Literature Summary #2 by HC121109045618


									Literature Summary #2                                                     Ed Pritchard

Deng, Yang, Solo-Gabriele, Helena et al. 2010. Impacts of hurricanes on surface water
flow within a wetland. Journal of Hydrology (2011) Vol. 392, Issues 3-4, 164-173

Y. Deng is with Montclair State University’s Department of Earth and Environmental
Studies in Montclair, NJ, USA. H.M. Solo-Gabriele, along with another author, M. Laas
are with the Department of Civil, Architectural, and Environmental Engineering at the
University of Miami in Coral Gables, FL, USA. Other authors include L. Leonard with
the University of North Carolina-Wilmington’s Department of Geography and Geology
based in Wilmington, NC, USA, D.L. Childers with the Department of Biological
Sciences and Southeast Environmental Research Center at Florida International
University in Miami, FL, USA, G. He with Zhejiang University’s College of Civil
Engineering and Architecture in Zhejiang, China, and V. Engel from the South Florida
Natural Resources Center at Everglades National Park in Homestead, FL, USA.

   1) Research problem or question: What are the hydrologic impacts of hurricane
      wind and rainfall conditions on water velocity and water elevations in the Florida
   2) Background knowledge leading up to study: Due to recent advancements in
      technology and proliferation of monitoring systems, researchers have been able to
      evaluate impacts of hurricanes on wetlands. These studies have been limited,
      however, in their scope and have focused on nutrient releases, changes in
      microbial and plant communities, impacts of sediment deposition and salinity, and
      changes in wetland size. So far there is a limited amount of research available on
      water flows and levels during hurricane conditions in wetlands. This study looks
      to evaluate the impact of extremely strong winds on water elevations and surface
      water velocity, two factors which are critical in the processes of particulate
      settling and re-suspension of wetlands. The Everglades serve as a good test site,
      as the ridge and slough ecosystems that make up the landscape are very dependent
      upon the processes mentioned above.
   3) Methods used by investigators: Water velocity measurements for this study
      were collected at sites within sawgrass marshes in the vicinity of two tree islands
      within the Shark River Slough of Everglades National Park, known as Gumbo
      Limbo Hammock and Satin Leaf Hammock (hardwood hammock communities)
      during and after two major hurricanes, Katrina and Wilma during the 2005
      hurricane season. Surface mean wind velocity data were available from several
      weather observation stations, the two closest of which were within Everglades
      National Park at a height of 2 m from ground surface, at stations known as
      Tenraw, and Chekika. Hourly rainfall and water elevation data were obtained
      from three monitoring stations in ENP, monitored by park officials.
   4) Results: Results of the study suggest that during each hurricane wind speeds
      increased by over 10 m/s at both SL and GL testing sites. The maximum mean
      wind speeds at GL and SL during Hurricane Wilma (31 m/s) were almost twice as
      that during Katrina (ca. 17 m/s), and, accordingly, the water flow was much more
      strongly affected in magnitude and direction by Hurricane Wilma than by
Hurricane Katrina. Thus, critical wind strengths appeared to exist, above which
the water flow was altered, with stronger winds causing greater impacts on water
flow. The researchers’ interpretation of the cause of the shift in flow speed and
direction were attributed to changes in the combined effects of wind shear,
differential rainfall, shift in hydraulic gradients, and changes in the structure of
submerged vegetation. Moreover, the characteristics of water flow after the two
hurricanes were significantly different and local vegetation likely played another
role, by minimizing the extreme changes in velocity during peak wind conditions.
5) Weakness of study: One weakness of this study lies in the lack of quantitative
   data and discussion related to the relationships between the various factors of
   hydrologic impacts. This study was highly qualitative and relationships were not
   described in detail, therefore, future studies should look in to disaggregating the
   different factors that influence water flow during hurricane conditions through
   improvements in wind measurements. Studies should also focus more on the
   changes in vegetative structure during these hurricane conditions, which might
   help explain some of the changes in velocity that were observed after hurricane
   conditions. Other suggestions would be to analyze wind velocities and impacts at
   various vertical scales such as different water depth gradients and at different
   hydroperiods throughout the hurricane season and across the Everglades
6) What was learned: From the results of this study, I was able to gather that
   baseline wind conditions (<10 m/s) were not a major factor influencing water
   flow at depth. During the periods of hurricane force winds produced from
   Hurricanes Katrina and Wilma, flow speed and direction were radically altered
   due to the combined effects of forces applied at the surface of the water (wind
   shear, rainfall, hydraulic gradients) plus forces placed on vegetation that is
   emerging above the surface of the water. The longer lasting effects of hurricanes
   (time scale of a few days) resulted in altered flow speeds that changed by 50% or
   less with flow directions very close to those observed during non-hurricane
   conditions. These longer lasting altered conditions could be a result of the
   redistribution and removal of emergent vegetation and sediments across the

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