Flow variability analysis with regard to instream ecology

1

• Flow variability analysis with regard to
  in-stream ecology
• in a large French basin.
• P. Breil, Cemagref
• Breil_at_lyon.cemagref.fr

2
An Eco-hydrological PremiseLandscape filters
(Poff, 1997)
Regional pool of species defined in terms of
multiple species traits
Flow regime characteristic, thermal regime,
vegetation, water chemistry composition. Flood
intensity , trophic ressource and thermal
extremes. Water velocity
Watershed/basin filters Valley/reach
filters Channel unit filters Microhabitat
filters
3
Hydrological data set in the Loire basin
150 discharge gauge stations
100 000 sq.km
4
 Eco -Hydrological indices
128 indices calculated from the litterature
(Colwell 1974, Poff Allan 1995, Richter 1996,
Clausen Biggs 2000, Cattaneo al. 2001, Olden
Poff 2003,
5
Hydrological indices redundancy
22
Mixing all basin scales!
35
6
Flow variability scale effect
7
Monthly flow characteristics distributions
350 to1000 sq.km
100 to140 sq.km
Max. Q25 Q75 Min.
1000 to 4500 sq.km
200 to 350 sq.km
8
Scale effect human influence on a flow regime
100 to 400 sq.km
100 to 400 sq.km
Natural flow
Influenced flow
400 to 4500 sq.km
400 to 4500 sq.km
9
As a first conclusion

• The Overall flow variability decreases with
  increasing basin area
• It Concerns mainly the infrequent flow domain
• The Human influence, in the limit of this study,
• increases the frequent flow variability,
• increases the frequent flow variability for
   large  size basin
• decreases the frequent flow variability for
   small  size basin
• Memory duration of autocorrelations between
  consecutive monthly (either daily) flows
  increases with basin area in natural conditions
• Eco-hydrological indices must be formalized with
  respect to their scale of application