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Ilao Åström, Sheryl, 2021. A two-stage ditch – a source or sinks of nutrients and sediment : evaluation of sediment loss and inundation frequency. Second cycle, A2E. Uppsala: SLU, Dept. of Soil and Environment

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Human-made channel systems in the agricultural landscape have received critical attention due to the dire consequences on water quality and increasing eutrophication polluting receiving aquatic systems. Trapezoidal-formed (traditional) ditches have been scrutinized and a new mitigation measure for channelized drainage systems has gained a great deal of attention i.e. the two-stage ditch. The two-stage ditch (SD) is a modification of the current traditional ditch by constructing terraces (floodplains) adjacent to the main channel (furrow), improving the stability of the ditch while providing the drainage capacity necessary.
There are two specific objectives in this study where one) is to investigate the development of four two-stage ditches by evaluating the channel dimension and the change in geometry and two) to estimate the inundation (flooding) frequency of the terraces in nine two-stage ditches in southern Sweden.
Pre-construction data was collected through personal communication from either the project consultant companies and/or the county administration board of each municipality while post-construction measurements were gathered in the field using a GPS device.
The results reveal that all the investigated ditches were subjected to erosion and aggradation on both the terraces and within the furrow. The average change on the left-side terrace ranges from -7.9 % in SD5 to 34.5 % in SD6 while the average change on the right-side terrace varied from 8.3 % at SD3 to 32.3 % in SD7. The average change in the furrow varied from -24.8 % in SD3 to the largest change in SD6 by 241%, where negative values signify erosion and positive values indicates aggradation. The inundation frequency varied between the sites ranging from a minimum of 3 days in SD8 to a maximum of 319 days in SD6. Furthermore, there was also a visible difference in terrace height between and within the SDs. The SDs with lower terraces in SD6 and SD7 (mean 0.45 and 0.41 m heigh, respectively) were flooded more frequently than those with higher terraces in SD1 and SD2 (mean 0.79 and 0.99 m heigh, respectively).
Improving the knowledge on the evolution of two-stage ditches is essential and contributes to understanding the effectiveness of this novel mitigation measure. This study provides some support to the ongoing research on SDs in Sweden and could potentially provide an insight into nutrient and suspended sediment retention potential and increase the understanding of the SDs hydromorphological evolution under Swedish soil and climate conditions.

Main title:A two-stage ditch – a source or sinks of nutrients and sediment
Subtitle:evaluation of sediment loss and inundation frequency
Authors:Ilao Åström, Sheryl
Supervisor:Bieroza, Magdalena and Hallberg, Lukas
Examiner:Aronsson, Helena
Series:Examensarbeten / Institutionen för mark och miljö, SLU
Volume/Sequential designation:2021:12
Year of Publication:2021
Level and depth descriptor:Second cycle, A2E
Student's programme affiliation:NM029 Soil, Water and Environment - Master's Programme, 120.0hp
Supervising department:(NL, NJ) > Dept. of Soil and Environment
Keywords:Two-stage ditch, geomorphology, inundation frequency, channel evolution, water quality, agricultural ditch
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Subject. Use of subject categories until 2023-04-30.:Water resources and management
Deposited On:27 Oct 2021 10:37
Metadata Last Modified:28 Oct 2021 01:14

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