[Coral-List] response - measuring sedimentation on reefs.

Martin, Alec MartinGA at Halcrow.com
Tue Mar 3 19:08:34 EST 2009

Response to measuring sedimentation on reefs.
Dear Leigh
A few ideas - by no means exhaustive but might help. 
In terms of sedimentation/ potential coastal construction impacts you will need to determine what you re trying to establish and why in order to formulate the methodology, and hence chose what to monitor. 
If you are merely wanting a record of rates of sedimentation/ scour you could use pegs/ stakes at reference locations which will enable you to measure the rate of sediment accumulation or scour at each peg/ stake over time. This is very straightforward but does require dive/ snorkel work. - box traps would achieve much the same. 
Alternatively you could use a buoyed (on bed/ or mid water) sedimentation measuring device - basically any graduated collector which will enable you to measure the amount of sediment settling in it over unit time and hence allow calculation of sedimentation rates - this will however not account for re-suspension etc, and hence may over calculate settlement in comparison to apparent rates in the sea bed. This method has the advantage of being possible to carry out from a boat without the need for diving etc.
If you are in fact wanting to actively manage and prevent impacts as opposed to just record them you might need to look at a combination of settlement rates, suspended sediment (TOSS) analysis, and turbidity measurements in real time - or indeed hindcast modelling. Any such activities will however be potentially more expensive, require specialist equipment and analysis - but can provide real time control for example of dredge spill impacts. 
In any case, it will be necessary to also determine a representative baseline control location(s) in order to provide a comparator site with similar current etc conditions but which is not affected by works - this may be difficult if there are numerous overlapping projects along the coast. 
The quantification of the 'extent to which a reef is affected' - i.e. the nature of the impact upon the viability of the reef receptors, their levels of stress, or sustainability indices, is however a complex field and it may prove very hard indeed to isolate the potential impacts of sedimentation within an overall complex system of environmental stresses. Data on the actual tolerances of different receptors is also a complex subject and it is a considerable exercise in order to attempt to make firm quantitative assessments of the magnitude of impact of different stressors such as sedimentation. 
There is however some literature data on what corals for example can and cannot tolerate in terms of accumulation/ unit time which may help as a guide.
I hope this is of some help, 
good luck,
Good morning,

I am trying to find information on best practices/methodologies or useful
lessons learnt for studies trying to measure sedimentation on reefs.  My
intention is the utilise the information to formulate an appropriate
methodology for carrying out an investigation to qualify/quantify the extent
to which a nearshore reef is affected by a nearby coastal construction

Thank you in advance,

leigh.weatherhead at gmail.com <mailto:coral-list%40coral.aoml.noaa.gov?Subject=Re:%20%5BCoral-List%5D%20Measuring%20sedimentation%20on%20reefs&In-Reply-To=%3C831799880902230811v4ee26864y34ddeb98c070cb56%40mail.gmail.com%3E> 
Alec Martin 
Principal Environmental Scientist, 
Technical Leader Environmental Water Quality, Environment 
Halcrow Group Ltd, Arndale House, Otley Road, LEEDS, LS6 2UL, UK 
tel: switchboard +44 (0) 113 2208220, mobile: + 44 (0) 7748761588 
fax: +44 (0) 113 2742924   email: martinga at halcrow.com           www.halcrow.com <http://www.halcrow.com/>  
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