Minding the Meander Belt

Minding the Meander Belt

Legislation and Policy CommitteeBow River Basin Council

Palliser Environmental Services Ltd.Cochrane, AlbertaFebruary 22, 2008

Overview

• River processes• Meander belt theory and application

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

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Rai

nfa

ll (

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Nose Creek West Nose Creek

Predevelopment Runoff

Total Annual Rainfall

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

• Human – caused alterations to the creek corridor– Land use

practices,– Agriculture, and– Development

Factors Affecting Channel Stability

• Floodplain material (surficial and bedrock geology)

• Channel width• Channel slope• Riparian vegetation• Flow regulation• Ice floes

(Parish geomorphic 2004)

(Parish geomorphic 2004)

• The Meander Belt provides a limit to development within the areas where the river system is likely to shift.

Grand River Conservation Authority (2008)

Photo Credit: Lorne Fitch

(Parish geomorphic 2004)

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

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)

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

• 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

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

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

Escarpment

(> 15% Slope)

1:100 year

Floodplain

Meander Belt Width = 20x bank full width

West Nose Creek at Confluence ParkScale 1:10 000

b) Escarpment (> 15% Slope)

d) 1:100 year Floodplain

c) Meander Belt Width = 20 x bank full widtha) Riparian

Soils

North

Refined Process

• Define reach boundaries– Similar valley

wall,– Channel slope– Processes

controlling channel form and function

Parish Geomorphic 200(Parish geomorphic 2004)

(Parish geomorphic 2004)

(Parish geomorphic 2004)

(Grand River Conservation Authority)

2005

2007 Photo Credit: Amanda Bogen-Halawell

Questions?