Modelling catchment sediment transfer: future sediment delivery to the Carlisle urban area Tom Coulthard Jorge A. Ramirez Paul Bates Jeff Neal Blue, flood outline before, Red flood outline after.... Project Aims/Summary • To model sediment delivery from the Eden catchment and how this can affect flooding in Carlisle • Using CAESAR, to model morphological change in the Eden river catchment and Carlisle reach • Use different climate & discharge records to simulate impact of climate and land cover change • Transfer updated DTM to Bristol for hydraulic modelling What is CAESAR? • Catchment or Reach based cellular model • Models Morphological Change • Hydrological model – Adaptation of TOPMODEL • Hydraulic model – Simple 2d steady state flow model • Sediment transport – Bedload, 9 fractions using Wilcock & Crowe eqtn. – Suspended sediment, multiple fractions • Slope Processes – Slope failure (landslips) – Soil Creep Main Tasks • Two modelling tasks: – 1. Model sediment and water from catchments draining into Carlisle – 2. Model morphological changes in Carlisle reach 1. CAESAR catchment scale tasks • Produce sediment output for the Eden river at Carlisle – Existing climate – Climate scenarios – Land cover change Eden river sub-catchments Petteril 50m spatial resolution • 6 sub-catchments • Divisions coincide with flow gauges • Irthing Carlisle Caldew Lower Eden Upper Eden Eamont 25 Km Linking sub-catchments Carlisle Carlisle Deposition Erosion Discharge Sediment Initial conditions: grain size distribution • 40 sites visited • 173 photographs taken of sediment on channel edge Initial conditions: grain size distribution Photo analysis technique utilized to estimate individual grain sizes Finer Sediment 20% Adjusted grain size Grain size distributions distributions to add per all records catchment/reach unmeasurable small grain sizes ( < 0.3mm ) Initial conditions: grain size distribution Grain Size (mm) Proportion Size 1 .063 0.10 Size 2 .25 0.10 Size 3 1 0.12 Size 4 2 0.24 Size 5 4 0.21 Size 6 8 0.13 Size 7 16 0.06 Size 8 32 0.02 Size 9 128 0.02 Climate change: What we wanted to do... • Use UKCP09 weather generator to predict future rainfall • Use rainfall predictions as divers for the CAESAR morphological model • Generate sediment yields (and updated DEMs) for futures. Eamont Lower Eden Irthing Petteril Caldew 100000 200000 0 100000 Upper Eden 0 Cumulative rainfall, mm 200000 Climate 0 200,000 400,000 600,000 0 200,000 400,000 Time, hours 600,000 0 200,000 400,000 600,000 Catchment simulations • 75 year simulation • 13 years of hourly rainfall repeated and amplified by climate factor – 13 years chosen as only continuous period across all catchments/raingauges – Climate factor increased by 10, 20 and 30% • Record DEM’s and sediment outputs Eamont Lower Eden Irthing Caldew Petteril 1000000 0 1000000 Upper Eden 0 Cumulative sediment, m3 Catchment Sediment output 0 200,000 400,000 600,000 0 200,000 400,000 Time, hours 600,000 0 200,000 400,000 600,000 2. CAESAR reach scale tasks • Produce future bed elevations for the Eden reach at Carlisle: • Determine how this affects flood inundation 30000000 Hourly Discharge Caldew 11% Eden 10000000 20000000 Petteril 5% Caldew Petteril 0 Cumulative Discharge ( m3/sec) Water inputs 0 200,000 400,000 Time, hours 600,000 Eden 84% Lower Eden Petteril 1000000 Caldew 0 Cumulative sediment, m3 Sediment inputs 0 200,000 400,000 600,000 0 200,000 400,000 600,000 0 200,000 Time, hours Hourly lumped sediment 83% Eden 12% 5% Caldew Petteril 400,000 600,000 Changes in bed elevation Baseline +10% +20% +30% 6m(Erosion) -6m(Deposition) LISFLOOD-FP reference DTM • Model formulation with inertia (Bates et al., 2010) • 2D channel and floodplain. • Normal depth at boundary with slope 0.0006 mm-1 (Horritt et al., 2010) +30% Depth, m 11 0 Bed elevations affect on flood levels Baseline +20% +10% +30% ∆ max water depth, m 3 (more flooding) Difference in maximum water elevation (new – original) - 2 (less flooding) Previous trial runs (increasing sediment input) -50% Baseline +50% +100% 5m(Erosion) -6m(Deposition) Conclusions • Morphological changes in the channel can have profound influences on inundation levels – relative to changes in flooding caused by climate change? • Changes in flood level directly linked to erosion/deposition – Incision/aggradation alters conveyance • Changes in channel pattern (cutoff) have a fairly profound affect on inundation patterns • Relationship between discharge increase and changes in sediment yield is very site specific.. – Hard to apply a generic rule to all reaches Aggradation in urban areas..