4 Modifying the design of subsurface drainage systems in rice growing areas

4.1 General

One of the findings of the investigations was that modification of the conventional layout of the subsurface drainage system would be necessary to meet the water man- agement requirement in areas where rice rotates with other summer crops. The impact of a modified layout on the design of the drainage system will be discussed in the following sections. The ensuing guidelines for the design of subsurface drainage sys- tems in rice growing areas have been used to formulate the concept of the modified layout for a sizeable prototype area in the eastern Delta, the Mahmudiya I area. The main objective was to test the practical and financial consequences of the modified system and its operation.

4.2 Design of drainage systems in rice growing areas

4.2.1 Technical design criteria and specifications

The modified layout of the subsurface drainage system implies that each subcollector serves an area coinciding with a cropping unit of the crop consolidation system. The subcollectors meet the main collector at a manhole, and closing devices should be installed to control the drainage unit outflow.

Theedesign criteria for this modified layout can be the same as those applied for other crops. In the conventional design, a higher drainage duty for areas with rice is currently applied to calculate the collector pipe diameters (4 "/day versus 2 mm/ day for non-rice crops). The results of the investigations clearly indicate that high drain discharges are undesirable, and consequently the farmers block the subsurface drainage system. Even on the rare occasions that rapid drainage i s desired, e.g. at the end of the rice season, this can still be achieved if the hydraulic capacity of the pipes is attuned to non-rice crops only. Temporary overpressure in the pipe is not a problem. Therefore drainage duties for the hydraulic design of laterals and collectors should be the same as for non-rice areas i.e. 2 "/day.

The lower design discharge of the modified system will imply a reduction in size of pipes as compared to the current design norms, and thus lead to cost savings. This will, however, be partly offset by extra costs due to the increased total length of subcol- lector pipes compared with the conventional layout (Section 4.3.3). Other design fea- tures, e.g. spacing and depth of laterals (Section 2.2), will not differ from those in non-rice areas.

4.2.2 Delimitation of the subcollector units

The crucial element in designing the modified layout is the delimitation of the subcol-

55

lector units. The areas drained by a subcollector unit should coincide with the prevail- ing crop consolidation blocks as far as possible. Information on the latter will have to be obtained from the agency responsible for the crop consolidation scheme, her- eafter referred to as ‘Agriculture”). The subcollector units should be of reasonable size. Very small cropping units should be consolidated in large units. To keep the length of the subcollectors within practical limits, the minimum size of the drainage unit should be set at approximately 6 ha.

4.2.3 Design procedure

Compared with the current design procedure, only a few extra steps should be taken. To prepare the layout of the modified drainage system, the design engineer should have all data readily available on cropping units of the crop consolidation system. This relevant information in the form of good quality maps at a appropriate scale (1: lO,OOO), are to be provided by or collected from ‘Agriculture’.

A preliminary layout is prepared according to the technical criteria and specifica- tions mentioned above. After field checks and discussions with ‘Agriculture’, the layout can be finalized. Copies of it are sent to ‘Agriculture’ who may use it to make minor modifications to cropping units wherever necessary and desirable, to increase the efficiency of the modified system.

4.3 Application of the modified layout to the Mahmudiya area

4.3.1 General

A design for the subsurface drainage system for the .Mahmudiya I area was made according to the above guidelines. The Mahmddiya I area covers approximately 1925 ha, and lies in the eastern Delta near the town of Zagazig (Figure 4.1). The net cropped area, consisting mainly of heavy clay soils, covers approximately 1700 ha. The area represents average conditions of the crop consolidated areas in the Nile Delta. The Mashtul pilot area (108 ha), located within Mahmudiya I area, was constructed in 1980 according to the modified design concept. The construction of the drainage works in the Mahmudiya I area was completed in 1982. A monitoring programme was con- ducted to study the effects of the modified system and its practical operation. Simulta- neously, the functioning of the subsurface drainage system with a conventional layout was monitored in a comparable neighbouring area, i.e. Mahmudiya 11.

9

4.3.2 Layout

The modified layout of the subsurface drainage system in the Mahmudiya I area is

’) The terms ‘Agriculture’ and ‘Irrigation’ may stand for the Ministry at National level, for the concerning sector at provincial level, or for officials at district or village level.

56

Mahmudiya-l (modified) Mahmudiya-ll (conventional) - irrigation canal

--- drain I town/viltage

MPA Mashtul Pilot Area

Zagazig

Figure 4.1 Location of the Mahmudiya area

shown in Figure 4.2a. The crop consolidation plans for three successive years were used to prepare this layout. The subcollector units could be adapted to the existing cropping units for 95% of the area. Near villages some small cropping units had to be grouped to one drainage unit. A complete match between subcollector units and the prevailing cropping units appeared possible, but is not strictly necessary. This was, however, left to ‘Agriculture’, who could easily make some minor modifications to the cropping units.

4.3.3 costs

The total construction costs, including materials (drainpipes, manholes, etc.) of the modified drainage system have been compared with the construction costs of the con- ventional system for the same area. The layout of the conventional system is shown in Figure 4.2b. The list of quantities and construction costs for both systems is pre- sented in Figure 4.3.

57

In a modified system the total length of the smallest collector pipes (diameter 15 cm) is much greater than in a conventional system, but there are fewer of the larger, more expensive sizes (diameter 20 to 50 cm). This is a directxesult of the larger number of subcollectors required in the modified system, and the smaller drainage rate for the hydraulic design. The final result of the cost comparison favours the modified system, the costs of the conventional system being 3% higher.

---- drain - irrigation canal 7 with flow regulatorls) - collector outflow end

500 1000 m

Figure 4.2a Modified layout of the subsurface drainage system in the Mahmudiya I area

58

The cost comparison for another area, i.e. the Nashart area in the Central Delta, also favoured the modified system, resulting in a 6% cost saving (DRI, 1986a).

As yet, no data are available on the operation and maintenance costs of either sys- tem. The operation and maintenance costs of the modified system may only be slightly higher than the conventional system. The incremental costs would be attributable to the control devices and would have no noticeable influence on the cost comparison.

Figure 4.2b Conventional layout of the subsurface drainage system in the Mahmudiya I area

59

pipe

- 14-

- 13- - 12- - 11-

2 300- 10-

J - 9

450-

. Lu

E .- 3 - T- E I

J - I 7 -

i F .- E - E 6- 5 150-z 5 -

* o -; 4 - -

- 2 3 - * -= 2 - I - 1

I

O-’

, in m/ha . .Y

e P a

lei 15-

-,i

1-

0 7 I 30

cost of modified system

modified I 1 LE =1.45 US$ ---- - cost of conventional system

D conventional

I n

15 401 15 20 25 30 35 40 45 50;

I concrete pipes, 0 in cm / reinforced concrete pipes, P, in cm i * I

lumber of units

7501

500

250

O

~ manholes, j cross pieces, ! @incm I D i n cm

Figure 4.fCost comparison between the conventional and modified system

4.3.4 Monitoring

The monitoring programme in the Mashtul pilot area started in the summer of 1981. From 1983 the programme covered the Mahmudiya I and I1 areas. It was conducted during the rice growing season for three consecutive years. Its objectives were mainly: - To test the consistency of the crop consolidation scheme and its usefulness in design-

- To test closing devices; - To measure drain discharges; - To quantify the saving in irrigation water; - To measure the effect of the modified system on soil salinity.

ing the modified drainage system;

4.3.5 Results and discussion

Crop consolidation

The consistency of the cropping units is very important for the operation of the modi- fied drainage system. Changes in the cropping pattern may lead to operational prob- lems in the event that another summer crop is grown with rice in the same subcollector unit. In the Mahmudiya area the summer crops are grown according to a three-year crop rotation. This means, for example, that the cropping pattern of 1985 should be

60

the same as that of 1982. There would be no operational problems if the total area of subcollector units were to change to another crop than expected on the basis of the three-year crop rotation. Operational problems could, however be ’expected if changes involve more than one crop being grown in one drainage unit. The changes in the Mahmudiya I area of each crop between the summer season of 1982 and 1985 are presented in Table 4.1.

These changes, if consistent for the years to come, could lead to operational prob- lems over a total area of 42.4 ha (373, while changes having no effect on the operation of the system would cover an area of 152.5 ha (9%). 88% of the area had the same cropping pattern as that in 1982.

In 1985 the total area with actual operational problems was 41.2 ha (2%). The areas per crop were 1% (cotton), 5% (maize), and 2% (rice). The small cropping units around villages, which had to be integrated into subcollector units of practical sizes, gave rise to problems. This could easily have been solved by adjusting the cropping units. A procedure for this has still to be developed by ‘Irrigation’ and ‘Agriculture’. It can be concluded that the crop consolidation plans form a good and reliable basis for preparing the layout of the modified drainage system. The deviations in the boundaries of the cropping units from the subcollector units are within acceptable limits. More than 95% of the area has a far more manageable drainage system compared with the conventional design.

Table 4.1 Changes in cropping patterns in the Mahmudiya I area

Cron Actuel Potential operational problems No operational problems Actual Ratio cropping cropping 1985/ pattern pattern 1952 1982 1985

Total area Increase in area Decrease in area Increase in area (ha) Decrease in area Total area (ha) (ha) (ha) (ha) (ha) (ha)

Cotton M+C R-C C-M C-R M-+C R-C C-M C-R

522 6.7 11.8 3.4 34.0 21.4 0.8 4.2 568 1.08

Maize C+M R-M M-C M-R C-M R-M M+C M-R

627 1 1 3 14.3 6.7 6.3 0.8 28.2 34.0 63.9 571 0.91

Rice __

M+R C+R R-C R+M M - + R C-R R-C R - + M

550 6.3 3.4 14.3 63.9 4.2 21.4 28.2 564 1.03

Total 1700 42.4 42.4 152.5 152.5 I700

M = Maize, C = Cotton, R = Rice

61

- Collectors without outflow from rice fields due to: o Closure of subcollectors of the rice area (modified system); o Absence of rice crop;

- Collectors with outflow from rice fields which cover a part of the total area drained.

The collector discharges of the first category seldom exceeded 1.0 "/day. In the second category maximum discharges of 4.5 "/day were measured.

In Figure 4.5 the average collector discharges are given against the percentage.rice area within the collector command area. The average collector discharge with restrict- ed subcollector outflow of the rice areas and of non-rice areas is . O S "/day. This is far below the design discharge of 2 "/day.

The average collector discharge, with unrestricted outflow from rice areas increases according to the following equation:

q = 0.5 + 0.03A, where q = average collector discharge in "/day A = drained rice area within the collector command area, in percent

The correlation coefficient ris 0.81. The 90% confidence limits of the regression coeffi- cient are 0.02 and 0.04, which are significant. The average collector discharge of an entire rice grown area would be 3.5 "/day.

In the Mashtul pilot area unrestricted outflows of lateral drains under rice fields were measured. The average discharges varied between 3 and 4 "/day, which agreed with the calculated discharges of rice areas according to the above relationship. More- over, it confirms the findings in Section 3.4. l , and those of VBB/ILACO (1973).

average collector dircharqe in mmldav

Figure 4.5 Average collector discharges in drained rice areas

63

Saving in irrigation water

From the data in the previous section it can be concluded that the restriction of the outflow of subcollector units with rice would save at least 3 "/day. The total area under rice is approximately 420,000 ha. The saving in irrigation water would thus be approximately 12.5 million m3 per day, or 1.5 billion m3 per growing season. In view of the increasing demand for irrigation water in Egypt, the implementation of the modified layout in rice growing areas could therefore contribute considerably to the saving of irrigation water.

Soil salinity

An investigation was carried out as to whether the closure of the subsurface drainage system during the rice season would increase the soil salinity. Measurement of the soil salinity before and after the rice season indicate minimal fluctuation (Table 4.2).

Salts were leached from the topsoil in 1983 and 1984. The slight increase in 1985 could easily have been removed during the non-rice season when there was no restric- tion on the subsurface drainage outflow.

Table 4.2 Soil salinity in the Mahmudiya I (modified) area before and after,the rice season

Year Soil layer in cm EC,, in mmhos/cm

Before After

1983 O- 25 2.2 1.8 25- 50 1.9 2.2 50- 100 2.2 2.3

1984 O- 50 1.3 0.9

1985 O- 25 1 .O 1.4 25- 50 1.2 1.4

. In experimental fields with a modified subsurface drainage system, the Drainage Research Institute (1986b) found that the soil salinity had decreased by the end of the rice season (Figure 4.6).

The investigations clearly showed that the modified system would not cause soil deterioration.

4.4 Final conclusions

Experience with the modified subsurface drainage system in the Mahmudiya I area was very positive. Water management in rice growing areas in the Delta could be

64

depth belovr in metres

O ’ O o r

0.75

1 .o0 O

Figure 4.6 Soil salinity before and after the rice season on three experimental fields with a modified system in the Nile Delta (after DRI, 1986b)

considerably improved by applying the modified system. Two other areas have already been designated for further investigations.

To reap the full benefits of the modified system there are, however, still a few items to be considered. These are: - Consultation between ‘Irrigation’ and ‘Agriculture’ on the most suitable drainage

units should these units deviate for any reason from the cropping units; - The planning of the location and delimitation of rice blocks from year to year ac-

cording to the subcollector units. ‘Agriculture’ should obtain copies of the drainage layout;

- Operation and maintenance of the closing devices. The similarity with the operation of the irrigation system is striking. Therefore, ‘Irrigation’ seems to be the obvious choice;

- Extension to the farmers. This work is normally within ‘Agriculture’s’ competence and responsibilities.

The arrangement between the above items should be institutionalized by an agreement between ‘Irrigation’ and ‘Agriculture’.

65

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Currently available ILRI publications No. Publications Author ISBN No.

1 1 14

15

16

16‘ 17 19 20 21 23 24 25

26

27 29

30

31

32

33

34

35

36

37

38

39

40

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Reclamation of salt-affected soils in Iraq. P. J. Dieleman (ed.) - I Irrigation requirements for double cropping of low- 90 70260 840 land rice in Malaya. Planning of service centres in rural areas ofdeveloping D. B. W. M. van Dusseldorp - countries Drainage principes and applications (in 4 volumes) 90 70260 123,

and -63 8

G . A. W. van de Goor and G . Zijlstra

-

-13 I , -62 X

Principos y aplicationes del drenaje (en 4 vollimenes). - - Land evaluation for rural purposes. R. Brinkman and A. J. Smyth 90 70260 859 On irrigation efficiencies. M. G. Bos and J. Nugteren 90 70260 875 Discharge measurements structures. M. G . Bos - Optimum use of water resources. N. A. de Ridder and A. Erez -

Drainage and reclamation of salt-affected soils. J. Martinez Beltrán - Proceedings of the International Drainage Work- shop Framework for regional planning in developing coun- J. M. van Staveren and tries

Land evaluation for agricultural development. K. J. Beek -

J. Wesseling (ed.) 90 70260 549

90 70260 832

90 70260 689 D. B. W. M. van Dusseldorp

Land reclamation and water management. Numerical modelling of groundwater basins: A user- oriented manual Proceedings of the Symposium on Peat Lands Below Sea Level. Proceedings of the Bangkok Symposium an Acid Sul- phate Soils. Monitoring and evaluation of agricultural change.

Introduction to farm surveys.

Evaluation permanente du développement agricole.

Introduction aux enquêtes agricoles en Afrique.

Proceedings of the International Workshop on Land Evaluation for Extensive Grazing (LEEG). Proceedings of the ISSS Symposium on ‘Water and solute movement in heavy clay soils’. .Aforadores de caudal para canales abiertos.

Acid Sulphate Soils: A baseline for research and devel- opment. Land evaluation for land-use planning and conserva- tion in sloping areas. Research on water management of rice fields in the Nile Delta, Egypt.

- J. Boonstra and N. A. de Ridder H. de Bakker and M. W. van den Berg H. Dost and N. Breeman (eds.) Josette Murphy and Leendert H. Sprei Josette Murphy and Leendert H. Sprey Josette Murphy and Leendert H. Sprey Josette Murphy and Leendert H. Sprey W. Siderius (ed.)

J. Bouma, P. A. C. Raats

M. G . Bos, J. A. Replogle and A. J. Clemmens D. Dent

(ed.)

W. Siderius (ed.)

S. EL. Guindy & I. A. Risseeuw; H. J. Nijland (Ed.)

No. Bulletins 1 The auger hole method. W. F. van Beers 4 On the calcium carbonate content of young marine

sediments. B. Verhoeven

90 70260 697

90 70260 700

9070260719

9070260743

90 70260 735

90 70260 891

90 70260 956

90 70260 948

90 72060 972

90 70260 921

90 70260 980

9070260999

90 70754 O8 8

90 70260 8 16 -

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No. Bulletins Author ISBN No.

6

8

9 The Managil South-Western Extension: An extension D. J . Shaw

Mud transport studies in cqastal water from the Western Scheldt to the Danish frontier. Some nomographs for the calculation ofdrain spac- ings.

A. J . de Groot

W. F. J . van Beers

10

I 1

I IS

1 IF

12

13

No. 7 8

9

I O 13

18

to the Gezira Scheme. A viscous fluid model for demonstration of ground- water flow to parallel drains. Analysis and evaluation of pumping test data.

Análisis y evaluación de los datos de ensayos por bombeo. ’ Interprktation et discussion des pompages d’essai

Gypsifereous Soils

Groundwater hydraulics of extensive aquifers

Bibliographies Agricultural extension in developing countries Bibliography on cotton irrigation.

Annotated bibliography on surface irrigation meth- ods. Soil Survey interpretation. Abstract journals on irrigation, drainage and water resources engineering. Drainage: An annotated guide to books and journals

Other publications Papers International Symposium Polders of the World (3 volumes). Final Report Symposium Polders of the World.

F. Homma

G. P. Kruseman and N. A. de Ridder G. P. Kruseman and N. A. de Ridder G. P. Kruseman and N. A. de Ridder J. G . van Alphen and F. de los Rios Romero J. H. Edelman

C. A. de Vries C. J . Brouwer and L. F. Abell S. Raadsma, G. Schrale

R. H. Brook L. F. Abell

G. Naber

-

90 70260 824

90 70260 808

-

9070260794

90 70260 93 X

9070260751 76 X and -778 -

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:.,

4 Modifying the design of subsurface drainage systems in rice growing areas4.1 General4.2 Design of drainage systems in rice growing areas4.2.1 Technical design criteria and specifications4.2.2 Delimitation of the subcollector units4.2.3 Design procedure4.3 Application of the modified layout to the Mahmudiya area4.3.1 General4.3.2 Layout4.3.3 Costs4.3.4 Monitoring4.3.5 Results and discussions4.4 Final conclusionsBibliography