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Öğe Determination of water content in drying soils: incorporating transition from liquid phase to vapour phase(C S I R O Publishing, 2004) Konukcu, F; Istanbulluoglu, A; Kocaman, IIn arid and semi-arid environments, soil profiles often exhibit a liquid - vapour displacement known as evaporation front characterised by a critical matric potential (psi(me)) or water content (theta(e)) located somewhere inside the unsaturated zone above a watertable ( WT). The objective of this study was to determine the theta(e) including the range of water content (theta) in the transition zone from liquid to vapour both theoretically and experimentally for different soil textures under saline and non-saline WTs. Characteristic shapes of water content and salt concentration profiles were the criteria to obtain. e experimentally, and the. - diffusivity relationship was used to compute the theta(e) and theta range in the transition zone. Measured theta(e) values of 0.05 and 0.12 m(3)/m(3) under non- saline WT and 0.07 and 0.15 m(3)/m(3) under saline WT were in agreement with the computed values of 0.05 and 0.10 m(3)/m(3) for sandy loam and clay loam soils, respectively. The model calculates roughly the same. e for saline and non- saline conditions. Besides experimental soils, theta(e) and range of theta in the transition zone were calculated for silty loam and coarse sand. The lighter the soil texture, the smaller is theta(e) and the steeper the transition zone. The results were further compared with those calculated by different authors.Öğe Effect of watertable depth on evaporation and salt accumulation from saline groundwater(Csiro Publishing, 2005) Rose, DA; Konukcu, F; Gowing, JWWhen the evaporative demand is greater than the ability of the soil to conduct water in the liquid phase, the soil pro. le above a watertable exhibits a liquid-vapour discontinuity, known as the evaporation front, that affects the depth of salinisation and the rate of evaporation. We conducted experiments on a sandy loam with shallow saline watertables under high isothermal evaporative demand (24 mm/day), monitoring rates of evaporation from the soil and upward movement of groundwater, and observing profiles of soil water and salinity over periods of up to 78 days. Three zones were distinguished in the soil pro. le: a zone of liquid flow above the watertable, a zone of vapour flow close to the surface, and an intermediate transition zone in which mixed liquid-vapour flow occurred. The vapour-flow zone above the evaporation front appeared after a few days and progressed downward to depths of 40, 60, and 120 mm, while eventual steady-state rates of evaporation were 1.3, 1.1, and 0.3 mm/day for watertable depths of 300, 450, and 700 mm, respectively. Salts mainly accumulated in the transition zone, suggesting that the depth of the evaporation front should be a criterion to locate and prevent salinisation as a result of capillary flow from a watertable in arid regions.Öğe Precise determination of Turkish spillway sizes from synthetic unit hydrographs to prevent flood damage(Taylor & Francis As, 2004) Istanbulluoglu, A; Konukcu, F; Kocaman, IIn Turkey, calculations of runoff hydrographs are made in practice by synthetic methods, among which Snyder and Mockus are the most widely used synthetic unit hydrographs. Using these methods without modification of the original coefficients, C-t and C-p for the Snyder and K and H for the Mockus, characterizing climatic, geological, topographic, soil texture, land use and cover features of a watershed, introduces problems in designing the capacity of spillways, in turn bringing risks for safety. The coefficients were optimized by the analysis of 127 unit hydrographs, using directly measured runoff values in 17 different experimental watersheds located in different part of Turkey between the years 1975 and 1999. After runoff analysis and statistical evaluation, C-t and C-p coefficients for the Snyder method were found between 0.10 and 1.22, and 0.52 and 0.92 while the original values ranged from 1.8 to 2.2 and from 0.5 to 0.7, respectively. K and H coefficients for the Mockus method were obtained between 0.192 and 0.330, and 0.45 and 2.23, respectively for Turkey in general, whereas the original values were 0.208 and 1.67, respectively. The size of spillways built in Turkey to date was found to be too small, and should be increased using these new coefficients to prevent flood damage.Öğe Simple sensors to achieve fine spatial resolution in continuous measurements of soil moisture and salinity(European Geophysical Soc, 2002) Konukcu, F; Gowing, JW; Rose, DAIt is increasingly necessary to be able to measure, simultaneously, continuously and at fine spatial resolution, the salinity and water content of soil. This paper reports the design, construction, calibration and laboratory testing of two simple but robust instruments that enable this to be achieved. Salinity in solution was measured reliably, at 10-mm spacing, by multi-electrode resistivity probes up to saturation with NaCl (c. 6 mol l(-1)), though these probes required individual calibration and were unable to detect precipitated salt. Volumetric water content was measured with great sensitivity over a wide range, from air-dryness (0.06 m(3) m(-3)) to saturation (0.55 m(3) m(-3)) in a sandy loam, using thermal-conductivity probes that used a common calibration and were unaffected by the salinity of the soil solution, by temperature and by ageing.Öğe Simultaneous use of newly adopted simple sensors for continuous measurements of soil moisture and salinity(Csiro Publishing, 2003) Konukcu, F; Istanbulluoglu, A; Kocaman, IMethods available to measure salinity and moisture content in arid and semi-arid regions are limited because of the high salinities and very wide range of water contents (i.e. from saturation near the water table to air dry in the evaporation front). This paper is focused on the instrumentation employed in monitoring salt and moisture profiles in a column study which has wide applicability in salinity research. Experiments were conducted in a specially designed evaporation chamber which provided high evaporative demand as experienced in arid and semi-arid regions. Intensively instrumented soil columns with a constant shallow saline water table were used. Moisture content was measured by thermal conductivity and salinity by 4-electrode probe. In each case, insruments were manufactured specifically for the purpose in order to provide the desired degree of spatial resolution. Two soil types, sandy loam and clay loam, were used. Results indicated that thermal-conductivity probes measured water content over a wide range from saturation to 0.16 m(3)/m(3) for clay loam and to 0.09 m(3)/m(3) for sandy loam soil with great sensitivity (R-2 > 0.95) and were unaffected by salt accumulation. The 4-electrode probes provided reliable measurements (R-2 > 0.95) of the salinity of the soil solution for the range relevant to agricultural application. However, the accuracy of the probe decreased with the decreases in the water content after permanent wilting point.
