Water Stewardship Information Sources

Citation Northwest Hydraulic Consultants Ltd. 2012. Cheakamus River Water Use Plan, Monitoring Channel Morphology in Cheakamus River, Implementation Year 5, Study Period: April 2008-April 2012. Prepared for BC Hydro.
Organization BC Hydro
URL https://www.bchydro.com/content/dam/BCHydro/customer-portal/documents/corporate/environment-sustainability/water-use-planning/lower-mainland/cmsmon-8-yr5-2014-05-07.pdf
Abstract/Description or Keywords Following  implementation  of  a  new  WUP  flow  regime  in  February  2006,  the  Cheakamus  WUP  
Consultative  Committee  expressed  concern  regarding  the  potential  effects  on  salmonid  habitat  
quality  and  availability  from physical  changes. To  address  these  concerns,  baseline  and  post-­‐WUP  
monitoring  was  recommended  to  examine the  effects  of  more  frequent,  higher  flows  that  would  
mobilize  and  distribute  sediment  introduced  by  large  floods,  debris  flows  and  mass  wasting.  The  
monitoring  program  also  examined  seasonal  minimum  flow  releases  from  Daisy  Lake  Dam  and  
access  to  side  channel  habitats.    
Cheakamus  River  extends  25  km  from  Daisy  Lake  Dam  to  the  confluence  of  Squamish  River.  The  
channel  can  be  broadly  characterized  by  four  distinct  sections:  Rubble  Creek  landslide  deposits,  a  
bedrock  canyon,  a  broad  alluvial  section  and  the  Cheakamus  River  fan.  These  sections  were  divided  
into  13  distinct  reaches  above  the  Cheakamus  fan  that  reflect  differences  in  slope,  morphologic  
characteristics,  sediment  supply,  and  discharge.  
Within  each  reach,  a  baseline  morphologic  map  was  prepared  from  1:5,000  colour  orthophoto  
mosaics  collected  during  low  water  conditions  in  April,  2008.  The  river  was  re-­‐flown  at  the  same  
scale  in  March,  2012  and  the  mapping  exercise  was  repeated  to  illustrate  the  types  and  magnitude  
of  channel  changes  during  the  past  four  years.    
The  wetted  low  flow  channel  dominates  the  areal  fraction  of  most  reaches,  and  is  representative  of  
the  available  overwinter  habitat  for  salmonids.  This  low  water  wetted  channel  area  has  remained  
constant  (averaging  59%  of  the  total  channel  area)  since  2008  indicating  no  substantive  changes  to  
the  channel  characteristics  since  implementation  of  the  WUP.  Unvegetated  bars  are the  second  
most  common  morphologic  feature  in  most  reaches,  averaging  28%  of  total  channel  area  in  2008  
and  23%  in  2012.  Together,  unvegetated  bars  combined  with  the  low  flow  wetted  channel  
represented  roughly  90%  or  more  of  total  reach  area  in  9  of  12  reaches  in  2008.  The  dominance  of  
bar  and  wetted  channel  areas  declined  to  7  of  12  reaches  in  2012.    
The  loss  of  open bar  surface  area  is  not  due  to  erosion  or  degradation,  but  to  the  establishment  and  
growth of  vegetation  on  previously  exposed  bar  areas.  The  increase  in  the  mean  area  of  young  
vegetation  on  formerly  bare  bars  was  statistically  significant.  There  was  also  an  increase  in  the  mean  
area  of  young  and  mature  islands  –  although  not  significant  –  which  supports  the  observed  trend  
that  the  channel  is  becoming  increasingly  stable.  Unperturbed,  the  expansion  and  maturation  of  
vegetation  is  expected  increase  bank  strength,  increase  channel  depths  and  reduce  channel  
complexity,  resulting in  a  loss  of  natural  side  channel  habitat.    Large  sediment  inputs  from  Rubble  
Creek  or  other  tributaries  could  reverse  or  modify  the  established  trend  and  help  mitigate  the  effect  
of  sediment  supply  reductions  from  the  construction  of  the  Daisy  Lake  Reservoir.  
The  low  flow  wetted  channel  was  further  divided  into  three  (3) hydraulic  mesohabitat  units:  pools,  
riffles,  and  rapids.  Riffle  habitats  were dominant  in  mainly  unconfined  reaches,  and  rapids  dominant  
in  steeper,  confined  channel sections.  Between  2008  and  2012 the  distribution  of  pools,  riffles  and  
rapids  remained  relatively  stable  along  the  study  reach.    The  variability  in  the  size  of  the  mapped  
units  also  remained  the  same  (p  <0.05).    Overall  the  Cheakamus  River  maintained  a  consistent  
morphology  and  distribution  of  habitat  and  channel  units  from  2008  to  2012.    During  the  same  
period  relatively  few  sediment  supplying  events  occurred  in  the  watershed. To  better  understand  the  linkages  between  the  habitat  and  fish  productivity  the  long-­‐term  study  
design  should  attempt  to  inventory overall  mesohabitat  proportions  in  key  alluvial  reaches  of  the  
Cheakamus  River,  as  this  was  also  undertaken  by  the  Fisheries  Technical  Committee  prior  to  the  
WUP.  These  reaches  should  be  selected  based  on  concurrent  fish  use,  populations  and  habitat  
quality  studies  undertaken  as  monitors  under  the  WUP  to  allow  some  comparative  analyses  prior  to  
review  of  the  WUP.  
Additional  work  could  be  undertaken  to  inventory  and  monitor  natural  side  channels  on  the  alluvial  
reaches  of  the  river,  and  document  their  change  through  time  as  it  relates  to  flood  history  and  
geomorphic  changes  in  the  river.  Side  channels  have  a  high  utilization  by  salmonids  in  the  
Cheakamus  River,  and  are  key  habitats  for  some  life  stages  and  species.    However,  since  these  are  
side  channels  are  located  a  ways  downstream  of  the  Daisy Lake  Reservoir,  separating  project  effects  
from  the  influence  of  unsteady  tributary  sediment  and  debris  inputs  will  be  difficult.  
Additional  data  should be  collected  on  sediment  quality  as  it  relates  to  substrate  use  by  rearing  and  
spawning  salmonids.  Changes  to  the  distribution  and  quality  of  spawning  substrates  within  the  
Cheakamus  River  area  especially  critical  to  chum  and  pink  salmon,  and  are  influenced  by  tributary  
and  lateral  supply  and  mobilization  due  to  high  flows.  Further  mapping  and  sampling  should  be  
completed,  correlated  to  documented  spawning  sites,  to  provide  direct  data  on  spawning  substrate  
conditions  and  how  it  changes  over  time.    
In  summary, Based  on  2008  and  2012  air  photos the  overall  morphology  of  the  Cheakamus  River  has  
been  shown  to  be  reasonably  stable,  but  a  more  detailed  set  of  data  looking  at  substrate  quality  and  
quantity  at  key  biologically  important  sites  is  missing.    Such  data  should  be  collected  to  characterize  
both  the  general  substrate  conditions  that  will  effect  habitat  use  by  parr  and  fry,  as  well  as  spawning  
substrate  surveys  that  characterize  the  availability  and  quality  of  the  substrate.    Inputs  from  
tributaries  also  need  to  be  qualitatively  monitored  to  assess  the  temporal  trends  in  supply  and  
explain  the  observed  channel  changes.
Information Type report
Regional Watershed Howe Sound & Sunshine Coast
Sub-watershed if known Cheakamus River
Aquifer #
Comments
Project status complete
Contact Name
Contact Email