Management of dynamic navigation channels using video techniques (the Teignmouth case) Mark Davidson – University of Plymouth, UK Ismael Mariño-Tapia - University of Plymouth, UK The CoastView Project

Contents 1. Site description General (Location, economic activities, wave climate). Morphodynamics 2. Problem description 3. Video solution Frame of reference & CSIs 3.1. Video-derived buoy positions Algorithm (Methods) Validation of the technique Results 3.2. Video-derived dredging tracks and dredging intensity Algorithm Results 4. Conclusion

Site Description..(1) General Located in the coast of South Devon, UK. Fronted by 2km beach, to the south meets the Teign. Infrequent wind-generated wave climate from NE to S Protected from Atlantic swell Macrotidal conditions (STR ~4.2m) Economic activity Dock, port and harbour 13% of total economic activity

Site Description..(3) Morphodynamics (updated version of cycle)

Due to dynamic nature of sanbanks the channel entrance is allowed to move within limits. Dredging (ploughing) occurs at will to maintain channel entrance, it has proven difficult to maintain an effective dredging strategy. Difficult to position buoys adequately relative to channel & hazardous sandbanks Problem Description

“Improve navigation safety and avoid human, economical or ecological damage by minimizing the possibility of ships going aground” SBID should not exceed X m / Invade buffer region 1.CSI: Sandbar-Buoy Inter-distance (SBID) 4. Evaluation procedure Current SBID 3. Move buoys2. Benchmarking exceeded Video solution “To ensure that the buoys accurately mark the channel perimeter” “Preserve integrity of channel entrance by effective dredging operations”

“Improve navigation safety and avoid human, economical or ecological damage by minimizing the possibility of ships going aground” Video solution “Preserve integrity of channel entrance by effective dredging operations” Video-derived variable: Dredging intensity Change dredging strategy Benchmarking exceeded “Innapropriate” channel Current channel entrance location/depth Assess effects of dredging (CSI) Morphological evolution (including subtidal) Contribution of natural processes (model?)

Video-derived buoy positions Methodology (Algorithm) 1.Reduce the search area 2.Isolate red band 3.Detection of buoy 4. Transform oblique coordinates to planview (UV to XYZ tide )

Video-derived buoy positions Validation of the technique Buoy position measured in June 03 and 04 with total station (24 hrs). Errors: X-shore = 1 m (0.25 resolution); L-shore = 2 m (1 m resolution) 07:0013:0019: Cross-shore position (Argus x ) Measured Video-derived 07:0013:0019: Along-shore position (Argus y )

Video derived buoy positions Results (images) Images: Permit the identification of buoy position relative to dangerous sandbanks and present the displacement of buoy positions in 2D.

Video derived buoy positions Results (time series) Time series permit the identification of subtle trends related to natural drift of the buoy, and to assess the effects of individual events (storms and tides) on variability of the displacement.

Video derived buoy positions Defining benchmarks Sandbank-buoy interdistance (SBID) works as a safe CSI only if morphology below the reference isobath does not change substantially or has a constant slope.

Video derived buoy positions Defining benchmarks

Video-derived dredging tracks and intensity Algorithm (Mathematical morphology) Dredging track Submerged Sandbank 1.Convert to grey 2.Correct uneven illumination (tophat filtering) 3.Apply threshold 4.Label interconnected elements as individual objects 1.Identify objects in common (sandbanks) 2.Filter them out using image segmentation 3.Filter other noise sources not related to sandbanks (size, distance form centre of mass, etc).

Video-derived dredging tracks and intensity Results Location of the dredging tracks, the intertidal morphology and the presence of submerged sandbanks (breaking patterns). Regions where dredging effort is focused can be identified

Video-derived dredging tracks and intensity Results (example)

Concluding remarks: Navigation l Video-derived buoy positions l Determine the position of navigation buoys relative to hazardous sandbanks. l Track their movement towards a dangerous position. l Accuracy within 1 m in the cross-shore and 2 m in the longshore. l Benchmarking : SBID from -2 m ODN with safety margins in case of ‘step’ on sub tidal morphology.

Concluding remarks: Navigation l Video derived dredging intensity l Able to determine the position of dredging and the intensity (areas of focus) in relation to sandbanks. l Not able to assess the effects of dredging on its own. l Very useful video derived variable if used in conjunction with extra information.

Thanks for your attention