With thanks to: Thames Water Utilities Limited

RESTORATIONRESTORATION DESIGNDESIGN FORFOR REROUTEDREROUTED WATERCOURSESWATERCOURSES ProjectProject DesignDesign TeamTeam

Colin Thorne, Nick Clifford Gary Priestnall GIS and Mapping Philip Soar Channel Design Kieran Conlan, Steve Dangerfield Project Management Tom Coulthard Sediment Modelling Steve Dunthorne Hydraulics Jenny Mant River Restoration Nick Reynard

OverviewOverview 1. Project Context 2. Need to Reroute Watercourses 3. Watercourse Design Objectives 4. Design Elements and Tools 5. Design Outcome 6. Conclusions 1. Project Context „ Significant difficulties prediucted in supplying sufficient water in the Southeast over the next 25 years. „ A preferred solution is a an embanked reservoir. „ But, there are objectors who will challenge ever aspect during Planning Enquiries. 2. Need to Reroute Watercourses

3. Watercourse Design Objectives

CoreCore designdesign criteria:criteria: „„ FloodFlood storagestorage compensationcompensation „„ SurfaceSurface waterwater drainagedrainage andand conveyanceconveyance „„ MaintainMaintain sedimentsediment regimeregime „„ BiodiversityBiodiversity gainsgains KeyKey assessmentassessment criteria:criteria: „„ LocalLocal communitycommunity acceptabilityacceptability „„ MinimiseMinimise futurefuture maintenancemaintenance Land Drainage & Storage Design Objectives Constraints Existing e.g. gradients & topography

Climate Initial with-reservoir Watercourse routes, Initial design change flood modelling connections & flood compensation

Constraints e.g. land use & services Regime & hydraulic geometry analyses Initial watercourse & floodplain cross-sections, Amend design planform & slope

Field Sediment

sediment balancing RRC channel design monitoring (Copeland) guidance In-channel & riparian habitats & features CBS & FA Reference reaches (VISION) River Ock ecological baseline information

Review ‘with-reservoir’ flood modelling outputs Climate change

Post-EIA Detailed design of channel Long term sediment Post-project appraisal and & floodplain form and modelling (CAESAR) adaptive management habitats/features

Establish auditable, site- Detailed design of channel specific geomorphological crossings & stabilisation Input to final design success criteria structures (Inter-active CD-ROM) CatchmentCatchment BaselineBaseline SurveySurvey UnderlyingUnderlying GeologyGeology GeomorphicGeomorphic SusceptibilitySusceptibility FluvialFluvial AuditAudit ReferenceReference ReachesReaches

Meandering planform with cut banks Complex cross-sections and margins

Wood jams and complex flows Riparian corridor to trap and store silt RegimeRegime && HydraulicHydraulic GeometryGeometry AnalysisAnalysis RRCRRC experienceexperience withwith clayclay streamsstreams

““AboveAbove all,all, rememberremember thatthat whateverwhatever bankbank profileprofile youyou digdig willwill bebe therethere forfor aa longlong timetime andand thatthat rere--adjustmentadjustment cancan bebe aa veryvery slowslow River Wandle – as built (1998) processprocess””

WhatWhat youyou buildbuild isis whatwhat youyou get!get!

River Wandle – 8 years on (2006)

HydraulicHydraulic ModellingModelling && FloodFlood CompensationCompensation SedimentSediment MonitoringMonitoring SedimentSediment MonitoringMonitoring ResultsResults

Turbidity not simply related to No significant relationship between suspended sediment concentration suspended load and flow intensity

Gravel/sand bed smothered by Channels prone to siltation layer of silt-clay 0.1 to 0.8 m thick CopelandCopeland MethodMethod -- DesignDesign CurvesCurves

Depth

Top width

Bed width ClimateClimate ChangeChange PredictionsPredictions

Rainfall Average Discharges

Evapotranspiration Flow Duration LongtermLongterm SedimentSediment ModellingModelling

2050 -- with project

2050 – without project

2050 -- with project and climate change

5. Design Outcome WatercourseWatercourse DiversionDiversion DesignDesign TemplateTemplate 6. Conclusions

„ ProvidedProvided aa practicalpractical demonstrationdemonstration ofof thethe valuevalue ofof usingusing ofof multiplemultiple designdesign toolstools andand teamteam work.work. „ HighlightedHighlighted thethe challengeschallenges ofof riverriver restorationrestoration designdesign withwith tighttight budgetsbudgets andand timetime constraints.constraints. „ ProducedProduced aa designdesign templatetemplate thatthat meetsmeets thethe needsneeds ofof thethe clientclient ANDAND isis acceptableacceptable toto regulators.regulators. „ DemonstratesDemonstrates thethe valuevalue ofof interdisciplinaryinterdisciplinary collaboration.collaboration. „ DesignDesign matchesmatches formform toto function,function, providingproviding aa sustainablesustainable basisbasis forfor optimisationoptimisation ofof biodiversity.biodiversity.