Operational problems of the drainage systems in Erzincan Plain and some suggestions

ABSTRACT Ph.D. Thesis OPERATIONAL PROBLEMS OF THE DRAINAGE SYSTEMS IN ERZİNCAN PLAIN AND SOME SUGGESTIONS Atatürk University Graduate School of Natural and Applied Sciences Department of Agricultural Buildings and Irrigation Supervisor: Assoc. Prof. Dr. Abdurrahman HANAY A part of the drainage area in Erzincan plain was taken as the research area for this study. It covers a total of 6120 hectare of land in which surface and subsurface drainage systems exist. Water table level has been measured for three years on 59 observation wells found in the research area and occasionally it was found to be very high as this happen from one well to another. Analysis of main cations and anions along with pH and EC were performed on the samples from observation wells, irrigation and drainage canals, and SAR and RSC values were determined. In addition, adjusted sodium adsorption ratio (adj SAR), adjusted sodium adsorption ratio (adj RNa), potential salinity, permeability index, Langelier saturation index and French water hardness degrees were also determined. Water table maps were drawn through geo-statistical methods with computer aid to identify the position and salinity class of the ground water. According to the isobath maps of the period with heavy irrigation, water table level was found to be above 150 cm in 87%, 44% and 91% of the irrigated area in 1999, 2000 and 2001 respectively. Also, salinity values more than 750 uS/cm were detected in 82%, 76% and 90% of the study area in 1991, 2000 and 2001 respectively. The area in where water table level is on the plant root zone throughout the whole vegetation period makes an important part of the study area where dry bean crop, highly sensitive to salinity, is widely grown. So, it can be assumed that the extent of the salinity limits the plant production in the study area. Texture and chemical analysis regarding pH, EC, CEC and ESP were performed on the samples from the two pilot areas chosen to represent one surface and other subsurface drainage systems. Although extreme values in terms of drainage limits were not observed, ESP values from the area of surface drainage system were found to be significantly different from those of subsurface drainage area (p<0,05). Especially in places with drainage problems, the need for maintenance and renovation was detected. Moreover, it was also observed that sediment accumulation caused system failure in places with lower slopes. Farmers in the study area usually use drainage water of medium salinity class, C2Si for irrigation. Yet, it was determined that drainage water of higher salinity class, C3Si was used for that purpose as well. Drainage water should not be used for irrigation and, if not possible, crops resistant to salinity should be included into the rotation programs. Accordingly, analysis of the data from the questionnaires completed with face to face farmer interviews revealed that 60% of the farmers had drainage problems. 2002, 153 pages Key words: Irrigation, drainage, water table, salinity, water table map