Coastal Management: Drag Force & Energy Attenuation
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Questions and Answers

What factors influence sediment transport and loss of coral/plants?

Shear stresses

What happens to wave damping when waves and current act in the same direction?

  • There is an increase in wave damping
  • There is a smaller wave damping (correct)
  • Wave damping becomes negligible
  • Wave damping remains the same

    • An increase in wave damping occurs for waves and currents flowing in the opposite direction.

    True

    Shear stress can be expressed as a function of a friction coefficient known as ______.

    <p>Jonsson</p> Signup and view all the answers

    What should be considered to influence sediment, nutrients, and oxygen transport in submerged canopies?

    <p>Gaps in between meadows</p> Signup and view all the answers

    What is the effect of shear stress around ecosystem elements?

    <p>Loss of ecosystem elements through sediment loss and force.</p> Signup and view all the answers

    What is drag force?

    <p>The force exerted by a fluid on a body moving through it, which depends on the object's shape and the fluid's speed.</p> Signup and view all the answers

    The Reynolds number, $Re$, is defined as $Re = \frac{UNd}{n}$, where $UN$ is the free-stream speed and $d$ is the ___ .

    <p>cylinder diameter</p> Signup and view all the answers

    In which conditions will the boundary layer be laminar?

    <p>When $Re &lt; 3 x 10^5$</p> Signup and view all the answers

    What happens to the drag coefficient when the Reynolds number reaches a certain threshold?

    <p>It decreases from 1.2 to 0.33</p> Signup and view all the answers

    What is energy attenuation in the context of waves?

    <p>Energy attenuation refers to the reduction of wave energy as waves travel through vegetation or other materials.</p> Signup and view all the answers

    Wave celerity increases as water depth decreases.

    <p>False</p> Signup and view all the answers

    What phenomenon occurs when waves encounter a dense vegetation field?

    <p>All of the above</p> Signup and view all the answers

    Match the following wave breaking types with their characteristics:

    <p>Spilling = Occurs when wave steepness is less than a critical limit Plunging = Wave energy is dissipated suddenly Collapsing = Occurs at intermediate steepness Surging = Takes place in very steep waves</p> Signup and view all the answers

    Wave steepness exceeds a physical limit when the particles' velocities are larger than wave ___ .

    <p>celerity</p> Signup and view all the answers

    What is the formula used to calculate the decay of the wave height as a function of an attenuation coefficient?

    <p>H1 = H0(1 + βx)</p> Signup and view all the answers

    Which of these approaches calculated the energy dissipation of waves assuming a steady flow?

    <p>Dalrymple et al. (1984)</p> Signup and view all the answers

    In the formula H1 = H0(1 + βx), β is known as the _____ coefficient.

    <p>wave attenuation</p> Signup and view all the answers

    The drag coefficient is predictable across different ecosystems.

    <p>False</p> Signup and view all the answers

    What does R𝑒 stand for in the context of drag coefficient formulations?

    <p>Reynolds number</p> Signup and view all the answers

    What can higher density and biomass values in ecosystems lead to?

    <p>Higher wave attenuation rates</p> Signup and view all the answers

    Match the following authors with their respective studies on wave energy attenuation:

    <p>Dalrymple et al. (1984) = Energy conservation for regular waves Mendez and Losada (2004) = Energy conservation for irregular waves Losada et al. (2016) = Wave height decay for waves and current conditions</p> Signup and view all the answers

    What is the wave height attenuation formula for a flume full of mangroves?

    <p>$H = H_0 (1 + \beta x)$</p> Signup and view all the answers

    The submerged solid volume fraction (SVF) is defined as the ratio between solid volume and water volume.

    <p>True</p> Signup and view all the answers

    What is the effective standing biomass equation used in coastal management?

    <p>Effective Standing Biomass = Dry Weight * min(h, h) * SR</p> Signup and view all the answers

    The common linear relationship for 96 cases includes 4 species, 2 meadow densities, and _____ wave conditions.

    <p>12</p> Signup and view all the answers

    Match the following species with their characteristics:

    <p>Halimione = Pioneer zone Salicornia = Upper saltmarsh Juncus = Lower saltmarsh Spartina = Salt marsh vegetation</p> Signup and view all the answers

    How do you measure the submerged volume fraction?

    <p>Define control volume and measure all roots.</p> Signup and view all the answers

    What experimental setup is used to conduct wave damping studies?

    <p>Wave-Current-Tsunami Flume (COCOTSU)</p> Signup and view all the answers

    The numerical tool implemented in the SWAN model is used for coastal management.

    <p>True</p> Signup and view all the answers

    What does the Keulegan Carpenter number (KC) represent?

    <p>It is a dimensionless parameter used in fluid mechanics to describe the effects of vegetation on wave dynamics.</p> Signup and view all the answers

    The range of the Keulegan Carpenter number (KC) is between _____ and _____.

    <p>3; 59</p> Signup and view all the answers

    What is the significance of Reynolds number (Re) in the context of vegetation?

    <p>It quantifies the relationship between inertial forces and viscous forces in fluid flow around vegetation.</p> Signup and view all the answers

    Which of the following vegetation types were studied for their drag coefficients?

    <p>All of the above</p> Signup and view all the answers

    The drag coefficient (CD) can vary based on the height of vegetation.

    <p>True</p> Signup and view all the answers

    What is the formula for calculating the drag coefficient for seagrass in relation to Reynolds number?

    <p>C_D = 0.06 + (R_e)</p> Signup and view all the answers

    What are the factors determining the drag coefficient for saltmarshes according to Jadhav and Chen (2012)?

    <p>Wave conditions</p> Signup and view all the answers

    The drag coefficient formula introduced by Ozeren et al. considers vegetation height and water depth as part of the expression: C_D = ___ + KC h_v/h^___.

    <p>0.08; -2</p> Signup and view all the answers

    New approaches in studying coastal protection services require extensive field measurement efforts.

    <p>True</p> Signup and view all the answers

    What objective is explored to estimate coastal protection services without requiring calibrated parameters?

    <p>Submerged Solid Volume Fraction and Standing Biomass</p> Signup and view all the answers

    Study Notes

    Nature-Based Solutions for Coastal Management: Flow Energy Attenuation

    • Coastal management is a multidisciplinary field that intersects with various disciplines, such as climate science, engineering, economics, sociology, hydrodynamics, ecology, morphodynamics, and biology
    • Nature-based solutions utilize natural elements like vegetation and coral reefs to manage coastal areas
    • Wave energy attenuation is a key focal point, primarily addressed through drag force and wave transformation

    Drag Force

    • Drag force is the resistance encountered by an object moving through a fluid
    • Flow interaction with a cylinder is dependent on the Reynolds number (Re)
    • For Re < 1, viscous forces are minimal
    • For Re < 3 x 10^5, the boundary layer (BL) remains laminar
    • For 3 x 10^5 < Re < 3 x 10^6, the BL transitions to turbulence
    • Drag force is influenced by complex flow interactions with vegetation, impacting energy attenuation

    Energy Attenuation in Uniform Flow

    • Vegetation influences flow patterns and energy attenuation
    • Nepf (1999) model incorporates the dependence of the drag coefficient on stem population density
    • The model predicts increased turbulence intensity with sparse vegetation, decreasing with higher density due to reduced flow speed

    Energy Attenuation in Waves

    • Wave energy attenuation is primarily due to drag force
    • Attenuation can be modeled using equations based on regular waves, such as the wave decay formulation
    • Losada et al. (2016) developed an empirical model for vegetation-induced damping under combined waves and currents
    • Wave attenuation through vegetation is validated using physical modeling, field campaigns, and numerical simulations

    Wave Transformation

    • Wave transformation encompasses refraction, diffraction, reflection, and breaking
    • Refraction involves wave direction and height changes due to varying water depths
    • Diffraction is the energy transfer across wave rays, occurring primarily behind obstacles like islands and breakwaters
    • Reflection occurs when waves encounter an ecosystem, particularly dense and emerged vegetation fields
    • Breaking occurs when wave steepness exceeds a physical limit, leading to energy dissipation and height reduction

    Waves and Currents

    • Wave attenuation is influenced by the interaction between waves and currents
    • Damping is reduced when waves and currents move in the same direction
    • Damping increases when waves and currents move in opposite directions

    Shear Stresses

    • Shear stresses play a crucial role in vegetation fields and coral reefs
    • They impact sediment transport and the potential uprooting of coral and plants
    • Analytical formulas exist to calculate bottom shear stresses based on water depth and wave characteristics

    Shear Stress

    • Shear stress is caused by the friction between a fluid and a solid surface
    • The formula to calculate shear stress is τ = ρν ∂u/∂z, where τ is shear stress, ρ is fluid density, ν is kinematic viscosity, u is velocity, and z is distance from the boundary
    • The maximum bottom shear stress is τb,max = ρνUm/ν/σ, where Um is maximum velocity
    • Shear stress is expressed as a function of a friction coefficient (Jonsson, 1966): τb = ρ fcU^2/2, or τb,max = ρ fwU^2m/2
    • Shear stress around ecosystem elements is high
    • High shear stress can cause loss of ecosystem elements through sediment loss and force
    • Shear stress on top of submerged canopies influences sediment, nutrients, and oxygen transport
    • Gaps between vegetation can be crucial to mediate shear stress

    Flow Energy Attenuation

    • Nature-based solutions play a significant role in attenuating flow energy

    Wave Attenuation

    • Wave energy dissipation from coastal ecosystems has been analyzed using analytical formulations based on energy conservation.
    • The energy gradient along the ecosystem is related to the dissipation induced by the flow, considering the drag force exerted on the ecosystem.
    • The drag force is calculated assuming a constant drag coefficient and a constant representative width of the ecosystem elements per unit height.
    • The wave height decay is calculated as a function of an attenuation coefficient (β).
    • Higher density and biomass values in ecosystems lead to higher attenuation rates.

    Attenuation Coefficient (β)

    • β is often fit using experimental data.
    • Analytical formulations for β have been developed for regular and irregular waves, as well as waves and current conditions.
    • Existing formulations for β consider flow parameters (wave height and period, draft) and geometric characteristics of the ecosystem (representative width, density, height).
    • β is directly related to the drag coefficient (Cd).

    Drag Coefficient (Cd)

    • Cd is a parameter that must be calibrated/validated using experimental and field data.
    • Cd formulations are typically based on the Reynolds number (Re) or the Keulegan Carpenter number (KC).
    • Re is calculated from the mean diameter of the ecosystem elements.
    • KC takes into account the relative vegetation height.

    Existing Formulations for β and Cd

    • Dalrymple et al. (1984) and Méndez and Losada (2004) developed formulations for β for regular and irregular waves, respectively.
    • Losada et al. (2016) developed formulations for β considering waves and current conditions.
    • Kobayashi et al. (1993), Mendez et al. (1999), Mendez and Losada (2004), Augustin et al. (2009), and Myrhaug et al. developed formulations for Cd.
    • These formulations consider different factors, including vegetation type, wave conditions, and flow parameters.
    • Cd formulations vary widely, highlighting the site-specific nature of drag and the need for careful calibration.

    Drag Coefficient Formulations

    • Different drag coefficient formulations exist for different vegetation types and wave conditions.
    • Formulations generally consider Reynolds number, vegetation height, water depth, and Keulegan-Carpenter number.
    • Some studies focus on regular waves while others consider irregular waves.
    • Some formulations account for vegetation motion, while others assume stationary vegetation.
    • Drag coefficients can vary significantly depending on the specific vegetation species and the wave regime.

    Drag Coefficient Parameters and Ranges

    • Reynolds number (Re): A dimensionless number that represents the ratio of inertial forces to viscous forces, typically calculated using vegetation diameter and flow velocity.
    • Keulegan-Carpenter number (KC): Represents the relative importance of inertia to drag forces, calculated based on vegetation diameter, wave period, and flow velocity.
    • Vegetation height (ℎ𝑣): Represents the height of the vegetation.
    • Water depth (ℎ): Represents the depth of the water column.

    New Approaches to Quantifying Coastal Protection

    • Submerged Solid Volume Fraction (SVF): Proposed as a new parameter to quantify the coastal protection service provided by vegetated ecosystems.
    • Advantages of SVF:
      • Easier to measure than traditional parameters like leaf traits and biomechanical properties.
      • Allows for estimation of coastal protection service across different species without specific calibration.
    • SVF Calculation:
      • Determined as the ratio between the solid volume and the water volume within a defined control volume.
      • Measured by analyzing frontal area distribution and deviations due to rotating angle.

    IH Cantabria Flume Experiments

    • A wave-current-tsunami flume ("COCOTSU") was used to conduct experiments on wave attenuation by mangroves.
    • The flume replicates real-life conditions with a scale of 1:6.
    • Mangrove Model: Rhizophora mature tree with 2 m → 12 m dimensions (scale 1:6).
    • Experiment Setup: Includes capacitance gauges to evaluate various parameters.
    • Results:
      • Demonstrated significant wave attenuation by mangroves.
      • Showed the effect of different water depths on wave attenuation.

    Conclusion

    • Understanding drag coefficients and developing new approaches like SVF is crucial for quantifying the coastal protection services provided by vegetation.
    • The IH Cantabria flume experiments provide valuable insights into the wave attenuation capabilities of different vegetation types.

    Nature Based Solutions for Coastal Management

    • The text discusses Nature Based Solutions (NBS) for coastal management with a focus on mangrove forests.
    • NBS offer a sustainable alternative to traditional coastal protection measures.
    • The text highlights the role of vegetation species in attenuating wave energy and reducing coastal erosion.
    • Different vegetation species have varying effects on wave attenuation due to their morphology and distribution.
    • Maza et al. (2019) developed a method for calculating hydraulic standing biomass, which represents the effective biomass of vegetation in attenuating wave energy.
    • The method utilizes a formula incorporating wave height (H), vegetation density, and water depth.
    • The concept of hydraulic standing biomass is based on the idea that the effectiveness of vegetation in attenuating wave energy is directly proportional to the amount of biomass that is submerged in water.
    • The text describes an experimental setup for studying the effects of different vegetation species on wave energy attenuation, showcasing the use of both numerical and experimental methods.

    Numerical Model

    • The text mentions a numerical tool, potentially a computational model or simulation, that is being used to simulate wave propagation in a coastal environment.
    • The tool is "Implementación en el modelo SWAN de la nueva formulación", which translates to "Implementation in the SWAN model of the new formulation."
    • SWAN likely refers to the "Simulating WAves Nearshore" model, a widely used nearshore wave model.
    • The tool was created using the "new formulation," which could refer to a novel mathematical model or representation of vegetation's impact on wave energy.
    • The text mentions the validation of the numerical tool.

    Validating the Model

    • The numerical tool was validated using data from the Scheldt estuary, focusing on two vegetation species: Scirpus maritimus and Spartina anglica.
    • Information about biomass in different water depths was sourced from Heuner et al. (2015) and Schulze et al. (2019).
    • The model's output was compared to real-world data, potentially validating the applicability of the numerical simulations.
    • Additionally, the text mentions the concept of "drag formula," a mathematical expression that quantifies the resistance a body experiences when moving through a fluid.
    • This drag formula was likely incorporated into the numerical model to represent the impact of vegetation on wave energy.

    Flow Energy Attenuation

    • The text presents an analytical formulation for calculating the flow energy attenuation by vegetation:
    • Attenuation = H / H0
    • Where H is the wave height after interacting with the vegetation, and H0 is the initial wave height.
    • This formula incorporates a coefficient β, which describes the effectiveness of vegetation in attenuating wave energy.
    • The text mentions the application of this analytical formulation in studying the efficiency of vegetation in wave attenuation.
    • The text states that by applying this formula, the effectiveness of vegetation in wave attenuation can be calculated.
    • The effectiveness is represented through the coefficient β.
    • The coefficient β is calculated based on factors including:
      • Wave characteristics
      • Vegetation characteristics
      • Water depth
    • This allows researchers to evaluate the efficiency of different vegetation types for coastal protection purposes.

    Key Figures

    • Biomass: This measures the weight of vegetation per unit area (g/m2). It is a key factor in determining the effectiveness of vegetation for coastal protection.
    • B = 4aNH0k sinh(kl) + 3sinh(kl) / 9π sinh2(kh) + 2kh sinh(kh): This is a formula for calculating the coefficient β, which quantifies the effectiveness of vegetation in wave attenuation. The Formula takes into account:
      • a: a factor representing the shape of the vegetation.
      • N: The number of vegetation stalks per unit area.
      • H0: The initial wave height.
      • k: Wave number.
      • l: Length of the vegetation.
      • h: Water depth.

    Key Researchers and Studies

    • Maza et al. (2019): Developed the "Hydraulic Standing Biomass" method to measure effective biomass in wave energy attenuation.
    • Maza et al. (2022): Developed a statistical method for predicting the relationship between wave height reduction and vegetation parameters.
    • Lopez-Arias et al. (2024): Contributed to the development of a numerical model for wave energy attenuation in mangrove forests.
    • Heuner et al. (2015) and Schulze et al. (2019): Provided data about biomass in the Scheldt estuary for validating the numerical model.
    • Vuik et al. (2018): Published findings about the importance of considering both vegetation biomass and distribution for accurate wave attenuation modeling.

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    Description

    Explore the multifaceted nature of coastal management through the lens of drag force and energy attenuation. This quiz delves into the role of nature-based solutions like vegetation and coral reefs in managing coastal dynamics. Understand the fluid interactions and their importance in engineering and ecological contexts.

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