[Coral-List] response - measuring sedimentation on reefs.
MartinGA at Halcrow.com
Tue Mar 3 19:08:34 EST 2009
Response to measuring sedimentation on reefs.
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,
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>
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/>
Halcrow Sustaining and improving the quality of people's lives
P Please do not print this e-mail and attachments unless absolutely necessary
Visit our website at http://www.halcrow.com
The contents of this email are confidential, for the sole use
of the intended recipient at the email address to which it has
been addressed and do not give rise to any binding legal
obligation upon Halcrow companies unless subsequently confirmed
on headed business notepaper sent by fax, letter or as an email
attachment. Whilst reasonable care has been taken to avoid virus
transmission, no responsibility for viruses is taken and it is
your responsibility to carry out such checks as you feel
appropriate. Emails supplied are as found and there's no
guarantee that the messages contained within the body of the
email have not been edited after receipt. If you receive this
email in error, please contact the sender immediately and delete
the message from your system.
Halcrow Group Limited. Registered office: Vineyard House, 44 Brook Green
London, W6 7BY. Registered in England and Wales, Number 3415971.
More information about the Coral-List