simulation of continuous and surge flow irrigation … · viabilite´ de la me´thode des deux...

IRRIGATION AND DRAINAGE

Irrig. and Drain. 54: 217–230 (2005)

Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/ird.168

SIMULATION OF CONTINUOUS AND SURGE FLOW IRRIGATION UNDERSHORT FIELD CONDITIONSy

SALEH M. ISMAIL1 AND HERMAN DEPEWEG2*1 Soil and Water Department, Faculty of Agriculture, Assiut University, Assiut, Egypt

2 Department of Water Engineering, UNESCO-IHE Institute for Water Education, Delft, the Netherlands

ABSTRACT

This paper describes the simulation results for continuous and surge flow irrigation under short field conditions by

the computer model SIRMOD III in order to evaluate the performance and applicability of the model for short

furrows and to investigate the viability of the two-point method for calculating infiltration parameters under

continuous and surge flow irrigation in short fields. These specific field conditions are found on farms smaller than

1 ha and with a furrow length of 70m. To evaluate the model a series of experiments has been carried out in two

locations in Egypt and in one site in the Netherlands. The experiments in Egypt were conducted on a field with clay

soil situated at the Agriculture Experimental Station, Assiut University, and on a sandy soil field located at the

Assiut University Experimental Station for Desert Land, El-Wadi El-Assuity, Assiut. The experiments in the

Netherlands were carried out at the Tunnel Experimental Setting of the Irrigation and Water Engineering Group of

Wageningen University. The tunnel was covered as a greenhouse to protect the investigations against the external

weather conditions, especially rainfall. Two soil types were available inside the tunnel, namely sandy clay and

sandy clay loam. All the experiments were carried out in furrows with a blocked end and their length and width

were 70 and 0.70m, respectively.

Measured field data were used to evaluate the computer model SIRMOD III. The results of the evaluation

indicated that the model can accurately simulate continuous and surge flow irrigation under short field conditions

for the measured infiltration parameters. These field data are very important for a good simulation of the advance

time and consequently the infiltration. The two-point method can be successfully used to obtain the infiltration

parameters for continuous and surge flow irrigation under short field conditions and for different soil types.

Copyright # 2005 John Wiley & Sons, Ltd.

key words: SIRMOD; simulation; furrows; surge flow; short field conditions

RESUME

Cet article presente les resultats de simulation de l’irrigation en continu et par intermittence en situation de

parcelles reduites par le programme SIRMOD III (Surface Irrigation Computer Simulation Model). Le but est

d’evaluer les performances et l’applicabilite du modele dans le cas des raies d’irrigation courtes, et d’evaluer la

viabilite de la methode des deux points pour calculer les parametres d’infiltration en condition d’irrigation

gravitaire en continu et en intermittence sur de petites parcelles. Ces conditions specifiques sont rencontrees dans

des parcelles de moins d’un hectare et dont la longueur des raies est de 70m comme c’est le cas en Egypte. Afin

d’evaluer le modele, une serie d’experimentations a ete conduite dans deux sites en Egypte et dans un site aux

Pays-Bas. Les sites en Egypte sont la station d’experimentation agricole de l’Universite d’Asyut, avec un sol de

type argileux, et la station experimentale des zones arides de l’Universite El-Wadi El-Assuity, Asyut, avec un sol

Received 3 March 2004

Copyright # 2005 John Wiley & Sons, Ltd. Accepted 10 February 2005

*Correspondence to: H. Depeweg, Department of Water Engineering, UNESCO-IHE Institute for Water Education, PO Box 3015, 2601DADelft, The Netherlands. E-mail: [email protected] simulation de l’irrigation en continu et par intermittence en situation de parcelles reduites.

de type sablonneux. Les experimentations au Pays-Bas ont ete conduites dans le tunnel experimental de

l’Universite de Wageningen, au Departement d’Irrigation. Le tunnel est couvert comme une serre pour l’isoler

des conditions climatiques exterieures, principalement la pluie. Deux types de sol, l’un a texture sablo-argileuse et

l’autre a texture sablo-argilo-limoneuse, ont ete utilises dans le tunnel.

Les raies, avec une longueur de 70m et une largeur de 0.70m, ont ete fermees a leurs bouts. Les donnees

mesurees sur les sites ont ete utilisees pour evaluer le modele.

Les resultats indiquent qu’a partir des donnees d’infiltration mesurees, SIRMOD III realise une bonne

simulation de l’irrigation en continu et par intermittence sur des parcelles de dimensions reduites. Il est

recommande d’utiliser les parametres d’infiltration mesures comme donnees pour le modele SIRMOD afin

d’obtenir la meilleure simulation du temps de progression de la lame d’eau et par consequent de l’infiltration. La

methode des deux points pourrait etre utilisee efficacement pour calculer les parametres d’infiltration pour

l’irrigation gravitaire en continu et en intermittence sur de petites parcelles et pour differents types de sol.

Copyright # 2005 John Wiley & Sons, Ltd.

mots cles: SIRMOD; simulation; raies; par intermittence; parcelles reduites

INTRODUCTION

Surge flow irrigation is the intermittent application of water to furrows in a series of relatively short on and off time

periods, which usually vary from about 5 minutes to several hours. With this technique water is applied

intermittently rather than with a continuous stream, as in conventional surface irrigation. The main objective of

surge flow irrigation is to improve the application efficiency by reducing deep percolation and runoff losses and to

obtain a uniform wetting of the root zone, with minor differences in the infiltration depth at the beginning and the

end of a furrow. Surge flow irrigation has been introduced in farms characterized by large sizes and long furrows.

Research indicates that surge flow irrigation helps to increase application efficiency and to improve crop

production. Guidelines about the proper stream size, initial on-time and cut-back phase for using surge flow

irrigation in long fields have been established (Ismail, 2003).

Computer models have been used for quite some time to simulate continuous irrigation in furrow, border and

basin irrigation. New versions of these models include the possibilities to simulate surge flow irrigation as they

consider the unique features of surge flow irrigation such as spatially and temporally varying infiltration, flow over

a wet–dry interface, simultaneous advance and recession, cycle time and cycle ratio of the surges. Blair et al.

(1984) compared two models based on the Kostiakov equation for predicting the surge flow phenomena, namely

the step function model and the cycle ratio time model. The main difference between the two surge flow models is

that the step function model assumes that the total reduction in effective infiltration resulting from surge flow

irrigation occurs during the first off-period; whereas the cycle ratio time model assumes that the reduction occurs

during each off-period, but the amount of reduction decreases with each successive off-period. Verification of the

models with field data shows that the step function model consistently underpredicts the cumulative infiltration;

while the cycle ratio time model is not a function of the basic infiltration rate. The results based on field data

indicate that the models appear to have general applicability in surge flow irrigation analysis.

Three other, but also general, models have emerged as being satisfactory, namely the zero inertia model (Purkey

and Wallender, 1988), the hydrodynamic model (Walker and Skogerboe, 1987) and the kinematic wave model

(Blair and Smerdon, 1987); the latter has become the standard for simulating surge flow irrigation in furrows

(Stringham, 1988). The SIRMOD III software package comprises all these three models and the viability of the

model to simulate surge flow irrigation with long furrows has been proven in the United States by Walker and

Humpherys (1983), for Bulgarian conditions by Popova (2000) and for Australian conditions by Hornbuckle et al.

(2003).

However, under short field conditions that are found on farms characterized by a small size (0.5–0.8 ha) and

short furrow length (less than 100m), the effects of surge flow irrigation are still not well known. The focus of

218 S. M. ISMAIL AND H. DEPEWEG

Copyright # 2005 John Wiley & Sons, Ltd. Irrig. and Drain. 54: 217–230 (2005)

recent investigations has been the study of the applicability of surge flow irrigation for water saving and a uniform

wetting of the root zone under these short field conditions. The aim of this paper is to assess the viability of the

SIRMOD III model to simulate surge flow irrigation phenomena under short field conditions and to investigate the

viability of the two-point method for obtaining the infiltration parameters under continuous and surge flow

irrigation in short fields. The hydrodynamic model of SIRMOD III has been used to simulate surge flow irrigation

under the specific research conditions of short furrows with a blocked end, as the kinematic wave model in

SIRMOD III cannot simulate this type of surge flow irrigation.

THE SIRMOD MODEL

The SIRMOD III model (Walker, 2003) simulates the hydraulics of three surface irrigation methods, namely

border, basin and furrow irrigation. Moreover it can simulate furrow irrigation under surge flow conditions. The

simulation routine used in SIRMOD III is based on the numerical solution of the de Saint-Venant equations

(Hornbuckle et al., 2003), which consist of the conservation of mass (continuity) and the momentum equations.

An approximation of these equations was developed by rewriting them in an integral form and by a numerical

integration by using weighted averages. The integral can be defined in either the Lagrangian coordinate system,

which describes the flow by a cell that moves at an average flow velocity and deforms as it moves (Elliot et al.,

1982; Wallender and Rayej, 1990), or in the Eulerian coordinate system, which consists of a space-time

solution grid (Walker and Skogerboe, 1987; Bautista and Wallender, 1992; Tabuada et al., 1995). The last

approach was followed in the hydrodynamic model for the conservation of mass and momentum as described

by Walker and Skogerboe (1987). A detailed description of the mathematical model is presented by Walker

(2003).

The ability of the SIRMOD III model to predict the advance and performance of surge flow irrigation largely

depends on the input parameters. The most important parameters are the infiltration rate, field length, inflow rate

and cycle on-time; all these have been carefully measured in the field. Relatively large variations in these

parameters result in relatively big changes in performance. The other parameters include the furrow slope,

roughness and area of the cross-section. They have a relatively small influence on the performance of surge flow

irrigation.

The two-point method (Elliott and Walker, 1982) has been used to determine the infiltration parameters for the

SIRMOD III model. Several researchers (Elliott et al., 1982; Levien and Souza, 1987; Singh and He, 1988) employ

the Kostiakov-Lewis equation to calculate the amount of water infiltrated. In a furrow section where the discharge

is relatively constant from surge to surge, infiltration can be evaluated by the following two equations (Walker and

Humpherys, 1983):

Z ¼ k�a þ f0� ð1Þ

Zs ¼ k0�a0 þ f 00� ð2Þ

in which Z and Zs represent the volume of infiltrated water per unit furrow length (m3m�1) for dry, continuous and

wet, intermittent flow conditions, respectively. The parameters k; k0; a; a0; f and f 0 are the empirical parameters

that are specific for the soil type and the effect of cycled wetting and drying. For Equation (2) the opportunity time

� is cumulative over all the surges applied.

The flow rate in a dry furrow section wetted by the first surge is substantially lower than the flow that will occur

in that section during succeeding surges. Field observations indicate that the infiltration can be described by

Equation (1) for the dry section, Equation (2) for the third and succeeding surges, and by a transition equation

between Equations (1) and (2) for the second surge. Letting �xxi�2 and �xxi�1 be the advance distance of the ‘i� 2’ and

‘i� 1’ surges, the transition equation is written as

T ¼ �xxi�1 � x

�xxi�1 � �xxi�2

� ��

; �xxi�2 � x � �xxi�1; T ¼ 0; x < �xxi�2 or x > �xxi�1 ð3Þ

SIMULATION OF CONTINUOUS AND SURGE FLOW IRRIGATION UNDER SHORT FIELD CONDITIONS 219


in which x is the location of the computational point of interest during the current time step i and � is an empirical

nonlinear distribution constant. Then the infiltration coefficients for the transition infiltration equation can be

presented as

k00 ¼ k þ ðk � k0ÞT ð4Þ

d00 ¼ aþ ða� a0ÞT ð5Þ

f 00 ¼ f þ ðf � f 0ÞT ð6ÞIn order to provide a nonlinear transition, the value of the exponent � in Equation (3) can range from 2 to 5; a

value of 3 was used in this research. Infiltration equations such as Equation (1) are based on the cumulative

opportunity time. The infiltrated volume supplied by a particular surge must be computed as a difference. For

instance, if at point x the opportunity time prior to the ongoing surge is �� and the opportunity time created by the

present surge is � , then the infiltration volume added during the present surge is

ZðtÞ ¼ Zð�� þ �Þ � Zð��Þ ð7Þ

DESCRIPTION OF THE EXPERIMENTS

Field experiments were carried out in Egypt and the Netherlands. One site in Egypt was at the Agriculture

Experimental Station of Assiut University and the soil was a clay soil. Another location was at the Assiut

University Experimental Station for Desert Lands, El-Wadi El-Assuity, Assiut. The area was newly reclaimed and

has never been irrigated; the soil at that site was a sandy soil. The experiments in the Netherlands were carried out

at the Experimental Tunnel of the Irrigation and Water Engineering Group, Wageningen University. The tunnel

was covered as a greenhouse to protect the experiments against the external weather conditions, especially rainfall.

Two soil textures were available inside the tunnel, namely sandy clay and sandy clay loam soil. A detailed

description of the soil characteristics is presented in Table I.

The furrows in all the experiments had a blocked end, their length was 70m and their width 0.70m. The slope

was 0.0024mm�1 in the clay soil, 0.004mm�1 in the sandy soil in Egypt and 0.0058mm�1 in the sandy clay and

sandy clay loam soils in the Netherlands. To monitor the advance and recession phase, five observation points were

established along the furrows, namely at 0L; 1=4L; 1=2L; 3=4L, and 1L. The distance between two consecutive

points was 17.5m.

Table I. Soil physical characteristics of the four soil types

Characteristic Egypt Netherlands

Soil (1) Soil (2) Soil (3) Soil (4)

Particle size distributionSand (%) 22.7 87.2 48.28 55.04Clay (%) 53.0 5.3 45.89 33.42Silt (%) 24.3 7.5 5.83 11.54Texture grade Clay Sandy Sandy clay Sandy clay loamWilting point (%) 27.8 1.9 12.5 2.3Field capacity (%) 46.3 15.2 31.3 24.2Saturation % 61.0 20.8 49.0 42.3Saturated hydraulic conductivity (m day�1) 0.04 1.8 0.03 0.05Bulk density (kgm�3) 1.20 1.60 1.20 1.30



Selection of the experiments

The experiments included the following variables: discharge (Q), cycle time and cycle ratio.

Discharge. For each soil type one discharge has been used and the discharge was 0.74 l s�1 for clay soil,

1.0 l s�1 for sandy soil and 0.76 l s�1 for sandy clay and sandy clay loam soil. The discharge was conveyed from an

open channel with a constant head to the furrows via calibrated siphons. In Egypt a PVC pipeline with a diameter

of 10 cm conveyed the flow to the furrows in the sandy soil. Special orifices were used to get the required discharge.

The applied amount of water was not the same for all tests, but the total amount depended on the number of surges

which was needed to bring the water to the end of the furrow.

Cycle time. The cycle time is the total on- and off-time of one cycle. It was the same for all soil textures: 16 and

24 minutes. The water supply was cut off at the end of the first surge that advanced the water to the end of the

furrow.

Cycle ratio. The cycle ratio is the ratio of the on-time to the total cycle time. For the cycle time of 16 minutes

the cycle ratio was 1/4, 1/2 and 3/4 and for the cycle time of 24 minutes the cycle ratio was 1/3, 1/2 and 2/3. Not all

cycle ratios have been used during the tests as some would give either the same result as continuous flow or the

advance becomes so short that the whole test would take a long time with too many surges that would be outside the

general recommendations for surge flow irrigation.

DETERMINATION OF INFILTRATION PARAMETERS

Measured infiltration parameters

The measured infiltration parameters for each soil type have been obtained by measuring the inflow and outflow

in one furrow until the outflow becomes constant. From the inflow and outflow the basic infiltration rate f0 has been

estimated as follows (Walker, 1989):

f0 ¼ Qin � Qout

Lð8Þ

where f0¼ basic infiltration rate (m3min�1m�1), Qin¼ inflow (l s�1), Qout¼ outflow (l s�1) and L¼ furrow length

(m).

The basic infiltration rate from Equation (8) was 0.00018m3min�1m�1 for clay soil, 0.00055m3min�1m�1 for

sandy soil, 0.0000686m3min�1m�1 for sandy-clay soil and 0.000339m3min�1m�1 for sandy-clay loam soil. Use

of these values in the two-point method (Elliott and Walker, 1982) resulted in the exponent a and the k-value in

m3min�a. The two-point method depends on the time required to advance the water to half of the furrow length

ðt0:5LÞ as well as on the time required to advance the water to the end of the furrow ðtLÞ. The two-point method has

been developed to determine the exponent a and the k-value for continuous flow in long furrows (more than 300m).

A detailed description of the method is given by Elliott and Walker (1982).

The application of the two-point method in short furrows and for surge flow irrigation is a completely new aspect

that has been investigated as part of the present study. Due to the short furrow length, the times t0:5L and tL are

different for each case and each soil type and consequently the exponent a and the k-values are not the same for

each case, but fluctuate with the surge effects that depend on the discharge, cycle time and cycle ratio. Values of the

exponent a and the k-values for the various cases are presented in Table II.

Selecting infiltration parameters from the SIRMOD default data

As explained previously, the two-point method mainly depends on the time required to advance the water to half

of the furrow length and to the end of the furrow. Hence, the values of the infiltration parameters for the same soil

are different for each case as the advance time fluctuates with the surge effects. From a practical point of view it is



obvious that farmers or designers are not able to simulate and evaluate various surge flow irrigation cases on the

same soil as they do not have the required infiltration parameters from field measurements. Therefore, the present

research has also used the default values of the infiltration parameters given in SIRMOD for further evaluation.

These parameters are given by the United States Department of Agriculture for each intake family and they can be

found from the measured advance time for continuous flow for each soil type and discharge.

To select the proper infiltration parameters for a soil type, equations for furrow design as developed by the Soil

Conservation Service of the United States Department of Agriculture (USDA-SCS, 1986) were used. These

equations describe the relationship between furrow length, inflow rate, deep percolation, surface runoff and field

application efficiency for design values of application depth, soil intake rate, furrow slope and spacing. The water

intake per unit length is related to the wetted perimeter (the furrow surface in contact with the water). The intake

from a furrow is in both vertical and horizontal directions and the wetted perimeter has to be increased by an

empirical constant to account for the horizontal intake caused by the lateral component of the soil moisture

gradient (the adjusted wetted perimeter):

P ¼ 0:265� Q�n=S0:5� �0:425þ 0:227 ð9Þ

where n¼Manning coefficient, S¼ slope (mm�1), P¼wetted perimeter (m) and Q¼ inflow (l s�1).

The measured advance time, being the time required for the water to flow from the inlet to the end of the furrow,

was used to find the intake family by trial and error. For each furrow the following parameters were derived:

� Adjusted wetted perimeter P according to the SCS equations (Equation 9);

� Advance coefficient �, used in the SCS equations (Equation 10 or 11).

� ¼ gx

QS1=2ð10Þ

� ¼ gL

QS1=2ð11Þ

Table II. Measured infiltration parameters (f, a and k) for all tests

Soil type The Netherlands Soil type Egypt

Discharge Cycle time Cycle Exponent k-value Discharge Cycle time Cycle Exponent k-value(l s�1) (min) ratio a (m3min�a) (l s�1) (min) ratio a (m3min�a)

Sandy clay f¼ 0.0000686 Clay soil f¼ 0.000183soil

0.76 Continuous 0.45731 0.00444 0.74 Continuous 0.52649 0.00427

16 16 1/4 0.19472 0.013551/2 0.47284 0.00395 1/2 0.57596 0.002893/4 0.40583 0.00517 3/4 0.38398 0.00589

24 1/3 0.35560 0.00451 24 1/3 0.10189 0.009811/2 0.38565 0.00420 1/2 0.31616 0.00863

2/3 0.51322 0.00370

Sandy clay f¼ 0.000339 Sandy soil f¼ 0.00055loam soil

0.76 Continuous 0.30858 0.00474 1.0 Continuous 0.44340 0.00435

16 1/2 0.24784 0.02030 16 1/2 0.39622 0.004903/4 0.21013 0.00804 3/4 0.55383 0.00315

24 1/3 0.30153 0.01388 24 1/3 0.35361 0.005181/2 0.20006 0.00839 1/2 0.30915 0.00543

2/3 0.40396 0.00459



The time for the water to advance to successive points along the furrow is a semi-logarithmic relationship of

length, inflow rate and slope:

TT ¼ L

f� e� for x ¼ L ð12Þ

where f and g¼ advance coefficient varying with intake family, e¼ 2.7, TT¼advance time (min), x¼ distance

from furrow inlet to point x (m) (x maximum is L) and L¼ furrow length (m).

Based on the measured advance time for continuous flow for each soil type and for each discharge the

intake family was obtained. The intake family was 0.25 for clay soil, 1.0 for sandy soil and 0.60 for sandy clay

and sandy clay loam, respectively. The a, k and f coefficients for those intake families are presented in

Table III.

RESULTS AND DISCUSSION

The SIRMOD III model has been calibrated by two different methods. In the first method the model has been

calibrated by using the measured infiltration parameters (a, k and f) as presented in Table II. The second calibration

method is based on the selected infiltration parameters from SIRMOD III default data, which is presented in

Table III. The two methods are discussed below.

Model calibration based on measured infiltration parameters

The results of the measured and simulated advance for continuous and surge flow irrigation under the

Netherlands and Egyptian field conditions are presented in Figures 1 and 2, respectively. The model gave a

very good fitting of the simulated advances with the measured ones for sandy clay and sandy clay loam under the

Netherlands conditions (Figure 1). The simulated advances for all the continuous and surge flow cases in both soil

types were exactly the same as those measured over the full length. Only a small deviation can be noticed in the

case of 16-min cycle time and half cycle ratio in sandy soil; the simulated advance was identical to the measured

advance over the first 95% of the furrow length (Figure 1).

Therefore it can be concluded that the simulation results based on the measured infiltration parameters fully

represent the actual infiltration under continuous and surge flow irrigation in sandy clay and sandy clay loam soils.

Moreover, the step change in infiltration rate that occurs between surges on previously wetted sections as presented

by the relatively simple approximation as well as the transition equation for the second surge in Equations

Table III. Required input data for model simulation

Egypt NetherlandsSandy clay and

Clay soil Sandy soil sandy clay loam soil

Infiltration parametersa 0.4150 0.5980 0.5290k (m3min�a) 0.0034 0.0033 0.00320f (m3min�1) 0.000068 0.000212 0.000136Manning coefficient nFirst irrigation 0.06 0.04 0.04Second irrigation 0.05 0.03 0.03Inflow rate (l s�1) 0.74 1.0 0.76Slope (mm�1) 0.0024 0.004 0.0058Furrow length (m) 70 70 70Furrow width (m) 0.70 0.70 0.70



Figure 1. Measured and calculated advance phase in continuous and surge flow irrigation for 0.76 l s�1 and for different cycle times and ratios insandy clay and sandy clay loam soils (A and B respectively) under the Netherlands conditions (based on measured infiltration parameters)



Figure 2. Measured and calculated advance phase in continuous and surge flow irrigation for a discharge of 0.74 l s�1 in clay soil (A) and for adischarge of 1.0 l s�1 in sandy soil (B) with different cycle times and ratios under Egyptian conditions (based on measured infiltration

parameters)



(3–6) fully represent the investigated soil types. Similar results have been reported by Walker and Humpherys

(1983).

Good simulation results were also obtained in both sandy and clay soil types under Egyptian conditions

especially with continuous flow (Figure 2). The simulated advance for continuous flow exactly matches the

measured one in both soil types. The simulated advance for all the surge flow cases in both soil types was the same

as the measured advance over the first 80% of the furrow length, and in some cases it was the same over the full

length of the furrow (Figure 2). The results indicated that the simulated advances based on the measured infiltration

parameters in sandy and clay soils can represent the actual infiltration rate under continuous and surge flow

irrigation but the special variability in soil intake properties has more impact on the model performance for surge

flow than for continuous flow.

The infiltration is influenced by the surge effects and it is different from one case to the other due to the

impact of cycle ratio and cycle time as well as discharge. The exponent a is different for each case due to these

factors, but it does not show a specific trend as follows from Table II. Any small change in the exponent results

in a change in the k-value; the latter has the greatest effect on the infiltration. The simulated advance for

clay soil under surge flow irrigation did not reach the end of the furrow (Figure 2). This may be due to an

overestimation of the basic infiltration rate. In clay soil the infiltration is slow and a longer time is needed

for the outflow to reach a constant value, which is used for the estimate of the basic infiltration rate f0. It

may also be related to the step change in infiltration that occurs between surges on previously wetted

sections as presented by the relatively simple approximation in Equations (3–6). For correct results the value

of the exponent � in Equation (3) should be changed according to the soil type. In this study �¼ 3 was

used.

Model calibration based on modified infiltration parameters

The infiltration parameters of the intake families (Table III) together with the number of surges and cycle on-

time have been used in the SIRMOD III model to simulate the advance for all cases of continuous and surge flow

irrigation and for all soil types under the Egyptian and the Netherlands conditions (Figures 3 and 4 respectively).

The clay soil under the Egyptian conditions gave relatively large differences between the measured and calculated

advance. The calculated advance for both continuous and surge flow irrigation reached the end of the furrow in a

short time compared with the measured one (Figure 3). In sandy soil the simulation results are better than in clay

soil especially for the surge cases, but they still show a large difference between the simulated and measured

advance especially in the last quarter of the furrow length. In sandy clay and sandy clay loam under the

Netherlands conditions (Figure 4) the simulated advance does not always reach the end of the furrow for both soil

types except for the continuous flow. The simulated advance in continuous flow for both soil types resembles the

measured one.

These results may be due to the values of a, k and f of the selected intake families which maybe do not correctly

represent the actual infiltration of the investigated soil types under the conditions of this field experiment. The

constant a has an effect on the shape of the cumulative infiltration curve, thus on the profile of the advance curve.

An increase in a leads to an increase in the slope of the advance curve (Strelkoff and Souza, 1984). Since the slope

of the presented advance curves is the same for all the simulations, the main effect on the advance might be due to

the k coefficient. An increase in k for a constant a and f will increase the cumulative infiltration and as a

consequence the advance along the furrow will be slower (Strelkoff and Souza, 1984). A decrease in kwill show the

opposite behaviour. The results of the simulation show that the advance reaches the end of the furrow faster than

the measured one, which might be attributed to a not fully correct value of the k coefficient. The results of the

simulations that are based on the default parameters as given by SIRMOD indicate that it is difficult to choose the

most proper infiltration parameters, which present the actual infiltration in a correct way, especially for clay soils.

In some cases, for example for surges with a short on-time (4min), SIRMOD did not correctly simulate the

advance. For example Figure 5 shows a large difference between the measured and simulated advance, especially

when the on-time is so short that the individual surges coalesce (merge together) along the furrow. The software

does not include the possibility to simulate this phenomenon.



Figure 3. Measured and calculated advance phase in continuous and surge flow irrigation for a discharge of 0.74 l s�1 in clay soil (A) and for adischarge of 1.0 l s�1 in sandy soil (B) with different cycle times and ratios under Egyptian conditions (based on one intake family)



Figure 4. Measured and calculated advance phase in continuous and surge flow irrigation for 0.76 l s�1 and for different cycle times and ratios insandy clay and sandy clay loam soil (A and B respectively) under the Netherlands conditions (based on one intake family)



The simulation results of all the experiments indicate that the most critical input parameters are the infiltration

coefficient a, k and f (basic infiltration rate). As explained before, the coefficient a mainly affects the slope of the

advance curve, while the basic infiltration rate f has almost no effect on the advance as indicated by Figure 6.

Hence, the coefficient k is the most critical infiltration parameter as it has a direct impact on the infiltration. It has to

be noted that it is very difficult to predict or assume these coefficients as they may be different for each furrow, are

affected by the surging mechanisms and change from one irrigation to another. Several efforts have been made to

describe the values of these parameters as a function of the soil types. Among the first attempts was that by the US

Department of Agriculture (1974), followed by an effort of Utah State University (Walker, 1989).

Another important factor in irrigation design is the roughness coefficient n. Values of 0.04, 0.06 and 0.08 have

been assumed for the simulation of the advance for some cases of this study. The sensitivity of the model in view of

changes in roughness n is presented in Figure 7, which indicates that a change in roughness will increase the

Figure 5. Simulated advance for a short on-time (4min on and 12min off) for a discharge of 0.74 l s�1 in clay soil under Egyptian conditions

Figure 6. Sensitivity of simulated advance to basic infiltration rate f, in m3min�1

Figure 7. Sensitivity of the Manning’s coefficient n on the advance



advance by almost 5% in relation to the measured one. Similar results are reported by Bautista and Wallender

(1992).

CONCLUSIONS

This study has shown that the SIRMOD III model can accurately simulate continuous and surge flow irrigation

under short field conditions when the appropriate infiltration parameters are used. The measured data resulted in

the most optimal simulation of the advance time and consequently of the infiltration. When the infiltration

parameters are selected from the SIRMOD III default data set, they failed to provide a reliable simulation of the

advance phase in each soil. The study has also revealed that the two-point method can be successfully used to

compute the infiltration parameters for continuous and surge flow irrigation under short field conditions and for

different soil types.

REFERENCES

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Engineering 118(3): 450–465.

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Conference, American Society of Civil Engineering: Flagstaff, Arizona; 691–700.

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515.

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ASCE 108(3): 179—195.

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Council of ICID and 20th European Regional Conference, Montpellier, France, 14–19 September.

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