0qd) and twice the design flow rate (2.0qd). Hence, an amplitude of 1.0q d was also introduced in the design flow rate. Next, two flow patterns -- an initially low flow rate followed by a high flow rate, and an initially high flow rate followed by a low flow rate -were simulated. In both cases, flow rates with a variation of a 0.50qd 3

r

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'1

i

7 E

v

rr

O -3 uZ

0

z

J

12

24

L

36 TIME (rain)

L

J

48

60

72

Fig.4. Sinusoidal inflow rate variability patterns around qd-

301 a r o u n d t h e design and m o d i f i e d design f l o w rates were simulated. T a b l e IV presents t h e e q u a t i o n s defining t h e f l o w p a t t e r n s f o r t h e variable f l o w rates simulated. In all cases, t h e average d e p t h o f a p p l i c a t i o n was k e p t the same. T h e r e was a d i f f e r e n c e , h o w e v e r , in t h e average d e p t h o f a p p l i c a t i o n b e t w e e n t h e s a n d y loams and clay loams because o f t h e d i f f e r e n c e in a p p l i c a t i o n efficiency. TABLE IV Flow rate patterns simulated into the basins Flow pattern

Flow rate,

Sinusoidal flow

{fl + A [sin

Initially low flow

[~--A ]qd [/3 + A]qd [/~ ÷ A ] q d [6--A]qd

Initially high flow

(1 s-') (i-1).

qi

] }qd

Time indices i = 1, 2, 3, . . . , K

2 i = 1, 2, 3, . . . , K/2 i = K/2 ..... K

i = 1 , 2 , 3 . . . . g/2 i = E l 2 , (g/2) + 1 . . . . . g

A = amplitude of the variation, 0.50 = design flow rate variation parameter, 0.50, 0.75, 1.00, and 1.50 K = number of time increments used in the hydraulic simulation model MATHEMATICAL SIMULATION MODEL T h e m a t h e m a t i c a l m o d e l used in t h e simulation o f flows was t h a t o f S t r e l k o f f and K a t o p o d e s ( 1 9 7 7 ) , and is given as: a__q + ay+ az = 0 ax at at ay ax

- So-Sf

(continuity)

(3)

(momentum)

(4)

w h e r e q = unit f l o w rate; x = distance along t h e length o f run; y = d e p t h o f surface water; So = slope o f t h e basin; and Sf = f r i c t i o n slope. F l o w leaving at t h e d o w n s t r e a m end o f t h e basin was zero. T h e u n i f o r m i t y c o e f f i c i e n t was calculated using Christiansen's ( 1 9 4 2 ) equation: N

Iz-zil UCC = 1 _ (

i=1

(5)

zN

w h e r e UCC is Christiansen's c o e f f i c i e n t o f u n i f o r m i t y ; ~- is t h e average d e p t h o f w a t e r infiltrated into t h e soil ( m m ) ; z i is t h e d e p t h o f w a t e r infiltrated at

302

the ith location in the field (mm); and N is the number of locations considered in the field for the analysis. The application efficiency (Ea) was defined as follows: Amount of water stored in the root zone Ea =

X 100%

Amount of water applied to the field

(6)

ANALYSIS OF RESULTS

Using the mathematical model described earlier, the inflow patterns presented in Figs.4, 5, and 6, and the constant flow rates, the flows were simulated in the basins. The distribution uniformity and the application efficiency for different cases were calculated. The advance and recession of water along the basin for the variable inflow rates into the basin under sandy loam and clay loam conditions are presented in Figs.7 and 8. Obviously, there was not much difference in the advance phase between a sinusoidal and a constant inflow rate. However, there was a significant difference in the advance rates between a constant inflow rate and an initially low one followed by a high inflow rate during the latter half of the irrigation. All points in a basin receded simultaneously as is obvious from Figs.7 and 8. :5

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48

60

72

TIME ( m i n ) Fig.5. Initially low followed by high during the latter half of the irrigation. 3

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214

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t E

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t~J <[ {z

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516 48 610 72 TIME (min) Fig.6. Initially high followed by low during the latter half of the irrigation.

303 140

120 ~

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I00 0 i N I T I A L L Y LOW FLOW RATE L~ SINUSOIDAL FLOW RATE o CONSTANT FLOW RATE

8O c:

E

~; 60 I--

40

20

0

16

32

48 DISTANCE ( m )

64

80

Fig.7. A d v a n c e and recession curves for d i f f e r e n t i n f l o w patterns at E! H a m m a m i . 480

O0

420

o

O0

g

360 o

I N I T I A L L Y LOW FLOW RATE SINUSOIDAL FLOW RATE

[]

CONSTANT FLOW

RATE

300

¢= •~ 2 4 0 v F-

180

120

60

0

0

30

60 90 DISTANCE (m~

120

150

Fig.8. A d v a n c e and r e c e s s i o n curves for d i f f e r e n t i n f l o w patterns at Beni Magdoul.

304

In both flow situations, the initially low flow rate receded slower, thereby compensating for the differences in the advance rate. Therefore, no difference was found in performance between the three different inflow patterns. The subsurface water distribution profiles for the two soil types, for the different inflow rates and patterns, are presented in Fig.9. More water infiltrates into the soil in the case of sandy soils. Slight differences in the subsurface water distribution are evident for the different inflow patterns. Since there was no difference in performance between flow patterns at higher flow rates, it may be concluded that the performance for all the different inflow patterns at 0.50qd will also be the same. Therefore, for 0 . 5 0 q d , flow patterns other than constant inflow were not simulated. CLAY 0

2O

it

IO 2

LOAMS

~ANDY

FIELD LENGTH(m) 40 60 80 I00 120 140

I0 F

•

,

,

-"

•

"---"°-'--"--°

20 L

o

F-

FIELD LENGTH(m) 40 60 80 I00 120 140

CONTINUOUS FLOW, ,~= 1.0 i

ot

20

e

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0

LOAMS

I0

20 INITIALLY HIGH FLOW, /~= 1.0 '

e

•

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20 INITIALLY LOW FLOW, /~ = 1.0

20

ot

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20 SINUSOIDAL FLOW, /~ =1.0

ot ,

I0

-~

2O

oI ,

=

~

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2

CONTINUOUS FLOW, /~ = 1.50

0 ~ ~

CONTINUOUS FLOW, ,8 : 0 75

IO, 20 C O N T I N U O U S FLOW~ /~ = 0 . 5 0

Fig.9. Subsurface water distribution profile for different f l o w rate and f l o w rate patterns.

305 At reduced inflow rates more water infiltrated at the upstream end of the border in b o t h soil types. In the case of sandy loams, at the upstream end of the borders, 13 cm infiltrated for the design flow rate whereas 15.6 cm infiltrated when the modified design flow rate was 0.5 times the design flow rate. In this case, the flow did not reach the end of the field. Conversely, in the case of clay loams, the depth infiltrated at the upstream end of the border was 9 cm for the design flow rate, whereas 10 cm infiltrated when the design flow rate was 0.50 times the design flow rate. The flow reached the end of the basin. Hence, the reduced flow rates are more critical in the case of sandy loams than in the case of clay loams. The application efficiency ranged from a high of 72% to a low of 65% and the distribution uniformity ranged from a high of 0.90 to a low of 0.79 for the sandy loams. For the clay loams the application efficiency ranged from a high of 80% to a low of 77% and the distribution uniformity changed from a high o f 0.95 to a low of 0.85. In addition, when the mean flow rate was 0.5 times the design flow rate, the flow did n o t reach the end of the basin for sandy loams which is unacceptable. This suggests that the reduction in design flow rate has a more pronounced effect on sandy loams than on clay loams, as shown in Fig.10. The results of the different analyses suggest that the effect of variable flow rates on application efficiency and distribution uniformity for level basins is not significant when the mean of the variable flow equals or exceeds the constant design flow rate. Level basin performance for an initially low flow followed b y a high flow and the sinusoidal flow variation were essentially the same as the constant inflow. The initially high flow followed by a ,

I00

,

,

1.0

CLAY LoAM

90

0 9

6

CLALOA. 70 _oZ w

/

0._~ 60

,

" ~ // "E°'~""'~° ,, _o......~ o

,.,"

~

~ND¥

~

LOAM, L = tSOm

~

o7-~ "

0.6 LU

50

/

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Fig.10.

0.5

i J a 0.75 1.00 1.25 DESIGN FLOW RATE VARIATION PARAMETER, ,8

Effect

of inflow rate on the performance

0.4 1.50

of basin irrigation

system.

306

low flow had a higher uniformity coefficient than all other inflow patterns including the constant inflow especially with mean flows less than the design flow. Unacceptable performance on the sandy loam occurred because the water did not reach the end of the field when the mean flow was half the design flow. Acceptable performance still resulted on the clay loam soil for these flow rates. No significant difference in the performance of the system with an amplitude of 1.0q d was observed when compared with the performance for a constant design flow rate and for a flow rate variability of 0 . 5 q d around the design flow rate. For clay loams, an application efficiency of 78% and a uniformity coefficient of 0.93 was obtained, which is not significantly different from the performance for constant design flow rate as shown in Table V. Similarly, an application efficiency of 71% and a uniformity coefficient of 0.86, which is not significantly different from the performance for constant design flow rate, was obtained for sandy loams.

TABLE V P e r f o r m a n c e o f basin irrigation s y s t e m s in E g y p t u n d e r variable flow rates Design flow rate variation parameter,/~

Sandy Loams (El H a m m a m i ) L =75m 1.50 1.00 0.75 O.50 L = 150m 1.50 1.00 0.75 0.50

F l o w characteristics Initially high

Constant

Initially low

Sinusoidal

Ea

UCC

Ea

UCC

Ea

UCC

Ea

UCC

73 68 68

0.92 0.91 0.89

72 67 65

0.90 0.86 0.79

69 67 68

0.89 0.85 0.82

70 71 63

0.91 0.85 0.81

X

+

68 64 62

0.84 0.82 0.82

67 63 60

+

+

0.84 0.81 0.73

68 62 63

×

+

0.84 0.86 0.81

65 62 60

+

0.87 0.83 0.74 +

Clay L o a m s

(Beni Magdoul) 1.50 1.00 0.75 0.50

81 80 82

0.95 0.95 0.93 +

80 81 80 77

X = F l o w did n o t reach e n d o f t h e field + = Case n o t a n a l y z e d

0.95 0.93 0.90 0.85

80 79 80

0.94 0.92 0.90 +

79 79 79

0.95 0.93 0.85 +

307 CONCLUSIONS

The effect of a variable inflow compared to a constant inflow on application efficiency and distribution uniformity for level basin irrigation systems is negligible. Reductions of the inflow rate below the design inflow rate began to reduce the distribution uniformity at 0.75 times the design flow, and produced unacceptable performance (water did not reach the end of the field) at 0.5 times the design flow rate on the sandy loam soil. The clay loam still had acceptable performance even at half of the design flow rate. Level basins should be designed for the mean flow rate when a variable flow rate is available. If the average flow rate is less than the optimal design flow rate, then optimal sizing of the basin is the next alternative. By reducing the basin size, a desired application efficiency and distribution uniformity can be obtained. ACKNOWLEDGEMENTS

The work reported was supported by the United States Agency for International Development through contract AID/NE-C-1351 with the Consortium for International Development for the Egypt Water Use and Management Project, and the Colorado State University Experiment Station through the Department of Civil Engineering. Their help is sincerely appreciated. REFERENCES AI-Hassan, A., 1978. An evaluation of the Soil Conservation Service design criteria for border irrigation using the zero-inertia mathematical model. M.S. Thesis, Washington State University, Pullman, WA, 110 pp. Christiansen, J.E., 1942. Irrigation by Sprinkling. Bulletin 670, University of California, Berkeley, CA, 124 pp. Clemmens, A.J., Strelkoff, T. and Dedrick, A.R., 1981. Development of solutions for level-basin design. J. Irrig. Drainage Div., Am. Soc. Civ. Eng., 107(3): 265--279. Clyma, W., 1978. Pakistan irrigation frequency analysis. Unpublished material, Dep. Agricultural and Chemical Engineering, Colorado State University, Fort Collins, Co. Clyma, W. et al., 1981. Engineering Diagnostic Analysis. In: Diagnostic Analysis of Farm Irrigation in the Mahi-Kadana Irrigation Project -- Gujarat, India. Special Report No. 9, Water Management Synthesis Project, Colorado State University, Fort Collins, CO. Dotzenko, A.D., Zanati, M., Abdel-Waheb, A.A. and Keleg, A.M., 1979. Preliminary Soil Survey report for the Beni Magdoul and El Hammami areas. Egypt Water Use and Management Project Technical Report No. 2, Colorado State University, Fort Collins, CO, 43 pp. El Kady, M., 1979. On-farm water management in Egypt. Ph.D. Dissertation, Ain Shams University, Cairo, Egypt, 244 pp. E1 Kady, M., Clyma, W. and Abu-Zeid, M., 1979. On-farm irrigation practices in Mansouria District, Egypt. Paper No. 79-2566, American Society of Agricultural Engineers, St. Joseph, MI, 28 pp. Fangmeier, D.D. and Strelkoff, T., 1979. Mathematical models and border irrigation design. Trans. Am. Soc. Agric. Eng., 22(1): 93--99.

308 Metawie, A.F., Ley, T.W. and Tinsley, R.L°, 1981. Small farm rice irrigation in Egypt. Staff Report of the Egypt Water Use and Management Project, Colorado State University, Fort Collins, CO, 28 pp. Strelkoff, T. and Katopodes, N.D., 1977. Border irrigation hydraulics with zero-inertia. J. Irrig. Drainage Div., Am. Soc. Civ. Eng., 103(3): 325--342. USDA-SCS, 1974. Border Irrigation. Chapter 4, Section 15, National Engineering Handbook, Washington, DC, 242 pp.