Modeling sediment transport after ditch network maintenance of a forested peatland

• Published in: Water resources research Vol. 52; no. 11; pp. 9001 - 9019
• Main Authors: Haahti, K., Marttila, H., Warsta, L., Kokkonen, T., Finér, L., Koivusalo, H.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01-11-2016
• Subjects: Annual rainfall; Assessments; Atmospheric precipitations; Bank erosion; Catchment area; Cleaning; Computer simulation; Consolidation; Deposition; ditch network; Drainage; Dredging; Ecological effects; Erosion; Erosion control; Excavation; FLUSH model; Forestry; Hydrologic models; Hydrology; Identification; Loads (forces); Maintenance; Mathematical models; modeling; Modelling; Peat; peat erosion; peatland drainage; Peatlands; Rain; Raindrop impact; Rainstorms; Receiving waters; Sediment; Sediment control; Sediment transport; Simulation; Snowmelt; Soil erosion; Spatial distribution; Summer; Summer storms; Suspended sediments; Transport; Water
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1002/2016WR019442

Elevated suspended sediment (SS) loads released from peatlands after drainage operations and the resulting negative effect on the ecological status of the receiving water bodies have been widely recognized. Understanding the processes controlling erosion and sediment transport within the ditch network forms a prerequisite for adequate sediment control. While numerous experimental studies have been reported in this field, model based assessments are rare. This study presents a modeling approach to investigate sediment transport in a peatland ditch network. The transport model describes bed erosion, rain‐induced bank erosion, floc deposition, and consolidation of the bed. Coupled to a distributed hydrological model, sediment transport was simulated in a 5.2 ha forestry‐drained peatland catchment for 2 years after ditch cleaning. Comparing simulation results to measured SS concentrations suggested that the loose peat material, produced during excavation, contributed markedly to elevated SS concentrations immediately after ditch cleaning. Both snowmelt and summer rainstorms contributed critically to annual loads. Springtime peat erosion during snowmelt was driven by ditch flow whereas during summer rainfalls, bank erosion by raindrop impact was identified as an important process. Relating modeling results to observed spatial topographic changes in the ditch network was challenging and the results were difficult to verify. Nevertheless, the model has potential to identify risk areas for erosion. The results demonstrate that modeling is effective in separating the importance of different processes and complements pure experimental approaches. Modeling results can aid planning and designing efficient sediment control measures and guide the focus of experimental studies.
Key Points
First attempt to model spatial peat erosion and transport in open‐ditch network of forestry area
Model applied to 5.2 ha drained peatland forest area for 2 years after ditch network cleaning
Results highlight erosion of loose material after ditch cleaning, and erosion from banks during rainstorms