DrenVSubIR design software validation for seepage drainage and subirrigation.

Gombos, Dan ; Sabau, Nicu Cornel ; Bodog, Marinela 等

1. INTRODUCTION

Agricultural land in the western part of Romania, affected by successive droughts and excessive moisture combination of rainfall and high level groundwater in the context of current global climate change, show a trend of desertification manifested by an increased frequency and periods of drought.

The main method of fighting desertification is by using irrigation, and in the sub--wet areas, provided with drainage systems, we have to analyze the possibility of using these systems for giving water from irrigation to the plant. The study of reversibility of the drainage is called the subirrigation.

Subirrigation or seepage irrigation is the irrigation method where water is brought at the base of the root area, with the help of some pipes buried underground, thus watering the plants through capillarity. This method has the advantage of cutting out all losses at the plant roots ends level in the soil.

2. METHODS AND SAMPLES

In the sub wet area of the Western Plain, 161 thousand hectares have been set up for irrigation in Bihor county, out of which 1540 ha with underground drainage (6). Areas set up with drainage systems, conceived for eliminating excess water (conventional drain), can be used for adjusting the level of the soil water (controlled drainage) or for administrating water through subirrigation (reversible irrigation drain).

This method has the advantage that in wet periods the system works as conventional drain, thus eliminating the excess water in the soil profile. The controlled drainage allows the soil humidity control in the root area by controlling the ground water level, and the water quantity coming from conventional drain. In drought periods the system is used as reversible drainage (i.e. subirrigation), when the water needed is brought through the drainage channels network back in the soil profile.

The reversible drainage, as subirrigation, allows the control of the soil water and water economy, with no extra investments, high yield gains and reduction of nutrient losses.

In order to work in controlled drainage or in subirrigation, for seepage drainage, it has to allow the ground water level to be maintained at the minimum easily available content at the field capacity (i.e. plant root ends depth).

[FIGURE 1 OMITTED]

The design of the seepage drainage is a continuous operation regime, by establishing the pose depth, the length of the drain, the drain spacing and after that checking the drain in non-permanent function.

Ernst relationship for designing the ideal drain spacing is (Sutton, 1971; Beers, 1976; Martinez Beltran 1978; Kroes & Van Dam, 2003; Teusdea et al., 2008):

h = [h.sub.v] + [h.sub.o] + [h.sub.r] = q x L/K x ([[zeta].sub.o](L) + [[zeta].sub.v] + [[zeta].sub.r]) = q x L/K x [[zeta].sub.0](L), (1)

where [h.sub.o], [h.sub.v], [h.sub.r], are the hydraulic head losses due to the horizontal, vertical and radial flow, respectively, [[zeta].sub.0](L) the total loss coefficient with an ideal drain, [[zeta].sub.o](L), [[zeta].sub.v], [[zeta].sub.r] are the resistance coefficients, corresponding to three flow types (Sutton, 1971; Beers, 1976; Martinez Beltran 1978; Kroes & Van Dam, 2003; Teusdea et al., 2008).

If the drains are real--with discontinuous slits--and overcasted with a filter prism, then David I. (Teusdea et al., 2008) proposes in addition to Ernst relationship a term for the load loss at the filter drain entrance, [delta][h.sub.if] ([[zeta].sub.if])--where [[zeta].sub.if] is the resistance coefficient for the filter drain entrance.

The drain spacing, L, is given by the equation (2) positive solution. After the calculation of this distance, the design of the drainage structure is finished. The next step consists in the verification of the drainage system as subirrigation (reversible drainage) system (figure 1b).

The goal of the subirrigation verification is to determine the subirrigation height [h.sub.sub] = [H.sub.0] - [H.sub.m]. This level difference represents the total load loss which secures the water reserve at the root end depth. The basic scheme of this structure is presented in figure 1b. The notations are as it follows: p--the width of phreatic water, [H.sub.0]--the width of the saturated soil zone at the drain, [H.sub.m]--the width of the saturated soil zone midway between the drains, [D.sub.0]--the distance between drains and the impermeable layer, [L.sub.dr] = L--the drain distance, H--the depth of the impermeable layer and K--the hydraulic conductivity of the soil. The validation criterion of the drainage structure for subirrigation usage is described by the following relationship:

([H.sub.c] + z) < H, (2)

where [H.sub.c] represents the water height in the collecting channel.

3. RESULTS AND DISCUSSIONS

Real drains involve some filter prisms located at the bottom of the possing drain channel. For the specified research field setup, there were considered the following filter prism types: Ff --no filter prism; Fa--filter prism out of soil for acidity correction with a 0.1 m height; Fm--filter prism out of rubble with a height of 0.1 m; Fr--rubble filter prism of 0.2 m; Cr--mole drain perpendicular on the drain direction; Sc--deep loosening through scarification, on the perpendicular direction of the drains (table 1). In table 1 there is presented the drain spacing, L, as the drainage design results made by the classical approach with the mentioned filter prisms versions. In table 2 the drain spacing, L is presented, as the drainage design results generated with DrenVSubIR software for the mentioned filter prism versions. Also, there are provided the subirrigation design conditions and their validation results. The valid subirrigation systems are only the drainage systems that have the drain spacing greater than 22 m. This limit is well known as good from the field engineering expertise, for the mentioned field parameters (1984-1990).

In table 3 the comparison between the maize productions with drainage drain spacing versions matched in the field setup (first part) and in the DrenVSubIR design (second part) are presented in two parts.

The last column presents the pay-off time (in years) that was validated for experimental field setup and forecast with the DrenVSubIR software within nowadays economical status.

Pay-off times for field setup (1984-1990) are almost twice (with 100%) greater than nowadays DrenVSubIR design conditions.

4. CONCLUSIONS

In the conditions of global warming the main method for fighting desertification is using irrigation, and in the sub-wet areas with irrigation drainage systems we can consider reversibility between drainage--irrigation--subirrigation, a method of watering that is more effective and environmental friendly.

In the Western Plain of Romania, in Avram Iancu, Bihor county, on a cambical, gleical phaeosiom, more conventional seepage drainage variants were studied between 1984-1990.

Using the DrenVSubIR software for designing the drain spacing with similar parameters to the ones from the field of Avram Iancu led to the same results indicating around 30 m drain spacing - this means the experimental DrenVSubIR validation.

DrenVSubIR software validates only the 22 m larger drain spacing drainage systems to work in reversible way as subirrigation. The investment in reversible drainage systems is about 1.2 - 1.5 times bigger than only drainage, but the yield increases about 2 - 3 times and, thus, a revenue about 1.5 times.

5. REFERENCES

Beers, W.F.J. (1976). Computing Drain Spacings--A generalized method with special reference to sensitivity analysis and geo-hydrological investigations, pp 14-19, IREI Bulletin 15, Wageningen, The Netherlands.

Kroes J.G. & Van Dam, J.C. (2003). Reference Manual SWAP version 3.0.3, pp 52-58, Alterra Report 773, Alterra, Green world Research, Wageningen.

Martinez Beltran, J. (1978), Drainage and Reclamation of Salt-Affected Soil--Bardenas Area Spain, pp 276-278, IERI Publication 24, Wageningen.

Sutton J. (1971). Section 16 Drainage of agricultural land, USDA - Soil conservation Service, National Engeneering Handbook, pp 4-1 - 4-122, Washington DC.

Teusdea, A.C.; David, I. & Mancia, A. (2008). Subsurface Drainage and Its Reversable Facilities in Subirrigation (2008). 1379-1380, Annals of DAAAM for 2008 & Proceedings of the 19th International DAAAM Symposium, ISBN 978-3-901509-68-1, ISSN 1726-9679, pp 690, Editor B. Katalinic, Published by DAAAM International, Vienna, Austria

Tab. 1. Research field drainage design results--Avram Iancu,
Bihor county, Romania

Versions [K.sub.1e] [K.sub.2]
 (m/day) (m/day)

Ff 0.1375 0.076
Fa 0.1969 0.076
Fm 1.5070 0.076
Fr 2.8844 0.076
Ff + Cr 0.2280 0.076
Fa + Cr 0.2437 0.076
Fm + Cr 1.5973 0.076
Fr + Cr 2.9657 0.076
Ff + Sc 0.3954 0.076
Fa + Sc 0.4109 0.076
Fm + Sc 1.7644 0.076
Fr + Sc 3.0939 0.076

Versions Filter Prism L (m)
 df (mm) Kfc (m/day)

Ff 0.065 0.076 3.60
Fa 0.159 0.218 17.4
Fm 0.159 12.40 22.2
Fr 0.223 12.40 29.9
Ff + Cr 0.065 0.076 5.40
Fa + Cr 0.159 0.218 16.5
Fm + Cr 0.159 12.40 22.5
Fr + Cr 0.223 12.40 30.1
Ff + Sc 0.065 0.076 7.50
Fa + Sc 0.159 0.218 15.8
Fm + Sc 0.159 12.40 23.0
Fr + Sc 0.223 12.40 30.4

Tab. 2. Avram Iancu, Bihor county--Romania, research field
drainage design and subirrigation validation results

Versions L (m) Hc (m) Hc+z H (m) Valid for
 (m) subirrigation

Ff 3.6 2.36 3.05 2.90 No
Fa 17.4 2.97 3.66 2.90 No
Fm 22.2 2.03 2.72 2.90 YES
Ft 29.9 1.95 2.64 2.90 YES
Ff + Cr 5.4 2.33 3.02 2.90 No
Fa + Cr 16.6 2.68 3.37 2.90 No
Fm + Cr 22.5 2.02 2.71 2.90 YES
Fr + Cr 30.1 1.95 2.64 2.90 YES
Ff + Sc 7.5 2.27 2.96 2.90 No
Fa + Sc 15.8 2.32 3.01 2.90 no
Fm + Sc 23.0 2.02 2.71 2.90 YES
Fr + Sc 30.4 1.95 2.64 2.90 YES

Tab. 3. Comparison of drainage design results from research
field and DrenVsubIR software

 Version Maize Price Price
 (L=30m) (kg/ha) (ROL */kg) (ROL */ha)

witness 3980 1.30
Fr 4420 1.24 12558
Fr+ Sc 5210 1,20 17832
Fr + Cr 4820 1.30 19656

 Version Gain Pay-off
 (L=30m) (ROL */ha) Time (years)

witness -- --
Fr 546 23
Fr+ Sc 1486 12
Fr + Cr 1092 18

* ROL is the Romanian currency before July 1st, 2005

Version Price Gain
 (RON/ha) (Kg/ha)

Fr, L = 29,9 m 2946 450
Fr + Cr, L = 30,1 m 3009 840
Fr + Sc, L = 30,4 m 2993 1220

Version Gain * Pay-off
 (RON/ha) Time (years)

Fr, L = 29,9 m 225 13
Fr + Cr, L = 30,1 m 420 7
Fr + Sc, L = 30,4 m 610 5

* with 0.5RON/kg (1 [euro] = 4,1963RON, June 13, 2009)