Show simple item record  

dc.contributor.authorHuisman, Christien E.
dc.contributor.authorBryan, Karin R.
dc.contributor.authorCoco, Giovanni
dc.contributor.authorRuessink, B.G.
dc.date.accessioned2011-08-30T22:27:39Z
dc.date.available2011-08-30T22:27:39Z
dc.date.issued2011
dc.identifier.citationHuisman, C.E., Bryan, K.R., Coco, G. & Ruessink, B.G. (2011). The use of video imagery to analyse groundwater and shoreline dynamics on a dissipative beach. Continental Shelf Research, available online 3 August 2011.en_NZ
dc.identifier.urihttps://hdl.handle.net/10289/5654
dc.description.abstractGroundwater seepage is known to influence beach erosion and accretion processes. However, field measurements of the variation of the groundwater seepage line (GWSL) and the vertical elevation difference between the GWSL and the shoreline are limited. We developed a methodology to extract the temporal variability of the shoreline and the wet-dry boundary using video imagery, with the overarching aim to examine elevation differences between the wet-dry boundary and the shoreline position in relation to rainfall and wave characteristics, during a tidal cycle. The wet-dry boundary was detected from 10-minute time-averaged images collected at Ngaranui Beach, Raglan, New Zealand. An algorithm discriminated between the dry and wet cells using a threshold related to the maximum of the red, green and blue intensities in Hue-Saturation-Value. Field measurements showed this corresponded to the location where the watertable was within 2 cm of the beachface surface. Timestacks, time series of pixels extracted from cross-shore transects in the video imagery, were used to determine the location of the shoreline by manually digitizing the maximum run-up and minimum run-down location for each swash cycle, and averaging the result. In our test data set of 14 days covering a range of wave and rainfall conditions, we found 6 days when the elevation difference between the wet-dry boundary and the shoreline remained approximately constant during the tidal cycle. For these days, the wet-dry boundary corresponded to the upper limit of the swash zone. On the other 8 days, the wet-dry boundary and the shoreline decoupled with falling tide, leading to elevation differences of up to 2.5 m at low tide. Elevation differences between the GWSL and the shoreline at low-tide were particularly large when the cumulative rainfall in the preceding month was greater than 200 mm. This research shows that the wet-dry boundary (such as often used in video shoreline-finding algorithms) is related to groundwater seepage on low-sloped, medium to fine sand beaches such as Ngaranui Beach (mean grain size~0.27 mm, beach slope ~1:70) and may not be a good indicator of the position of the shoreline.en_NZ
dc.format.mimetypeapplication/pdf
dc.language.isoen
dc.publisherElsevieren_NZ
dc.relation.urihttp://www.sciencedirect.com/science/article/pii/S0278434311002640en_NZ
dc.rightsThis is an author’s accepted version of an article published in the journal: Continental Shelf Research. © 2011 Elsevier. Used with permission.
dc.subjectbeach groundwateren_NZ
dc.subjectgroundwater seepageen_NZ
dc.subjectvideo imageryen_NZ
dc.subjectvideo imageryen_NZ
dc.subjectshoreline detectionen_NZ
dc.titleThe use of video imagery to analyse groundwater and shoreline dynamics on a dissipative beachen_NZ
dc.typeJournal Articleen_NZ
dc.identifier.doi10.1016/j.csr.2011.07.013en_NZ
dc.relation.isPartOfContinental Shelf Researchen_NZ
pubs.begin-page1728en_NZ
pubs.elements-id36453
pubs.end-page1738en_NZ
pubs.issue16en_NZ
pubs.volume31en_NZ


Files in this item

This item appears in the following Collection(s)

Show simple item record