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Some data are very strange[[BR]]
[[Image(source:data/Docs/trac/RiverWidth/largeurlameeauUpcatchmentarea.jpeg,600px)]] [[BR]]
2 points with an up_catchment_area >40000 and a st_cs_largeurlameeau very small (<15).[[BR]]
View with the up_catchment area >40000 - they correspond to the riversegement with the maximal higth, so the problems don't come from the calculation of the up_catchment_area, but when we join the CCM layer and the BDMAP points.[[BR]]
[[Image(source:data/Docs/trac/CCM21/upcatchment40000.jpg,600px)]] [[BR]]

2 st_codecsp (ers[ers$up_catchment_area>40000,"st_codecsp"]) : 06840051, 0547C025 [[BR]]

||gid||st_codecsp||uga||strahler||op_cs_largeurlameeau||op_surfaceechantillon||up_catchment_area||
||328337||06840051||!RhoneMediterranee||8||5.38||344.32||72120.24||
||243756||0547C025||Garonne||7||9||1215||44687.99|| 
||288926||04430072||Loire||4||61.8||1854||1815.24||
||240081||06250162||!RhoneMediterranee||1||39||1638||1.09||
||305966||0532B006||Adour||5||40.0||2200||1254.41||

[[BR]]
||[[Image(source:data/Docs/trac/RiverWidth/surfaceechantillon_largeurlameeau.jpeg,400px)]]||[[Image(source:data/Docs/trac/RiverWidth/altgradie_largeurlameeau.jpeg,400px)]]||[[BR]]

||[[Image(source:data/Docs/trac/RiverWidth/largeurlameeau_strahler.jpeg,400px)]]||[[Image(source:data/Docs/trac/RiverWidth/upcatch_strahler.jpeg,400px)]]|| [[BR]]
L’ordre de grandeur des largeurs de cours d’eau pour le bassin de la Loire en fonction du rang de Strahler est de (Wasson ''et al.'' 2006) :[[BR]]
- 0,5 à 2 m pour le rang 1 [[BR]]
- 2 à 4 m pour le rang 2 [[BR]]
- 4 à 8 m pour le rang 3 [[BR]]
- 8 à 12 m pour le rang 4 [[BR]]
- 18 à 20 m pour le rang 5 [[BR]]

Correspondance entre rangs de Strahler et surfaces de bassins versants amont (valeurs médianes en km²) par grands bassins hydrographiques (Wasson ''et al.'' 2006) :[[BR]]
||Strahler||AP||AG||RM||RMC||SN||LB||
||3||252||106||104||148||199||91||
||4||489||411||389||309||629||163||
||5||1 338||1 811||1 762||1 194||3 037||580||
||6||||6 761||7 425||6 545||9 507||2 728||
||7||||34 740||||27 686||64 953||12 889||
||8||||||||63 706||||38 454||
(AP Artois Picardie ; AG Adour Garonne ; RM Rhin Meuse ; RMC Rhône Méditerranée Corse ; SN Seine Normandie ; LB Loire Bretagne)[[BR]]

In blue : BDCarthage In red : CCM[[BR]]
Point 06840051[[BR]]
The join is good between the CCM and BDMAP, maybe it's the largeurlameau which is wrong.[[BR]]
[[Image(source:data/Docs/trac/RiverWidth/st_codecsp06840051.jpg,400px)]] [[BR]]

Point 0547C025[[BR]]
No match with the CCM layer, we can delete this point[[BR]]
[[Image(source:data/Docs/trac/RiverWidth/st_codecsp0547C025.jpg,400px)]] [[BR]]

'''Model with and without these points'''[[BR]]
[[Image(source:data/Docs/trac/RiverWidth/upcatch_largeurlameeau.jpeg)]] [[BR]]

'''Model log largeur lame eau ~log up_area'''
[[Image(source:data/Docs/trac/RiverWidth/Mod_log_largeur_log_up_area.jpeg)]][[BR]]

lm(formula = log(ers0_station$st_cs_largeurlameeau) ~ log(ers0_station$st_up_area))[[BR]]

Residuals:[[BR]]
      Min        1Q    Median        3Q       Max [[BR]]
-2.279056 -0.272438  0.002999  0.253847  2.319976 [[BR]]

Coefficients:[[BR]]
||                            ||Estimate|| Std. Error|| t value|| Pr(>|t|)||[[BR]]    
||(Intercept)||                   0.44761||  0.04596   || 9.74||   <2e-16 ***||[[BR]]
||log(ers0_station$st_up_area)||  0.29407   || 0.01025  || 28.69 ||  <2e-16 ***||[[BR]]
---[[BR]]
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1 [[BR]]
[[BR]]
Residual standard error: 0.4814 on 1143 degrees of freedom[[BR]]
  (1 observation deleted due to missingness)[[BR]]
Multiple R-squared: 0.4186,	Adjusted R-squared: 0.4181 [[BR]]
F-statistic: 822.9 on 1 and 1143 DF,  p-value: < 2.2e-16