Spatial patterns of fine sediment supply and transfer in the River Esk, North York Moors.

Abstract

A detailed field study of spatial and temporal patterns of fine sediment transfer was undertaken in the River Esk catchment, North York Moors in response to ecological problems associated with in-channel fine sedimentation. Fine sediment flux and specific sediment yields were estimated from bulk suspended sediment samples collected from a network of 17 spatially distributed Time Integrated Samplers (TIMS). These samplers were deployed over a six month monitoring period from December 2005 - June 2006.Channel characteristics (bank height; bank material; vegetation cover I type; and erosion extent I type); catchment properties (e.g. drains, tributaries and areas of saturated runoff); and land use were mapped using a stream reconnaissance survey covering 61 km of the River Esk and dominant tributaries. These mapped attributes were combined in ArcGIS with other spatial data (e.g. geology; land elevation and slope) to create a GIS database. Dominant sediment source areas were identified by comparing sediment characteristics (e.g. colour; magnetic susceptibility; and metal concentrations) of the suspended material retained in the TIMS samplers with those of channel bank and catchment source samples. Two main areas of high fine sediment flux were identified on the Esk between: Danby to Duck Bridge; and Egton Bridge to Grosmont. Fine sediment in the Danby to Duck Bridge reach was sourced predominantly from local channel banks as a result of geotechnical failures. However from Egton Bridge to Grosmont, catchment sediment sources, from the steep, forested, boulder clay sub-catchments of the dominant tributaries (Glaisdale Beck and Butter Beck), were most significant. To alleviate high level of sedimentation in these locations, the main areas requiring management are the channel banks of the Esk near Danby; intensively farm areas of Danby Beck and Great Fryup Beck; and the steep, wooded regions in Glaisdale Beck and Butter Beck sub-catchments. Suitable target initiatives should include: riparian fencing; bank reinforcements; livestock rotation; and the creation of buffer zones.