1 River Processes and Morphology A Case Study of the Souteyran valley

2 General Information: The Massif Central, contains a landscape of enormous variety characterised by a number of distinctive landforms. Water is an important and dynamic component of this landscape system. The physical geography of the Massif Central means that the region forms a vast watershed from which rivers flow to the Mediterranean, and the Atlantic coasts.

3 General Information (Cont) The Massif is well watered. Lozère has more than 2700 km of water courses. River management is an important aspect of water control and conservation in the Massif. Much of the management in the Cévennes is entrusted to the National Park Good management can only be achieved by gaining a full understanding of the physical processes acting within river channels

4 Specific Information: The Souteyran Valley lies along the southern slopes of Mont Lozère. It contains two rivers, the Souteyran and Rieumalet. Both of these flow into the Tarn at Le Pont de Montvert. The rivers are characteristic of upland streams which drain a granite and peat area. Both rivers are important to the valley communities: The Eagle's Nest relies upon them for its water supply as do Finiels and Prat Souteyran. Both rivers flow continuously and much of this flow can be attributed to a slow release from stores held high up on Mont Lozère. These are peat bogs that play an important role in the basin hydrological cycle.

The Hydrological Cycle:

6 What is a Drainage basin?? An area of land drained by a river and its tributaries. It is the catchment area from which a river system obtains its supplies of water. It can be described as an open system with inputs, transfers, storage and outputs.

Drainage Basin System: Throughfall Interception Transpiration Percolation Evaporation Groundwater Storage Infiltration Vegetation Storage Surface Storage Soil water storage Precipitation Surface Runoff Throughflow Baseflow Channel Flow Inputs Storage Transfers Outputs KEY:

In Summary: The dominant movement of water down the valley slopes on Mont Lozère is at or just below the surface. The soil is saturated quickly and large volumes of water go rapidly into the river channel at the valley floor. Therefore this area is prone to dramatic flooding.

Storm Hydrograph (3 rd – 6 th October 2001) Lag Time Peak Rainfall Peak Discharge

Storm Hydrograph (Souteyran 17 th – 30 th October 2011)

11 The Results of the Storm!

12

13

14 Aims: To Investigate the downstream changes within the river channel and to account for the changes which take place. To investigate if the river Souteyran is a ‘model’ river.

15 Map of Study Sites: Site No. Distance Downstream (km) Altitude (m) Key: - Study Site - River

16 WHAT CAN WE MEASURE ?

17 Cross Section Measurements: Present Flow Width Bank Full Width Present Flow Depth Bank Full Depth Channel Width (Present flow and bank full) (m) Channel Depth (Present flow and bank full) (m) Wetted perimeter (m) What will happen to these channel variables as you move downstream and why?

18 Velocity (m/s) How do we measure velocity? Slowest flow at the bottom due to friction from bed and banks Less fast on surface due to wind resistance Greatest velocity where friction is least (away from bed, banks and surface How will velocity change as you move downstream?

19 Changes in river characteristics downstream: Hypotheses  Friction  Channel Roughness  Velocity  Channel Width  Channel Depth  Cross Sectional Area  Discharge  Sediment Size  Angularity of Bedload  Conductivity  Channel Gradient

20 In Summary: The upper course: More turbulence More friction More angular bedload Larger bedload Steepest gradient The lower course: Higher discharge Higher velocity Higher hydraulic radius Greatest cross sectional area Concave Profile A model river should have the following characteristics but will the Souteyran show these characteristics?