Initial

The construction of the Palm Islands and The World was immediately felt by the surrounding ecosystem. Sand dredging and depositing resulted in the burial, death, and asphyxiation of a variety of wildlife. In addition, the project has resulted in increased fine sediment suspension in the waters off the coast of Dubai. Such sediment suspension allows less light to filter to the sea floor, and can suffocate and endanger the health of marine life in the area.
  
Dredging and Beach Nourishment/Development
   
Beach nourishment/development refers to the process used to either add to an existing beach, or, as is the case with the Palm Islands, to build an entirely new beach. Dredging is the process by which sand is collected, or dredged, from one location, usually the intertidal zone, and deposited on the existing beach. Beach nourishment is especially common along the U.S. Atlantic coast, where areas such as the Outer Banks in North Carolina have valuable stakes in the condition of their coastlines. With much development and tourism concentrated in such areas which are particularly vulnerable to coastal erosion and storm-based changes, beach nourishment represents an important and strategic means of "protecting" coastal economic interests.

  
     
The Dredging Process:

Sand for the Palm Islands was dredged form the sea floor in the Persian Gulf near the islands, and transported via a "rainbowing" process (shooting the sediment in an arch to the islands' location) to build the actual island. Hopper and cutter dredges were used for the dredging process. Cutter dredges draw sediment (sand, gravel, etc.) from the seafloor via a rotating cutter and centrifugal pump which turn the sediment mixture into slurry. A network of floating and submerged pipes then transports the water to the nourishment site. Cutters work well in situations when the sediment being extracted is particularly compact. (Greene 2002) Hopper dredges suctions layers from the seafloor using a hydraulic pump, then transports the material to the site through a pipe system. Water is drained out of the original sediment, so the slurry produced by a cutter dredge is avoided. Various machinery, namely bulldozers, are then used to shape the beach and disperse the imported sediment. (Greene 2002)

One of the primary initial effects of nourishment, both at the mine and nourishment sits, and along the piping in between, is the suspension of fine silt and clay sediments in the surrounding waters. Since fine sediments stirred up by the dredging process take longer to settle, they remain suspended in the water for longer periods of time. Nakheel also failed to use silt screens while dredging in order to keep turbidity low at the dredge sites (Salahuddin 2006). These finer sediments often result in the asphyxiation of fish and benthic fauna, such as crustaceans and echinoderms, as they become l
odged in gills and lungs of organisms while they are breathing. Studies in the U.S. have shown that sediment from turbid environments have also inhibited filter feeders such as clams and crabs by decreasing their food intake by 30-40.5%. Many species are also simply suffocated by the mere shifting of sediment during the mining process, or are killed from being sucked into the hoppers themselves. As benthic organisms serve as a major food source for a variety of marine animals, a decrease in their population also has adverse effects on all upper levels of their food chain. In addition, an increased level of particles in the water can "reduce growth and increase calcification rates in coral reefs" (Greene 2002), threatening those reefs that may have survived the initial development. A study in Miami showed that fourteen years after a nourishment event, coral heads were sill dying. (Greene 2002)

Susp
ended sediments in both sites can also prevent sufficient sunlight from reaching the lower depths of water; as species die off, decomposed organic materials can increase hydrogen sulfide levels in the water, making it toxic. It is often impossible for an ecosystem to revive after such an event, and in the rare cases where recovery has occurred, the time needed was over a year. In past U.S. dredging situations where such toxification did not occur, and when conditions were more favorable towards species re-growth, it has typically taken around a year for the ecosystem of the mine site to re-equilibrate itself. In general, biomass takes at least 1.5 years and up to 2.5 years to recover itself. Other effects from suspended sediment include decreased visibility, making it more difficult for organisms to locate prey, as well as changes in the chemistry of the water affected. As disturbed particles settle on the ocean floor, they can inhibit the functioning of bottom feeders, kill mi
cro-plants, and inhibit the spawning and hatching of various types of fish. It is also very common for fine sediments to become re-suspended multiple times during the years following
development as they settle on the very top layer of the seabed.



The settling of suspended sediment is dependent on four main factors:

    "1) wave energy (more turbid during storms)

    2) amount of sand placed on the beach (more sand may increase turbidity)

    3) the quality of the sand (higher content of silt/clay caused elevated levels)

    4)the mode of placement (i.e., hydraulic pipeline or barge pump-out)"

   (Greene 2002)



Benthic recovery in dredged areas in the U.S. has been found to be dependent on a number of factors inc
luding "1) duration and timing of dredging; 2) the type of dredging equipment used to extract the sediment; 3) sediment composition of the mine site; 4) amount of sand removed from the site; 5) the fauna present in the mine pit and surrounding area prior to dredging a
nd their ability to adapt to change; 6) characteristics of the new sediment interface; 7) life history characteristics of fauna that recolonize; 8) water quality at the site; 9) hydrodynamics of the mine pit and surrounding area; and 10) degree of sedimentation that occurs following dredging [. . .] In general, it appears that areas where biological impacts are greatest and most prolonged, are areas where bottom sediment composition has been altered" (Greene 2002)

The effects of dredging on fish are more varied. It is often difficult to measure effects of such development on fish species since they are always in motion, and because initial turbidity can decrease on a timescale from hours to days (though there have been cases studied in which turbidity remained and inhibited visibility up to seven years following initial development - Greene 2002). In some instances, however, the nutrients churned up by the mining process have shown to increase the abundance of various species of fish; in others, while fish have left during the initial period of disturbance, they have eventually returned; in yet third instances, native fish species have left the area while new species moved in. Various sources cite the difficulty of measuring the impact on fish given the tendency of fish to naturally move from place to place. In fact, the greatest effects to fish species can be found in those that prey on benthic organisms, which are most sensitive to the initial mining process.

The effects on marine mammals are more direct, and often result either from
the disruption of feeding grounds, or direct collisions with the boats or dredging equipment, as has been the case with sea turtles in the United States. Lighting used by the boats can also confuse sea turtle hatchlings, or throw off other marine mammals and predatory fish, especially at night. Still, some species, such as Pacific Salmon, can benefit from increased turbidity, as they become less visible to predators.

Local diving associations in the area near Palm Jumeirah also reported that a slimy grey cement-like substance had been found on the beaches near Palm Jumeirah following the construction of the island. Sources later confirmed that the sediment was caused by the deep-sea mining of sediment for the islands. (Salahuddin 2006)


Microclimate Effects of Buildings in Dubai

So far effects on the macroclimate have been addressed, but what about the effects on the localized climate conditions within an urban area - its microclimate? 

Background of Dubai's Climate:

Dubai is located on the southern end of the Gulf. Its climactic cycle can be divided into three periods, (December to March) which has mild weather and temperatures of 20-23 C, (November to April) which has warm weather and temperatures of 25-26 C and (May to October) which has hot weather and temperatures of 29 to 34 C. The first two periods are relatively comfortable if it is well-shaded and there are continuous breezes from the Gulf. The hot period is more burdensome because of the high incidence of solar radiation, humidity, and limited evaporative cooling. Yet, there is relief from nocturnal radiative cooling which happens year-round and winds traveling at velocities 4.0m/s (Thapar & Yannas, 2007).

Microclimate Effects of Buildings:

There are three types of structures being built in Dubai: high skyscrapers, mid-rise blocks, and low-rise compact courtyard structures. Each has different shading effects on the ground. Below is a diagram illustrating exactly those effects of the different types of structures with the same volumes. Courtyard structures and more dense developments provide better shading for streets and people. However, future plans are gearing toward the development of high-rise buildings because of advantages such as privacy, exclusivity and views.                                                                  

                                       



Top Left Corner: High-rise building  

Top Right Corner: Mid-rise building

Low-rise, Courtyard Building

                                                                                                             

             






There was a study done on the effects of different built forms on ambient temperature and airflow. The results revealed that during the daytime, the low-rise courtyard form left a larger microclimatic footprint because more of its mass was constructed closer to the ground. In terms of temperature, the courtyard was coolest out of all the structures and the open courtyard being the absolute coolest. However, because of the obstruction of airflow in courtyard forms, courtyards had the lowest wind speeds, and as a result, were warmer in the areas where there was less wind movement (east-west as opposed to north-south) (Thapar & Yannas, 2007).


Envi-met predictions of air temperatures for 2:00pm on a July day around a constant built volume on a 100x100m site. First picture on the left represents a high-rise building, second, mid-rise, and last, courtyard blocks.

The conclusions to this study include that built forms of any kind should strive to incorporate well-shaded and ventilated spaces. Water can help provide cooling, although humidity is still a challenge. Vegetation can also help with cooling and increase the market value of property, but humidity and the high-cost of maintenance may pose challenges. Shading, permeability to airflow for convective cooling and the employment of right construction materials are indispensable for sustainable urban designing. (Thapar & Yannas, 2007)


WORKS CITED

Greene K. 2002. Beach Nourishment: A Review of the Biological and Physical Impacts. Atlantic States Marine Fisheries Commission. ASMFC Habitat Management Series #7. Available from: http://www.asmfc.org/publications/habitat/beachNourishment.pdf

Salahuddin B. 2006. The Marine Environmental Impacts of Artificial Island Construction, Dubai, UAE [dissertation]. [Durham (NC)]: Duke University. p. 1-96.

Thapar H, Yannas S. 2008. 491: Microclimate and Urban Form in Dubai. Architectural Association School of Architecture. PLEA 2008 -- 25th Conference on Passive and Low Energy Architecture; 2008 Oct 22-24; Dublin.

IMAGES CITED

DREDGING PICS

A Spectacular Sight. 9 June 2009. Havant Borough Council. Web. 4 Dec. 2009. <http://images.google.com/imgres?imgurl=http://www.havant.gov.uk/images/Rainbowing%2520cover%2520image_colour1.JPG&imgrefurl=http://www.havant.gov.uk/havant-8340&usg=__HXGJ8DmOl8VtDtM5zIfP3odmfFo=&h=521&w=770&sz=74&hl=en&start=2&tbnid=tQPymQuoWRAUIM:&tbnh=96&tbnw=142&prev=/images%3Fq%3Dbeach%2Bnourishment%2Brainbowing%26gbv%3D2%26hl%3Den>.


South Shore Park Shoreline Revetment. 2008. Edgerton Contractors. Web. 4 Dec. 2009. <http://images.google.com/imgres?imgurl=http://www.edgertoncontractors.com/projects/south_shore/images/Southshore-Shoreline-001.jpg&imgrefurl=http://www.edgertoncontractors.com/projects/south_shore/south_shore.html&usg=__k6emmDtPthEtFeV35J3DGlcAaBo=&h=267&w=440&sz=49&hl=en&start=146&tbnid=w2W-KQtMi2X8ZM:&tbnh=77&tbnw=127&prev=/images%3Fq%3Dbeach%2Bnourishment%26gbv%3D2%26ndsp%3D21%26hl%3Den%26sa%3DN%26start%3D126>.

Thirty inch pipe discharged up to 60,000 cubic yards of sand per day onto the beach. 2009. Palm Beach County. Web. 4 Dec. 2009. <http://images.google.com/imgres?imgurl=http://www.co.palm-beach.fl.us/erm/coastal/shoreline/_images/orpipe1_3.jpg&imgrefurl=http://www.co.palm-beach.fl.us/erm/coastal/shoreline/beach-nourishment.htm&usg=__k7O9Bx6upqvtiSQOP7bWTtic2aE=&h=260&w=389&sz=43&hl=en&start=91&tbnid=d1Enk_e58tpUoM:&tbnh=82&tbnw=123&prev=/images%3Fq%3Dbeach%2Bnourishment%26gbv%3D2%26ndsp%3D21%26hl%3Den%26sa%3DN%26start%3D84>.

Unknown. US Army Corps of Engineers. Web. 4 Dec. 2009. <http://images.google.com/imgres?imgurl=http://www.lrd.usace.army.mil/_storage/Pages/1077/dul_bu1.jpg&imgrefurl=http://www.lrd.usace.army.mil/navigation/glnavigation/dredgedmaterialmanagement/&usg=__x_Gc4DwCg1D0xRA1ysgdBFgjK0Y=&h=267&w=400&sz=124&hl=en&start=174&tbnid=xemavQkXDcpaiM:&tbnh=83&tbnw=124&prev=/images%3Fq%3Dbeach%2Bnourishment%26gbv%3D2%26ndsp%3D21%26hl%3Den%26sa%3DN%26start%3D168>.

MICROCLIMATE EFFECTS OF BUILDING IN DUBAI PICS (3)

Thapar H, Yannas S. 2008. 491: Microclimate and Urban Form in Dubai. Architectural Association School of Architecture. PLEA 2008 -- 25th Conference on Passive and Low Energy Architecture; 2008 Oct 22-24; Dublin.


 


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