|
|
| Bildiri Özetleri | |
| Ana Sayfaya Dönüş |
| ISD Ana Sayfası |
|
OF THE PILOT AREA IN THE LOWER SEYHAN PLAIN, ADANA, TURKEY Mahmut Çetin 1, Hasan Özcan 2, Fatih Topaloğlu 1 1 Department of Agricultural Structures and Irrigation, Faculty of Agriculture, University of Çukurova, 01330 Balcalı-ADANA/TURKEY 2 The Sixth Regional Directorate of State Hydraulic Works, Planning Section, 01330 Seyhan-ADANA/TURKEY ABSTRACT This study has been conducted in the pilot area of the Lower Seyhan Plain (ASO), Adana, Turkey. The purpose of the study is to monitor and evaluate possible changes of the in situ hydraulic conductivity (K, m/d), groundwater (GW) electrical conductivity (EC, dS/m), groundwater depth (GWD, cm) and sodium adsorption ratio [SAR, (meq/l)0.5] of GW with regard to soil series and agricultural practices prevailing in the area within two decades between 1980 and 1999. To achieve the aim, the archive data, collected in 1980 for the purposes of drainage planning works by General Directorate of State Hydraulic Works (DSI), and detailed field investigation data gathered by researchers in 1999, have been utilised. In situ hydraulic conductivity values varied, on the average, from 2.57 to 4.11 m/d during the monitoring period. The increase on the average was found insignificant at the 95 % probability level. Change map of K indicated highly variation over the area reflecting the alluvial origin of the study area soils. No relation was found between K and other variables as well as soil types. Average EC values decreased remarkably from 26.1 to 9.6 dS/m within two decades showing a trend towards improvement in favour of agriculture. This improvement in the EC was attributed to drainage development works and irrigation practices having been conducted in the area. Spatial distribution pattern of changes in EC showed that GW EC tended to increase in the depression areas, but to decrease in other places. GWD increased approximately 50 cm in the area. It was concluded that drainage development works contributed to this increase. SAR values of GW remained constant around 26 (meq/l)0.5. This result was verified statistically at the level of significance of 5%. Map of changes in SAR showed that no association was available among soil series or K, EC, and GWD. INTRODUCTION Where land, water, and people meet, people invariably manipulate the ecosystem to assure their survival. People's livelihood is threatened when the ecosystem no longer produces enough to meet their needs. While the inhabitants face more and more problems in eking out a living in that harsh environment, the fragile ecosystem is increasingly under pressure. As a result of this pressure, particularly over-exploitation of land and water resources, or use of those resources under unfavourable conditions leads to degradation on the resource base and causes irreversible problems. For example, irrigation developments may conduce to waterlogging, alkalinity and/or salinity, and reduction on soil permeability owing to mismanagement or project faults. Nevertheless, irrigation is essential in arid and semiarid regions (Boonstra, 1996). A prime requirement for successfully irrigated agriculture is the development and maintenance of a root zone in which the moisture-oxygen-salt balance is favourable for plant growth (Schrevel, 1997; Kelleners and Chudhry, 1998). The balance in question is maintained to a considerable extent by an adequate drainage. Poor irrigation and drainage water management, and unfavourable soil physical characteristics reverse that balance at the expense of creating both environmental problems and land degradation (Kelleners et al., 1996). On the other hand, the transition from dry-land farming to irrigated farming takes a long time and needs special care. In arid and semi-arid regions, a number of examples can be found easily that a lot of irrigation projects have failed and let the farmers down gently because of serious problems, such as aforementioned ones, emerged after irrigation practices. Therefore, the monitoring and evaluation is an integral part of agricultural practices. The average horizontal hydraulic conductivity, K, of soil profile below the water table (Russo, 1984; Moustafa and Yomota, 1998), groundwater salinity, EC, and sodium adsorption ratio, SAR, (Johnston, 1977; Ayers, 1977; Kelleners and Chudhry, 1998), and groundwater depth, GWD, from soil surface (Kelleners et al., 1996; Kelleners et al., 1997) were studied with intent to detect causes and effects of drainage and irrigation developments as well as management level in the course of time. The aim of this study was to determine if there were any changes in the horizontal hydraulic conductivity of soil horizons below a water table, groundwater table depth, groundwater salinity and sodium adsorption ratio data collected in 1980 and 1999, and to show areal extend of any changes over a period of twenty years. MATERIALS AND METHODS Description of The Study Area : The study area covering 4200 ha of land consists of a part of the Fourth Stage Irrigation Project Area of the Lower Seyhan Plain (ASO), is located in the southern part of Turkey. Typical Mediterranean climate prevails in the area. The annual rainfall varies between 366 and 1365 mm, with an average of 772 mm. Fifty one percent of rainfall falls during the winter season, but only 3% in the summer season. The average annual temperature is about 18.8 °C. Average annual Class A Pan evaporation is 1580 mm.  Although no irrigation development works have still existed in the area, but drainage canals, farmers have been using drainage effluent and poor quality deep well water for irrigation practices since 1980's. At the very beginning of 1980's, there was only one main drainage conveyance canal passing through the study area, named YD3 (Figure 1), and carrying out all drainage effluent of irrigated areas located in the northern part of the study area. Step by step, secondary and tertiary lateral drainage canals have been constructed lately in the area. The Authorities of State Hydraulic Works state that the command area is planned to be irrigated in the forthcoming years. Dinç et al. (1990) report that there exist mainly three physiographic units in the study area, namely, young and old river terrace soils, and delta soils. Young and old river terrace soils are dominant in the study area and stretch eastward and northward, respectively. However, delta soils show a patchy pattern (Figure 1). The soil texture is generally clay to silty-clay-loam. Data Collection, In Situ Measurements and Laboratory Analysis : The area was surveyed by the State Hydraulic Works (DSI) for the purpose of preparing planning drainage report in 1980. The data on in situ hydraulic conductivity, depth to water table, groundwater quality, and soil characteristics were collected from 24 sampling sites. The findings were stored in the archive files. In this study, a detailed field survey was conducted in 1999. Data on in situ horizontal hydraulic conductivity of soil profile under groundwater table, depth to water table from the soil surface, and groundwater samples for electrical conductivity and sodium adsorption ratio measurements were collected contemporaneously from both just the same sampling sites where DSI staff visited in 1980 and also 9 additional sites. In situ soil hydraulic conductivity (K, m/d) and depth to water table (GWD, cm) measurements were determined through following the procedures given by Boonstra (1996), Oosterbaan and Nijland (1994). Furthermore, Ca+++Mg++ and Na+ analysis for sodium adsorption ratio calculation (SAR, [meq/l]0.5), and electrical conductivity (EC, dS/m) measurements of collected groundwater samples were performed by following the principles presented by USSLS (1954) and Ayers (1977). Tests for Stationarity and Mapping of Areal Changes : Descriptive statistics of the two data set obtained within the monitoring period were calculated by following the procedure of Ott (1995). The F-test was utilised to test hypothesis which states that two samples are drawn from the populations having equal variances. Through following Montgomery and Runger (1994); Topaloğlu et al. (1999) and Davis (1986), Student t test was performed to test hypothesis which states that the mean of the population from which the first sample was sampled in 1980 is the same as the mean of the parent population of the second sample sampled in 1999. Each value of the variates observed in 1980 was subtracted from the ones observed in 1999 and resultant values were mapped to show areal extend of any changes (Davis, 1986) over two decades. RESULTS AND DISCUSSIONS Statistical Analysis : Descriptive statistics for in situ soil hydraulic conductivity (K, m/d), electrical conductivity (EC, dS/m) of groundwater (GW), depth to water table (GWD, cm), and calculated SAR [(meq/l)0.5] values of GW were calculated (Table 1). Table 1 shows clearly that mean of K and GWD increased considerably, EC decreased remarkably and SAR remained unchanged between two decades.  Standard deviations increased from 0.72 to 5.24 m/d, from 28 to 33 cm, and from 8.94 to 14.16 (meq/l)0.5 for K, GWD and SAR, respectively (Table 1). The increase in standard deviations indicates that values are scattered widely about the mean and the tendency for central clustering is weak. This implies that spatial variations do exist in K, GWD and SAR, and also tend to increase in the course of events. The tendency to increasing spatial variations might be ascribed to the drainage development works, transition from dry-land farming to irrigated farming, and other different agricultural practices as well as hydrological changes in the area. Reversely, standard deviation of EC of GW decreased in the course of time, reflecting less spatial variation in EC and the tendency for clustering around the mean. Coefficient of variation (CV) increased from 28 to 127 %, from 56 to 86 %, from 34 to 53 % for K, EC and SAR, respectively. The increase in CV manifests obviously the fact that the change in S is greater than the change in the mean value (Table 1). However, the reverse of that remark is true for CV of GWD. The changes in variances of data sets collected in 1980 were tested against those of the ones collected in 1999. Test results showed that the changes in variances of all variates, accept for GWD, were significant at the level of significance of 5 % (Table 2), reflecting the fact that activities performed in the area during the monitoring period disturbed the homogeneous structure of the variates. Average K and SAR values appear to have increased over the study area (Table 1). However, this conclusion could not be justified by statistical tests at 95 % probability level (Table 2), verifying that the changes could be ascribed to the inherently random character of the variate. The decrease in the mean of EC and the increase in the mean of GWD were found significant, indicating in plain words that reclamation works could affect efficiently on the phenomena.  Mapping Areal Extent of Changes : The aforementioned results of classical statistics are far from indicating areal changes over the area. For this reason, data sets for K, EC, GWD and SAR observed in 1980 were subtracted from those observed in 1999. The resultant difference data sets were gridded by the method of Inverse Distance to a Power 2 and mapped so that a visual comparison could be made. Difference maps for each variable were presented in Figure 2.  Figure 2a shows that K values increased somewhat in the northwest part of the study area. However, it appears that K values decreased along a corridor from north to southwest and in the eastern part of the area. There is no clear evidence that drainage development works and soil types contribute to any decrease or increase in K. This result could be attributed to the alluvium origin of soils. Additionally, no relation was found between K and other variables (Figure 2). Groundwater electrical conductivity decreased remarkably during the observation period, except for small patchy areas in the middle of the study area (Figure 2b). Inappropriate topography having a relatively small depression is dominant in this part. This decrease in EC could be ascribed to the transition from rain-fed agriculture to irrigated agriculture, construction of lateral drainage canals, and excessive irrigation practices in the fields located in the vicinity of the northern part of the study area. It is remarkable to state that the most decrease in EC emerged in the delta soil types (Figure 1 and 2b). Over the study area, no relation was found between soil types and GWD increase (Figure 1 and 2c). GWD increased more or less 50 cm, on the average, between the observation period. It is obvious from Figure 2c that GWD responded to construction of lateral drainage canals with very well development in terms of agriculture. This increase in GWD is an indicator of the effectiveness of the drainage canals in controlling the water table. Maximum increase in GWD occurred in the middle of the study area. However, it should be stated clearly that drainage development works could not contribute well enough to increase GWD to a certain level in favour of agriculture. Possible reasons for that could be attributed to the lack of enough open drainage canal density and inappropriate drainage outlet conditions, no pipe drains installation, the problem of side slope stability of open drainage canals stemming from "soupy" material and also siltation due to alluvial character of soils, and sloughing in due to high sodium concentration in soils. SAR values of GW remained almost stable during the observation period, but showed high variation (Table 1). Although EC of GW decreased remarkably between the years 1980 and 1999, the change in SAR values is generally greater than zero over the area (Figure 2b and 2d). The maximum increase realised in depression areas. No association was detected between soil types and SAR changes. Additionally, it could be concluded that drainage development works had no effect on the average SAR changes in terms of agriculture. The increase in SAR might be attributed to irrigation practices helping the salts leach to the groundwater body. ACKNOWLEDGMENT This research was partially supported by the Research Fund Office of Rectorate of Çukurova University through a Research Contract ZF.99.14. The Authors would like to thank Mr. Hasan MERT of the Deputy Director of DSI and Mr. Adil AKYATAN of Manager of Planning Section of DSI, Adana, Turkey, for giving us access to data of the Fourth Stage Planning Drainage Report of the Lower Seyhan Plain and for providing us with equipment during field survey. REFERENCES Ayers, R. S., 1977. Quality of Water for Irrigation. Journal of the Irrigation and Drainage Division, ASCE, Vol. 103, No. IR 2, Proc. Paper 13010, pp. 135-154. Boonstra, J., 1996. Constraints and Opportunities for Integrated Water-Management Models. ILRI Annual Report, The Netherlands, pp. 8-25. Davis, J. C., 1986. Statistics and Data Analysis in Geology. John Wiley & Sons, Inc., New York, NY, 646 p. Dinç, U., Sarı, M., Şenol, S., Kapur, S., Sayın, M., Derici, M.R., Çavuşgil, V., Gök, M., Aydın, M., Ekinci, H., Ağca, N., Schlichting, E., 1990. Çukurova Region Soils. University of Çukurova, Faculty of Agriculture, Publication Number 26, Çukurova University Printing Office, Adana, Turkey (published in Turkish). Johnston, W. R., 1977. National Water Quality Goals and Irrigated Agriculture. Journal of the Irrigation and Drainage Division, ASCE, Vol. 103, No. IR 2, Proc. Paper 12988, pp. 109-114. Kelleners, T. J., and Chudhry, M. R., 1998. Drainage Water Salinity of Tubewells and Pipe Drains: A Case study from Pakistan. Agricultural Water Management Vol. 37, pp. 41-53. Kelleners, T. J., Sharma, R. D., and von Hoffen, R. A., 1997. Salinity of Drainage Water from Pipe Drains in Clay Soils. ILRI Annual Report, The Netherlands, pp. 26-38. Kelleners, T. J., von Hoffen, R. A., and Oosterkamp, H. C., 1996. Effluent Salinity of Pipe Drains: Case Studies in the Punjab Province, Pakistan, and the Fayoum Depression, Egypt. ILRI Annual Report, The Netherlands, pp. 34-52. Montgomery, D. C., and Runger, G. C., 1994. Applied Statistics and Probability for Engineers. John Wiley & Sons, Inc., New York, 895 p. + Appendices. Moustafa, M. M., and Yomota, A., 1998. Spatial Modeling of Soil Properties for Subsurface Drainage Projects. Journal of Irrigation and Drainage Engineering, Vol. 124, No. 4, pp. 218-228. Oosterbaan, R.J., and Nijland, H. J., 1994. Determining the Saturated Hydraulic Conductivity. In Drainage Principles and Applications by H. P. Ritzema (editor-in-chief), ILRI Publication 16, The Netherlands, 1125 p. Ott, W. R., 1995. Environmental Statistics and Data Analysis. Lewish Publishers, New York, 313 p. Russo, D., 1984. A Geostatistical Approach to Solute Transport in Heterogeneous Fields and Its Applications to Salinity Management. Water Resources Research, Vol. 20, No. 9, pp. 1260-1270. Schrevel, A., 1997. Water, Agent of Change: Transition to Irrigated Farming in the Snip Area, Rajasthan, India. ILRI Annual Report, The Netherlands, pp. 8-25. Topaloğlu, F, Yücel, A., Tülücü, K., Çetin, M, 1999. Use of Peak Discharges in Flood Frequency Analysis. TÜBİTAK Turkish Journal of Agriculture and Forestry 23 (1999), Supplementary Issue 1, 187-192, (Only abstract in English, original text in Turkish), ANKARA. USSLS (U. S. Salinity Laboratory Staff), 1954. Diagnosis and Improvement of Saline and Alkali Soils. USDA Handbook 60, U. S. Department of Agriculture, Washington, D.C. |