Geomorphic units are the elementary spatial physical features of the river mosaic at the reach scale that are nested within the overall hydromorphological structure of a river and its catchment. Geomorphic units also constitute the template of physical habitats for the biota. The assessment of river hydromorphological conditions is required by the European Water Framework Directive 2000/60 (WFD) for the classification and monitoring of water bodies and is useful for establishing links between their physical and biological conditions. The spatial scale of geomorphic units, incorporating their component elements and hydraulic patches, is the most appropriate to assess these links. Given the weakness of existing methods for the characterisation and assessment of geomorphic units and physical habitats (e.g., lack of a well-defined spatiotemporal framework, terminology issues, etc.), a new system for the survey and characterisation of river geomorphic units is needed that fits within a geomorphologically meaningful framework. This paper presents a system for the survey and classification of geomorphic units (GUS, geomorphic units survey and classification system) aimed at characterising physical habitats and stream morphology. The method is embedded into a multiscale, hierarchical framework for the analysis of river hydromorphological conditions. Three scales of geomorphic units are considered (i.e., macro-units, units, sub-units), organised within two spatial domains (i.e., bankfull channel and floodplain). Different levels of characterisation can be applied, depending on the aims of the survey: broad, basic, and detailed level. At each level, different, complementary information is collected. The method is applied by combining remote sensing analysis and field survey, according to the spatial scale and the level of description required. The method is applicable to most of fluvial conditions, and has been designed to be flexible and adaptable according to the objectives (e.g., reach characterisation, assessment, monitoring) and available data (e.g., image resolution). The method supports integrated hydromorphological assessment at the reach scale (e.g., the Morphological Quality Index, MQI) and therefore contributes to better establishing links between hydromorphological conditions at the reach scale, characteristic geomorphic units, and related biological conditions

Photographic guidance is presented to assist with the estimation of Manning's n and Darcy-Weisbach f in high-gradient plane-bed, step-pool, and cascade channels. Reaches both with and without instream wood are included. These coefficients are necessary for the estimation of reachaverage velocity, energy loss, and discharge. Using data collected in 19 stream channels located in the State of Colorado and the Eastern Italian Alps, on slopes ranging from 2.4 to 21 percent, guidance is provided for low through bankfull flows. Guidance for low flow resistance estimation is additionally provided using data collected in 29 channels in the State of Washington, New Zealand, Chile, and Argentina. Bankfull n values range from 0.048 to 0.30 and low flow n values range from 0.057 to 0.96. Discussions of flow resistance mechanisms and quantitative prediction tools are also presented.

The storage, longitudinal distribution and recruitment processes of in-stream large wood (LW) were studied comparing channel segments draining four Chilean mountain catchments with different land use. The segments were divided into relatively uniform reaches of different lengths and surveyed for LW (piece dimensions, position in the channel, orientation to flow and aggregation) and stream morphology (slope and bank full channel width and depth) characterizations. LW volume stored in the Pichun, El Toro and Vuelta de Zorra study channels are within the range informed in international researches from streams draining catchments with similar forest covers. However, the 1057 m 3 /ha of LW stored in Tres Arroyos is extremely high and in the same order of magnitude than the reports from old-growth forests in the Pacific Northwest of USA. The size of the area that can potentially provide wood to streams depends on the wood supply mechanisms within any catchment, and the LW stored in the study segments increases as the size of this area increases. This study aims to contribute to the knowledge on the effects of LW in mountain channels, gathering new information and expanding investigations developed in Chile since 2008. This research was carried out within the framework of Project FONDECYT 11106209.

Vegetation growing in river bars and banks determines the morphological processes in river channels. The presence and dynamics of riverine vegetation depend on the magnitude and frequency of floods able to change morphology pull-out. A series of pull-out experiments were carried out with the objective to determine the resistance of riverine vegetation to be uprooted and its effects on river-bed dynamics. Nine riverine species were used for the experiment: seven of them are native from Chile, and the other two are exotic and invasive in Chilean environments. A total of 200 specimens were transplanted in a substrate simulating a bar of a gravel-bed river, and after 7 months they were individually pulledout, and the force and time needed to uproot the plant quantified. Data were analysed by means of generalised linear models (GLM) and linear regressions, and force-time curves were interpreted and related to the root morphology of the species. GLM results showed that resistance values are dependent on root and plant physical characteristics, and by the factor species. Among the species studied, the three species showing higher resistance values were native, while the less resistant was an exotic invasive species. The time needed to uproot the individuals did not seem to be influenced by plant parameters nor by the factor species. Root architecture seemed to have an effect on plant pull-out resistance and uprooting rapidity, being heart-shaped roots the ones that registered higher resistance values. Despite this, when incorporating flow strength on the findings, the exotic invasive ones seemed to be some of the more resistant to uprooting. The findings of this paper contribute to the better understanding of river vegetational and sedimentary dynamics, and are useful for parameterising the modelling of fluvial landscapes evolution and for the design of river restoration projects.