Influence of Flow Regime on the Vegetation Zonation along Mountain Streams in the Western Cape, South Africa

Zonation patterns of riparian vegetation have been sampled and described in mountain streams in two catchments in the Hottentots-Holland Mountains, Western Cape, South Africa. Six main vegetation types that differ in structure and species composition, are dominant along these river banks: Aquatic vegetation, Wetbanks, Palmiet, Scrub, Forest and Shrubland(Fynbos). The study aims to correlate the vegetation patterns to flooding patterns, in particular the inundation frequency and stream power. A problem arises: because these catchments are ungauged, like most mountain catchments, with the only weirs at the downstream end of the catchment. Discharge data at the weirs are extrapolated to the sites upstream by multiplication with a factor based on the size of the subcatchment that drains through a sample site. In this way, recurrence intervals for floods in mountain streams are derived. Discharges at sites are also calculated using bed roughness(Manning's n) and slope in straight sections with uniform flow conditions. Stream power is derived from the discharges calculated in this manner. The combination of stream power and recurrence intervals explains the occurrence of most vegetation types occurring on the banks, except for one type: Afromontane Forest. This type is probably more dependent on other factors, such as protection from fire and the depth of the groundwater table.

Assessment of sediment connectivity using modelling and field-based approaches in the Slavíč River catchment(MoravskoslezskéBeskydy Mts,Czech Republic)

Mountain streams act as conveyors of sediments within the river continuum,where the physical transport of sediments between river reaches through the catchment or between individual parts(e.g.,between hillslopes and channels)of the catchment is assumed.This study focused on sediment connectivity analysis in the SlavíčRiver catchment in the MoravskoslezskéBeskydy Mts in the eastern part of the Czech Republic.The connectivity index and connectivity index target modelling were combined with an analysis of anthropogenic interventions.Additionally,field mapping,grain size of bed sediments and stream power analysis were used to obtain information about connectivity in the catchment.Based on the analysis and obtained results,terrain topography is the current main driving factor affecting the connectivity of sediment movement in the SlavíčRiver catchment.However,the modelling provided valuable information about high sediment connectivity despite different recent land use conditions(highly forested area of the catchment)than those in historical times from the 16th to 19th centuries when the SlavíčRiver catchment was highly deforested and sediment connectivity was probably higher.The analysis of anthropogenic interventions,field mapping,grain size of bed sediments and stream power analysis revealed more deceleration of sediment movement through the catchment,decreased sediment connectivity with bed erosion,and gradual river channel process transformation in some reaches.Field mapping has identified various natural formations and human-induced changes impacting the longitudinal and lateral connectivity in the SlavíčRiver.For instance,embankments along 48%of the river's length,both on the right and left banks,significantly hinder lateral sediment supply to the channel.Stream power index analysis indicates increased energy levels in the flowing water in the river's upper reaches(up to 404.8 W m^(-2)).This high energy is also observed in certain downstream sections(up to 337.6 W m^(-2)),where it is influenced by human activities.These conditions lead to intensified erosion processes,playing a crucial role in sediment connectivity.Similar observations were described in recent studies that pointed out the long-term human interventions on many streams draining European mountains,where a decrease in sediment connectivity in these streams is linked with sediment deficits and the transformation of processes forming channels.

Hydrodynamic parameters in a flood impacted boulder block ramp： Krzczonówka mountain stream, Polish Carpathians

Boulder block ramps are river engineering structures used to stabilise river beds. Block ramps provide a semi-natural and aesthetically pleasing solution to certain river engineering problems in mountain streams. When constructing block ramps,one can use the dissipative behaviour of large macroroughness elements randomly placed on the river bed to enhance fish migration in an upstream direction thus, in this sense, meeting the requirements of the EU Water Framework Directive. Block ramps are often designed and constructed to replace damaged drop hydraulic structures in the channels of mountain streams. This paper investigates the resilience of a particular block ramp placed in the Krzczonówka stream(Polish Carpathians) in terms of the engineering design function and its durability against damaging. A hydrodynamic analysis of a block ramp is presented before and after a flood event that changed the configuration of the blocks. The seminatural unstructured hydraulic structure was built on the Krzczonowka stream to protect gas pipes which are located beneath it. As a result of several floods, the boulder block chute described in this paper was damaged, and some boulders were dislodged and transported downstream. Our post-flood investigations of bathymetry and velocity revealed that even damaged boulder blocks, removed from the chute and displaced downstream of the structure, still provide significant energy dissipation of the flowing water. The novel of our paper is for the first time showing very detailed analysis of unstructured block ramp hydrodynamics parameters done in the field.Also the novel finding of our investigations shows that before and after the flood event the unstructured block ramp structure, is still fish friendly in terms of hydrodynamics.

Regional- to local-scale controls on waterfalls in Rocky Mountain National Park,Colorado

Previous work on the eastern side of Rocky Mountain National Park(RMNP),Colorado indicated correlations among waterfall location,waterfall morphology,and the characteristics of bedrock joints.Characteristics of waterfalls on the western side of the national park do not correlate as strongly with joint geometry.Longitudinal river profiles on the western side are less concave and waterfalls account for a greater proportion of the total elevation loss.We interpret these differences to result from more widely spaced joints,lithological differences,and complex glacial history.These results demonstrate that waterfall shape and typology may change due to both local and regional controls operating in a mountain region.Both regions had alpine valley glaciers,but continued landscape evolution via fluvial erosion has developed waterfalls with diverse locations and morphologies that reflect the influences of glacial deposits,bedrock erosional resistance,and joint geometry.

Seasonal influence and local factors affecting macroinvertebrate structure in a high-altitude Andean stream

Small water bodies are critical for maintaining freshwater biodiversity,but are among the least investigated aquatic environments.We examined physical and chemical variables at two reaches in Arroyo Tambillos,a small,high-elevation Andean stream,in NW Mendoza province,Argentina,across four seasons to examine how local factors and seasonality affected the structure of the macroinvertebrate community.The Arroyo Tambillos community was numerically dominated by ephemeropterans(mainly Massartellopsis irarrazavali)while the dipteran Chironomidae were the most species rich.Total macroinvertebrate abundance was highest in summer,driven mainly by taxa that were secondary in dominance(Austrelmis sp.and Andesiops peruvianus),while richness did not differ between seasons.However,benthic composition was different in Fall 2013(March)compared to other seasons,largely because of the increased abundance of Chironomidae.Canonical correspondence analysis discriminated Chironomidae species distributions in Fall 2013 by substrate type(i.e.,big and small boulder substrate).By contrast,discharge,velocity,and depth were the variables which most affected the macroinvertebrate abundance and distributions.Contrary to our expectations,most community changes observed occurred in fall instead of summer.Nivo-kryal stream communities like the one described here have become increasingly important for conserving mountain stream biodiversity as anthropogentic impacts and climate change increasingly impact lower stream reaches.Therefore,monitoring high-altitude streams like the Arroyo Tambillos may be critical for preventing the future loss of unique and sensitive stream biota.