Modelling water flow and soil erosion in clayey, subsurface drained agricultural fields

Soil erosion in clayey, subsurface drained agricultural fields in Finland can cause problems due to the export of suspended sediment and sediment-bound nutrients into nearby waterways. Suspended sediment is transported from the field via two main hydrological pathways: 1) surface runoff and 2) preferential flow in macropores to subsurface drains. In clayey fields especially, the sediment load via the subsurface drains can be a considerable part of the annual load. The mechanisms contributing to the sediment load during the growing season and the following autumn were quantified with a new numerical model (FLUSH) developed in the study, using sample data from two clayey, subsurface drained field sections in southern Finland. The simulated field was computationally divided into two-dimensional overland and three-dimensional subsurface domains. Existing mechanistic approaches were applied to describe both surface and subsurface domain processes in the model. A dual-permeability model can simultaneously simulate flow in both soil matrix and macropore systems. The model supports simulation of suspended sediment transport in macropores, drainage systems, soil swelling and shrinkage processes and the effects of cropping and tillage operations on water and sediment yields. A new pentadiagonal matrix algorithm-based solution was developed to directly solve subsurface flow in both pore systems. A custom time integration method was derived to run the solution algorithms with different time steps in concurrent fashion. All the finite volume-based partial differential equation solution algorithms were parallelised with the OpenMP application interface. Computational grids, created with an automatic grid generation system, were used to test the effects of grid resolution on results. The numerical model successfully described water flow and soil erosion in the study fields indicating that the hypothesised mechanisms for water flow and soil erosion were appropriate. The simulation results confirmed that preferential flow has a profound impact on field-scale hydrology. Runoff distribution between surface runoff and drainflow changed in the autumn due to tillage operations and soil swelling. Soil erosivity also increased after autumn tillage. In the simulations, hydraulic erosion was the primary process leading to high erosion rates in the Sjökulla field. In the Hovi field, lack of surface runoff notably lowered the sediment loads. Simulations with 1-D and 2-D grids indicated that the application of a 3-D model to undulating, clayey, subsurface drained fields was well justified. Tests with spatial variation of macroporosity presented evidence that the spatial variability of soil properties has a notable effect on runoff and sediment loads

Applicability of open rainfall data to event-scale urban rainfall-runoff modelling

Rainfall-runoff simulations in urban environments require meteorological input data with high temporal and spatial resolutions. The availability of precipitation data is constantly increasing due to the shift towards more open data sharing. However, the applicability of such data for urban runoff assessments is often unknown. Here, the feasibility of Finnish Meteorological Institute's open rain gauge and open weather radar data as input sources was studied by conducting Storm Water Management Model simulations at a very small (33.5 ha) urban catchment in Helsinki, Finland. In addition to the open data sources, data were also available from two research gauges, one of them located on-site, and from a research radar. The results confirmed the importance of local precipitation measurements for urban rainfall-runoff simulations, implying the suitability of open gauge data to be largely dictated by the gauge's distance from the catchment. Performance of open radar data with 5 min and 1 km' resolution was acceptable in terms of runoff reproduction, albeit peak flows were constantly and flow volumes often underestimated. Gauge adjustment and advection interpolation were found to improve the quality of the radar data, and at least gauge adjustment should be performed when open radar data are used. Finally, utilizing dual-polarization capabilities of radars has a potential to improve rainfall estimates for high intensity storms although more research is still needed. (C) 2017 Elsevier B.V. All rights reserved.Peer reviewe

Simulating 3-D water flow in subsurface drain trenches and surrounding soils in a clayey field

Subsurface drain trenches are important pathways for water movement from the field surface to subsurface drains in low permeability clayey soils. The hydrological effects of trenches installed with well conducting backfill material and gravel inlet patches are difficult to study with only experimental methods. Computational three-dimensional soil water models provide additional tools to assess spatial processes of such drainage system. The objective was to simulate water flow pathways with 3-D FLUSH model in drain spacing and trench depth scale with two model configurations: (1) the total pore space of soil was treated as a single continuous pore system and (2) the total pore space was divided into mobile soil matrix and macropore systems. Both model configurations were parameterized almost solely with field data without calibration. Data on soil hydraulic properties and drain discharge measurements were available from a clayey subsurface drained agricultural field in southern Finland. The effect of soil hydraulic variability on water flow pathways was assessed by generating computational grids in which the hydraulic properties were sampled randomly from five measured soil sets. Both model configurations were suitable to describe the recorded drain discharge, when model was parameterized in finer scale than drain spacing and the parameterization described highly conductive subdomains such as macropores in a dual-permeability model or the trench in a single pore system model. Models produced similar hourly discharge and water balance results with randomly sampled soil hydraulic properties. The results provide a new view on consequences of soil heterogeneity on subsurface drainage. The practical implication of the results from different drainage scenarios is that gravel trench appears to be important only in soils with a poorly conductive subsoil layers without direct macropore connections to subsurface drains. Solely drain discharge data was not sufficient to determine the differences in water flow pathways between the two model configurations and more output variables, such as groundwater level, should be taken into account in making assessments on the effects of different drainage practices on field drainage capacity. (C) 2016 Elsevier B.V. All rights reserved.Peer reviewe

Metsäteollisuuden energiatuotannossa syntyvän tuhkan hyötykäyttö: haitallisten asineiden kulkeutuminen

Suomen metsäteollisuuden energiantuotannossa syntyy vuosittain noin 350 000 tonnia maa- ja ympäristörakentamisessa hyödyntämiskelpoista lentotuhkaa. Lähitulevaisuudessa logistiikka- ja varastokustannukset tulevat kasvamaan edelleen ympäristölainsäädännön kiristyessä. Tuhkan uusiokäyttöastetta pitäisi kasvattaa edelleen, jotta kulut pysyisivät alhaalla. Suurin hyötykäyttöpotentiaali tuhkalle muodostuu sen käytöstä luonnon kiviainesta korvaavana materiaalina erilaisissa rakennuskohteissa. Metsäteollisuus ry:n koordinoimassa hankkeessa tutkittiin tierakenteen sisällä käytetyn lentotuhkan ympäristövaikutuksia. Tuhkasta liukenee veteen aineita kuten fluoridia, kloridia, molybdeenia, seleeniä ja sulfaattia. Aineet kulkeutuvat veden mukana ympäristöön nostaen maa- ja pohjaveden pitoisuuksia. Suurina pitoisuuksina monet tuhkan aineista ovat terveysriski lähiseudun ihmisille ja eläimille. Aineiden kulkeutumista tierakenteista ympäristöön tutkittiin työtä varten ohjelmoiduilla numeerisilla laskentamalleilla. Laskentamallien avulla työssä voitiin tutkia moninkertainen määrä tilanteita empiiriseen mittaamiseen verrattuna ja seuloa tuloksista kulkeutumiseen vaikuttavat päätekijät. Vesien virtausta kuvattiin Richardsin yhtälöön perustuvalla ratkaisulla. Aineiden kulkeutumismallissa otettiin huomioon advektio, dispersio sekä aineiden pidättyminen maahan. Aineiden kulkeutumista tutkittiin tierakenneprototyypeillä, joihin sijoitettiin tutkittavat tuhkamäärät. Teiden päällysteitä simuloitiin imeynnän määrän avulla. Päällystetyn asfalttitien läpi imeytyvä vesimäärä oli kaksi tai kolme kertaa pienempi kuin peitetyn eli pintastabiloidun hiekkatien. Pitoisuuksia seurattiin tierakenteen vieressä olevassa kaltevassa rinteessä ja niitä verrattiin Sosiaali- ja terveysministeriön asetukseen talousveden laatuvaatimuksista. Tuhkasta liukenevaan ainemäärään vaikutti tutkitun tierakenteen leveys, tuhkarakenteen paksuus, liukenevan aineen määrä tuhkassa ja tiepäällysteen läpi imeytyvä vesimäärä. Pitoisuusrintaman etenemiseen maassa vaikuttivat imeyntämäärän lisäksi maan vedenjohtavuus, rinteen kaltevuus, vettä johtavan maaprofiilin paksuus ja aineen kemialliset ominaisuudet. Suurimmat pitoisuudet suhteessa aineiden raja-arvoihin syntyivät sulfaatista ja fluoridista. Päällystetyillä rakenteilla pitoisuusrajat ylitettiin suurimmilla tuhkamäärillä ja rinteen kaltevuuksilla. Peitetyillä rakenteilla pitoisuusrajat ylitettiin kaikilla suurimmilla tuhkarakenteilla kaltevuusarvosta riippumatta

Modelling urban stormwater management changes using SWMM and convection-permitting climate simulations in cold areas

Funding Information: This work was supported by the EviBAN project (Evidence based assessment of NWRM for sustainable water management), which is under the EU Water JPI WaterWorks2017 ERA-NET Cofund and funded in Finland by the Academy of Finland (no 326787). The HCLIM simulations were performed by the NorCP (Nordic Convection Permitting Climate Projections) project group, a collaboration between the Danish Meteorological Institute (DMI), Finnish Meteorological Institute (FMI), Norwegian meteorological institute (MET Norway), and the Swedish Meteorological and Hydrological Institute (SMHI). Publisher Copyright: © 2023 The AuthorsUrbanization coupled with climate change is expected to put pressure on the urban stormwater network. To predict and mitigate the effects of these trends, accurate modeling of urban stormwater changes is required at scales and resolutions meaningful to stormwater management. Although numerous studies have analyzed the effect of climate change on urban flooding risk using the event-based approach, none have incorporated the continuous modelling approach to investigate the whole spectrum of changes in an urban catchment. This study analyzes seasonal changes in future urban hydrological behavior using a mini-ensemble of six state-of-the-art climate model projections and a calibrated hydrological-hydraulic Storm Water Management Model (SWMM). The modelling results show future changes in seasonal and monthly hydrological behavior. The notable winter warming is the major driver in the future snow processes, resulting in considerably less snow days and an increase in the flow events frequency during the winter months. The modelling results also suggest an increase in the annual maximum hourly flow in all seasons, with the clearest trend modelled in winter. Monthly average runoff during the cold period is modelled to increase, while no clear trends are detected for the rest of the year. There is a clear added benefit in using convection-permitting regional climate models throughout the year. Overall, the climate change mitigation and adaption strategies in urban catchments should focus more on the whole spectrum of changes rather than only on urban pluvial flooding risk. These findings call for a transition from traditional to a more advanced stormwater management.Peer reviewe

Analysing performance and contributing areas of a subsurface drainage system with a hydrological model

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