Author(s): Ponnambalam Rameshwaran; Pamela Naden; Gareth Old; Colin Roberts; Peter Scarlett
Linked Author(s): Ponnambalam Rameshwaran
Keywords: No Keywords
Abstract: This study examines seasonal aquatic vegetation growth and the hydraulic response to its management. This is often poorly understood and approximated in modelling studies. Instream aquatic vegetation is a dominant influence on river hydraulics particularly on flow conveyance in lowland rivers during spring and summer seasons. Vegetation growth increases flow resistance which in turn decreases the flood conveyance capacity. To maintain conveyance capacity and enhance habitat, aquatic vegetation management practices are employed in many parts of the world. This research was carried out on a reach of the CEH River Lambourn Observatory at Boxford, UK (Figure 1) between 2008 and 2017 and sixteen vegetation cuts were performed in that period. The River Lambourn is a tributary of the River Thames, the principal river in the south -east of England. The river and its floodplain are designated as a Special Area of Conservation and a S ite of Special Scientific Interest. The river flow is largely driven by the chalk aquifer in the catchment. The site represents one of the most pristine chalk stream environments within England. The bed material of the River Lambourn Observatory is typically gravel and predominant aquatic vegetation species at the site include: Ranunculus penicillatus subsp. pseudofluitans var. pseudofluitans, Berula erecta and Callitriche obtusangula. This aquatic vegetation is managed by undertaking several cuts per year depending on rates of vegetation growth and water levels. Typical seasonal vegetation cutting approaches are checkerboard in spring, trimming along the river in summer and removing vegetation at center of the river and leaving marginal vegeta tion along the edges in autumn. In this research, we use detailed hydraulic and vegetation data collected over multiple years to examine the effects of the current management practices on both hydraulic resistance and flood conveyance of the stream. We also develop relationships for predicting and quantifying the aquatic vegetation resistance based on traditional equations such as Manning, Darcy-Weisbach and Chezy as well as alternative more appropriate drag based approach.
Year: 2018