20 Aug 2025

Examining the Impact of the 2007 Zaca Fire on the Long-Term Hydrological Recovery of the Santa Cruz Creek Watershed in Southern California

Abstract: This study focuses on the Santa Cruz Creek watershed in Southern California, an area severely impacted by the 2007 Zaca Fire. The region is representative of wildfire-prone Mediterranean-climate catchments. We assess long-term post-fire hydrological recovery using a novel dual approach: (1) simulating 16 storm events over a 23-year period to evaluate pre-fire, post-fire, and recovery conditions, and (2) directly comparing two similar storm events—one pre-fire and one during recovery—to isolate changes in watershed response. Hydrological modeling employed HEC-HMS with the Deficit and Constant Loss Method, the ModClark Transform Model, and the Linear Reservoir Baseflow Model. Remote sensing data, including Enhanced Vegetation Index and SERVES Soil Moisture, enhanced modeling and analysis. Vegetation cover, soil moisture, and several watershed parameters show substantial recovery after five years. EVI reached 84 % of pre-fire values, while initial soil moisture deficit, time of concentration, and storage coefficient each recovered to roughly 70 %. Fast baseflow exceeded pre-fire levels at 143 %, but slow baseflow declined to 20 %. Peak discharge and direct runoff volume declined from post-fire highs of 173 % and 136 % to 125 % and 84 % of pre-fire levels, respectively. Although vegetative conditions stabilize, watershed hydrology remains altered.

20 Aug 2025

Bioturbation Increases Time Averaging Despite Promoting Shell Disintegration: A Test Using Anthropogenic Gradients in Sediment Accumulation and Burrowing on the Southern California Shelf

Abstract: Bioturbation increases time averaging of young and old shells within the entire mixed layer and accelerating the burial of shells into a sequestration zone. Bioirrigation by oxygenated pore-water promotes carbonate dissolution in the TAZ, and biomixing itself can mill shells weakened by dissolution or microbial maceration, and/or expose them to damage at the sediment–water interface. We fit transition rate matrices to bivalve age–frequency distributions from four sediment cores to assess the competing effects of bioturbation on disintegration and time averaging. Disintegration covaries positively with mixing at all four sites. Mixing and disintegration rates decline abruptly at the base of the 20- to 40-cm-thick, age-homogenized surface mixed layer at the three well-bioturbated sites. In contrast, they are very low in the upper 25 cm at an effluent site with legacy sediment toxicity. Assemblages formed during maximum wastewater emissions vary strongly in time averaging. Thus, even though disintegration rates covary positively with mixing rates, reducing postmortem shell survival, bioturbation has the net effect of increasing the time averaging of skeletal remains on this warm-temperate siliciclastic shelf.

20 Aug 2025

Coastal Sand Dunes: A Review of Management Strategies for Dune Stabilization

Abstract: The primary objective of this technical note is to provide a US-centric review on historic and current management approaches for dune stabilization efforts. This includes methods for promoting dune formation via natural aeolian processes, as well as more hands-on management approaches, including hybrid dune construction.

20 Aug 2025

SandSnap Filtering Techniques

Abstract: The aim of this Coastal and Hydraulics Laboratory Special Report is to elucidate the new SandSnap image filters. These SandSnap filters distinguish between high-quality and poor-quality images and enhance accuracy in high-quality images. To achieve this goal, a dataset of 5,000 photos was created and curated for this endeavor. Images were collected that had varying levels of focus, sedimentological conditions, foreign objects present, distances from the sediment bed, coin types, and geographic locations. This dataset was used to train multiple quality control check models and uncover beneficial correlations. Additionally, an existing dataset of high-quality images was analyzed using various filtering techniques to highlight key features, leading to higher-accuracy scores. Using the findings from both the high-quality and poor-quality datasets, SandSnap was updated to increase usability and efficiently identify images that may lead to poor results. This ensures that user results can be calculated in less than a minute, emphasizing the commitment to maintaining a fast and responsive model.

20 Aug 2025

Trade-offs Between Field and Remote Geomorphic Monitoring of Coastal Marsh Restoration Sites

Abstract: Coastal marsh restoration presents geomorphic monitoring challenges because these sites are often remote or inaccessible, and time and financial resources for field data may be limited. Yet, elevation and shoreline characteristics contribute to the overall health and longevity of coastal marshes. The expansion of Uncrewed Aircraft System (UAS) technology and new satellite platforms offer opportunities to complement ground-based geomorphic monitoring and overcome the challenges of traditional field methods. Here, we compare field-based and remote-sensing approaches to monitor two restored coastal wetlands in Louisiana. At Spanish Pass, methods for measuring site elevation, shoreline position, and shoreline geomorphic types were compared. Ground surveys strongly correlated with UAS-lidar digital elevation model (DEM) elevations (R2 = 0.97. UAS and satellite imagery were accurate to within 3 meters of field-shoreline positions, and UAS-lidar-derived shorelines had the lowest error. At LaBranche, UAS-lidar DEM data were paired with airborne lidar and legacy ground surveys to track temporal changes in elevation, indicating minimal elevation change. The study demonstrates the accuracy and utility of satellite and UAS remote sensing for monitoring shoreline positions and elevations but notes that shoreline classifications could be improved with additional quantification. These findings help practitioners assess the trade-offs and benefits of various monitoring methods.

19 Aug 2025

Do Land Models Miss Key Soil Hydrological Processes Controlling Soil Moisture Memory?

Abstract: Soil moisture memory is critical for understanding climatic, hydrological, and ecosystem interactions. Most land surface models overestimate surface soil moisture and its persistency, sustaining spuriously large soil surface evaporation during dry-down periods. Do LSMs miss or misrepresent key hydrological processes controlling SMM? We used Noah-MP with advanced hydrology that represents preferential flow and surface ponding and provides optional schemes of soil hydraulics. Effects were tested, which are generally missed by LSMs in SMM. We compare SMMs computed from various Noah-MP configurations against that derived from the Soil Moisture Active Passive L3 soil moisture and in situ measurements from the International Soil Moisture Network between 2015 to 2019 over the contiguous US. Results suggest soil hydraulics plays a dominant role and the Van Genuchten hydraulic scheme reduces overestimation of the long-term surface SMM produced by the Brooks–Corey scheme; explicitly representing surface ponding enhances SMM for the surface layer and the root zone; and representing preferential flow improves overall representation of soil moisture dynamics. The combination of these missing schemes can significantly improve the long-term memory overestimation and short-term memory underestimation issues in LSMs. LSMs for use in seasonal-to-subseasonal climate prediction should, at least, adopt the Van Genuchten hydraulic scheme.

19 Aug 2025

Numerical Modeling of Coastal Processes with Beneficial Use of Dredged Sediment in the Nearshore at Jekyll Island, Georgia

Abstract: This report provides numerical model results to assist the US Army Corps of Engineers–Savannah District (SAS). These results evaluate beneficial use alternatives for the sediment from an advance maintenance widener of the Brunswick Harbor Entrance Channel between stations −14+000 and −28+000. This study applied a coastal wave, hydrodynamic and sediment transport model (Coastal Modeling System), and a shoreline change model (GenCade), focusing on developing and simulating placement alternatives. Subaerial placement model results indicate better shore and beach preservation than at the nearshore nourishment. Placing sediment closer to the “transition zone” between the revetment and natural beach will increase the volume of sand that remains in that area. Some sediment is predicted to return to the channel, but these volumes are small fractions of the placed material. GenCade results indicate that the transition zone rock debris decreases shoreline erosion. Removing it has less impact on that area than any of the subaerial nourishments, but this prediction does not include profile equilibration that may occur after the first 4 months. Overall, model results indicate that subaerial placement will have strong positive response at the eroding beach, and related increases to channel infilling rates are relatively small.

12 Aug 2025

Assessing Shorelines Extracted from Satellite Imagery Using Coincident Terrestrial Lidar Linescans

Abstract: Previous analyses comparing CoastSat satellite-derived shorelines to morphological data highlighted site-specific errors in outputs related to concurrent wave runup conditions. We present a comparison of lidar-derived runup and beach elevation data to CoastSat satellite-derived waterlines extracted using two image sources and two threshold algorithms. Results show SDW extracted using Otsu thresholds correlated better with lidar-derived waterlines, SDW extracted using the weighted peaks threshold were consistently positioned in the upper swash and correlated better with a runup bulk statistic. Assigning the best-fit runup bulk statistic as the waterline elevation to weighted peaks SDW resulted in SDS with less scatter than the Otsu SDW. Horizontal errors for converted datum-referenced shoreline were lowest when SDW were converted to SDS using best-fit measured runup bulk statistics and a measured slope. For weighted peaks SDW from both image sources, assigning the best-fit parameterized runup bulk statistic and an average slope in the SDW to SDS conversion reduced error by ∼ 20% to ∼ 35% when compared to tidal elevation and average slope. These findings confirm runup corrections can improve native SDS outputs, although the magnitude of final shorelines error depended on specific imagery product, local beach slope, threshold technique, runup parametrization, and chosen reference contour.

5 Aug 2025

Vessel Draft and Velocity Updates for Tybee Island Vessel Wake Analysis

Purpose: This Coastal and Hydraulics Engineering technical note (CHETN) updates the results of a previous study (ERDC/CHL TR-22-21; Bain et al. 2022) and evaluates whether newly available datasets offer greater insight into the relationship between vessel characteristics and wake conditions near Tybee Island, Georgia. Whereas the original study used vessel drafts from the Automatic Identification System (AIS), the present analysis substitutes more accurate draft information from US Customs Foreign Vessel Entrances and Clearances (FVEC) records. In addition, cross-sectionally averaged flow velocities from the US Geological Survey (USGS) gauge at Fort Pulaski, Georgia, are used to update the AIS-reported speed over ground (SOG), yielding the vessels’ speed relative to the water. The combination of these two updates generates a visible improvement in wake forecasting ability. However, the mechanisms underlying drawdown oversteepening and bore formation near the beach remain poorly understood, and further study is recommended to determine the cause of this hazardous behavior.

4 Aug 2025

Acoustic and Seismic Wave Transmission Throughout the Multidomain Environment: Experimental Design, Methods, and Construction of a Prototypical Littoral Zone

Abstract: The future operational environment is projected to be a multidomain, transparent battlefield in which the Army must be able to act as both a supported and supporting force. An accurate detection and interpretation of acoustic and seismic signals propagating across land-air-water (LAW) interfaces are required to meet future requirements of a fully “transparent” domain. The LAW domains converge at the significant contested littoral zones. Historically, interpreting signals crossing media boundaries has been studied by stovepiping each distinct medium. These fragmented perspectives led to discrepancies in boundary and adjacent media descriptions and media-specific governing physics. No comprehensive physics framework exists to accurately predict how disorderly waveforms freely traverse LAW media boundaries. To understand these complex phenomena, a highly controlled physical experiment was designed and implemented. Repeatable controls were conducted. Epistemic uncertainty was decreased, and high waveform fidelity was maintained in the experimental setup by not interfering with wave transmission or sensor accuracy between controls. This report summarizes the experimental design, implementation, challenges, and repeatability.