During the 20th century, afforestation resulted in plantations of Pine and Eucalypt becoming the main crops in north‐central Portugal with associated and well‐known soil water repellency (SWR). The aim of this study was to improve the insights in the temporal dynamics and abrupt transitions in water repellency of the topsoil and the mechanism that determine the behaviour of SWR. Topsoil water repellency was monitored in the Caramulo Mountains (north‐central Portugal) between July 2011 and June 2012. The intensity of SWR was measured in situ at soil depths of 0, 2.5 and 7.5 cm using the ‘molarity of an ethanol droplet’ test. Volumetric soil moisture content was monitored in situ using a Decagon ECH2O EC‐5 probe. SWR behaviour broadly followed five alternating dry and wet periods during the 12‐month period, with more pronounced differences in the Pine site than in the Eucalypt site. SWR under Eucalypt was substantially more temporally dynamic than under Pine, with double the number of moderate and large SWR changes at the 7.5 cm depth. Soil moisture content and antecedent rainfall were better correlated to SWR under Pine than under Eucalypt, although in both cases insufficient to predict the temporal variations. Copyright © 2013 John Wiley & Sons, Ltd.

Terraces are a common Mediterranean feature influencing soils, slopes and subsurface hydrology; however, little is known about their impact on hydrological processes, especially in humid regions. This work studied hydrological and erosion processes in the “águas de lima” terrace system common in northwestern Iberia, characterized by wet season irrigation to keep soils saturated and avoid frost on winter pastures. Soil moisture, vegetation height, runoff and sediment yield were monitored for a terraced field in northern Portugal during 19 months. Relationships between rainfall, soil, vegetation, runoff and erosion were analyzed for 49 rainfall events, and within‐storm patterns of soil moisture and runoff were further evaluated for the 12 largest events. Monitoring included two wet seasons with 1264 and 951‐mm rainfall. Runoff followed rainfall with 20 · 5 and 3 · 8 mm, and was mostly related with event and pre‐event rainfall. Combined with hydrograph analysis, this indicated a dominance of saturation‐excess runoff generation, probably related with the presence of a shallow water table caused by limited drainage and constant irrigation during winter. Rill erosion was only observed as a result of run‐on from the irrigation network. Sediment yield was low, 0 · 01 and 0 · 02 Mg ha−1 in the first and second year, and related with runoff, but vegetation cover was found to limit sediment concentration. This work indicates that “águas de lima” terraces promote saturation, runoff generation and a small amount of sediment yield which does not appear relevant for soil conservation. Further work is needed to better understand and conceptualize these processes. Copyright © 2016 John Wiley & Sons, Ltd.

Hydrological interaction between surface and subsurface water systems has a significant impact on water quality, ecosystems and biogeochemistry cycling of both systems. Distributed models have been developed to simulate this function, but they require detailed spatial inputs and extensive computation time. The soil and water assessment tool (SWAT) model is a semi‐distributed model that has been successfully applied around the world. However, it has not been able to simulate the two‐way exchanges between surface water and groundwater. In this study, the SWAT‐landscape unit (LU) model – based on a catena method that routes flow across three LUs (the divide, the hillslope and the valley) – was modified and applied in the floodplain of the Garonne River. The modified model was called SWAT‐LUD. Darcy's equation was applied to simulate groundwater flow. The algorithm for surface water‐level simulation during flooding periods was modified, and the influence of flooding on groundwater levels was added to the model. Chloride was chosen as a conservative tracer to test simulated water exchanges. The simulated water exchange quantity from SWAT‐LUD was compared with the output of a two‐dimensional distributed model, surface–subsurface water exchange model. The results showed that simulated groundwater levels in the LU adjoining the river matched the observed data very well. Additionally, SWAT‐LUD model was able to reflect the actual water exchange between the river and the aquifer. It showed that river water discharge has a significant influence on the surface–groundwater exchanges. The main water flow direction in the river/groundwater interface was from groundwater to river; water that flowed in this direction accounted for 65% of the total exchanged water volume. The water mixing occurs mainly during high hydraulic periods. Flooded water was important for the surface–subsurface water exchange process; it accounted for 69% of total water that flowed from the river to the aquifer. The new module also provides the option of simulating pollution transfer occurring at the river/groundwater interface at the catchment scale. Copyright © 2015 John Wiley & Sons, Ltd.