Distributed hydrological modeling with channel network flow of a forestry drained peatland site

Abstract

Peatland drainage has been an important component of forestry management in the boreal zone and the resulting ditch networks are maintained regularly to sustain forest productivity. In Finland, this is recognized as the most detrimental forestry practice increasing diffuse loads of suspended solids. Alongside forestry management on peatlands, interest in peatland restoration has grown lately. Distributed hydrological modeling has the potential to address these matters by recognizing relevant physical mechanisms and identifying most suitable strategies for mitigating undesired outcomes. This study investigates the utility of such a modeling approach in a drained peatland forest environment. To provide a suitable tool for this purpose, we coupled channel network flow to the three-dimensional distributed hydrological model FLUSH. The resulting model was applied to a 5.2 ha drained peatland forest catchment in Eastern Finland. The model was calibrated and validated using field measurements obtained over frost-free periods of five months. The application showed that distributed modeling can disentangle the importance of spatial factors on local soil moisture conditions, which is significant as peatland drainage aims to control these conditions. In our application, we limited the spatial aspect to the topography and the drainage network, and found that the drainage configuration had a clear effect on the spatial soil moisture patterns but that the effect was less pronounced during the wetter summer. Future applications of distributed modeling in this field comprises investigating the impacts of other spatial factors, modeling channel erosion and solid transport to address strategies for their mitigation, and evaluating restoration schemes.

Model-based evaluation of sediment control in a drained peatland forest after ditch network maintenance

“…Poor performance of PRC at this initial stage has not been reported in earlier experimental 417 studies. However, many other common features with earlier studies were observed, including change 418 in the form of the hydrograph (Amatya et al 2003, increased deposition (Marttila 419 and Kløve 2010), and the highest reductions occurring during snowmelt (Kløve 2000).…”

“…In the boreal region, peat soils 34 have been drained mainly for forestry, agriculture, and peat harvesting (Päivänen and Hånell 2012). 35 Controlling sediment loads from these areas has been addressed, e.g., by flow control structures or 36 ditch-blocking (Amatya et al 2003, Holden et al 2007), wetland buffers (Nieminen et al 2005, 37 Hansen et al 2013), and sedimentation ponds (Joensuu et al 1999, Samson-Dô 2015. 38 In forestry-drained sites, SS loads return close to pre-drainage conditions after the effect of initial 39 first-time drainage levels down Huttunen 1999, Prévost et al 1999).…”

“…PRC structures, consisting of a set of throughflow pipes, 65 are designed to retain runoff during peak flows with the aim of decreasing erosion and enhancing 66 deposition. Amatya et al (2003) applied a paired catchment approach and reported annual reductions 67 of 0.3-89% over five years. In a corresponding setup in Finland by , 68 sediment exports were reduced by 81-90%.…”

Hydrology of Drained Peatland Forest: Numerical Experiment on the Role of Tree Stand Heterogeneity and Management

“…These include one-dimensional (1-D) models such as DRAINMOD-FOREST [17,18] and the CoupModel [19], and quasi-two-dimensional FEMMA model which has been widely applied in Finland [20][21][22][23]. Three-dimensional (3-D) distributed hydrological modeling in drained peatlands has been conducted with GEOtop [24] and FLUSH models [25]. While some of the model applications have embedded a spatial description of the peatland, the effect of spatially varying stand characteristics and evapotranspiration has not been considered in earlier studies.…”

“…While some of the model applications have embedded a spatial description of the peatland, the effect of spatially varying stand characteristics and evapotranspiration has not been considered in earlier studies. Physically-based 3-D hydrological models, such as FLUSH [25,26], are among the most promising tools to analyze spatial differences of soil moisture, WT levels and water balance within a drained peatland. We expect that such modeling can significantly increase the understanding of the effect of heterogeneous vegetation on spatial and temporal variability of WT levels.…”