Evaluation of water-use in traditional irrigation

Agricultural Water Management 75 (2005) 137–151 www.elsevier.com/locate/agwat

Evaluation of water-use in traditional irrigation An application to the Lemos Valley irrigation district, northwest of Spain ´ lvarez, T.S. Cuesta*, J.J. Cancela X.X. Neira, C.J. A Department of Agroforestry Engineering, University of Santiago de Compostela, Campus Universitario, E-27002 Lugo, Spain Accepted 23 December 2004

Abstract The approval of the National Irrigation Plan (NIP) in Spain in 2001 accelerated the improvement and modernisation of the irrigated areas. The first step towards the implementation of performance of the actions envisaged in the plan is to analyse water-use in traditional irrigation. Moreover, the social impacts of irrigation on rural areas must be evaluated, and the common irrigation practices must be determined. This paper presents the results of a study conducted in the Lemos Valley irrigation district (NW of Spain). Irrigation evaluations were conducted in nine trial sites, representing the existing soil types. A sample of irrigation users were interviewed to gather information about wateruse, land tenure and irrigation socioeconomics. This irrigation district is characterised by low wateruse efficiency, significant losses in the distribution network, fragmented land ownership and a poor use of the available infrastructure. Yet, water availability and an important distribution network render the modernisation of this traditional irrigated land a challenging task that must be faced. # 2004 Elsevier B.V. All rights reserved. Keywords: Irrigation management; Modernisation; Social participation

* Corresponding author. Tel.: +34 982 223996x23290; fax: +34 982 241835. E-mail address: [email protected] (T.S. Cuesta). 0378-3774/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2004.12.007

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1. Introduction During the last few years, water demand has increased worldwide and, accordingly, in Spain. The greatest requirements are detected in agriculture (Del Moral et al., 2003). Traditionally, to attain a better use of water resources, water supply was managed by constructing great works for the regulation and conveyance of surface water (Vlachos, 2003). Among other authors, Loucks (2000) highlighted that the new trends in water management combine actions on supply and actions on demand, reducing the amount of water required to satisfy demand. Arrojo (2003) suggested that these actions reveal the need to allocate resources for the modernisation of traditional irrigation systems. According to Delgado (1992), the changes in the collective interests of society have provided irrigation with new functions besides the traditional objectives of irrigation development. Irrigation is an essential element of landscape structure and a decisive landuse variable in the configuration of total water demand (MIMAM, 1998). Irrigation has also an important role in rural development strategies (Ortega et al., 2000). Water is considered an ‘ecosocial’ asset (Aguilera, 1994) that goes beyond the economic conception of irrigation and pursues other formulations with greater social usefulness and future sustainability (Martı´n de Santa Olalla et al., 1999). These considerations are magnified by the new political aims of the European Common Agricultural Policy (CAP) and by the Directive 2000/60/EC of the year 2000 establishing a framework for community action in the field of water policy (WFD, Go´ mez-Limo´ n et al., 2002). The Common Agricultural Policy is an amplification of the 1992 reform, reflected in Agenda 2000, approved in March 1999 at the Berlin European Council. Within this framework, the National Irrigation Plan (NIP) was approved in Spain (MAPA, 2001), according to the Spanish law 10/2001 of the National Hydrological Plan (NHP). The NIP provides actions to modernise irrigated areas until 2008 over a surface of more than 1 million ha, with a projected investment of 6113 million euros. According to Beceiro (2003), the aim of this intervention is to achieve water savings of up to 2700 hm3/year, totalling more than 10% of the water required by Spanish irrigated areas. Water savings are based on a decrease in conveyance and distribution losses and on the reduction of return flows. Some authors, such as Playa´ n (2002) and Perry (1999), question the fact that irrigation modernisation causes a higher availability of water in the catchment area. The improvement and modernisation of traditional irrigation must be preceded by an analysis of current water-use. According to Playa´ n et al. (2000), detecting specific problems that affect the management of water resources enables the proposal of solutions needed to achieve a higher efficiency in water-use by farmers. The purpose of this paper is to analyse water-use in traditional irrigation, specifically, in the Lemos Valley irrigation district, NW of Spain. This area is defined in the NIP as a modernisable area. This definition includes social participation issues besides the technical ´ lvarez et al., 2004). Apart from water management, the degree of aspects of irrigation (A involvement of the social agents concerned and the social impacts of irrigation must be evaluated, and the attitude of water users must be assessed. These data are required for the modernisation.

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Fig. 1. Map showing the location of the study area.

2. Characterisation of the area The Lemos Valley irrigation district, NW of Spain, is located to the South of the province of Lugo, in the Autonomous Community of Galicia, as shown in Fig. 1. The establishment of this district in 1966 provided for the irrigation development of about 5300 ha by using the natural flows from the river Cabe and the regulated water flows from the river Mao. The design criteria used in 1996 were based on the limited capacity of the distribution network and on the lack of internal water storage (Cuesta, 2001). The main distribution network (Fig. 2) consists of three main canals, with a total length of 78.5 km and flows ranging from 5.5 m3/s at the inlet to 0.2 m3/s at the outlet, directly before discharging into the river Cabe. A network of ditches with different capacities and states of maintenance and with an approximate total length of 147 km, branch from these canals. The northern zone of the study area is characterised by a Mediterranean climate, gradually becoming cold–temperate to the South (De Leo´ n, 1988). Average annual temperature for 2000 was 13.7 8C. Average monthly temperature reached a maximum of 20.6 8C in July and August, and a minimum of 3.6 8C in January. Annual effective rainfall in 2000 was 387 mm. The maximum values were 145 mm in December and 108 mm in November, which accounted for 53.6% of total annual effective rainfall. A remarkable value of 100 mm was recorded in April. Conversely, the driest months were January, with no rainfall recorded, and June, with 2 mm (Table 1). Summer rainfall (22 June–23 September) was erratic in the study area. In the period 1967/2000, the mean value of summer rainfall was 96 mm, with a minimum of 12 mm, a maximum of 274 mm and a standard deviation of 51 mm (Fig. 3). Annual reference evapotranspiration (ETo) for 2000 was 1164.4 mm. ETo was calculated by applying the method by Hargreaves and Samani (1985). This value shows adequate agreement with the results reported by Carballeira et al. (1983) for the same area, obtained by applying different methods.

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Fig. 2. Map showing the location of irrigation sectors.

Three soil types of interest for irrigation were identified in the study area (Fig. 4), according to the classification of soil types made by Dı´az-Fierros and Gil (1984) for Galicia following the method proposed by Brikman and Young (1976). Type A soils consist of soils with silty–clay–loam texture and silty–clay texture, and represent almost 72.5% of the irrigated area. These soils do not show any problem relating to potential rooting depth. Type B soils represent 12.1% of the study area and show moderate restrictions for the cultivation of deep-rooting species. Textures range from silty–clay–loam to silty–loam. Type C soils present clear restrictions for deep-rooting crops. Type C soils have silty–loam texture and cover 8.7% of the study area. The other soil types in the area represent less than 6.7% of the study area. These soil types were excluded from the present study because they show serious problems for surface irrigation. Cuesta (2001) described water retention properties based on 50 samples taken from all the soil units considered, by using the methods reported by Walker (1989). Table 2 shows the results from this study.

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Table 1 Monthly climatic data for 2000 in the Lemos Valley: average temperature, reference evapotranspiration (ETo) and effective precipitation (Pe) Month

Average temperature (8C)

January February March April May June July August September October November December

3.6 10.1 10.6 10.7 16.6 20.1 20.6 20.6 18.8 13.4 9.8 9.6

ETo Hargreaves (mm) 30.6 44.7 87.5 83.1 142.1 187.0 179.2 166.6 124.4 69.4 31.4 21.4

Pe (mm) 0 12.7 9.6 99.7 48.5 2.1 25.2 16.2 41.2 49.3 108.0 145.1

Annual

13.7

1167.4

387.2

The traditional cropping pattern of the area consists of an annual rotation of artificial pasture and silage corn. This rotational scheme is characteristic of cattle-oriented agriculture in the region (Lo´ pez et al., 1999). Rotations of forage crops lead to the use of pastures and silage corn or to the combined rotation of both crops. Other patterns tested in previous studies are less suitable (Lloveras, 1996). The on-farm irrigation system is free draining borders, a type of surface irrigation. Irrigation is only applied to a small percentage of the surface of those fields bordering on canals, due to the incomplete state of the distribution network within the irrigation perimeter. Therefore, water must be conveyed to many fields through furrows, leading to excessive water delivery, estimated at 12,500 m3/ha (CHN, 1993). From the demographic standpoint, the area affected by the Lemos Valley irrigation district, has more than 30,000 inhabitants and suffers a serious and continuous

Fig. 3. Variation of summer rainfall (June 22–September 23) between 1967 and 2000, measured at the Monforte weather station.

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Fig. 4. Distribution of soil units.

Table 2 Mean values of soil water storage capacity: field capacity (FC) and permanent wilting point (PWP), for each soil type Soil type

A B C

FC (%)

PWP (%)

Mean

Standard deviation

Mean

Standard deviation

22.1 20.3 19.3

1.2 0.7 0.5

11.3 8.7 6.9

0.9 0.7 0.5

FC and PWP are expressed on a gravimetric basis.

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depopulation process (Bertrand, 1992). The studied irrigation district has 3423 inhabitants, 730 of which were farmers in 1999 (IGE, 2001).

3. Materials and methods To study social participation and irrigation management, 119 out of the 730 farmers established in the irrigated area were interviewed during the year 2000. Crop water requirements of the traditional crops in the area were determined, and surface irrigation evaluations were conducted in nine trial sites to complement the data obtained from the survey. 3.1. Crop water requirements Daily climatic data were used to estimate crop water requirements using FAO methodology (Doorenbos and Kassam, 1979; Doorenbos and Pruitt, 1990). The crop coefficients (kc) obtained were similar to the values proposed for Galicia by other authors (Lo´ pez et al., 2000; Paz and Dı´az-Fierros, 1984). Crop evapotranspiration rate (ETc), effective rainfall (Pe) and net irrigation requirements (NIR) were determined using the CropWat software (Clarke et al., 1998). 3.2. Irrigation evaluation One evaluation of border irrigation was conducted in each plot, according to the method described by Heermann et al. (1990). These evaluations consisted in a series of procedures directed to the acquisition of information about an irrigated area (Pereira and Trout, 1999). The shape, the dimensions, and the slope of the border were determined by using a topographic total station. To determine the field slope and the quality of land levelling, soil surface elevation was measured at a series of points separated 10 m along each border. The field slope was obtained by regression. The deviations between the observed elevations and the regression line were used to estimate the quality of land levelling. The standard deviation of the elevation deviates (S.D.e) was used for this purpose. Irrigation discharge was computed using in situ measurements of flow cross-sectional area and velocity. Flow velocity was measured using a propeller meter. The time of advance was recorded at stations separated 15 m along the border. Infiltration was determined in the evaluated fields by using two double ring infiltrometers. In each border, Kostiakov equations were obtained by regression using data from the infiltrometers (Kostiakov, 1932): Z ¼ kt a where Z is the cumulative infiltration (m), t the opportunity time (min), and k and a are empirical coefficients. The adjusted infiltration approach (Merriam and Keller, 1978; Walker and Skogerboe, 1987) was used to estimate the Kostiakov coefficients at each border and each irrigation event. The Kostiakov k parameter was adjusted, so that the point formed by the average infiltration

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depth (calculated as the total volume applied divided by the area of the field), and the average opportunity time was contained in the equation. According to Cavero et al. (2001), adjusted infiltration equations are a valuable tool because they integrate the value of infiltration into a wide domain. Therefore, these equations are representative of irrigation units. Based on the infiltration curves obtained, a standard curve was defined for each soil unit. Field length, flow per unit width of the field, advance time and cut off time were obtained from irrigation evaluations. The irrigation quality parameters were obtained based on these data, on the Kostiakov equations adjusted for each soil type, and on the estimated Manning roughness coefficient, using the SIRMOD surface irrigation software (Walker, 1993). The results obtained were application efficiency (Ea, %) and distribution uniformity (DU, %) of the simulated irrigation (Burt et al., 1997): Ea ¼

amount of water stored in the root zone 100 total water applied

DU ¼

average depth infiltrated in the low  quarter of the field 100 average depth infiltrated in the field

Nine fields of different sizes and covering soils type A, B and C were selected for evaluation. These fields were cropped with corn and irrigated pasture. 3.3. Interviews to irrigation users The purpose of the questionnaire was to collect information about the irrigation techniques used and about the social component of irrigation. The questionnaire was divided into seven modules, which reflected different aspects of irrigation during the year of evaluations. The first module contained data to identify and differentiate each survey. The second and third modules provided information about the structure of the holding and the characteristics of the landowner. This information enabled a differentiation between holdings under different social or economic assumptions, and a comparison of the suitability of the visited holdings in order to obtain valid conclusions. The fourth module addressed general information about rainfed agriculture and expectations about irrigation. The next module was devoted to holdings with irrigated land, and to irrigation management and water-use issues. The sixth module contained questions about the surface irrigation techniques used for each crop. The last module enabled the introduction of interesting impressions or remarks that could not be fitted in any other module. In order to obtain a significance level of 90%, a total of 119 farmers out of 730 were interviewed, which resulted in an error of 5.37%.

4. Results and discussion 4.1. Crop water requirements The crop evapotranspiration (ETc) calculated for pasture and silage corn was 1167 and 510, respectively. In this zone, corn is normally seeded at the beginning of May and ensiled

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Table 3 Net irrigation requirements (NIR) for 2000, estimated as the difference between crop evapotranspiration (ETc) and effective rainfall (Pe) Month

NIR 2000 (mm) Pasture

January February March April May June July August September October November December Annual

Corn

30.6 32.0 77.8 93.5 184.9 154.0 150.4 83.1

73.0 113.2 158.5 64.3

806.4

408.8

during the first 2 weeks of October. During 2000, some farmers harvested in November or even at the beginning of December due to the climatic conditions in autumn. Therefore, the establishment of pasture was severely delayed. The net irrigation requirements (NIR), calculated as the difference between ETc and effective rainfall, were 806.4 mm for pasture and 408.8 mm for silage corn (Table 3). 4.2. Results of irrigation evaluations Trial sites had a relatively uniform longitudinal slope. In all cases, the mean slope exceeded the upper limit of 0.5% recommended for border irrigation (Bertmone, 1985). Most trial sites were rectangular in shape, with excessive width. The relationship between width and length exceeded 0.25, except for site number 7. The flows per unit width used are too low due to excessive width and to the low discharges available for irrigation. Table 4 summarises these results. Laser levelling produces well-levelled fields, with values of standard deviation of soil surface elevation (S.D.e) of around 10 mm and gentle slopes for border irrigation (Bucks and Hunsaker, 1987). The results for S.D.e obtained in the levelling of the fields where irrigation was evaluated were rather negative, because they all exceeded 40 mm. Table 5 presents the infiltration parameters of the Kostiakov equation obtained for each border. Then, a curve was obtained by regression for each soil type (Fig. 5). The irrigation simulation, based on the data acquired from the evaluations, provides the value of the total volume of water applied during irrigation, the infiltrated curve, the surface runoff volume, the application efficiency (Ea) and the distribution uniformity (DU) for each irrigation evaluation (see Table 6).The values obtained for Ea in almost every trial can be considered as low or very low (Williardson, 1972; Clemmens and Dedrick, 1994). The resulting mean value reaches 35.2%, with a minimum of 20.2% and a maximum of 79.1%. The maximum value for efficiency, 79.1%, was obtained in site 6, where the water applied

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Table 4 Parameters used in evaluations: standard deviation of soil surface elevation (S.D.e), Manning roughness parameter (n), unit discharge (Q) and target irrigation depth (Zr) Trial site

Crop

Soil depth (cm)

Slope (%)

Area (m2)

Border width (m)

Length (m)

Irrigation time (h ha1)

S.D.e (mm)

n

Q (L/s m)

Zr (mm)

1 2 3 4 5 6 7 8 9

Corn Pasture Pasture Corn Corn Pasture Pasture Corn Pasture

70 25 30 80 60 30 35 90 30

1.03 1.54 0.54 2.32 0.94 0.78 1.25 1.23 0.85

11550 8060 6580 6750 15540 14744 5920 8845 8160

66 62 47 45 74 76 37 61 48

175 130 140 150 210 195 160 145 170

5.48 3.93 6.33 12.22 7.72 2.32 6.76 12.15 5.72

57 96 58 46 78 62 89 79 106

0.03 0.15 0.21 0.06 0.07 0.12 0.13 0.04 0.15

1.11 0.94 1.39 1.19 1.18 0.42 1.32 0.64 1.19

70 30 30 60 60 30 30 70 30

amounted to just 69.2% of the water deficit in the root area. The results of trials conducted in group A soils show very low efficiency values, except for the evaluation in site 8. No satisfactory conclusion can be drawn from Ea values for soils type B and C due to the disparity of results and the small number of experimental sites. DU values can be considered as normal, except for trial sites 1 and 8, with values lower than 80% (Hanson et al., 1995). This result appears to be logical, considering the high average irrigation depth. It is interesting to compare the values obtained for target irrigation depth (Zr) (Table 4) ¯ shown in Table 6. In the case of with the values obtained for average irrigation depth (Z), the evaluations conducted in corn fields, the mean value of Z¯ is 169 mm and the mean value of Zr is 65 mm. In the case of pastures, the mean value of Z reaches 60 mm, while the mean value of Zr is only 30 mm. 4.3. Results of the survey on social participation About 26.1% of landowners of the 119 interviewed holdings admitted having irrigated at least some fields. Half of the landowners who did not apply irrigation to any field Table 5 Infiltration parameters of a Kostiakov equation (k and a) corresponding to the irrigation evaluations Trial site

1 2 3 4 5 6 7 8 9

Soil type

B C A A B C A A A

Infiltration parameters k

a

0.0110 0.0035 0.0079 0.0150 0.0128 0.0028 0.0122 0.0142 0.0131

0.453 0.503 0.378 0.382 0.451 0.383 0.331 0.403 0.356

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Fig. 5. Infiltration curves corresponding to the defined soil types.

declared to have no access to water due to the incomplete or damaged state of the distribution infrastructure or due to insufficient or irregular flow. In irrigated holdings, the irrigated area amounted to 42.2% of the utilised agricultural area, with almost two irrigated fields per holding, on the average. The mean area of irrigated fields was 7144 m2. Farm fragmentation and the small size of the holdings pose a problem for traditional irrigation (Crecente et al., 2002). These factors often compel the farmer to move from one field to another continuously. The large number of fields and the irrigation times currently applied in the irrigation area make water management difficult, and demand complex distribution systems, vast drainage ditches and dense road networks. Land consolidation appears absolutely necessary in this irrigation district, although the size of consolidated Table 6 Mean results of irrigation evaluations in trial sites: soil type, total volume of water applied during irrigation (Vt), ¯ application volume of infiltrated water (Vi), volume of water losses due to runoff (Vs), average irrigation depth (Z), efficiency (Ea) and distribution uniformity (DU) Trial site

Soil type

Vt (m3)

Vi (m3)

Vs (m3)

Z¯ (mm)

Ea (%)

DU (%)

1 2 3 4 5 6 7 8 9

B C A A B C A A A

1674 665 978 1588 3780 391 705 1514 961

1598 398 436 1030 3414 294 435 1447 753

86 267 541 560 366 81 270 64 205

139 49 66 152 220 20 73 164 92

48.3 36.3 20.2 25.5 24.7 79.1 21.0 40.9 21.2

74.4 96.7 98.8 92.2 80.9 91.6 94.4 75.0 90.1

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Table 7 Distribution of the surveyed farmers depending on their attitude towards potential future irrigation Farmers who applied irrigation during 2000

Farmers who did not irrigate during 2000

31

88 Farmers who have never irrigated 71 Would not irrigate under any new circumstance 58

Would irrigate under new circumstances

Farmers who irrigated in some previous season 17 Would not irrigate under any new circumstance

Would irrigate under new circumstances

13

14

3

farms would still be too small for household sustenance without appropriate crop intensification. About 19.3% of the farmers who did not irrigate during the season of year 2000 had irrigated in previous seasons. The reasons alleged for irrigation abandonment were related to irregularities in water supply, inadequate irrigation flows, conflicts among users, failure of expectations about new crops, low temperature of the supplied water, or abandonment of farming. About 18.2% of these farmers would restart irrigation of some field under other circumstances. The rest of the farmers think they would not irrigate under any circumstance. As shown in Table 7, just 11.0% of those farmers who have never used irrigation think they would if appropriate supply was guaranteed and if the distribution infrastructure was improved. In addition to 26.1% of farmers who have irrigated during this season, there are 13.5% of potential irrigation users. 4.4. Results of the survey on irrigation management The water source used for both corn (31.7% of the area) and artificial pastures (68.3% of the area) was the distribution canals. A high temporal variability was observed in flow measurements, conducted in different ditches during the irrigation evaluations. The irrigation water supply largely depends on the capacity of the canal from which water is delivered and on the state of preservation of secondary and tertiary ditches. Irrigation time and irrigation frequency data also show high variability. Results vary not only among different irrigation users, but also among different irrigations on the same field. During the studied season, the average irrigation times declared by farmers were significantly different depending on the type of irrigated crop: seven hours per field in the case of corn and 5 h per field in the case of pasture. Just 23.4% of the surveyed landowners have infrastructure for runoff disposal in some of their fields. None of the users declared to have systems for field drainage, although 48.4% of the irrigation users admitted having drainage problems in some fields.

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5. Conclusions The application efficiency (Ea) values obtained are low or very low, reaching a mean value of 35.2%. The results of the trials conducted on type-A soils show very low efficiency values. To draw reliable conclusions about Ea values for type-B and type-C soils, more trials would be required. Distribution uniformity (DU) values are acceptable, except for evaluations 1 and 8, where slightly low values were obtained. In view of the results obtained, irrigation efficiency can be improved by dividing plots into smaller irrigation units. Plot division would allow users to multiply the volume of water per unit by 2 or by 3, and to achieve a uniform advance of the waterfront. A significant decrease would therefore be obtained in the volume of water used for irrigation. DU values could be increased with better plot levelling. A low percentage of farmers (26.1%) admitted having irrigated at least some field during the studied season. Just 19.3% of farmers who did not irrigate during that season declared to have irrigated in previous years. About 50% of the holdings with no irrigated fields have no access to water due to the incomplete or damaged state of the distribution infrastructure or due to insufficient or irregular flow. A significant number of the surveyed farmers considered as non-users (13.5%) would irrigate under other circumstances. They would accept to pay for irrigation water costs and for the investments needed. The structure of land tenure limits the improvement and modernisation of this irrigation area. Land consolidation does not provide a solution for the fragmented land ownership, because the consolidated plots would still be too small. The discharge and volume applied to fields and canals must be controlled by installing flowmeters. A significant improvement of the organisation of the irrigable perimeter requires irrigation on demand and the control over the water demanded by each user. In addition to these actions, farmers must be given advice and information about irrigation techniques must be diffused among them. This information was not provided when this area was established as an irrigation district.

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