Arun and Western Streams Catchment Flood Management Plan

25 Pages·2009·1.61 MB·English

Arun and Western Streams Catchment
Flood Management Plan
Summary Report December 2009
managing
flood risk
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Introduction
I am pleased to introduce our summary of the Arun
and Western Streams Catchment Flood
Management Plan (CFMP). This CFMP gives an
overview of the flood risk in the Arun and Western
Streams catchment and sets out our preferred plan
for sustainable flood risk management over the
next 50 to 100 years.
The Arun and Western StreamsCFMP isone of77 The Arun and Western StreamsCFMP hasa historyof
CFMPsfor England and Wales. Through the CFMPs, we fluvial, surface water, groundwater flooding and tidally
have assessed inland flood riskacrossallofEngland influenced flooding. Flood riskislocated in Arundel,
and Walesfor the firsttime. The CFMP considersall Littlehampton and Horsham.
typesofinland flooding, from rivers, groundwater,
We cannotreduce flood riskon our own, we will
surface water and tidalflooding, butnotflooding
therefore workcloselywith allour partnersto improve
directlyfrom the sea (coastalflooding), which is
the co-ordination offlood riskactivitiesand agree the
covered byShoreline ManagementPlans(SMPs). Our
mosteffective wayto managementflood riskin the
coverage ofsurface and groundwater ishowever
future. The keypartnerswe have worked with to carry
limited due to a lackofavailable information.
outthe actionsto reduce flood riskinclude Arun
The role ofCFMPsisto establish flood risk DistrictCouncil, Chichester DistrictCouncil, East
managementpolicieswhich willdeliver sustainable Hampshire DistrictCouncil, NaturalEngland,
flood riskmanagementfor the long term. Thisis Hampshire CountyCouncil, HavantBorough Council,
essentialifwe are to make the rightinvestment Horsham DistrictCouncil, Mole ValleyDistrictCouncil,
decisionsfor the future and to help prepare ourselves Southern Water, WaverleyBorough Council, West
effectivelyfor the impactofclimate change. We will SussexCountyCouncil.
use CFMPsto help ustargetour limited resources
Thisisa summaryofthe main CFMP document, ifyou
where the risksare greatest.
need to see the fulldocumentan electronicversion
ThisCFMP identifiesflood riskmanagementpoliciesto can be obtained byemailing
assistallkeydecision makersin the catchment. Itwas [email protected] alternatively
produced through a wide consultation and appraisal paper copiescan be viewed atanyofour officesin
process, however itisonlythe firststep towardsan Southern Region.
integrated approach to flood riskmanagement. Aswe
allworktogether to achieve our objectives, we must
monitor and listen to each othersprogress, discuss
whathasbeen achieved and consider where we may TobyWillison
need to review partsofthe CFMP. RegionalDirector, Southern Region
EnvironmentAgency Arun and Western StreamsCatchmentFlood ManagementPlan 3
Contents
The purpose ofa CFMP in managing flood risk 5
Catchmentoverview 6
Currentand future flood risk 8
Future direction for flood riskmanagement 11
Sub-areas
1 Rother Valley/Middle Arun/The Weald 13
2 Horsham 14
3 Petersfield and Midhurst 15
4 Pulborough 16
5 The South Downs(Eastand West) 17
6 CoastalPlainsand EastWittering 18
7 Lower River Arun 19
8 Manhood Peninsula and RuralChichester Harbour/20
Upper ChalkStreams
9 Chichester and Lower ChalkStreams 22
Map ofCFMP policies 24
4 EnvironmentAgency Arun and Western StreamsCatchmentFlood ManagementPlan
The purpose of a CFMP
in managing flood risk
CFMPshelp usto understand the • IDBs, water companiesand CFMPsaim to promote more
scale and extentofflooding now other utilitiesto help plan their sustainable approachesto managing
and in the future, and setpolicies activitiesin the wider context flood risk. The policiesidentified in
for managing flood riskwithin the ofthe catchment; the CFMP willbe delivered through a
catchment. CFMPsshould be used combination ofdifferentapproaches.
• Transportation planners;
to inform planning and decision Together with our partners, we
making bykeystakeholderssuch as: • Land owners, farmersand willimplementthese approaches
land managersthatmanage through a range ofdeliveryplans,
• The EnvironmentAgency, who will
and operate land for projectsand actions.
use the plan to guide decisions
agriculture, conservation
on investmentin further plans, The relationship between the CFMP,
and amenitypurposes;
projectsor actions; deliveryplans, strategies, projects
• The publicand businessesto and actionsisshown in figure 1.
• Regionalplanning bodiesand
enhance their understanding
localauthoritieswho can use the
offlood riskand how itwill
plan to inform spatialplanning
be managed.
activitiesand emergencyplanning;
Figure 1. The relationship between CFMPs, deliveryplans, projectsand actions.
Policy planning
•CFMPsand Shoreline ManagementPlans.
•Action plansdefine requirementfor delivery
plans, projectsand actions.
Policy delivery plans (see note) Projects and actions
•Influence spatialplanning to reduce risk •Make sure our spending deliversthe best
and restore floodplains. possible outcomes.
•Prepare for and manage floods •Focuson riskbased targets, for example
(including localflood warning plans). numbersofhouseholdsatrisk.
•Managing assets.
•Water levelmanagementplans.
•Land managementand habitatcreation.
Note: Some plansmaynotbe led byus– we may
•Surface water managementplans. identifythe need and encourage their development.
EnvironmentAgency Arun and Western StreamsCatchmentFlood ManagementPlan 5
Catchment overview
The river catchmentsofthisCFMP Although largelyrural, the area is The CFMP coversan area
lie mainlyin the WestSussex home to approximately300,000 approximately1400km2 drained by
DistrictsofChichester, Arun and people, with urban centresincluding the River Arun and itstributarythe
Horsham, together with smallparts Littlehampton, Chichester, Bognor Rother, together with the
ofEastHampshire and ofthe Regisand Arundelon the coastal catchmentsofseveralsmaller
Waverleyand Mole Valleyin Surrey. plain, and Petersfield, Midhurst, streamsto the westofthe River
Pulborough and Horsham to the Arun thatdischarge directlyinto
The landscape variesfrom the hills
north ofthe South Downs. Chichester Harbour. These include
and steep scarp slopesofthe South
the Aldingbourne Rife; the Rifes
Downs, to the gentlyrolling hillsof Much ofthe area isrecognised for
surrounding Selseyand East
the Low Weald and the wide Arun itsenvironmentaland cultural
Wittering; the River Lavant, the
valleyflood plain south of value, with the South Downsbeing
Bosham Stream and the River Ems.
Pulborough. Flow characteristicsof an Area ofOutstanding Natural
the riversvarycorrespondingly, with Beauty(AONB) and a proposed Mostwatercourseshave been
fastflowing streamsemerging from NationalPark. heavilymodified over the years, for
the High Weald area to the north, example the land beside the middle
There are manyvaluable natural
flowing into the low-lying coastal reachesofthe Arun and Rother was
habitatsin the area, such asthe
plain where the gradientislessand drained to provide fertile
Arun Valleysouth ofPulborough,
the river flowsare much slower. agriculturalland from the original
which contain spring fed floodplain
marshesand the lower reachesof
Tidalinfluence affectsthe character marshesand wetlandsdesignated
the Arun were trained and dredged
ofthe lower partsofthe River Arun bynational, internationaland
for navigation. In Roman timesthe
and extendsto above Pulborough. European conservation law.
River Lavantwasdiverted through
Chichester to provide water.
➜AmberleyWildbrooks– partofthe Arun
ValleySPA and Ramsar site.
6 EnvironmentAgency Arun and Western StreamsCatchmentFlood ManagementPlan
Map 1. Overview ofArun and Western StreamsCFMP.
‘The CFMP covers a large catchment drained by the
River Arun and its tributary the Rother, together with
the catchments of several smaller streams to the west
of the River Arun that discharge directly into
Chichester Harbour.’
EnvironmentAgency Arun and Western StreamsCatchmentFlood ManagementPlan 7
Current and future flood risk
Overview of the current flood risk Where is the risk?
Flood riskisthe combination ofthe Notable flood eventshave occurred The map on page 10 illustratesthe
probabilityofflooding and itsimpact, seven timesin the last40 years, consequencesofa 1% annual
thatis, the chance ofithappening with the mostseriousbeing in probabilityevent(1 in a 100 year)
and the consequencesifitdoes December 1993 when over 200 occurring within the CFMP area.
happen. We have assessed flood propertieswere flooded acrossthe
The areaswith the highest
riskacrossthe CFMP area using catchment, and in Autumn 2000
concentration ofpropertiesatrisk
broad-scale computer modelling, when over 150 housesflooded.
from river flooding are tabulated
though making bestuse ofexisting
Flood riskislikelyto increase in the opposite:
knowledge and modelswhere
future, asclimate change increases
appropriate. Flood riskfigurestake
the magnitude and frequencyof
into accountcurrentflood defences.
flood events. We expectwintersto
The Arun and Western Streams be wetter and for heavyrainfallto
CFMP area hasa historyoffluvial, become more common.
surface water, groundwater flooding
and tidallyinfluenced flooding.
➜ River Arun floodplain atPulborough.
8 EnvironmentAgency Arun and Western StreamsCatchmentFlood ManagementPlan
How we currently Table 1. Locationsoftownsand villageswith 25 or more propertiesatrisk
in a 1% annualprobabilityriver flood.
manage the risk
Number ofpropertiesatrisk Locations
Our activityisprioritised on a risk
basis. Our main activitiesinclude: >1000 None
• The maintenance ofexisting and
500 to 1000 Lower River Arun (Arundeland
the construction ofnew and
Littlehampton)
replacementflood defencesor
structures.Examplesinclude the
100 to 500 Manhood Peninsula and Chichester
flood alleviation scheme on the
Harbour, Lower ChalkStreams
Lavant. The scheme is
implemented before flooding, as
50 to 100 Weald, Horsham, Bognor Regis
we monitor the groundwater
levelsfrom the River Lavant
25 to 50 Pulborough
around Chichester.
• Flood forecasting and warnings.
• Developmentcontrolto influence Table 2. Criticalinfrastructure atrisk:
spatialplanning so thatnew
developmentsare sited away 2 emergencyservices, 6 schools, 4 sewage/water treatmentworks,
from flood riskareas, or take 9 electricitysub stations, 4 hospital/clinics
appropriate mitigation measures.
• Flood riskmapping.
Table 3. Designated sitesatrisk:
• Strategicplanning to plan long
term investment.
Arun ValleySPA and RAMSAR, The MensSAC
• Environmentalimprovements.
Figure 2. Currentand future (2100) flood riskto propertyfrom a 1% annual
probabilityriver flood, taking into accountcurrentflood defences.
1100 Current Future
1000
sk 900
od ri 800
o
at fl 700
es 600
perti 500
o
of pr 400
er 300
b
m
u 200
N
100
0
Horsham Bognor Regis Arundel and Manhood Chichester/
Littlehampton Peninsula/ Lower Chalk
Chichester Streams
EnvironmentAgency Arun and Western StreamsCatchmentFlood ManagementPlan 9
Map 2. Flood riskto propertyin a 1% annualprobabilityriver flood, taking into accountcurrentflood defences.
The impact of climate change and future flood risk
The effectthatflooding willhave in respectto land use, due to economic tide-locking eventscaused bysea
the future isinfluenced bya range of pressures, partsofthe Rother valley levelrise. Our appraisalofthe future
issuessuch asclimate change, are currentlyintensivelyfarmed which riskin the catchmentrevealsthe
changesin land use such as due to localconditionsmayresultin number ofpropertiesatriskto the 1%
development, and changesin how more rapid run-offand soilerosion. annualprobabilityeventwillincrease
land ismanaged. These conditionsare unlikelyto be from 1576 to 3066 propertiesby
replicated elsewhere in the catchment the year 2100. The majorityofthese
Predictionsoffuture change are
so we have, therefore, onlylooked propertiesare located in Arundel,
based on understanding the existing
atmore intensive land use asa Littlehampton, Bognor Regis,
condition ofthe catchment, an
componentofour future scenario for Horsham, Bosham and Westbourne.
extrapolation oftrendsover the long
the River Rother. There isan increase
term (up to 100 years), and a high The keytrendsare:
of17% in flowsin thispartofthe
levelreview oflikelyfuture change
catchment. The scenario which has • More frequentand intense storms
based on research findingsand
the greatesteffecton future flood causing more widespread and
knowledge. Within the Arun
riskisclimate change with up to 20% regular flooding from drainage
catchment, the predicted increase in
increase in peakflood flows. This systemsand some rivers.
urban developmentrelative to the
scenario isused to assesslikely • More rain in winter, increasing
catchmentarea isrelativelysmalland,
impactsin the catchment. In the Arun the likelihood oflarge scale
asa result, the impacton flooding at
catchmentthe future flood riskis flood events.
the catchmentscale issmall. With
likelyto be from river flooding and
10 EnvironmentAgency Arun and Western StreamsCatchmentFlood ManagementPlan