Portable Free Fall Penetrometers (PFFPs) are lightweight tools used for rapid and economic characterization of surficial subaqueous sediments. PFFPs vary in weight, shape and size with options for using add-on units. The different configurations enable deployments in various environments and water depths, including the nearshore zone where conventional methods are challenged by energetic hydrodynamics and limited navigable depth. Moreover, PFFPs offer an opportunity to reduce the high site investigation costs associated with conventional offshore geotechnical site investigation methods. These costs are often a major obstacle for small projects serving remote communities or testing novel renewable energy harvesting machines. However, PFFPs still face issues regarding data analysis and interpretation, particularly in energetic sandy nearshore areas. This includes a lack of data and accepted analysis methods for such environments. Therefore, the goal of this research was to advance data interpretation and sediments characterization methods using PFFPs with emphasis on deployments in energetic nearshore environments. PFFP tests were conducted in the nearshore areas of: Yakutat Bay, AK; Cannon Beach, AK; and the U.S. Army Corps of Engineers' Field Research Facility's beach, Duck, NC. From the measurements, the research goal was addressed by: (1) introducing a methodology to create a regional sediment classification scheme utilizing the PFFP deceleration and pore pressure measurements, sediment traces on the probe upon retrieval, and previous literature; (2) investigating the effect of wave forcing on the sediments' behavior through correlating variations in sediment strength to wave climate, sandbar migration, and depth of closure, as well as identifying areas of significant sediment mobilization processes; and (3) estimating the relative density and friction angle of sand in energetic nearshore areas from PFFP measurements. For the latter, the field data was supported by vacuum triaxial tests and PFFP deployments under controlled laboratory conditions on sand samples prepared at different relative densities. The research outcomes address gaps in knowledge with regard to the limited studies available that investigate the sand geotechnical properties in energetic nearshore areas. More specifically, the research contributes to the understanding of surficial sediment geotechnical properties in energetic nearshore areas and the enhancement of sediment characterization and interpretation methods. / PHD / The increasing demand for energy, fluctuations of oil prices, and the expected reduction in the world’s oil production in addition to concerns associated to the global climate change drive the search for renewable energy sources. Out of the different sources of renewable energy, the reliable availability of waves is an advantage over other sources like solar and wind. However, different challenges are still facing the advancement of generating energy from waves. One important challenge is the reliability of the anchoring or foundation system, and the associated site characterization and data collection. The stability of the systems depends on the sediment strength (ability accommodate loads), sediments susceptibility to scour (removal of the sediments around the foundations), and local morphodynamics (changes in the seabed shape). In fact, the stability of the foundations in the seabed represents a major concern for many nearshore and offshore structures. Accordingly, the site characterization stage of any project is essential to mitigate the risks of failures, as well as to achieve cost-effective designs. Portable Free fall penetrometers (PFFPs) are rapid and economical tools used to characterize uppermost seabed sediments. The variability of such devices in weight, shape and size enables the use in different environments and water depths. However, data of PFFPs in sandy sediments is still limited which contradicts the fact that sand represents the most common soil type on the beaches worldwide. Accordingly, the aim of this research is to investigate the sediment behavior in energetic wave areas, and to advance the methods of interpreting the PFFP data in sandy nearshore zones. A PFFP was used to characterize the sediments in three main areas: Yakutat Bay, AK, Cannon Beach, AK and the U.S. Army Corps of Engineers’ Field Research Facility’s beach, Duck, NC. The results were utilized to introduce a sediment classification scheme and complete an existing sediment distribution map for Yakutat Bay, AK; study the effect of storms on the seabed sediment strength; and to determine sand strength parameters using PFFP measurements. The results of this research will contribute to improve the sediment characterization methods and to understand topmost sediment layers’ properties.