Optimised Complexity 2D Modelling

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Plan & Depth Animation – Levisham Reach  (2km x 30Ha Build 4)

2km 24 hr 25 cumec synthetic event; solved (to 5%) @ 120 x real-time;  animated @ 2000 x real-time

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Click to Zoom

Overview:  The 2km x 30ha Levisham reach is solved under high and low friction landuse. Background to the study site is here. Latest analysis is here. This exploratory modelling further tests methodology prior to 2D numerical analysis of 12km x 160ha (Pickering) and 27km x 450ha (R. Elwy) floodplains. Landuse strategy in more detail here.

Analysis Features

  • point-cloud (node) productivity goal is to resolve 30,000 nodes within real time
  • processing by non-specific (cpu) hardware (with core-to-core sync options);  some hydraulic/terrain features sampled to 8m
  • indicative catchment approach for adaptive decision making  (eg 20km2 @ 15nodes/ha)
  • open source 2D shallow water engine code assembled generically (‘offline’) in GIS and Excel
  • easy roughness adjustment for testing attenuation characteristics of both infra-structure and ‘agri-structure’ features
  • no specialist river modelling experience required; no 1D weir equations;  published for LFRM public interest

Finite (optimised) point management for finite element analysis (Build Strategy 1.4)

  1. GIS feature lines resampled as points within above productive point-cloud budget;
  2. Finite element computational mesh synchronised to terrain TIN for reduced complexity
  3. Discharge flumes with efficient boundary equations tested under end-to-end canalised flow;
  4. QT100 computational boundary from gradient viewsheds; main channel solution with and without floodplain
  5. Reach 1 capped under 1000 nodes to solve 24 hours in 10 minutes (1440 time-steps to 5% solution goal)
  6. Catchment end to end QT50 calibration at low (existing pasture)  friction
  7. Catchment model with high (imposed) friction run with imposed ‘agri-structure’ and infrastructure features

* * * * * * * * * * *

Water Depth Animation showing water depth hydrographs upstream [U] and downstream [D] of  friction zones assigned high [H] and low [L] roughness values. Red lozenges are indicative green storage gain upstream of frictional features

depth-anim9

Click for frame by frame interpretation

Interim conclusions for further models

  1. Smooth ‘risk-contour-buffer-line’ points at QT50 and perimeter QT100 (national archive) Flood Map
  2. Buffer and resampled bank-points at 5m rather than 8m (relative to channel centre line)
  3. Harden solution convergence to 1% (rather than 5%)

Further research focus

  1. METHODOLOGY TEST at Pickering Beck Study Site (c.12km x 160ha)
    • Extend 2km Levisham model to 12km discharging out of the model at Ropery Bridge gauge
    • Decrease average channel width whilst maintaining bank-line point density; increase point density of floodplain ‘risk-contour-lines’; increase c/line resample from 16m to 8m
    • Introduce high friction cross sections at 250m intervals and floodplain pinch-points to reduce/diffuse Ropery Bridge peak by 0.5m
    • Increase complexity: point cloud from 2400 to 10000 nodes (ie 15 nodes/ha to 60 nodes/ha)
  2. FRM SOLUTION from River Elwy Study Site (c. 27km x 450ha)
    • Progress ‘Pickering’ point cloud density to improve precision within horizon productivity goals (below); try 12000 – 24000 nodes (ie 25 nodes/Ha to 50 nodes/Ha)
    • relate high friction features (here, here; here; here) to Elwy site field by field.
    • Introduce high friction cross sections at 250m intervals and floodplain pinch-points to reduce/diffuse St Asaph bridge Q75 peak by 0.8m (ie reduce QT75 to QT25 levels)
  3. HORIZON GOALS
    • Stream real event models in real time to compare low friction and high friction floodplain performance; 15 min time steps to be solved in approximately 4 minutes (ie real-time x 4)..
    • .. ..
    • Johnson’s Creek Attenuation Model before conclusion of 2013-2015 EPSRC Blue-Green City research programme (built on Oregon foundations)

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Keywords: Agristructure, Pickering Beck; Flood; Slow_the_Flow; STF; Forestry; Attenuation

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