Assessing water and sediment balances in clayey agricultural fields in high-latitude conditions

Mika Turunen

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

Comprehensive knowledge of hydrological processes controlling water flow, erosion and transport of substances is a prerequisite for the design of water management procedures for sustainable crop production. Knowledge gaps currently exist regarding hydrological processes and flow paths of water and sediment in subdrained clayey soils in high-latitude conditions. This thesis aimed to quantify the dominating water and sediment balance components in subdrained clayey soils in different drainage, topographic and hydrometeorological conditions. Moreover, the thesis aimed to quantify the dominating erosion processes and evaluate the capability of a three-dimensional (3D) dual-permeability model to tackle the preceding objectives. The simulation results and data covered a range of experimental conditions and produced a closure of water and sediment balances. Lateral preferential groundwater outflow, which has not been quantified in previous studies, was shown to form a major water balance component, and terrain slope was shown to control its magnitude. Due to the groundwater flow processes, field areas were linked to non-local processes. Topography of the field areas and the surrounding areas were shown to have an impact on the hydrological effects of drainage installations. Evapotranspiration (ET) dominated the annual water balances. However, the results suggested that standard ET estimation methods have to be adjusted to accurately estimate ET in high-latitude conditions. During the growing seasons, groundwater outflow formed the highest outflow component. Most water and sediment outflow occurred outside the growing seasons when ET was minimal. Drain discharge was the highest outflow component during the dormant seasons, and subsurface components dominated the water outflow. The results suggest that tillage layer runoff (TLR) typically occurred due to saturation a excess mechanism. Typically, soil frost did not have a high impact on runoff generation, although occasionally frost conditions increased the amount of TLR. Subsurface transport pathways dominated the sediment loads. Load via subdrains formed the highest load component, and load via groundwater outflow contributed to the simulated load generation. Simulations provided a quantification of sediment balances and demonstrated that the majority of the eroded particles at the field surface did not form load. Three model structures demonstrated how structural uncertainties can impact the simulation results. The 3D dual-permeability approach was found to be a suitable method for water and sediment balance analyses. More detailed analyses would require detailed data on hydraulic properties in deep soil layers and erosion and sediment transport processes within the fields. The results suggest that the design of drainage and water protection measures should focus more on subsurface flow and load pathways.
Translated title of the contributionVesi- ja kiintoainetaseiden määritys savipelloilla pohjoisissa olosuhteissa
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Koivusalo, Harri, Supervisor
  • Warsta, Lassi, Advisor
Publisher
Print ISBNs978-952-60-7379-8
Electronic ISBNs978-952-60-7378-1
Publication statusPublished - 2017
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • drainage
  • preferential flow
  • groundwater outflow
  • erosion
  • sediment transport
  • dual-permeability model
  • 3D model
  • hydrological connection

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