Basin-scale and travertine dam-scale controls on fluvial travertine, Jiuzhaigou, southwestern China

Travertine deposition in fluvial systems builds dams and other forms that create diversity in geomorphic processes, morphology, and associated wetland ecosystems. In Jiuzhaigou Natural Reserve, Sichuan Province, China, we investigate the relation between contemporary fluvial travertine morphology, slope, and water chemistry at the fluvial-system scale and at the local scale of large individual dams in order to address two fundamental questions. First, what factors determine the spatial distribution of such large valley-spanning, or primary, travertine dams? Second, what factors govern smaller but distinctive travertine dams and other secondary travertine morphology present on the sloping downstream side of primary travertine dams? Through remote sensing analysis and field work, we recognize two factors as paramount in controlling spatial distribution of primary fluvial travertine dams: watershed-scale steps in the longitudinal profile and water chemistry, based on a proxy for dissolved calcite. In the steep Jiuzhaigou watershed, hillslope erosion processes that contribute large boulders to the channel influence the majority of the primary dams. However, two valley-spanning primary dams, Pearl Shoals and Norilang Lakes, appear to be dominated by travertine precipitation. The submerged upstream sides of these two dams are nearly vertical with heights > 30 m. Slope varies with position along the longitudinal profiles over the downstream sides of these two primary dams because the profile shapes are convex. With downstream-dam profile lengths > 500 m, flow encounters secondary travertine morphology organized as an array of travertine bedforms that vary with local channel slope along the convex profiles. The secondary travertine bedforms include sequences of repeating patterns including smaller dams that impound correspondingly small waterbodies. Morphologic differences between two types of secondary dams are quantified on the basis of their relative size, spacing, and the slope on which they form. Increasing slope is correlated with a decrease in height of secondary travertine bedforms according to a power law where y = 0.0053x− 1.68. Results of the investigation demonstrate that slope, a main influence on river hydrodynamics, influences and is influenced by fluvial travertine morphology at two discrete fluvial scales. This work advances our understanding of geomorphic factors that influence travertine morphology, a critical need for conservation and management of travertine natural resources and their wetland ecosystems.