Hydraulic Geometry, Hydraulics and Sediment Properties of Forest Brooks after Extensive Erosion from Upland Peatland Drainage

Hannu Marttila,Simo Tammela,Bjørn Kløve

doi:10.4236/ojmh.2012.23008

Abstract

Peatland drainage can affect headwater systems, causing changes in bed substrate composition and hydraulic geome-try in small brooks. We studied hydraulic geometry and sediment properties in 14 boreal forest brook reaches (width < 2 m), characterised by well-vegetated banks, high sinuosity and low width-to-depth ratio, in north-east Finland. The aims were to obtain information from channel geometry and to study brook response to extensive sediment load from land use. The results indicate that bed sediment in brooks is almost continuously mobile, which negatively reflect to ecological status of the brooks. These headwater meandering parts have limited sediment transport capacity and require a long period to recover from artificially increased sediment input from peat drainage. However, different reaches can be prioritised for restoration according to the characteristics of silted bed sediment or sediment origins. Brook width appeared to have large natural variation, causing great local velocity variations. This needs to be taken into consideration when restoring straightened reaches in small headwater areas, e.g., width in restored reaches cannot be uniform but should include variations.

Highlights

Assessing the hydraulic geometry and sediment properties of boreal forest brooks is important for improving management and restoration of these fluvial systems
The results indicate that bed sediment in brooks is almost continuously mobile, which negatively reflect to ecological status of the brooks
All reaches were degraded by siltation of transported sediment from peatland drainage areas, as drainage channels were excavated straight to the natural channel

Summary

Introduction

Assessing the hydraulic geometry and sediment properties of boreal forest brooks is important for improving management and restoration of these fluvial systems. Hydraulic and sediment conditions in streams support a number of physical, chemical and biological processes, resulting in suitable habitats for flora and fauna. Headwater brooks occupy an extensive area of landscape and differ from larger stream systems in a great many of ways (e.g. channel dimensions, sediment transport, fish abundance and the disturbance regime associated with low flows). These different physical conditions shape and support a high level of biological diversity that differs from larger river systems. Small headwater streams are crucial in larger river catchments as collectors of surface waters and receivers of loads from the catchment area. About 80% - 90% of the water flows through the first and second order streams [1] and the state of small streams obviously reflects that of downstream waterways

Methods

Results

Conclusion