USING SIMPLE 1D-2D MODELLING AND

GEOMORPHOLOGY - HABITAT

ASSOCIATIONS TO ASSIST IN

FLOODPLAIN RESTORATION

Caroline Anderton

& George Heritage

Introduction

• A study has been carried out to consider floodplain restoration on the Scottish River Dee

• The study included a number of surveys / assessments:

– Hydrological Assessment

– Topographic Survey – River Cross Sections + Embankment Crest Levels

– Geomorphological Audit

– Ecological Survey

– Hydraulic Modelling

• The study brief requested that the plan aims to restore natural channel form and function

Impacts / Constraints

• Adverse impacts / constraints:

– Evaluate the potential risks to wetland sites (including RSPB) from river

naturalisation and identify any mitigation.

– Potential impacts of restoration on flooding and low river flows, particularly

at the grade B listed Mar Lodge and low lying properties in Braemar.

– Risk of exposure of Scottish and Southern Electric Power Cables through

channel migration.

– Risk of unintended adverse impacts on fisheries and habitats.

River Dee Catchment

Study Reach

Stakeholders

• Aberdeenshire Council

• Dee Catchment Partnership

• Scottish Natural Heritage

• SEPA

• Cairngorm National Park

• National Trust for Scotland

• Dee Fisheries

• Estates

SSSI

SPA

SAC

Study Area

0 1 20.5Kilometers

±

Contains Ordnance Survey data © Crown copyright and database right 2010

Cairngorms SAC & SPA

Eastern Cairngorms SSSI

Cairngorms SPA

River Dee SAC

Morrone Birkwood SAC & SSSI

Anthropogenic Influences

Bank toe reinforcement Flood Embankment Agricultural Embankment

Revetment Landfill – car chassis Landfill – concrete blocks

Study Reach Channel Type Zonation

Hydrometric Data – Model Input

0

100

200

300

400

AM

AX

(m

3/s

)

Water Year

0

1

2

3

4

5

6

7

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Nu

mb

er

of

AM

AX

O

ccu

ren

ces

March/April 1990

QMED – 191.8 m3/s

Q5 - 234.9 m3/s

Q25 - 306.4 m3/s

Q200 – 421.3 m3/s

Topographic Survey- Model Geometry 1D-2D Model Domain

Options Being Considered

• Option A - Do Nothing

• Option B1 - Remove waste material and leave void (car embankment)

• Option C1 – Complete removal or set back of embankments

• Option C1a – Target removal or set back of embankments

• Option D1 – Complete removal of hard bank reinforcement

• Option E1 – Option C1 + D1

• Also a number of combinations of each option

Options

Hydraulic Modelling (5, 25 & 200 year flows)

• Model was run for 5 year, 25 year & 200 year flows

– Base run - Existing channel, floodplain and embankment conditions

– Restoration scenarios

• Model Outputs

– mapped water extents, depth grids, velocity data and duration.

Hydraulic Conditions – Flood Map (Water Extents)

Habitat Morphology Relationships

Linking Geomorphology & Habitat Association Methodology

• The natural vegetation communities present across the River Dee floodplain west of Braemar were mapped using a Phase 1 Habitat Survey.

• In order to predict the changes in habitat likely under the proposed options the distribution of habitats was effectively calibrated against the hydraulic conditions being predicted across the floodplain.

Phase 1 Habitat Survey Maps

Phase 1 Habitat Survey Maps

Habitat Analysis

Description Habitat Area (m2) Perimeter (m) Patchiness

Woodland - Mixed - Semi-Natural A1.3.1 417,294 9,728 42.90

Grassland and Marsh - Marsh/Marshy Grassland B5 1,110,339 32,662 33.99

Heathland - Dry dwarf shrub heath - acid D1.1 391,423 18,950 20.66

Swamp , marginal and inundation - Swamp F1 7,370 656 11.23

Open Water - Standing Water - Oligotrophic G1.3 12,424 1,810 6.86

Open Water - Running Water - Oligotrophic G2.3 476,830 31,752 15.02

G1.3

G1.3

A.1.3.1

D1.1

D1.1

F1

B5

B5

Modelled Compared with Existing – B5 (5yr)

Return

Period

Minimum

Depth

Maximum

Depth

Minimum

Velocity

Maximum

Velocity

A1.3.1 5yr 0 0.3 0 0.25

B5 5yr 0 1.3 0 0.3

D1.1 5yr 0 0.4 0 0.6

F1 5yr 0 0.17 0 0.45

G1.3 5yr 0.300

1.100

0.400

1.700

0.000 1.500

G2.3 5yr 0.350 3.700 0.100 1.500

Optimal Parameters

• It became immediately clear that the present distribution of vegetation communities across the floodplain is far more limited than the hydraulic conditions would suggest. This may be attributed to a number of factors including:

– Intensive direct management of the floodplain vegetation (Vegetation

removal, planting etc.)

– Floodplain drainage

– Inter-specific competition between vegetation communities

– Unmeasured controlling variables

– Inaccuracies in the defined empirical hydraulic threshold values.

Map – B5 Existing & All Embankments Removed

Map – B5 Existing & Car Embankment Lowered

Map – B5 Existing & Target Embankment Removal

Community Coverage

• Implementation of any of the scenarios investigated within this study will potentially lead to an improved floodplain and in-channel vegetation community structure with community coverage and diversity increasing across all areas of the floodplain.

HabitatModelled - All

Removed

Modelled - Car

Embankment

Removed

Modelled - Targeted

Embankment

Removal

A1.3.1 1.15 0.90 1.10

B5 1.10 0.80 1.05

D1.1 0.42 1.05 1.04

F1 1.05 1.01 1.08

G1.3 1.14 0.90 0.96

G2.3 0.82 1.14 0.95

Note: Predicted Community divided by Modelled/Predicted Existing

Community Patchiness

HabitatModelled - All

Removed

Modelled - Car

Embankment

Removed

Modelled -

Targeted

Embankment

Removal

A1.3.13.39 3.83 3.60

B5 6.96 9.47 9.08

D1.1 6.21 6.50 6.10

F1 3.35 3.48 3.31

G1.3 2.85 3.35 3.37

G2.316.86 16.70 16.80

Note: Predicted Community Area / Predicted Community Perimeter

• Change in community patchiness and potential diversity predicted by the hydraulically linked ecological modelling was calculated by dividing predicted community perimeter by predicted community area.

Conclusions

• Hydraulic modelling is an ideal tool to facilitate an assessment of geomorphological & ecological assemblages linkages.

• During this study analysis indicated that overall the impact of selective breaching is much the same as for complete removal using the model assumptions.

– It is expected, however, that the improvements in community richness is

likely to be concentrated around breach locations and along activated

palaeo-features.

• Removal of the protection at the „car embankment‟ has the greatest impact on the floodplain with areas upstream being less responsive.

• Important to note limitations (managed floodplain & model does not predict morphological change).

Acknowledgements

• Thank you to the project steering group

• Project Team at JBA

– George Heritage, Nicola Buckley, Laura Hicks & Christopher Toop

Unravelling the complexities of fish habitat interactions for successful river rehabilitation

Michelle Smith, Ian Cowx and Tom CoulthardUniversity of Hull

Hull International Fisheries Institute, Department of Biological Sciences And

Department of Geography

Drivers:

• the European Union Water Framework Directive

2000/60/EC

• the Habitats Directive 92/43/EEC.

Pressure to protect and improve ecological status

and habitat and biodiversity under legislation:

Require improvement and maintenance of fish

habitat

Fish:•Abundance•Species composition•Age structure

Hydromorphology:•Water flow•Depth/width variation•Substrate structure•River morphology

Physical Habitat:

Understanding requirements of fish and factors that create, maintain and influence these habitats.

Fishery habitat requirements (simplified)

River specific factors

-geomorphology, water quality

- regulation practices

Distribution of riparian

and littoral habitat

types

Bottom fauna habitats

Fish feeding-feeding areas

-benthic fauna

- zooplankton

Young fish

- fry, juveniles

Fish stocks- recruitment

- mortality

- growth

Spawning- spawning areas

- eggs

- nursery areas

Aquatic vegetation

habitats

Bank specific factors, river

width & gradient, back waters,

water level & flow, lateral &

longitudinal connectivity

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Date

Dail

y m

ean

dis

ch

arg

e (

m3

s-1

)

Type 2 - Afon Ceirw, Maesmor

Channel maintenance floods

Habitat maintenance floods

Dis

charg

e

Time

Flow as a driving force:Depends upon connectivity

Hydromorphology = Habitat diversity = biodiversity?

Small scale erosion and

deposition

Large scale erosion and deposition

Migration freshets

“trigger” flows

Pressures:Weirs and Dams

River Don, Sheffield

Channelisation

River Lea

Drivers

Pressures

State

Impacts

Response

Rehabilitation Measures:Small scale weir removal

Addition of gravels

Channel narrowing

BUT

Are we getting it

right?

Rehabilitation of Rivers

•Lack of understanding can lead

to poor rehabilitation

‒Of fluvial processes

‒Of habitat requirements of

fish at different life stages

•Need for community approach

•Need to optimise habitat

•Reinstate natural fluvial

processes

•MonitoringBradshaw, 1978

Importance of monitoring fish populations and communities

Electric fishing surveysFish speciesFish lengthScale sample

Scale ageingAbundanceDensityComposition

Important to look at community not single species

Importance of monitoring Habitat conditions

•Flow velocity•Width•Depth•Substrate

•Discharge per unit width

•Froude number

•Width depth ratio

Population density

Fish length

Thresholds?

Conclusions (1)

• Need for improved understanding of relationships between flow, habitat and fish community dynamics

• Need for recognition that rivers and reaches of rivers behave differently

• Need for understanding of habitat at all scales

• Need for monitoring river rehabilitation projects

• Need for defined objectives for monitoring in river rehabilitation

• Dissemination of both positive and negative results

Macro scale: Whole catchment perspective

http://www.bbc.co.uk/scotland/education/int/geog/rivers/drainage/index.shtml

•Substrate•Vegetation•Flow velocity•Depth

Riffle

Pool

Meso scale:Interaction of channel processes

Channel morphology:•Pool•Riffle•Glide

Riffle

Pool

Micro scale:Smallest area influencing daily routine

Elliot

Conclusions (2)

• Need for improved understanding of relationships between flow, habitat and fish community dynamics

• Need for recognition that rivers and reaches of rivers behave differently

• Need for understanding of habitat at all scales

• Need for monitoring river rehabilitation projects

• Need for defined objectives for monitoring in river rehabilitation

• Dissemination of both positive and negative results

Next steps of Research

• Assess age structure within populations

• Post rehabilitation monitoring

• Compare differences between before and after studies

Acknowledgements

• HIFI staff, postdocs and postgrads

• Trent Rivers Trust

• Wild Trout Trust

• Environment Agency

• East Yorkshire Chalk Rivers Trust

• Cain Bioengineering

• Land owners

• Fishery owners