Estimating Steepness at NDBC: Leveraging Dominant Wave and Windwave Data for Open Earth Science Analysis

Getting Started

Wave steepness is an important parameter in oceanography and coastal engineering because it provides valuable insight into the behavior of ocean waves. It quantifies the ratio of wave height to wavelength and is a critical factor in determining wave breaking, wave-induced forces on structures, and sediment transport processes. The National Data Buoy Center (NDBC) is a valuable resource for accessing wave data, and while it does not directly provide wave steepness, it is possible to calculate this parameter using the available dominant wave and wind wave data. In this article, we will explore how to calculate wave steepness at NDBC using these datasets.

Understanding dominant wave and wind wave data

Before delving into the calculation of wave steepness, it is important to understand the data provided by the NDBC. The dominant wave data includes information on the significant wave height (Hs), which is the average height of the highest one-third of the waves recorded during a given period. It also provides the dominant wave period (Tp), which is the time interval between successive wave crests at the peak of the wave spectrum. On the other hand, wind wave data provides the significant wave height (Hsw) and mean wave period (Tsw) of wind-generated waves.

Wave Steepness Calculation

Wave steepness (St) can be calculated by dividing the significant wave height (Hs) by the wavelength (L). However, calculating the wavelength directly from the given data is not straightforward. To overcome this challenge, we can use the wave period (T) and the dispersion relation, which relates the wave period to the wavelength for deep water waves.

In deep water, the dispersion relation is given by

L = g * T^2 / (2π)

Where L is the wavelength and g is the acceleration due to gravity (about 9.81 m/s²). Substituting the dominant wave period (Tp) or the wind wave period (Tsw) into the equation, we can determine the corresponding wavelength.
Once we have the wavelength, we can calculate the wave steepness using the formula

St = Hs / L

It is important to note that wave steepness is typically expressed as a dimensionless ratio or as a percentage.

Implications and Applications of Wave Steepness

Wave steepness plays a critical role in many aspects of geoscience and coastal engineering. Understanding wave steepness is essential for assessing wave stability, determining the likelihood of wave breaking, and predicting wave-induced forces on structures such as offshore platforms, coastal defenses, and ships. Wave steepness also affects the sediment transport process along coastlines and can influence coastal erosion and accretion patterns.

In addition, wave steepness is valuable in the study of wave climate variability and long-term trends. Changes in wave steepness can provide insight into the effects of climate change on coastal areas, helping scientists and policy makers make informed decisions about coastal management, infrastructure design, and coastal hazard mitigation.
In conclusion, while the NDBC does not directly provide wave steepness, it is possible to calculate this parameter using the available dominant wave and wind wave data. By understanding the relationship between wave height, period, and wavelength, we can calculate wave steepness, a critical parameter in coastal engineering and geoscience research. The calculated wave steepness provides valuable insights into wave behavior, wave-induced forces, sediment transport, and coastal dynamics, enabling better understanding and management of coastal areas.

FAQs

Q1: How can the stepness be computed at NDBC from a site with only dominant wave data and windwave data?

A1: The stepness at NDBC (National Data Buoy Center) can be computed using the available dominant wave data and windwave data through a mathematical formula. The stepness, also known as the wave steepness, is the ratio of wave height to wavelength. It provides information about the steepness or steepness of a wave.

Q2: What is dominant wave data?

A2: Dominant wave data refers to the measurement or estimation of the primary waves present in a given area or at a specific location. It typically represents the most significant waves in terms of height or energy content. Dominant wave data is crucial for understanding wave characteristics and predicting wave behavior.

Q3: What is windwave data?

A3: Windwave data refers to the information related to waves generated by wind. It includes measurements or estimations of wave parameters such as height, period, and direction that are influenced by wind conditions. Windwave data helps in assessing the impact of wind on wave formations and understanding the interaction between wind and waves.

Q4: How is stepness calculated using dominant wave data and windwave data?

A4: Stepness can be calculated by dividing the wave height by the wavelength. The wave height can be obtained from the dominant wave data, while the wavelength can be estimated using the windwave data. The formula for calculating stepness is: Stepness = Wave Height / Wavelength.

Q5: What does the stepness value indicate?

A5: The stepness value provides information about the steepness or steepness of a wave. A higher stepness value indicates a steeper wave, while a lower stepness value suggests a flatter wave. Stepness is an essential parameter for understanding wave breaking, wave energy dissipation, and the interaction of waves with coastal structures.