PUB Working Group 10 (WG10): Drought and Flood Risk: Hydrology and Sediment Transport in Mountain Catchments

Objectives
The goal of this working group is to develop new methods for quantifying and modelling the interactions between the hydrological cycle and sediment transport with specific reference to droughts and extreme events, especially floods, in mountain catchments. Of special interest will be the quantification of neglected components of the water cycle inducing droughts, in particular evaporation and transpiration on steep slopes, as well as those causing severe flood risk, such as extreme precipitation and bedload transport. These are important aspects that need to be considered for sustainable and integrated watershed management.

Specific objectives are as follows:

• Improve the prediction of evapotranspiration over vegetated as well as snow-covered surfaces on mountain slopes and valley floors, identify water sources and flow routing as well as the interaction between evapotranspiration, subsurface flow and the water cycle.
  
  
• Improve the prediction of flood risk through extreme precipitation and the availability of solid material and its transport potential in mountain torrents. Identify the local flood risks through erosion and sedimentation.
  

Both objectives are addressed from similar methodological approaches - ie through intensive, field-based experimental setups in two or more test catchments, combined with the definition of landscape units based on geomorphological, topographical and remote sensing interpretations. The intention is to transfer this knowledge into ungauged basins.

Objective 1: Measurement and modelling of evapotranspiration and flow routing in mountain catchments is being investigated through

• a field-based and modelling approach for evapotranspiration and flow routing
  
  
• a modular modelling approach to evapotranspiration

Objective 2: Measurement and modelling of flood risk though extreme precipitation - including snowmelt � and solid material (bedload) transport in mountain catchments is being investigated through

• a field-based approach for estimation of extreme events including bedload transport and validation of bedload models / functions in mountain catchments
  
  
• a solution-oriented geomorphologically-based approach to sediment transport
  
  
• an experimental and applied, bedload-oriented approach to watershed planning
  
  
• a modular modelling approach to flood risk and sedimentation

Working Group Outcomes
Although the two objectives treat different subject areas, the methodologies are complimentary in that they are both born out of strongly experimental, field-based approaches on fluid and sediment transport that are modelled on the basis of hydrological response units.

The main intention is to transfer the knowledge gathered from intensively instrumented basins into ungauged basins. For a better understanding of the water cycle, a simple measuring set-up will be developed that focuses more on the regional diversity of evaporation and transpiration and discharge estimation instead of extrapolation of precipitation. To increase our understanding of flood risk and sediment transport, an approach will be developed that defines in detail the characteristics of the stream network and in particular the moisture content and stability of the lower slopes.

Other methods of estimation may be required based on historical, geomorphological and sedimentological evidence and on "fuzzy" interpretations of catchment variables. A hierarchy of measuring networks will be developed in accordance with local and regional processes, derived from meteorological, hydrological and sedimentological investigations. This will be particularily important for cases where a dense network of precipitation gauges is insufficient to solve problems such as flood risk through sedimentation or nodes of evaporation.

Studies will be performed in the humid Alps and in the semi-arid Atlas mountains. Other mountain research areas are welcome for comparison reasons. At present it is recognised that there is a 'paradigm-lock' (UNESCO-HELP Program) in Integrated Watershed Management which naturally encompasses a major mountain component. The demand for more experimental hydrological and sedimentological work was expressed at the last European CHOP (Change of Paradigm in Hydrological Modelling) workshop. This is particularly important for model validation.

PUB-WG3 � Orographic precipitation, surface and groundwater interactions and their impacts on water resources is addressing similar objectives, although their focus is in the western U.S.

Key Participants:

• Carmen de Jong, Institut de la Montagne, Chambery, France
• Hans Schreier, University of British Columbia, Canada
• George Leavesley, US Geological Survey, Denver, USA
• Benno Zarn, Hunziker, Zarn and Partners, Dornat, Switzerland