River Leith Realignment
The River Leith is an historically modified tributary of the River Lyvennet. The moderate gradient system drains a low relief rural landscape and would have been characteristically active, sinuous and single thread in form prior to extensive straightening and revetting associated principally with the Lancaster and Carlisle Railway. The current watercourse is laterally inactive due to bank protection constraints, over-deep linked to historic dredging and devoid of a natural gravel/cobble bed. The current bedload transport regime is severely impacted by a lack of source sediment. All of these impacts are seen at Thrimby Grange Farm where straightening has also moved the watercourse away from the valley bottom.
Across the restoration site the river has developed only a limited floodplain with other fluvio-glacial landforms and human modification of the topography adding to the mosaic of features across the valley bottom. The Ordnance Survey map of 1860 suggests that most of the watercourse had been straightened by then with the remaining sinuous reach running through the southern field straightened by 1890. The former course is, however, defined by the parish boundary and some of it can be traced on site through vegetation difference. It is presently unclear if this planform could be re-established following local modification to the topography.
AquaUoS undertook a detailed feasibility study and detailed design of this section of the River Leith through a fluvial audit and 2D hydraulic modelling using TUFLOW and a drone survey to produce a DEM of the river and floodplain.