to the Cumbria floods November 2009

lameubiquityMécanique

21 févr. 2014 (il y a 3 années et 8 mois)

71 vue(s)

Physical Science Research:

Geomorphological impact and fluvial system response
to the Cumbria floods November 2009

Jeff Warburton
, Danny Donoghue

(Durham University)

Andy Large, Andy Russell
(Newcastle University)

Stuart Dunning (Northumbria
University)

Structure:



Background


Current Research


Upland impacts


Lowland impacts


Mapping Change


Challenges

Background: Recent upland flood events

Shetland, Scotland September 2003

North York Moors, England June 2005

Northern England January 2005

Northern England October 2008

Valley erosion and deposits

Flood extent image, 23 June 2005

Rollei ARSF NERC digital camera

From: Watkins and Whyte (2008)


‘updated’

Cumbria floods


‘flood rich’ periods

Ouse Bridge
-

Largest flood on ‘record’

Dissection
& Gullying

Mass Movements
& debris flows

Sheet & Wash
Erosion

Suspended Load

Wind
Erosion

Slope Deposits

Stream Course &
Bank Erosion

Pipe erosion

Scar & Peat
Margin Erosion

Bedload

Channel Sediments

Lakes & Reservoirs

HILLSLOPE

CHANNEL

Streambank

Solute &
Flotation Load

storage

process

Background


contemporary sediment budgets

U
P
L
A
N
D

L
O
W
L
A
N
D

Objectives:

1.
Structured field inventory of the geomorphic
impact on the River
Derwent

river corridor

2.
Provide a rapid geomorphic assessment of
the role of scour and sedimentation in the
river

3.
Identify areas of risk for remobilisation of
flood
-
deposited sediments; delivery of
hillslope

sediments and hotspots of erosion

4.
Compare post
-
flood field
-
derived data with
pre
-
existing surveys to quantify/ areas of
greatest geomorphic change

5.
Work with stakeholders in designating
catchment zones that are ‘at risk’ from
erosion and sedimentation

Aim:
to examine flood impacts the whole river corridor of the river Derwent from the
headwaters
, through Bassenthwaite Lake to the Lowland agricultural/urban
catchment

Scale of river and catchment management

(Newson, 1992)


1.
Survey headwater impacts
-

Coledale
,
Newlands and
Borrowdale

areas


2.
Bassenthwaite

Lake
-

collect a series of short
cores and grab samples from the Lake and
compared with a survey undertaken in 2008.


3.
Lowland channel change in the floodplain
downstream of
Bassenthwaite

Lake
-

focussing on ‘typical’ reaches e.g.
Isel

and
Camerton
.


4.
Support field survey with low
-
level high
-
resolution aerial surveys carried out using a
UAV (Unmanned Aerial Vehicle)
-

provide
rapid repeat, high resolution aerial imagery
and Digital Elevation models of key sites (cf.
larger scale ARSF and EA remote sensing
data).

Plan of Research:


Upland Impacts

Seathwaite, Borrowdale 2009

Coledale, 2009

Goldscope Valley, Northern Lake District 2009

Mapping elements





Source area 1


Runout


Source area 2



Runout






Debris fan

Map and sediment
budget

Landslide erosion


518 m
3


Deposition


400 m
3


Sediment loss


118 m
3

Completed inventory of erosion / deposition Coledale flood 2008

Shallow
landslide

Landslide
deposition

Surface
wash

Sediment
deposition

Stream erosion

Stream deposition

Dam pond
deposition

Debris flow

Slope
undercutting

Fan deposition

Torrent erosion

Channel erosion

Debris flows

Landslides

Slope undercutting

Footpath wash

Delivery to main
fluvial system

Channel deposition

Debris flow fans

Landslide deposits

Slope wash deposit

Summary sediment budget (Coledale, 2008)

Values in t

817

183

195

102

7

189

933

92

97

7

14 %

Bassenthwaite Lake Coring and Sampling

Ouse Bridge & Herdwick Croft

Lowland Impacts

Ouse Bridge Gauging Station

Ouse Bridge

Isel Church

Sediment supply: landslides

Sediment supply: erosion of coarse gravel sediment

‘Hidden’ scour of river bed

New gravel bar: Downstream of Isel Hall

Downstream of A595 Bridge below Cockermouth

Flood debris

Sediment supply: localised scour around trees

Camerton

Sediment supply: erosion of river deposits

Sediment supply: localised bridge pier scour

Localised gouging and scour of cohesive flood plain sediment

Localised gouging and scour of cohesive flood plain sediment

Localised gouging and scour of cohesive flood plain sediment

Ground survey: ‘
Reach
-
based
’ assessments

Mapping flood limits

Mapping change


Airborne Remote Sensing

Downstream impacts
-

Workington

Papcastle

Future challenges / research problems?

1.
Assembling an evidence base

a)
Determining the sources of catchment sediment and linkages

b)
Assessing the role of lakes in flood routing and timing

c)
Investigate the impact of gravel management on flood impact

2.
Determining whether current problems are ‘natural’ or human
-
driven

3.
Recognising flood impacts are space and time specific

4.
Establishing the ‘whole catchment’ context

5.
Turning case studies into policy
-

impact