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A recently developed model, SWATDRAIN, was used to assess the alterations in water balance components, discharge, and sediment loads due to tile drainage practices in a heavily tile drained watershed in Ontario, Canada. Furthermore, the model was implemented to determine the spatial variability of sediment loads which can be explained by a combination of spatially distributed variables within a watershed, including those controlling the hydrology, geology, soil and land use. Three scenarios were examined across the watershed, including conventional drainage (existing condition), controlled drainage, and no tile drainage. The model predicted that streamflow was not significantly impacted due to tile drainage, while the total runoff and sediment loads from the basin due to controlled drainage were increased by 27.1% and 22.2%, respectively, while removing tile drain infrastructures resulted in 37.1% increase in surface runoff and 55% increase in sediment load from the watershed The areas with high sediment load generation were identified by the model and the impact of tile drainage in producing sediment in those areas was assessed. The results showed that the sediment load generation rate in the areas with the highest load (class V) increased by 8% only due to controlled drainage, while in the second ranked sediment generating areas (class IV), the sediment load generation rate was increased by 32%. [ABSTRACT FROM AUTHOR]

Soil salinization is the major factor affecting the sustainable development of agriculture in the Kaidu River Irrigation District (KRID) in Xinjiang Province, China. To better understand water and salt variation regularity in the KRID, this study established a watershed-scale distributed water and salt transport model for the KRID based on the new Soil and Water Assessment Tool with a salinity module (SWAT-Salt). Its point source salt module and irrigation water salt module were modified in the study to obtain more accurate simulation results. Based on evaluation indices, the simulation results of streamflow, salt loading, and crop yield showed that the modified model can more accurately depict water and salt transport processes in the KRID and has good applicability. According to the simulation results, the average annual amount of water and salt entering Bosten Lake through the drainage canal accounted for 15 % and 51 %, reaching 4.29 × 108 m3 and 57.87 × 104 t respectively. The drainage and salt discharge during winter irrigation accounted for 69 % and 74 %, reaching 2.95 × 108 m3 and 42.47 × 104 t, respectively. However, the regions along Bosten Lake had high groundwater and soil salinity, facing a risk of increased salinization and necessitating land or water management to decrease salinization. In conclusion, the modified SWAT-Salt can be applied in agricultural irrigation areas with more diverse irrigation sources and is a useful tool for investigating and assessing watershed-scale salinization, as well as implementing targeted management strategies to reduce salinization. ● The point source and irrigation water salt module of the SWAT-Salt model was modified. ● The model can be applied in agricultural irrigation areas with more diverse irrigation sources. ● The model can effectively analyze the water-salt process at the watershed scale. ● The regions around Bosten Lake in the KRID are at risk of increased salinization. [ABSTRACT FROM AUTHOR]

Abstract: A new watershed model, DRAIN–WARMF, was developed to simulate the hydrologic processes and the nitrogen fate and transport that occur in small, predominantly subsurface-drained, agricultural watersheds that experience periodic freezing and thawing conditions. In this modeling approach, surface flow is simulated using a watershed scale model, WARMF, and subsurface flow is estimated using a field-scale model for subsurface-drained shallow water table fields, DRAINMOD 5.1. For subsurface flow calculations, the watershed is subdivided into uniform cells, and DRAINMOD is run on each cell with inputs based on the individual hydrologic characteristics of the cell. The coupling results in a distributed parameter model that calculates the total flow at the outlet of a watershed as well as the nitrogen losses. The model was evaluated for the St. Esprit watershed, located approximately 50km northeast of Montreal. Simulations were carried out from 1994 to 1996; data from 1994 and 1995 was used for model calibration and data from 1996 was used for model validation. The new model was able to adequately simulate the hydrologic response and nitrate losses at the outlet of the watershed. Comparing the observed daily flow/monthly nitrogen with the model''s outputs over the validation period returned an R 2 value of 0.74/0.86 and modeling efficiency of 0.72/0.83. This clearly demonstrates the model''s ability to simulate hydrology and nitrogen losses occurring in small agricultural watersheds in cold climates. [Copyright &y& Elsevier]