Yazar "Safak, Ilgar" seçeneğine göre listele

Listeleniyor 1 - 3 / 3
  • Küçük Resim Yok
    Öğe
    Boat wake effects on sediment transport in intertidal waterways
    (Pergamon-Elsevier Science Ltd, 2021) Safak, Ilgar; Angelini, Christine; Sheremet, Alex
    Boat traffic and resulting wakes are among the major human-mediated stressors on coastal ecosystems. Modulation of sediment transport by wakes and tides in an intertidal waterway with boat traffic is studied here. The hypothesis that boat wakes cause significant increases in sediment transport in intertidal settings is tested. Field observations of tides, currents, boat wakes and turbidity were collected on a transect within the Atlantic Intracoastal Waterway in Northeast Florida, USA. Hydrodynamic and sediment processes were evaluated by analyzing this field data set. A daily average of 60 wake events of varying energies were identified in the observations using time-frequency analysis methods. Due to differences in sediment suspension in response to each wake and unpredictable evolution of the bed state, decomposition of the effects of each individual wake on sediment is not possible. Therefore, the sediment dynamics during the periods of boat activity were compared in their entirety with the sediment dynamics during the periods of boat inactivity. Throughout the experiment, all periods of boat activity had consistently greater suspended sediment concentration near the bed compared to their preceding and succeeding periods of boat inactivity. In the first eight days of the experiment where tidal forcing was relatively similar between boat activity and inactivity periods, sediment transport rates were estimated as 0.048 m3/m/hr and 0.043 m3/m/hr during boat activity and inactivity, respectively, indicating a 12% increase in sediment transport due to boat traffic. A larger increase in sediment transport rates during boat activity compared to boat inactivity occurred over the last three days of the experiment. Volumes of sediment transported in low-tide, mid-tide and high-tide during boat activity were greater than their low-tide, mid-tide and high-tide counterparts during boat inactivity. Therefore, the results confirm the earlier mentioned hypothesis.
  • Küçük Resim Yok
    Öğe
    Challenges and opportunities for sustaining coastal wetlands and oyster reefs in the southeastern United States
    (Academic Press Ltd- Elsevier Science Ltd, 2021) Kyzar, Tricia; Safak, Ilgar; Cebrian, Just; Clark, Mark W.; Dix, Nicole; Dietz, Kaitlyn; Gittman, Rachel K.
    Formed at the confluence of marine and fresh waters, estuaries experience both the seaside pressures of rising sea levels and increasing storm severity, and watershed and precipitation changes that are shifting the quality and quantity of freshwater and sediments delivered from upstream sources. Boating, shoreline hardening, harvesting pressure, and other signatures of human activity are also increasing as populations swell in coastal regions. Given this shifting landscape of pressures, the factors most threatening to estuary health and stability are often uncertain. To identify the greatest contemporary threats to coastal wetlands and oyster reefs across the southeastern United States (Mississippi to North Carolina), we summarized recent population growth and land-cover change and surveyed estuarine management and science experts. From 1996 to 2019, human population growth in the region varied from a 17% decrease to a 171% increase (mean = +43%) with only 5 of the 72 SE US counties losing population, and nearly half growing by more than 40%. Individual counties experienced between 999 and 19,253 km(2) of new development (mean: 5725 km(2)), with 1-5% (mean: 2.6%) of undeveloped lands undergoing development over this period across the region. Correspondingly, our survey of 169 coastal experts highlighted development, shoreline hardening, and upstream modifications to freshwater flow as the most important local threats facing coastal wetlands. Similarly, experts identified development, upstream modifications to freshwater flow, and overharvesting as the most important local threats to oyster reefs. With regards to global threats, experts categorized sea level rise as the most pressing to wetlands, and acidification and precipitation changes as the most pressing to oyster reefs. Survey respondents further identified that more research, driven by collaboration among scientists, engineers, industry professionals, and managers, is needed to assess how precipitation changes, shoreline hardening, and sea level rise are affecting coastal ecosystem stability and function. Due to the profound role of humans in shaping estuarine health, this work highlights that engaging property owners, recreators, and municipalities to implement strategies to improve estuarine health will be vital for sustaining coastal systems in the face of global change.
  • Küçük Resim Yok
    Öğe
    Comments on wave-induced behavior of a coastal mud
    (Elsevier, 2023) Robillard, David J.; Mehta, Ashish J.; Safak, Ilgar
    The need for the prediction of phenomenal attenuation of sea waves as they approach mud-laden shores has led over the past decades to both analytic and numerical modeling of wave-mud coupling. A feature common to most analyses has been the use of canonical relationships relating stress to strain in mud, with time-independent coefficients in site-specific cases. For cohesive mud from the Atchafalaya River Delta along the Gulf of Mexico coast of Louisiana, laboratory work is described using a rheometer and a wave flume to highlight short-term and long-term responses of elastoviscoplastic mud to waves. Short-term may amount to perhaps no more than a few minutes, whereas tens of minutes or longer may be characterized as long term. For short-term response, a simple physical framework is used with rheometric data in preference to a mechanistic model to estimate the thickness of the dissipative mud layer formed by waves, an important parameter commonly deduced by model tuning against measured wave attenuation. In the long-term, characteristically time-dependent rheological parameters have an asymmetric, thixotropic response to the imposition and relaxation of stress. As the thixotropic timescale is commensurate with coastal storms, interpretation of wave attenuation predicted from short-term modeling must be treated with caution in prototype application.