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Turunen M.,Aalto University | Warsta L.,Aalto University | Paasonen-Kivekas M.,Sven Hallin Research Foundation | Nurminen J.,Finnish Field Drainage Association | And 3 more authors.
Agricultural Water Management | Year: 2015

Water outflow pathways affect environmental loads from agricultural fields, but the pathways and effects of terrain topography on their proportions and on drainage design are not known in detail. In this study, a long-term hydrological dataset and 3D FLUSH model were applied to a field-scale assessment of multi-yearly and seasonal water balance in two adjacent clayey subsurface drained agricultural fields with different slopes (1% and 5%). The model was calibrated and then run with an hourly time step of input data throughout five studied years, and it was able to reproduce the measured water balance components. The results suggested that macropore flow had an essential role in the field-scale hydrological processes in clayey agricultural fields. The model provided a quantification how terrain slope increased the amount of groundwater outflow and correspondingly decreased the amount of drain discharge. The implication is that the hydrological effects of topography of the field and surrounding areas should be taken into account when optimizing drainage intensities. Though most of the groundwater outflow occurred outside the growing periods, sustained groundwater outflow occurred throughout all seasons. A correspondence was observed between the near-saturated surface soil conditions and tillage layer runoff (TLR) events, which suggests that TLR events in high-latitude clayey fields are mainly triggered by saturation excess mechanism. During two springs (once in both field section) TLR was clearly higher than during other seasons, which was likely induced by soil frost. However, the model without computational schemes for frost-induced changes on soil hydraulic properties satisfactorily reproduced drain discharge during most spring periods, and the amount of measured TLR was low during most springs, which indicates that typically frost-induced changes on TLR generation may be small. However, inaccuracies in the quantification of TLR induced by snowmelt formed uncertainty to the estimate of the water balance components during snowmelt. © 2014 Elsevier B.V.

Turunen M.,Aalto University | Warsta L.,Aalto University | Paasonen-Kivekas M.,Sven Hallin Research Foundation | Nurminen J.,Finnish Field Drainage Association | Koivusalo H.,Aalto University
Acta Agriculturae Scandinavica Section B: Soil and Plant Science | Year: 2015

Secondary drainage impact of groundwater outflow can affect drainage design and form a pathway for nutrient loading in agricultural areas. Holistic assessment of water balance and all outflow pathways can benefit design of sustainable drainage in a changing climate. In this study, three-dimensional, hydrological FLUSH model was applied to investigate a field-scale data set and to produce a closure of water balance throughout all seasons in a clayey subsurface drained agricultural field in high-latitude conditions. Description of evapotranspiration (ET)-groundwater interactions using a three-dimensional hydrological model provides a new approach for evaluating standard computational methods to estimate ET with limited crop data. Different ET estimates were tested in the context of total water balance, and the coupling of ET and groundwater outflow was assessed. Comparison of measured and simulated water balance components demonstrated that reference ET (Penman–Monteith method) overestimated ET in the cropped field in high latitude conditions. The FAO-56 single crop coefficient approach was also noted to overestimate ET in the studied conditions. A calibrated constant crop coefficient satisfactorily described ET in spring and in autumn, but underestimated it during summer periods. The results suggest that care should be taken when applying standard methods in high-latitude conditions. Groundwater outflow and ET were shown to be interlinked, but even a relatively high potential ET affected the amount of groundwater outflow only slightly. The results demonstrate that groundwater outflow can form an important component of the water balance in clayey subsurface drained fields. The strength of the 3D model was demonstrated in showing how ET had an impact on all outflow components of drained field sections. Such a modelling tool is useful for generating scenarios that show how changes in climate forcing and thereby ET can alter the partitioning of the field-scale water balance. © 2015 Taylor & Francis.

Salo H.,Aalto University | Warsta L.,Aalto University | Turunen M.,Aalto University | Paasonen-Kivekas M.,Sven Hallin Research Foundation | And 2 more authors.
Acta Agriculturae Scandinavica Section B: Soil and Plant Science | Year: 2015

A new generic, three-dimensional, solute transport component was developed into FLUSH, which is a hydrological model developed for Nordic conditions. Water flow and solute transport descriptions in FLUSH follow the dual-permeability concept, which divides the total soil pore space into mobile soil matrix and macropore systems. The solute transport model was parameterized to simulate the main processes of nitrogen (N) cycle in clayey, subsurface-drained soils during autumn periods after the harvest. The model simulates transport of nitrate and ammonium N, as well as mineralization, nitrification, and denitrification. Reactions in soil are affected by temperature and moisture, as simulated by FLUSH. Ammonium can adsorb on soil particles in both pore systems, while organic N is described in simulations as an immobile solute in the soil matrix. One-dimensional version of the model was applied to two subdrained field sections (1.3 and 3.4 ha) in the Nummela experimental field in southern Finland during two autumn periods (2008 and 2011). The model was able to replicate the measured dynamics of nitrate N concentrations in drain discharge during both the periods. Concentrations were the most dependent on drain discharge dynamics and the rate of nitrification. Measured and simulated ammonium concentrations in drain discharge were about 10 times smaller than nitrate concentrations, even though the levels of N input with initial values and deposition for both inorganic fractions were similar. Successful solute transport simulation results further increase the confidence in the description of the water flow processes in FLUSH. © 2015 Taylor & Francis.

Turunen M.,Aalto University | Warsta L.,Aalto University | Paasonen-Kivekas M.,Sven Hallin Research Foundation | Nurminen J.,Finnish Field Drainage Association | And 5 more authors.
Agricultural Water Management | Year: 2013

Proper drainage practices to remove excess water are crucial for crop cultivation in the humid climatic conditions of the boreal areas. The objectives of this study were to close the water balance, to quantify the amount of groundwater outflow, to identify the effects of topography on drain discharge, and to determine the effects of different subsurface drain installation methods and spacing of drainage lines on water outflow components in a clayey agricultural field. Hydro-meteorological, soil and topographic data were available from paired field sections in southern Finland including two control sections and two sections where different subsurface drainage methods were applied. A 3D hydrological model (FLUSH) was applied to the whole field area for snow- and frost-free periods in three measurement years to decipher the hydrological effects of the drainage improvements. The simulated field area was 14. ha. Simulation results revealed that a steep slope outside of the field decreased drain discharge with 40% and increased groundwater outflow, which was quantified to be a major component of the water balance, approximately 9-15% of the precipitation. The model simulations demonstrated and quantified how drainage improvements in a treatment section affected the hydrology of an adjacent control section. This revealed that the sections shared a hydrological connection through subsurface flow processes. Such connection is typically neglected in the experimental comparison of measurement results from paired field sections. According to the simulations trenchless drain installation changed soil hydraulic properties by decreasing the volumetric fraction of connected soil macropores and by increasing the rate of water exchange between soil matrix and macropores. This affected more the dynamics than the absolute amount of drain discharge. The 3D model was useful in closing the water balance although the limitations were lack of data outside monitored sections and exclusion of snow and frost processes. © 2013 Elsevier B.V.

Warsta L.,Aalto University | Taskinen A.,Finnish Environment Institute | Paasonen-Kivekas M.,Sven Hallin Research Foundation | Karvonen T.,Waterhope | Koivusalo H.,Aalto University
Soil and Tillage Research | Year: 2014

Runoff and sediment transport are distinctively three-dimensional (3D) processes and occur through overland, tillage layer and subsurface pathways. The objective was to quantify water balance and sediment concentrations in runoff waters and to assess sediment loads via surface runoff and drainflow in a clayey, subsurface drained field section using the FLUSH model. The model can simulate field scale two-dimensional overland flow and 3D unsaturated and saturated subsurface flow, including preferential flow in macropores. The erosive processes, comprised of hydraulic and raindrop splash erosion, occur in the overland domain while suspended sediment is conveyed from the field surface to subsurface drains via preferential transport in macropores in the subsurface domain. The study site, located in southern Finland, is a clayey, subsurface drained field section with an area of 12ha and an average slope of 2.8%. The growing seasons and the following autumns of two years with distinctly different rainstorm characteristics were modelled. The simulated sediment loads via tillage layer runoff and drainflow were 85 and 117kgha-1, respectively in 1988, and 63 and 189kgha-1 in 1984. Despite the high precipitation in October 1984 (143mm), erosion in the field area was low due to minimal surface runoff and consequently minimal hydraulic erosion. The suspended sediment at the site was generated by raindrop impacts and the eroded material was transported to the open ditch through tillage layer flow and subsurface drainflow. The model was able to reproduce the measured sediment concentrations in the main open ditch into which both tillage layer runoff and drainflow are discharged from the field. Spatially distributed erosion simulations facilitate the detection of net erosion and deposition locations in the field and could be used to design intensive measurement campaigns and guide erosion control practices in the future. © 2014 Elsevier B.V.

Warsta L.,Aalto University | Taskinen A.,Finnish Environment Institute | Koivusalo H.,Aalto University | Paasonen-Kivekas M.,Sven Hallin Research Foundation | Karvonen T.,Waterhope
Journal of Hydrology | Year: 2013

Soil erosion is an important environmental issue in agricultural areas of northern Europe where clayey soils are prevalent. Clayey soils are routinely subsurface drained to accelerate drainage which creates an additional discharge route for suspended sediment. Previously, assessment of the sediment load from clayey fields has been difficult, because process-based models were only able to simulate sediment loads via surface runoff. A new distributed, process-based erosion model was developed and incorporated into the FLUSH modelling system to fulfil this void. The model facilitates simulation of spatially distributed soil erosion on the field surface and sediment loads via surface runoff and subsurface drainflow. Soil erosion on the field surface is simulated with the two-dimensional sediment continuity equation coupled with hydraulic and rain drop splash erosion, sediment settling, and transport capacity processes. Subsurface sediment transport in macropores is described with the three-dimensional advection-dispersion equation. The model was applied to a clayey, subdrained field section (~3.6ha) in southern Finland. The results demonstrated the capability of the model to simulate soil erosion and sediment transport in terms of the match between the measured (2669kgha-1) and modelled (2196kgha-1) sediment loads via surface runoff and the measured (2937kgha-1) and modelled (2245kgha-1) loads via drainflow during the validation period of 7months. The model sensitivity analysis pointed out the importance of the flow model parameters in simulation of soil erosion through their control on the division of total runoff into surface runoff and drainflow components. The key parameters in the erosion model were those that affected hydraulic and splash erosion rates. The model application in the experimental field suggested that both hydraulic and splash erosion were the factors behind the sediment losses during the growing season and early autumn, whereas high sediment loads in late autumn were caused by hydraulic erosion due to overland flow in tilled soil. © 2013 Elsevier B.V.

Warsta L.,Aalto University | Karvonen T.,Waterhope | Koivusalo H.,Aalto University | Paasonen-Kivekas M.,Sven Hallin Research Foundation | Taskinen A.,Finnish Environment Institute
Journal of Hydrology | Year: 2013

Water flow is a key component in the evaluation of soil erosion and nutrient loads from agricultural fields. Field cultivation is the main non-point pollution source threatening water quality of surface waters in Nordic and many other countries. Few models exist that can describe key hydrological processes in clayey soils, i.e. overland flow, preferential flow in macropores and soil shrinkage and swelling. A new three-dimensional (3-D) distributed numerical model called FLUSH is introduced in this study to simulate these processes. FLUSH describes overland flow with the diffuse wave simplification of the Saint Venant equations and subsurface flow with a dual-permeability approach using the Richards equation in both macropore and matrix pore systems. A method based on the pentadiagonal matrix algorithm solves flow in both macropore and matrix systems directly in a column of cells in the computational grid. Flow between the columns is solved with iteration accelerated with OpenMP parallelisation. The model validity is tested with data from a 3-D analytical model and a clayey subsurface drained agricultural field in southern Finland. According to the simulation results, over 99% of the drainflow originated from the macropore system and drainflow started in some cases within the same hour when precipitation started indicating preferential flow in the profile. The moisture content of the clay soil had a profound effect on runoff distribution between surface runoff and drainflow. In summer, when the soil was dry and cracked, drainflow dominated the total runoff, while in autumn, when the shrinkage crack network had swollen shut, surface runoff fraction clearly increased. Observed differences in surface runoff fraction before and after tillage indicated that the operation decreased hydraulic conductivity of the profile. © 2012 Elsevier B.V.

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