Estimation of Water Table Fluctuations in Paddy Fields by Using Drainmod Model (case study: Rasht)

Outdoor study was done in 2004 (1384) in farms with 2 meter drain spacing and 15centimeters drain depth and without drainage in 4×10 basins in Rasht - Rice Research Institute of Iran (Rasht). In this study fluctuation of water table depth during growing season was measured in respect of weather condition. Consequently DRAINMOD model was run to evaluate and predicting water table depth in physical condition and boundary value of the site. Because of the canola’s negative response to water logging، predicting of water table is important. Indeed a model can be used for predicting various processes and as a management tool، when it is evaluated in the region. Results indicated that DRAINMOD was successful in predicting water table fluctuations. Evaluations in predicting daily water table depth showed that the root mean square error (RMSE) was about 8 centimeters in both treatments. Results also indicated that the potential of the model in predicting water table depth toward measured water table depth was about 4% in surface drainage treatment and 17% in without drainage treatment. Precise information on deep seepage is operative to improvement of estimation of the model.