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 SSSI ± SPA SAC • Cairngorm National Park Study Area Cairngorms SAC & SPA • National Trust for Scotland Eastern Cairngorms SSSI • Dee Fisheries Morrone Birkwood SAC & SSSI River Dee SAC • Estates Cairngorms SPA 0 0.5 1 2 Contains Ordnance Survey data © Crown copyright Kilometers and database right 2010 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 March/April 1990 7 400 6 /s) 300 3 3 5 200 QMED – 191.8 m /s 4 100 3 3 Q5 - 234.9 m /s 0 3 2 Q25 - 306.4 m /s AMAX (m AMAX Occurences 1 Q200 – 421.3 m3/s Number of AMAX Number of AMAX 0 Jul Oct Apr Jan Jun Mar Feb Aug Sep Nov Dec May Water Year 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 B5 A.1.3.1 F1 G1.3 D1.1 B5 D1.1 Modelled Compared with Existing – B5 (5yr) Return Minimum Maximum Minimum Maximum Period Depth Depth Velocity 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 0.400 0.000 1.500 1.100 1.700 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. Modelled - Car Modelled - Targeted Modelled - All Habitat Embankment Embankment Removed Removed 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 • 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. Modelled - Modelled - Car Modelled - All Targeted Habitat Embankment Removed Embankment Removed Removal A1.3.1 3.39 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 G2.3 16.86 16.70 16.80 Note: Predicted Community Area / Predicted Community Perimeter 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 Coulthard University of Hull Hull International Fisheries Institute, Department of Biological Sciences And Department of Geography Drivers: Pressure to protect and improve ecological status and habitat and biodiversity under legislation: • the European Union Water Framework Directive 2000/60/EC • the Habitats Directive 92/43/EEC. Require improvement and maintenance of fish habitat Physical Habitat: Understanding requirements of fish and factors that create, maintain and influence these habitats. Hydromorphology: •Water flow •Depth/width variation •Substrate structure •River morphology Fish: •Abundance •Species composition •Age structure Fishery habitat requirements (simplified) River specific factors -geomorphology, water quality - regulation practices Bank specific factors, river Distribution of riparian width & gradient, back waters, and littoral habitat types water level & flow, lateral & longitudinal connectivity Bottom fauna habitats Aquatic vegetation habitats Fish feeding -feeding areas Young fish Spawning -benthic fauna - fry, juveniles - spawning areas - zooplankton - eggs Fish stocks - nursery areas - recruitment - mortality - growth Depends Depends force: a driving as Flow Discharge upon connectivity upon Hydromorphology Channel maintenance Channel Time Large scaleerosion anddeposition = Habitat diversity = biodiversity diversity = Habitat 25 Type 2 - Afon Ceirw, Maesmor 20 Habitat maintenance Habitat floods 15 10 deposition scaleerosionSmall and 5 “trigger” flows “trigger” freshets Migration Dailymean discharge (m3s-1) ? 0 floods 01/01/1991 01/02/1991 01/03/1991 01/04/1991 01/05/1991 01/06/1991 01/07/1991 01/08/1991 01/09/1991 01/10/1991 01/11/1991 01/12/1991 01/01/1992 01/02/1992 01/03/1992 01/04/1992 01/05/1992 01/06/1992 01/07/1992 01/08/1992 01/09/1992 01/10/1992 01/11/1992 01/12/1992 Date 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 •Monitoring Bradshaw, 1978 Importance of monitoring fish populations and communities Electric fishing surveys Fish species Fish length Scale sample Scale ageing Abundance Density Composition 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