Draft review on
Fate of dredge material and Environmental Partitioning
Download 0.86 Mb.
|
Fate of dredge material and Environmental PartitioningOnce a dredge occurs, sediment is transported and degraded according to numerous physical, chemical, and biological processes. The sediment characteristics (e.g. composition and size) will determine its environmental fate. Moreover, other factors such as location of the deposition and weather conditions (e.g. temperature, wind speed) will impact the distribution and fate of sediments. The general factors involved in the transport, distribution, and the fate of deposited sediments that may occur at the deposition site in the application are described below. There are two major facets to sediment fate during dredging and depostion. The first is the production of a sediment plume in the region where dredging activities are occurring. Depending on the dredging technique being used, a plume of sediments is generated which may spread depending on local currents. This plume can be restricted to an area as small <100 hundred metres to an area in excess of several hundred, depending on dredging physical parameters of dredged sediments, dredging techniques and currents. These sediments will eventually settle, proximity to site of dredging dependent on particulate size and local current regimes (e.g. tidal v. unidirectional). Currents may eventually return these sediments to their origin (Bray 2008; Wasserman et al. 2013). Dredging at the MOF is expected to occur using a clamshell dredge, which typically releases up to 1% of sediment due to bottom wake (disturbance of the sediment-water interface) from: capturing sediment in the clamshell bucket; release during closing; loss of sediments from the shovel while rising through the water column; draining during slewing and washing from descent through the water column; and debris captured in the dredge (Schroeder and Ziegler 2004). About half of the sediment release occurs at the bottom 5 m of the water column (Hayes et al. 2007). Dredging at the MOF and disposal of dredged material at Brown Passage will result in resuspension of marine sediment and potential for dispersal of contaminants from sediment. Dredging at the marine berths during construction will removing approximately 7 million m3 of sediment, which is expected to be of somewhat similar chemical composition to sediment found in the MOF. Dredging is expected to occur using a cutter-suction dredge, which has similar sediment release rates to a clamshell dredge. The second facet of sediment fate in dredging operations occurs when the sediments are deposited into the receiving environment. Three types of aquatic placement exist; unconfined, semi-confined and confined. The first will be explored further as it remains the most common due to ease and cost (Bray 2008) and is to be used in the application by Canpotex. 
Figure 2. Unconfined, semi-confined and confined aquatic placement (Adpated from Bray et al. 1997). A: unconfined (unrestricted aquatic placement; B and C: Semi-confined aquatic placement (with lateral containment); D to F: confined (contained) aquatic placement. Directory: wp-content -> uploads uploads -> 587 Return function, r i(X) r i(0) r i(1) r i(2) r i(3) 1 0 2 4 6 Thermal Station, I 2 0 1 5 6 3 0 3 5 6 10 uploads -> The Case Against the nypd’s Quota-Driven ‘Broken Windows’ Policing What Is It? uploads -> For want of a nail uploads -> Police Militarization uploads -> Stop Militarizing Law Enforcement Act of 2014 uploads -> 2017 afoCo Landmark Scholarship Program uploads -> Instructions for the Preparation of Camera-Ready Contributions to the Conference Proceedings uploads -> Medical Radiography Program uploads -> Ihbb asian Championships 2014 middle school bowl Round 4 First Quarter uploads -> Ihbb european Championships 2014 Bowl Round 4 First Quarter Download 0.86 Mb. Share with your friends:
|