Deciphering the origin and geometry of freshwater tufa barrages. From process understanding to sustainable management

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Not all rocks originate from volcanoes (igneous, like granite), deposition (sedimentary, like sandstone) or transformation of these two types (metamorphic, like marble). Some rocks like travertine originated from the progressive deposition of concrete-like carbonate minerals near hot springs. One more peculiar type of travertine is called tufa, and it's created in freshwater environments such as springs, wetlands, and streams. Modern tufa is a porous rock that's freshy deposited over existent pebbles, vegetation and logs, and its precipitation is facilitated by biological elements such as algae and moss. In limestone and chalk streams in Britain, tufa can create series of barrages that resembles reefs, and these environments provide habitats for a variety of plants, macroinvertebrates and fish. Unfortunately, tufa barrages are not well known nor well protected, and some ill-informed river management practices or changes in water quality can affect them negatively. This project focuses on sequences of tufa barrages in streams of Lincolnshire. We will survey the geometry of tufa barrages, and determine their shape, growth and age in natural environments, as well as identify if these barrages have withstood past floods. We will then focus on a specific reach of the Dunston Beck, a stream near Lincoln with abundant tufa barrages. Here we will install slabs of different materials in different parts of the stream, and we will monitor the growth of freshwater tufa in order to determine what are the best conditions for tufa to deposit. Results obtained from these field surveys will give us the information needed to design leaky barrages (made up of brushwood and fascines/faggots) that will facilitate the deposition of tufa. Leaky barrages of these kind are often used in river restoration and natural flood management projects, as they improve the river ecology, slow down the water and help prevent flooding downstream. However, their persistence and stability could improve dramatically if tufa could grow on them given that the conditions for its deposition are provided. Also, building these leaky barrages in places where tufa could be potentially present (given the good water quality and presence of moss) may facilitate its deposition. Our field surveys will guide us in designing and planning the right shape for these barrages, and we will install a pilot trial in the Dunston Beck. Tufa barrages are a hidden and undervalued treasure of many streams in Britain, and their presence needs recognition and protection. This project will gain further understanding on how and where tufa grows the most, and will go beyond by mimicking real tufa barrages in river restoration projects. In this project, basic Earth Science and Biology knowledge will inform Engineering solutions for the benefits of the environment and communities, as improved ecosystem services support healthier societies.