River basin planning and sediment management

Transcription

1 River basin planning and sediment management Georg Rast, WWF Germany Sediment deficit, channel incision and sediment extraction along the Danube a brief overlook 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 2

2 Key user sectors influencing sediment balance and transport Hydropower Navigation Flood protection But also Land use Construction businesses 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 3 Sediment components bed load, considered as relevant for - hydropower and flood protection - inland navigation (often neglected) suspendid solids, considered as relevant for - navigation in lowland sections and estuaries - flood protection and hydropower (often neglected) 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 4

3 Alterations of sediment balance/transport are WFD relevant not only by quantity, but also by quality at basin level from freshwater via transitional to coastal zones! 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 5 Main physical interventions influencing sediment balance and transport land use changes (i.e. from forests to arable land), disclosure/reduction of floodplains by dykes straightening of river beds building of weirs and dams with impoundments reinforcement of river banks and erection of groynes dredging and deepening of river beds with extraction of aggregates 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 6

4 Historical river training on the Elbe Overlaid maps of Elbe section from 1792 and 1893 (red) 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 7 Intensive particle sedimentation in groyne fields Groyne fields are sites of intensive sedimentation processes This results in the disappearance of shore habitat diversity and in huge accumulations of contaminants (e.g. 50kg Pb in 1 groyne field) 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 8

5 Main effects on sediment balance and transport, also concerning WFD targets interruption of river bed sediment transport - with loss of longitudinal connectivity reduction of morpho-dynamic processes - with loss of habitat and - reduction of self purification capacity of the river bed 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 9 Main effects on sediment balance and transport, also concerning WFD targets incision of river beds - with lowering of mean/low water levels in river bed and connected groundwater bodies accumulation of fine sediments - with aggradations of floodplains and - siltation of side arms/oxbows loss of lateral connectivity 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 10

6 River training measures and effects HWL = High Water Level Levee/ Terrace MWL=Mean Water Level LWL=Low Water Level Side arm 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 11 River training measures and effects HWL MWL LWL Side arm Systematic bank protection and/or groyns Damming of side arms for concentration of flow in main riverbed Continuous aggradation of floodplain, more dense vegetation in floodplain/banks elevation of flood water levels 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 12

7 River training measures and effects HWL MWL LWL Side arm Systematic bank protection and/or groyns Damming of side arms for concentration of flow in main riverbed incision of riverbed, decrease of low and even mean water levels subsidence of groyns and bank reinforcements, increased maintenance 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 13 River training measures and effects HWL MWL LWL (former) Side arm Systematic bank protection and/or groyns Damming of side arms for concentration of flow in main riverbed loss of flood water conveyance capacity, further increase of flood water levels and decrease of low water levels 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 14

8 Additional effects on uses river bed incision is affecting the stability and the safety of - river training structures - foundations of bridges crossing river beds and - even river barrages trapping of sediments in backwaters reduces - flood water conveyance capacity - navigable depth (draught) 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 15 Timing of interventions and effects effects at the bigger scale often appear very slow but long term but in the past side effects usually not considered when carried out or even not predictable 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 16

9 Where are we now? Modelling has been developed at many scales and different sectors Long term research has fundamentally improved understanding of ecosystem functions Awareness of the problems and needs as well as available modelling tools is limited, especially related to sediment issues 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 17 Central channel sediments the river s liver Bottom sediments swiftly overflown by river water form a hot spot of microbial activity Fischer, Kloep, Wilczek, Pusch (2005) Biogeochemistry 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 18

10 Good practise examples for feasibility of improved sediment management River management concept for the Danube river east of Vienna Dutch concept for free space for rivers on the lower Rhine and Maas rivers Artificial bed load supply on Upper Rhine and Elbe river in Germany French concept for Espace de Liberté (Allier- Loire river) Swiss concept for bed load transport through hydropower schemes on High Rhine river 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 19 What is to be done more? improve awareness about needs for sediment management widen the scope to the basin scale (WFD), i.e. tributaries and natural genesis of sediments develop integrated sustainable management schemes with - plans for change or even abandonment of uses (e.g. extraction of aggregates) - increase in maintenance and monitoring efforts (e.g. shift from maintenance-free waterways) - consideration of climate change impacts 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 20

11 Thank you for attention 31 Jan 2007 PIANC Conference Navigation and the WFD Sediment transport and hydromorph. processes Page: 21