The Effect of Flow Regulation on Channel Geomorphic Unit (CGU) Composition in the Soča River, Slovenia.

This paper sets out to examine the effects of flow regulation on the size, spatial distribution and connectivity of physical habitats or channel geomorphic units (CGU) of an upland river system in Slovenia. A river channel survey was completed along three reaches (totalling 14.3km) of the Soča River in order compare an unregulated stretch (reach 1), with two regulated reaches with lower discharges, i.e. a bypassed section that experiences significant flow reduction (reach 2), and a stretch regulated by dam operation (reach 3). CGU’s were classified according to a modified version of the Hawkins et al (1993) system, and mapped on foot and from a boat using a combination of visual assessment and physical measurement. Mapping-grade GPS was used to locate CGU boundaries to sub-metre accuracy, and the application of GIS (MapInfo) enabled the description and analysis of the longitudinal distribution of CGU’s along each reach. Results demonstrated significant differences in the CGU composition between the unregulated and regulated reaches. The unregulated stretch (reach 1) was dominated by the glides (55%) with relatively fast-flowing and turbulent features (runs, riffles and rapids) making up the rest of the reach. The dominant feature of both of the regulated reaches were the slow flowing pool CGU’s occupying 44% of the bypassed section (reach 2), and 76% of the dam regulated section (reach 3), with glides, runs, riffles and rapids forming the remainder of the CGU’s. Physical measurements highlighted the extent to which the reduced discharge in the regulated reaches was dewatering the channel and reducing the size of the CGU’s. The average CGU size in the unregulated stretch (reach 1) was 58m2 of water area per m of channel length (m2/m) compared to 18.42m2/m in the reach 2, and 29.22m2/m in reach 3. CGU’s tended to be shorter, and hence there was greater habitat division or fragmenta-tion evident in the two regulated reaches, particularly the bypassed section. For example, there were on aver-age 6.81 CGU’s per km in the unregulated reach (reach 1), 18.12 CGU/km in reach 2, and 8.08 CGU/km in reach 3. This study suggests that in the Soča River under the flow conditions present during the survey, flow regula-tion alters the dominant types of CGU’s present (to slower flowing and less turbulent features), significantly reduces the size of CGU’s, and affects the longitudinal distribution of types by reducing habitat connectivity and creating greater habitat fragmentation

River Habitat Mapping: are Surface Flow Type Habitats Biologically Distinct?

Current river habitat mapping uses several methods, many relying on descriptions of habitat units based on depth, velocity, substrate and water surface patterns. Water surface patterns are controlled by local geomorphology and hydraulics and can be remotely sensed, if surface flow type habitats are physically and biologically distinctive this may provide a faster surveying method. Six UK lowland rivers were investigated, surface flow types were mapped and the physical characteristics of each habitat unit recorded. Samples of benthic macroinvertebrates were taken from representative units and quantified. The results show that habitat mapping, using surface flow types in small lowland streams, is viable and that those habitats have some degree of physical distinctiveness. Analysis of benthic macroinvertebrate communities shows that there is some association with mapped habitats, and therefore are potentially biologically relevant

The Effect of Flow Regulation on the Spatial Distribution and Dynamics of Channel Geomorphic Units (CGU’s) in the Soča River, Slovenia.

This research examines the impact of flow regulation on the spatial distribution and dynamics of physical habitats or channel geomorphic units (CGU) of the Soca River, an upland river system in Slovenia. In order to assess the impact of flow alteration on the spatial pattern of CGU type, size, hydraulics and distribution, a river channel survey was completed along three reaches (totalling 14.3km), i.e. an unregulated stretch and two regulated reaches (with reduced flows). In addition, one regulated reach was re-surveyed at different discharges to investigate the dynamics of CGU’s and their relationship with flow. CGU’s were classified and mapped on foot and from a boat using a combination of visual assessment and physical measurements of velocity and depth in each CGU. Mapping-grade GPS was used to locate CGU boundaries to sub-metre accuracy, and the application of GIS (MapInfo) enabled the description and analysis of the longitudinal distribution of CGU’s along each reach. The effect of flow regulation on the hydraulic character of the river becomes apparent by highlighting significant differences in the dominant types of CGU’s present between the regulated and unregulated reaches. Reduced flows from river regulation also significantly reduces the size of CGU’s, alters their hydraulic character, and affects the longitudinal distribution of types by creating greater habitat fragmentation. This work also highlights the need to assess CGU’s along continuous stretches of river in order to understand the nature and dynamics of river habitats

Instream habitat assessment: a geomorphological approach

Instream habitat assessment methods are required to evaluate the biological quality of streams in relation to flow and channel morphology and to distinguish the effects of river management on the instream biota. A range of techniques are described and developed in this study ranging from a simple reconnaissance survey to the detailed Physical Habitat Simulation Model (PHABSIM) in order to establish a method for the classification of river channels, identification of key parameters that determine the biota and assessment of the influence of flow and bed morphology on habitat availability. [Continues.

Ascent trajectory optimisation for a single-stage-to-orbit vehicle with hybrid propulsion

This paper addresses the design of ascent trajectories for a hybrid-engine, high performance, unmanned, single-stage-to-orbit vehicle for payload deployment into low Earth orbit. A hybrid optimisation technique that couples a population-based, stochastic algorithm with a deterministic, gradient-based technique is used to maximize the nal vehicle mass in low Earth orbit after accounting for operational constraints on the dynamic pressure, Mach number and maximum axial and normal accelerations. The control search space is first explored by the population-based algorithm, which uses a single shooting method to evaluate the performance of candidate solutions. The resultant optimal control law and corresponding trajectory are then further refined by a direct collocation method based on finite elements in time. Two distinct operational phases, one using an air-breathing propulsion mode and the second using rocket propulsion, are considered. The presence of uncertainties in the atmospheric and vehicle aerodynamic models are considered in order to quantify their effect on the performance of the vehicle. Firstly, the deterministic optimal control law is re-integrated after introducing uncertainties into the models. The proximity of the final solutions to the target states are analysed statistically. A second analysis is then performed, aimed at determining the best performance of the vehicle when these uncertainties are included directly in the optimisation. The statistical analysis of the results obtained are summarized by an expectancy curve which represents the probable vehicle performance as a function of the uncertain system parameters. This analysis can be used during the preliminary phase of design to yield valuable insights into the robustness of the performance of the vehicle to uncertainties in the specification of its parameters

The Rivers of Worcestershire: a Baseline Geomorphological Survey

This report provides details of the approach, method and results of a project undertaken to define and evaluate the geomorphological characteristics of the streams and rivers of Worcestershire. The project was completed in two phases. A desk-based assessment was used to identify catchment characteristics and to select representative sites for the field data collection and analysis. Representative field sites were identified and surveyed and the resulting data were used to further characterise the fluvial geomorphology of Worcestershire’s rivers

Assessing the Viability of Complex Electrical Impedance Tomography (EIT) with a Spatially Distributed Sensor Array for Imaging of River Bed Morphology: a Proof of Concept (Study)

This report was produced as part of a NERC funded ‘Connect A’ project to establish a new collaborative partnership between the University of Worcester (UW) and Q-par Angus Ltd. The project aim was to assess the potential of using complex Electrical Impedance Tomography (EIT) to image river bed morphology. An assessment of the viability of sensors inserted vertically into the channel margins to provide real-time or near real-time monitoring of bed morphology is reported. Funding has enabled UW to carry out a literature review of the use of EIT and existing methods used for river bed surveys, and outline the requirements of potential end-users. Q-par Angus has led technical developments and assessed the viability of EIT for this purpose. EIT is one of a suite of tomographic imaging techniques and has already been used as an imaging tool for medical analysis, industrial processing and geophysical site survey work. The method uses electrodes placed on the margins or boundary of the entity being imaged, and a current is applied to some and measured on the remaining ones. Tomographic reconstruction uses algorithms to estimate the distribution of conductivity within the object and produce an image of this distribution from impedance measurements. The advantages of the use of EIT lie with the inherent simplicity, low cost and portability of the hardware, the high speed of data acquisition for real-time or near real-time monitoring, robust sensors, and the object being monitored is done so in a non-invasive manner. The need for sophisticated image reconstruction algorithms, and providing images with adequate spatial resolution are key challenges. A literature review of the use of EIT suggests that to date, despite its many other applications, to the best of our knowledge only one study has utilised EIT for river survey work (Sambuelli et al 2002). The Sambuelli (2002) study supported the notion that EIT may provide an innovative way of describing river bed morphology in a cost effective way. However this study used an invasive sensor array, and therefore the potential for using EIT in a non-invasive way in a river environment is still to be tested. A review of existing methods to monitor river bed morphology indicates that a plethora of techniques have been applied by a range of disciplines including fluvial geomorphology, ecology and engineering. However, none provide non-invasive, low costs assessments in real-time or near real-time. Therefore, EIT has the potential to meet the requirements of end users that no existing technique can accomplish. Work led by Q-par Angus Ltd. has assessed the technical requirements of the proposed approach, including probe design and deployment, sensor array parameters, data acquisition, image reconstruction and test procedure. Consequently, the success of this collaboration, literature review, identification of the proposed approach and potential applications of this technique have encouraged the authors to seek further funding to test, develop and market this approach through the development of a new environmental sensor