sediment – structures interaction in the sedalp project · contents • sedalp wp6 –interaction...

SEDIMENT – STRUCTURES INTERACTIONin the SedAlp project

Final Conference – Bolzano9h- 10th of June, 2015

Jošt SodnikSimon RusjanMatjaž Mikoš

Contents

• SedAlp WP6 – Interaction with structures

• Improved concepts of responses of torrent/river control structures to floods and debris flow impact (including wood)

• Efficient torrent control structures with low impact on sediment continuity

• Hydropower plants (upstream – downstream continuity)

• Effective flood protection systems, river training and restoration projects with low impact on sediment continuity

• Recommendations

WP6

• Duration from September 2012 to March 2015

• WPL : PP9 UL FGG

• Project partners– LP BMLFUW– PP1 Province of Bolzano– PP2 ARPAV– PP3 UNI PD TESAF– PP5 Regione Piemonte– PP7 IRSTEA Grenoble– PP12 IZVRS– PP13 AKL (Carinthia)

WP6 actions

• Action 6.1: Assessment of mutual interactions between control structures, torrential‐river sediments and large wood.

• Action 6.2: Evaluation of the effects of hydropower dams on sediment continuity for design and planning purposes.

• Action 6.3: Evaluation of river hydro‐morphological alterations due to longitudinal sediment‐continuity disruption and performance analysis of river restoration measures.

• Action 6.4: Performance analysis and definition of optimal planning and design of torrent control works to reduce their impact on longitudinal sediment continuity.

WP6 outputs:

‐ 6.1: Improved concepts of responses of torrent/river control structures to floods and debris flow impacts (including wood)

‐ 6.2: Guidelines for planning/designing of efficient torrent control structures with low impact on sediment continuity between upstream torrential headwaters and downstream river reaches

‐ 6.3: Guidelines for improved planning of hydropower plants aimed to improve the longitudinal sediment continuity between upstream torrential headwaters and downstream river reaches

‐ 6.4: Guidelines for planning and designing of effective flood protection systems, river training and restoration projects that have lower impact on sediment continuity

Improved concepts of responses of torrent/river control structures to floods and debris flow impact (including wood)

• Up to date insight on main driving forces for improving flood control management from EU and Alpine Space context

• Flood control & Sediment management in the context of integral flood risk management –SedAlp recommendation on improved planning approach

• Modern protection concepts with cross‐sectional structures in torrent and erosion control in Alpine torrent catchments

• Effectiveness of check dams

Improved concepts of responses of torrent/river control structures to floods and debris flow impact (including wood)

• Effectiveness of barriers documented during events in Austria (real case scenario research)

• Check dams influence on sediment transport in steep slope stream (lab experiment)

• Analysis on protection work system on Maira river (case study)

• Concept of torrent control in Bistricica torrent (case study)

• Maintenance of torrent control structures (improved concepts of maintenance practices)

Efficient torrent control structures with low impact on sediment continuity

Problem description

• Natural hazard mitigation with building permanent structures on Alpine streams since 2nd half of 19th century (from 1970s filtering check dams)

• Questions: – Effect of protection structures on sediment transport?

– Retaining sediments and risk reduction vs. reactivating sediment supply and arising risk costs

• Aimeffectively reactivate the hydro‐morphological and ecological system dynamics, while keeping risk below acceptable level


Design framework

• What we want to achieve how we choose to satisfy the need

• New (adapted) frameworks proposed

– 5 indicators computational architecture

– Iterative approach

– Design for problem solving


5 indicators:• Disturbancies • Risks • Costs • Natural value • Externalities


Iterative approach• Problem identification and description• Formulation and visualization of the Ideal Final Result (IFR) to be achieved.• Analysis of resources (physical, spatial and temporal) for an optimal attainment of

the IFR. • Definition of admissible system changes• Elaboration of solution concepts• Evaluation of the developed solution strategies.

– what has been enhanced, – what has been worsened– what has been substituted– what remains to do with reference to the attainment of the IFR and – whether the systemic and developmental contradictions could be solved?

Selection of the optimal solution (consideration cost‐benefit criteria)


Design for problem solving


• Design criteria for sediment traps (review and new concepts)

• Construction, functionality and management of the retention basins of torrent control structures

• Torrent check dam failure hazard ranking

• Refining process comprehension and torrent control structure design (physical scale modeling)

Procedures for improved planning


• Field assessment of the self‐cleaning behavior of an open check dam (Italy)

• Application of failure hazard ranking method on selected check dams (Slovenia)

• A physical scale model to investigate torrential filter structures (Austria)

• Hydraulic scale model tests for the analysis of bedload transport processes in stepped torrent channels (Austria)

Good practice examples

Hydropower plants (upstream – downstream continuity)

Problem description

• Reservoirs reduce velocities sediment trapping effect

• Effects of dams construction• Downstream: reduced sediment input• Reservoir: sediment trapping lower energy production• Upstream: river bed aggradations, inundation phenomena

• Sediments:– Suspended sediment– Bed load– Plant debris fine material with high organic content


Problem description

• Effects of sedimentation in HPP reservoirs• Reduction in live storage capacity of the reservoir• Interference with functioning of water intakes• Influence of sediment inflow on design of water conductor systems, desilting basins,

turbines etc.• Rise of flood levels• Sediments (location and quantity) affect the performance of sluicing and flushing

measures to restore capacity

• Various environmental impacts (hydromorphology, habitat diversity, ground water levels, water temperature)


• Overview on types of hydropower plants and main operations


• Problem process description

– River morphology implications • Aggradations• Degradations

– Ecological implications• Changed water regime• Modification of habitat• Negative effects of flushing operations

– Economic implications

– Social aspects


Measures against reservoir sedimentationDeposition control Removal of deposited sediments

• Presentation of actual sediment management project (actual plan)– Experience of Veneto region


Management plans optimizations (good practice)

• Proposal of coarse sediment removal and introduction downstream the dam channel reach


Management plans optimizations (good practice)

• Multi Criteria Analysis

Energyenergy hydropower productionnational energy improvement

HP producer economyfinancial outcomes for the collectivitycosts for the sediment removalspecific investments

EconomyCosts for downstream sediment input

EnvironmentRiver ecosystem

FishMacrobenthos

Morphology

Social usesRiver fruition

FishingTourismLandscape

Effective flood protection systems, river training and restoration projects (with low impact on sediments)

Ecological, economical and technical problems

Effective flood protection systems, river training and restoration projects

Problem description

• Decrease of lateral dynamics

• Bed degradation

• Bed aggradation


Processes and theoretical relations

• Sediment transport

• Longitudinal river training– River straightening– River narrowing

• Transverse structures– Weirs and dams– Ramps and steps

• Gravel mining

• Levees


Procedures for improved planning

• Counter measures for mitigating bed degradation


Procedures for improved planning• Tools for planning river bed widening

– Historic maps– Regime equations– Calculations in representative cross section– Numerical modeling

• Implementation of bed widening

• Consideration of sediment transport in flood risk management– Positioning of levees– Sediment deposition in flood retention basins

• Assessing the morphological spatial demand of rivers

• Design of step‐pool sequences and rapids in mountain streams


Practice examples

• River restoration at the Drau River via bed widening– Estimation of the appropriate channel width for countering bed degradation– Considering bed level changes for flood water levels

• Mitigating Channel Incision at the Mur River, Austria– Selection of the appropriate measure – Positioning the measures– Temporal sequence of measure implementation– Measure implementation

Recommendations

• Separate recommendations for each field of work (Chapter)

• Over 50 recommendations

• Recommendations for Policy makers Practitioners Researchers

Recommendations for Policy makers

• Adequate risk‐based land use planning

• Holistic (whole river system) approach when planning flood protection and control measures

• Timely and adequate monitoring and maintenance of existing water infrastructure (sufficient financing)

• Awareness of vulnerability of control structures for events with longer return period than the designed one – evacuation plans, risk management, additional measures

Recommendations for Policy makers

• Sediment continuity problem solving might lead to strong modifications of existing protection systems

• Restoring sediment dynamics involves “giving space” to water and sediment deposits

• When planning structures, measures and hydropower structures, morphological point of view must also be taken into account, not only hydrological/hydraulic and ecological point of view

• Environmental impact assessment should precisely determine the magnitude of disturbance and lead to a detailed prescription of compensation measures

Recommendations for Practitioners

• Prevailing extreme sediment transport process should be identified for each reach of the torrent ( floods, fluvial solid transport, debris flood and debris flow)

• Functions of torrential barriers can be divided in the following functional types in view of processes: stabilization/consolidation, retention, dosing and filtering, energy dissipation

• Torrent control measures should be scenario‐oriented

• In the case of building open barriers, it is recommended to plan two or three barriers with complementary functionality in chain rather than only one open »bigger barrier«

Recommendations for Practitioners

• Practitioners should be open to consider deriving knowledge for the planning process from backward‐oriented indication, mathematical modelling and physical lab experiments.

• Planning or designing efficient torrent control structures involves providing verifications of the obtained solutions with respect to the system performance at different scales

• Sediment continuum and the impact of dams on channel morphology must be considered in the Management plans of HP managers

• Sediment transport process should be considered already in planning phase, not only in post‐project restoration. River engineering in general should be performed with the aim to maintain sediment transport dynamics.

Recommendations for Researchers

• Long‐term data collection, analysis and survey of sediment retention basins – also surveying during filling and self‐cleaning (self‐cleaning optimization) and after disaster (focus on sediments & driftwoods)

• Further development of sediment connectivity management implementation guidelines

• Interdisciplinary research at the interface between processes, risk consequences and resilience

• Applied research targeted at improving the quality of protection system design

• Specific research to better understand river morphology, eco‐hydraulic processes, system functions and the related, monetarily quantified system services

Recommendations for Researchers

• Research activities supporting the effectiveness of the decision, communication and participation process.

• Researches have to be carried out through field and flume surveys, and monitoring analyses. They should be made at different spatial (catchment, hydrographic network, channel reach) and time (short and long time variations of hydromorphological and ecological parameters) scales, in order to better understand the response of the various river system aspects to the human impacts

• There is discrepancy between the number of theoretical, numerical or laboratory investigations and the number of investigations in the field, where factors may appear that otherwise would remain undetected. Future research should find a balance with field verification, implying a close collaboration with policy makers and practitioners.

Dissemination of WP6

• 9 Conference papers

• 7 Journal papers

• 2 Oral presentations

Thank You for your attention…

sediment – structures interaction in the sedalp project · contents • sedalp wp6 –interaction...

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