تقويم الجريان غير المشبع لمبزل الحر تحت الظروف الحقمية لتربة مزيجة طينية غرينية :ألتنبأ عن األيصالبة المائية غير المشبعة ومقدات المحتوى المائي

Abstract

Since no in situ studies exist for determining unsaturated hydraulic characteristics of Iraqi soilsduring internal drainage under no evaporation conditions, a field study was conducted on a silty clay loam soil to determine unsaturated hydraulic conductivity using the Instantaneous ProfileMethod(IPM) and to solve the one dimensional flow equation under gravity flow theory for obtaining easier method to predicting unsaturated hydraulic conductivity and water content profiles. An 8m  8m field plot was flooded for forty days and then covered to prevent evaporation from soil surface. Gravimetric samples were augured during 90 days of drainage following flooding as a function of depth. Soil water potentials was estimated from fitting a functional relation to laboratory measured water content and matric potential relations for the studied soil horizons. Unsaturated hydraulic conductivity was calculated according to Darcian flow theory. Unit gradient theory was used to obtain an analytical solutions for the general flow equation according to Lax-Sisson method by utilizing three explicit K(θ) functions. Unsaturated conductivity values for the studied layers ranged from 1.0964 to15.2389 cm.d-1 and from 0.00001 to 0.0004 cm.d-1 after 0.025d and 88.75 d of drainage respectively. A 1:1 relationship between measured and predicted conductivities reveled highly significant r-squared values of 0.918, 0.933, and 0.927 for the three functions respectively. Predicted conductivity values were higher by factors 1.378, 1.418, and 1.296 for the three equations respectively. Same amount of water was drained from studied depths during drainage cycle which resulted in parallel water content profiles. Except at the early drainage time, predicted water contents profile with Lax-Sisson's method matched satisfactorily measured water content profiles. Also 1:1 relationship of zero-intercept between measured and predicted water content values during drainage period produced high r-squared values of 0.960, 0.935, and 0.918 for the three functions respectively. Predicted water content values were higher by a factor 1.008, 1.011, and 1.043 than measured values for the three functions respectively. Results of this study showed that the Lax-Sisson's method was accurate in predicting unsaturated hydraulic conductivity and water content profiles under theory Of gravity drainage flow.