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

Contents1. Site description General (Location, economic activities, wave climate). Morphodynamics

2. Problem description

3. Video solution Frame of reference & CSIs3.1. Video-derived buoy positions Algorithm (Methods) Validation of the technique Results3.2. Video-derived dredging tracks and dredging intensity AlgorithmResults

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 agroundVideo solution

Improve navigation safety and avoid human, economical or ecological damage by minimizing the possibility of ships going agroundVideo solution

Video-derived buoy positionsMethodology (Algorithm)Reduce the search areaIsolate red band Detection of buoy

4. Transform oblique coordinates to planview (UV to XYZtide)

Video-derived buoy positionsValidation of the techniqueBuoy 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)

Video derived buoy positionsResults (images)

Images: Permit the identification of buoy position relative to dangerous sandbanks and present the displacement of buoy positions in 2D.

Video derived buoy positionsResults (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 positionsDefining 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 positionsDefining benchmarks

Video-derived dredging tracks and intensityAlgorithm (Mathematical morphology)Dredging trackSubmerged SandbankConvert to greyCorrect uneven illumination (tophat filtering)Apply thresholdLabel interconnected elements as individual objects

Identify objects in common (sandbanks) Filter them out using image segmentationFilter other noise sources not related to sandbanks (size, distance form centre of mass, etc).

Video-derived dredging tracks and intensityResults

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 intensityResults (example)

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

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

Thanks for your attention

My name is Ismael Marino and I am from the University of Plymouth. I will be talking to you today about the development of CSIs at Teignmouth over the last 4 months focused on the management topics of Navigation and Recreation.

Teignmouth is a relatively small community located in the coast of South Devon, UK (Figure 1). It is fronted by a beach 2 km long facing ESE into the English Channel. To the south the beach meets the mouth of the small estuary (the Teign with 3.7 km square), and a prominent headland, the Ness, protrudes restricting the estuarys inlet.

The site is protected from the Atlantic swell and the local wave climate is dominated by infrequent periods of relatively small and short period wind-driven waves coming from the South and East quadrants. Teignmouth is subject to macrotidal conditions with semi-diurnal periods, mean Neap tidal range is 1.7 m and the mean Spring tidal range is 4.2 m. Tidal current speeds typically reach 2 ms-1 0.3 m above the bed, close to mid-flood and mid-ebb near the estuarys mouth.

The beach and the estuary support the main economic activities in the site, of which dock, port and harbour industry represented 13% of total economic activity by 1997 (Buck, 1997). Based on a qualitative analysis of the ARGUS database, and the beach surveys gathered during the COASTVIEW experiment, the Robinsons cycle has been updatedThe new cycle also contains three stages and maintains very similar characteristics with the offshore (North) sandbank moving onshore and attaching to the beach, but a substantial difference is the behaviour of the Ness sandbank, which is never observed to migrate NEwards (offshore), but in the opposite direction. The Ness sandbank tends to form offshore and migrate shoreward towards the Ness headland (at least 2 times). The cycle (shore atachment) can take from 12 to 28 months.Because of the dynamic nature of the sanbanks at the site, which move substantially on scales of months, the channel entrance is not stabilised and is allowed to move. Removing sand from system not worth?? (would not be necessarily approved from all interest groups.

Some human intervention exists in the form of dredging operations, but there is not much guidance as which is the optimum dredging strategy, hence to maintain the channel entrance has proven a difficult task.

Also, the moving sandbanks make difficult to position the channel marker buoys on a safe location. Due to this difficulties, in the past there have been a few cases of ship grounding on the site, luckily with no regrettable consequences so-far; you are familiar with this photo taken on 27 April 1999 of a ship stranded on the outer sandbars, and here is another more recent image of a ship stranded on Spratt sand on the 30 January this year.Not recognised as navigational buoys as they do not guarantee the marking of the channel positionThe video can provide information on the position of hazardous sandbanks, the location and movement of navigational buoys, and the location and intensity of the dredging operations. This information facilitates decision making and could be regarded as CSIs.

But, in order to provide an effective management procedure the CSIs need to be embebed in a frame of reference. Our strategic objective (overall aim) is to we accomplish this through 2 operational objectivesThe first one related to maintain the buoy positions on an appropriate position relative to the channel perimeter (partially revised in Bologna).And the second one related to aid the manager in maintaining an appropriate dredging strategy that keeps the integrity of the channel entrance. This two topics represent the main trust of the Teignmouth contribution of the paperand the presentation will focus on these two .

Regarding the Buoy position CSI, From the images we can extract the position of the buoys. If the SBID is exceeded either because the buoy has dragged or because the sandbank has moved, The buoys have to be moved .Images of dredging location and intensity relative to the sandbanks are not enough information to assess is the dredging strategy is adequate to maintain an appropriate channel in terms of location and depth, but it provides very useful information which combined with other sources such as could help on a detailed assessment of the effects of dredging on the morphology and helps decide if the dredging strategy is adequate. This assessment is not necessarily a CSI.1. The first step is to reduce the search area as much as possible but ensuring the area is large enough to accommodate the daily buoy movement (e.g. due to tidal currents). If the buoy is repositioned by the harbour master a new are might be needed.

2. The red band of the colour image is isolated and in this new image we apply the buoy detection algorithm by applying this formula. The algorithm compares the mean value of the an intensity profile I in the x direction with the minimum value of the intensity profile at that row. The row at which the maximum difference exists will be the row at which Imin represents the buoy position. The procedure is repeated in the vertical y direction and where the two methods coincide is where the buoy is assumed to be.Identification of the four buoys relativeand also can show us longer term variability of buoy displacement in 2D.The high-frequency oscillation is a result of the buoy moving back and forth on its mooring in response to the tide, the more radical changes in position related to the buoy being physically relocated by the coastal manager (e.g. end of January), and more subtle trends relate to the natural drift of the bouy (e.g. July to December). Identification of the four buoys relativeand also can show us longer term variability of buoy displacement.Identification of the four buoys relativeand also can show us longer term variability of buoy displacement.1. We noticed that the variance images showed a clear signal related to the track of the dredger. But also, this image shows the patterns of wave breaking over the shoals. On the other hand, the oblique timex images usually show the breaking patterns but not the dredging tracks, so the idea emerged to use the timex images to filter where the breaking patterns are.

2. The process starts by converting the images to gray scale, correct for uneven illumination using a morphological top-hat filter with a square structuring element of 20 pixels. Once illumination is even a global threshold technique is applied to convert the gray scale image to binary black and white. Interconnected elements of the binary image are labeled as individual objects.

Image segmentation divides the image into regions that correspond to the objects, as we already know which objects are sandbanks we can just eliminate them. Results show the location of the dredging tracks, the intertidal morphology and the presence of submerged sandbanks (breaking patterns). By overlaying dredging tracks, the regions where dredging effort is focused can be identified This is an attempt to assess the effects of dredging on the morphology by using the video derived variable that we can now produce. Two images on consecutive spring tides at about the same tidal level. In one we see a clear (big) sandbank and it seems from the images that two weeks after the sandbank dissapears. Waves (the main driver of sediment transport in the site) are very small and the only contribution for sand transport can come from tides.

If we plot the dredging effort for these two weeks, we can clearly identify the region where the dredging is focusing. The dredge is observed to pass over the sandbank, but its the sporadic presence over the sandbank casts doubts about its role on the dissapearance of the feature, some aspects to consider are:

We see dredge only for 10 min every hour it is possible that we are missing a substantial amount of information.

The sea level measured at the pier might not be the same as the sea level close to the inlet (point out differences). With the help of coastal video systems:System has been validatedWith the help of coastal video systems:System has been validatedWith the help of coastal video systems:System has been validated