minding the meander belt
TRANSCRIPT
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Minding the Meander Belt
Legislation and Policy CommitteeBow River Basin Council
Palliser Environmental Services Ltd.Cochrane, AlbertaFebruary 22, 2008
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Overview
• River processes• Meander belt theory and application
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Predevelopment Runoff Volumesin a “Built” Environment
• Predevelopment runoff volumes for Nose Creek and West Nose Creek were about 6.1 mm and 9.6 mm, respectively.
• Average precipitation is about 350 mm.
• Predevelopment runoff volumes represented about 2% of total rainfall volumes.
0
50
100
150
200
250
300
350
400
Rai
nfa
ll (
mm
)
Nose Creek West Nose Creek
Predevelopment Runoff
Total Annual Rainfall
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ST
RE
AM
FL
OW
RA
TE
TIME
More Runoff Volume
Higher and More Rapid Peak Discharge
Higher Baseflow
Lower and Less Rapid Peak
Pre-development
Post-development
Gradual Recession
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• Human – caused alterations to the creek corridor– Land use
practices,– Agriculture, and– Development
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Factors Affecting Channel Stability
• Floodplain material (surficial and bedrock geology)
• Channel width• Channel slope• Riparian vegetation• Flow regulation• Ice floes
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(Parish geomorphic 2004)
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(Parish geomorphic 2004)
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• The Meander Belt provides a limit to development within the areas where the river system is likely to shift.
Grand River Conservation Authority (2008)
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Photo Credit: Lorne Fitch
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(Parish geomorphic 2004)
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Criteria used to define riparian setbacks.
Perennial streams require larger setbacks since they are higher in order than intermittent streams and generally convey more water
As defined by the Alberta Provincial Line Network
Perennial or Intermittent Stream
Allows for natural stream channel migration
20 times the bank full width for given reaches
Meander Belt Width
Escarpments often define watercourses.
Lands having equal to or greater than 15% slope
Adjacent Escarpments
Flood risk area that may be public safety concern.
As defined by Alberta Environment
1:100 year Floodplain
Riparian soils are unique and reflect the presence of water or poorly drained soils.
Saturated soils that are influenced by the presence of water.
Riparian Soils
RationaleDescriptionCriteria
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Meander Belt Applied
• For unconfined systems, where the watercourse is free to shift across the floodplain, allowance is twenty (20) times the bankfull channel width
(OMNR)
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Empirical Relationships
• Relationships between channel parameters and meander belt have been published
• Migration rates have been determined based on:– Discharge– Slope– Bank material (e.g., sands)– Shape of meander bend
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• Gregory and Walling (1973)– 14 to 20 times the bankfull channel width
• Carlston (1965) – Belt width = 65.8*Annual Discharge0.47
• Newbury (1996)– 5.3 to 36.8 times the bankfull channel width
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b) Escarpment (> 15% Slope)
d) 1:100 year Floodplain
c) Meander Belt Width = 20 x bank full width
e) Intermittent Stream
f) Perennial Stream
a) Riparian Soils
North
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Riparian Protection• The riparian setback width should be determined
on a site-specific basis as the greater of:
– the 1:100 year floodplain width, – the meander belt width (20x the bank full width) and– the width of escarpments (lands having > 15% slope)
that lie adjacent to the meander belt and/or floodplain.
Escarpment
FloodplainMeander Belt
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Escarpment
(> 15% Slope)
1:100 year
Floodplain
Meander Belt Width = 20x bank full width
West Nose Creek at Confluence ParkScale 1:10 000
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b) Escarpment (> 15% Slope)
d) 1:100 year Floodplain
c) Meander Belt Width = 20 x bank full widtha) Riparian
Soils
North
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Refined Process
• Define reach boundaries– Similar valley
wall,– Channel slope– Processes
controlling channel form and function
Parish Geomorphic 200(Parish geomorphic 2004)
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(Parish geomorphic 2004)
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(Parish geomorphic 2004)
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(Grand River Conservation Authority)
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2005
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2007 Photo Credit: Amanda Bogen-Halawell
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Questions?